Kinetics of the Reaction of CH3O2 Radicals with OH Studied over the 292-526 K Temperature Range.

PubMed

Yan, Chao; Kocevska, Stefani; Krasnoperov, Lev N

2016-08-11

Reaction of methyl peroxy radicals with hydroxyl radicals, CH3O2 + OH → CH3O + HO2 (1a) and CH3O2 + OH → CH2OO + H2O (1b) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 292-526 K temperature range and pressure 1 bar (bath gas He). Hydroxyl radicals were generated in the reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N2O at 193.3 nm, with H2O. Methyl peroxy radicals were generated in the reaction of methyl radicals, CH3, produced in the photolysis of acetone at 193.3 nm, and subsequent reaction of CH3 with O2. Temporal profiles of OH were monitored via transient absorption of light from a DC discharge H2O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The overall rate constant of the reaction is k1a+1b = (8.4 ± 1.7) × 10(-11)(T/298 K)(-0.81) cm(3) molecule(-1) s(-1) (292-526 K). The branching ratio of channel 1b at 298 K is less than 5%.

OH Production from Reactions of Organic Peroxy Radicals with HO2 : Recent Studies on Ether-Derived Peroxy Radicals

NASA Astrophysics Data System (ADS)

Orlando, J. J.; Tyndall, G. S.; Kegley Owen, C. S.; Reynoldson, N.

2013-12-01

There is now ample evidence supporting significant formation of OH radicals in the reaction of HO2 with certain organic peroxy radicals (RO2). These reaction channels serve to promote radical propagation, and thus have the potential to alter HOx budgets and partitioning and hence tropospheric oxidative capacity. While much focus has been placed on OH production from reactions involving carbonyl-containing RO2 species, it is also the case that other oxygen- substituted peroxy species (e.g., CH3OCH2OO, HOCH2OO) likely generate OH in their reactions with HO2 (see ref. 1 and refs therein). In this work, the Cl-atom-initiated oxidation of two ethers, diethyl and diisopropyl ether, is investigated over ranges of conditions in an environmental chamber, using both FTIR and GC-FID methods for product quantification. Preliminary analysis suggests that significant OH production is occurring in the reaction of HO2 with CH3CH2OCH(OO)CH3, and also provides evidence for a rapid unimolecular reaction of diisopropyl ether-derived peroxy radicals. Details of these and other results will be described. 1. Orlando, J. J., and G. S. Tyndall, 2012: Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance, Chemical Society Reviews, 41, 6294-6317, doi: 10.1039/C2CS35166H.

Atmospheric chemistry of cyc-CF2CF2CF2CH=CH-: Kinetics, products, and mechanism of gas-phase reaction with OH radicals, and atmospheric implications

NASA Astrophysics Data System (ADS)

Guo, Qin; Zhang, Ni; Uchimaru, Tadafumi; Chen, Liang; Quan, Hengdao; Mizukado, Junji

2018-04-01

The rate constants for the gas-phase reactions of cyc-CF2CF2CF2CH=CH- with OH radicals were determined by a relative rate method between 253 and 328 K. The rate constant k1 at 298 K was measured to be (1.08 ± 0.04) × 10-13 cm3 molecule-1 s-1, and the Arrhenius expression was k1 = (3.72 ± 0.14) × 10-13 exp [(-370 ± 12)/T]. The atmospheric lifetime of cyc-CF2CF2CF2CH=CH- was calculated to be 107 d. The products and mechanism for the reaction of cyc-CF2CF2CF2CH=CH- with OH radicals were also investigated. CO, CO2, and COF2 were identified as the main carbon-containing products following the OH-initiated reaction. Moreover, the radiative efficiency (RE) was determined to be 0.143 W m-2 ppb-1, and the global warming potentials (GWPs) for 20, 100, and 500 yr were 54, 15, and 4, respectively. The photochemical ozone creation potential of the title compound was estimated to be 1.3.

Kinetics of OH- and Cl-initiated oxidation of CH2dbnd CHC(O)O(CH2)2CH3 and CH2dbnd CHCH2C(O)O(CH2)2CH3 and fate of the alkoxy radicals formed

NASA Astrophysics Data System (ADS)

Rivela, Cynthia; Blanco, María B.; Teruel, Mariano A.

2016-05-01

Rate coefficients of the reactions of OH and Cl radicals with vinyl and allyl butyrate were determined for the first time at 298 K and 1 atm using the relative method to be (in cm3 molecule-1 s-1): k1(OH + CH2dbnd CHC(O)O(CH2)2CH3) = (2.61 ± 0.31) × 10-11, k2(Cl + CH2dbnd CHC(O)O(CH2)2CH3) = (2.48 ± 0.89) × 10-10, k3(OH + CH2dbnd CHCH2C(O)O(CH2)2CH3) = (2.89 ± 0.31) × 10-11, and k4(Cl + CH2dbnd CHCH2C(O)O(CH2)2CH3) = (2.25 ± 0.96) × 10-10. Reactivity trends and atmospheric lifetimes of esters are presented. Additionally, a product study shown butyric acid and polifunctional products for the reactions of vinyl and allyl butyrate, respectively and general mechanism is proposed.

Tropospheric reactions of the haloalkyl radicals formed from hydroxyl radical reaction with a series of alternative fluorocarbons

NASA Technical Reports Server (NTRS)

Atkinson, Roger

1990-01-01

In the present assessment, the hydrogen containing halocarbons being considered as alternatives to the the presently used chlorofluorocarbons are the hydrochlorofluorocarbons (HCFCs) 123 (CF3CHCl2), 141b (CFCl2CH3), 142b (CF2ClCH3), 22 (CHF2Cl) and 124 (CF3CHFCl) and the hydrofluorocarbons (HFCs) 134a (CF3CH2F), 152a (CHF2CH3) and 125 (CF3CHF2). All of these HCFCs and HFCs will react with the hydroxyl (OH) radical in the troposphere, giving rise to haloalkyl radicals which then undergo a complex series of reactions in the troposphere. These reactions of the haloalkyl radicals formed from the initial OH radical reactions with the HCFCs and HFCs under tropospheric conditions are the focus here.

Atmospheric chemistry of n-butanol: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation in the presence and absence of NO(x).

PubMed

Hurley, M D; Wallington, T J; Laursen, L; Javadi, M S; Nielsen, O J; Yamanaka, T; Kawasaki, M

2009-06-25

Smog chamber/FTIR techniques were used to determine rate constants of k(Cl+n-butanol) = (2.21 +/- 0.38) x 10(-10) and k(OH+n-butanol) = (8.86 +/- 0.85) x 10(-12) cm(3) molecule(-1) s(-1) in 700 Torr of N(2)/O(2) diluent at 296 +/- 2K. The sole primary product identified from the Cl atom initiated oxidation of n-butanol in the absence of NO was butyraldehyde (38 +/- 2%, molar yield). The primary products of the Cl atom initiated oxidation of n-butanol in the presence of NO were (molar yield) butyraldehyde (38 +/- 2%), propionaldehyde (23 +/- 3%), acetaldehyde (12 +/- 4%), and formaldehyde (33 +/- 3%). The substantially lower yields of propionaldehyde, acetaldehyde, and formaldehyde as primary products in experiments conducted in the absence of NO suggests that chemical activation is important in the atmospheric chemistry of CH(3)CH(2)CH(O)CH(2)OH and CH(3)CH(O)CH(2)CH(2)OH alkoxy radicals. The primary products of the OH radical initiated oxidation of n-butanol in the presence of NO were (molar yields) butyraldehyde (44 +/- 4%), propionaldehyde (19 +/- 2%), and acetaldehyde (12 +/- 3%). In all cases, the product yields were independent of oxygen concentration over the partial pressure range of 10-600 Torr. The yields of propionaldehyde, acetaldehyde, and formaldehyde quoted above were not corrected for secondary formation via oxidation of higher aldehydes and should be treated as upper limits. The reactions of Cl atoms and OH radicals with n-butanol proceed 38 +/- 2 and 44 +/- 4%, respectively, via attack on the alpha-position to give an alpha-hydroxy alkyl radical which reacts with O(2) to give butyraldehyde. The results are discussed with respect to the atmospheric chemistry of n-butanol.

Direct observation of unimolecular decay of CH 3 CH 2 CHOO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Liu, Fang; Klippenstein, Stephen J.

2016-07-28

The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH3CH2CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice-Ramsperger-Kassel-Marcus calculations of the microcanonical unimolecular decay rate for CH3CH2CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronic structure calculations, contributes significantlymore » to the decay rate. Infrared transitions of CH3CH2CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH3CH2CHOO of ca. 10(7) s(-1), which are slower than those obtained for syn-CH3CHOO or (CH3)(2)COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH3CH2CHOO under atmospheric conditions, giving a rate of 279 s(-1) at 298 K.« less

Analysis of the kinetics and yields of OH radical production from the CH3OCH2 + O2 reaction in the temperature range 195-650 K: an experimental and computational study.

PubMed

Eskola, A J; Carr, S A; Shannon, R J; Wang, B; Blitz, M A; Pilling, M J; Seakins, P W; Robertson, S H

2014-08-28

The methoxymethyl radical, CH3OCH2, is an important intermediate in the low temperature combustion of dimethyl ether. The kinetics and yields of OH from the reaction of the methoxymethyl radical with O2 have been measured over the temperature and pressure ranges of 195-650 K and 5-500 Torr by detecting the hydroxyl radical using laser-induced fluorescence following the excimer laser photolysis (248 nm) of CH3OCH2Br. The reaction proceeds via the formation of an energized CH3OCH2O2 adduct, which either dissociates to OH + 2 H2CO or is collisionally stabilized by the buffer gas. At temperatures above 550 K, a secondary source of OH was observed consistent with thermal decomposition of stabilized CH3OCH2O2 radicals. In order to quantify OH production from the CH3OCH2 + O2 reaction, extensive relative and absolute OH yield measurements were performed over the same (T, P) conditions as the kinetic experiments. The reaction was studied at sufficiently low radical concentrations (∼10(11) cm(-3)) that secondary (radical + radical) reactions were unimportant and the rate coefficients could be extracted from simple bi- or triexponential analysis. Ab initio (CBS-GB3)/master equation calculations (using the program MESMER) of the CH3OCH2 + O2 system were also performed to better understand this combustion-related reaction as well as be able to extrapolate experimental results to higher temperatures and pressures. To obtain agreement with experimental results (both kinetics and yield data), energies of the key transition states were substantially reduced (by 20-40 kJ mol(-1)) from their ab initio values and the effect of hindered rotations in the CH3OCH2 and CH3OCH2OO intermediates were taken into account. The optimized master equation model was used to generate a set of pressure and temperature dependent rate coefficients for the component nine phenomenological reactions that describe the CH3OCH2 + O2 system, including four well-skipping reactions. The rate coefficients were fitted to Chebyshev polynomials over the temperature and density ranges 200 to 1000 K and 1 × 10(17) to 1 × 10(23) molecules cm(-3) respectively for both N2 and He bath gases. Comparisons with an existing autoignition mechanism show that the well-skipping reactions are important at a pressure of 1 bar but are not significant at 10 bar. The main differences derive from the calculated rate coefficient for the CH3OCH2OO → CH2OCH2OOH reaction, which leads to a faster rate of formation of O2CH2OCH2OOH.

Thermochemical and kinetic analysis on the reactions of O2 with products from OH addition to isobutene, 2-hydroxy-1,1-dimethylethyl, and 2-hydroxy-2-methylpropyl radicals: HO2 formation from oxidation of neopentane, Part II.

PubMed

Sun, Hongyan; Bozzelli, Joseph W; Law, Chung K

2007-06-14

Unimolecular dissociation of a neopentyl radical to isobutene and methyl radical is competitive with the neopentyl association with O2 ((3)Sigma(g)-) in thermal oxidative systems. Furthermore, both isobutene and the OH radical are important primary products from the reactions of neopentyl with O2. Consequently, the reactions of O2 with the 2-hydroxy-1,1-dimethylethyl and 2-hydroxy-2-methylpropyl radicals resulting from the OH addition to isobutene are important to understanding the oxidation of neopentane and other branched hydrocarbons. Reactions that correspond to the association of radical adducts with O2((3)Sigma(g)-) involve chemically activated peroxy intermediates, which can isomerize and react to form one of several products before stabilization. The above reaction systems were analyzed with ab initio and density functional calculations to evaluate the thermochemistry, reaction paths, and kinetics that are important in neopentyl radical oxidation. The stationary points of potential energy surfaces were analyzed based on the enthalpies calculated at the CBS-Q level. The entropies, S(degrees)298, and heat capacities, C(p)(T), (0

Atmospheric Chemistry of the Carbon Capture Solvent Monoethanolamine (MEA): A Theoretical Study

NASA Astrophysics Data System (ADS)

da Silva, G.

2012-12-01

The development of amine solvent technology for carbon capture and storage has the potential to create large new sources of amines to the atmosphere. The atmospheric chemistry of amines generally, and carbon capture solvents in particular, is not well understood. We have used quantum chemistry and master equation modelling to investigate the OH radical initiated oxidation of monoethanolamine (NH2CH2CH2OH), or MEA, the archetypal carbon capture solvent. The OH radical can abstract H atoms from either carbon atom in MEA, with negative reaction barriers. Treating these reactions with a two transition state model can reliably reproduce experimental rate constants and their temperature dependence. The products of the MEA + OH reaction, the NH2CHCH2OH and NH2CH2CHOH radicals, undergo subsequent reaction with O2, which has also been studied. In both cases chemically activated reactions that bypass peroxyl radical intermediates dominate, producing 2-iminoethanol + HO2 (from NH2CHCH2OH) or aminoacetaldehyde + HO2 (from NH2CH2CHOH), making the process HOx-neutral. The operation of chemically activated reaction mechanisms has implications for the ozone forming potential of MEA. The products of MEA photo-oxidation are proposed as important species in the formation of both organic and inorganic secondary aerosols, particularly through uptake of the imine 2-iminoethanol and subsequent hydrolysis to ammonia and glycolaldehyde.

Direct observation of unimolecular decay of CH{sub 3}CH{sub 2}CHOO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Liu, Fang; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2016-07-28

The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH{sub 3}CH{sub 2}CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice–Ramsperger–Kassel–Marcus calculations of the microcanonical unimolecular decay rate for CH{sub 3}CH{sub 2}CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronicmore » structure calculations, contributes significantly to the decay rate. Infrared transitions of CH{sub 3}CH{sub 2}CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH{sub 3}CH{sub 2}CHOO of ca. 10{sup 7} s{sup −1}, which are slower than those obtained for syn-CH{sub 3}CHOO or (CH{sub 3}){sub 2}COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH{sub 3}CH{sub 2}CHOO under atmospheric conditions, giving a rate of 279 s{sup −1} at 298 K.« less

Real-time observation of formation and relaxation dynamics of NH4 in (CH3OH)m(NH3)n clusters.

PubMed

Yamada, Yuji; Nishino, Yoko; Fujihara, Akimasa; Ishikawa, Haruki; Fuke, Kiyokazu

2009-03-26

The formation and relaxation dynamics of NH4(CH3OH)m(NH3)n clusters produced by photolysis of ammonia-methanol mixed clusters has been observed by a time-resolved pump-probe method with femtosecond pulse lasers. From the detailed analysis of the time evolutions of the protonated cluster ions, NH4(+)(CH3OH)m(NH3)n, the kinetic model has been constructed, which consists of sequential three-step reaction: ultrafast hydrogen-atom transfer producing the radical pair (NH4-NH2)*, the relaxation process of radical-pair clusters, and dissociation of the solvated NH4 clusters. The initial hydrogen transfer hardly occurs between ammonia and methanol, implying the unfavorable formation of radical pair, (CH3OH2-NH2)*. The remarkable dependence of the time constants in each step on the number and composition of solvents has been explained by the following factors: hydrogen delocalization within the clusters, the internal conversion of the excited-state radical pair, and the stabilization of NH4 by solvation. The dependence of the time profiles on the probe wavelength is attributed to the different ionization efficiency of the NH4(CH3OH)m(NH3)n clusters.

Degradation of poly(2-hydroxyethyl methacrylate) by gamma irradiation

NASA Astrophysics Data System (ADS)

Hill, David J. T.; O'Donnell, James H.; Pomery, Peter J.; Saadat, Giti

1996-11-01

Electron Spin Resinance (ESR) spectroscopy has been utilised to examine the effect of high energy radiation on poly(2-hydroxyethyl methacrylate) PHEMA. Radiation chemical yields ( G-values) for radicals were 1.7 and 1.2 for γ-irradiation at 77 K and ambient temperature, respectively. The ESR spectra at 77 and 300 K were simulated. The ESR spectrum at 77 K is a combination of six types of radicals ·CH 3, ·CH 2CH 2OH, COOCHCH 2OH, ·COO-, -CH- and ·CHO. However, after room temperature irradiation, the spectrum is a combination of methacrylate main chain scission radical and -CH-. The high stability of this radical at room temperature indicates the system is very rigid as a result of hydrogen bonding from the inherent side chain structure and radiation induced crosslinking due to labile hydrogen atoms in the side chain.

The reaction between CH 3O 2 and OH radicals: Product yields and atmospheric implications

DOE PAGES

Assaf, Emmanuel; Sheps, Leonid; Whalley, Lisa; ...

2017-01-25

The reaction between CH 3O 2 and OH radicals has been shown to be fast and to play an appreciable role for the removal of CH 3O 2 radials in remote environments such as the marine boundary layer. Two different experimental techniques have been used here to determine the products of this reaction. The HO 2 yield has been obtained from simultaneous time-resolved measurements of the absolute concentration of CH 3O 2, OH, and HO 2 radicals by cw-CRDS. The possible formation of a Criegee intermediate has been measured by broadband cavity enhanced UV absorption. A yield of Φ HO2more » = (0.8 ± 0.2) and an upper limit for Φ Criegee = 0.05 has been determined for this reaction, suggesting a minor yield of methanol or stabilized trioxide as a product. The impact of this reaction on the composition of the remote marine boundary layer has been determined by implementing these findings into a box model utilizing the Master Chemical Mechanism v3.2, and constraining the model for conditions found at the Cape Verde Atmospheric Observatory in the remote tropical Atlantic Ocean. Inclusion of the CH 3O 2+OH reaction into the model results in up to 30% decrease in the CH 3O 2 radical concentration while the HO 2 concentration increased by up to 20%. Finally, production and destruction of O 3 are also influenced by these changes, and the model indicates that taking into account the reaction between CH 3O 2 and OH leads to a 6% decrease of O 3.« less

The reaction between CH 3O 2 and OH radicals: Product yields and atmospheric implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assaf, Emmanuel; Sheps, Leonid; Whalley, Lisa

The reaction between CH 3O 2 and OH radicals has been shown to be fast and to play an appreciable role for the removal of CH 3O 2 radials in remote environments such as the marine boundary layer. Two different experimental techniques have been used here to determine the products of this reaction. The HO 2 yield has been obtained from simultaneous time-resolved measurements of the absolute concentration of CH 3O 2, OH, and HO 2 radicals by cw-CRDS. The possible formation of a Criegee intermediate has been measured by broadband cavity enhanced UV absorption. A yield of Φ HO2more » = (0.8 ± 0.2) and an upper limit for Φ Criegee = 0.05 has been determined for this reaction, suggesting a minor yield of methanol or stabilized trioxide as a product. The impact of this reaction on the composition of the remote marine boundary layer has been determined by implementing these findings into a box model utilizing the Master Chemical Mechanism v3.2, and constraining the model for conditions found at the Cape Verde Atmospheric Observatory in the remote tropical Atlantic Ocean. Inclusion of the CH 3O 2+OH reaction into the model results in up to 30% decrease in the CH 3O 2 radical concentration while the HO 2 concentration increased by up to 20%. Finally, production and destruction of O 3 are also influenced by these changes, and the model indicates that taking into account the reaction between CH 3O 2 and OH leads to a 6% decrease of O 3.« less

Hydroxo radicals, C-H activation, and Pt-C bond formation from 77 K photolysis of a platinum(IV) hydroxo complex.

PubMed

Wickramasinghe, Lasantha A; Sharp, Paul R

2014-11-17

Photolysis (380 nm) of trans,cis-Pt(PEt3)2(Cl)2(OH)(4-tft) (4-tft = 4-trifluoromethylphenyl) at 77 K in 2-methyltetrahydrofuran gives triplet emission, platinum(III), and a hydroxo radical. Benzyl radical emission is observed in toluene from the reaction of a portion of the OH radicals with toluene. Warming the photolyzed solutions gives platinacycle trans-Pt(CH2CH2PEt2)(PEt3)(Cl)2(4-tft) by hydrogen-atom abstraction from a PEt3 ligand and trans-Pt(PEt3)2(Cl)(4-tft) from net HOCl photoelimination. The platinacycle undergoes thermal reductive elimination at 298 K or photolytic reductive elimination, even at 77 K.

Characterization of supramolecular (H2O)18 water morphology and water-methanol (H2O)15(CH3OH)3 clusters in a novel phosphorus functionalized trimeric amino acid host.

PubMed

Raghuraman, Kannan; Katti, Kavita K; Barbour, Leonard J; Pillarsetty, Nagavarakishore; Barnes, Charles L; Katti, Kattesh V

2003-06-11

Phosphorus functionalized trimeric alanine compounds (l)- and (d)-P(CH(2)NHCH(CH(3))COOH)(3) 2 are prepared in 90% yields by the Mannich reaction of Tris(hydroxymethyl)phosphine 1 with (l)- or (d)- Alanine in aqueous media. The hydration properties of (l)-2 and (d)-2 in water and water-methanol mixtures are described. The crystal structure analysis of (l)-2.4H(2)O, reveals that the alanine molecules pack to form two-dimensional bilayers running parallel to (001). The layered structural motif depicts two closely packed monolayers of 2 each oriented with its phosphorus atoms projected at the center of the bilayer and adjacent monolayers are held together by hydrogen bonds between amine and carboxylate groups. The water bilayers are juxtaposed with the H-bonded alanine trimers leading to 18-membered (H(2)O)(18) water rings. Exposure of aqueous solution of (l)-2 and (d)-2 to methanol vapors resulted in closely packed (l)-2 and (d)-2 solvated with mixed water-methanol (H(2)O)(15)(CH(3)OH)(3) clusters. The O-O distances in the mixed methanol-water clusters of (l)-2.3H(2)O.CH(3)OH and (d)-2.3H(2)O.CH(3)OH (O-O(average) = 2.857 A) are nearly identical to the O-O distance observed in the supramolecular (H(2)O)(18) water structure (O-O(average) = 2.859 A) implying the retention of the hydrogen bonded structure in water despite the accommodation of hydrophobic methanol groups within the supramolecular (H(2)O)(15)(CH(3)OH)(3) framework. The O-O distances in (l)-2.3H(2)O.CH(3)OH and (d)-2.3H(2)O.CH(3)OH and in (H(2)O)(18) are very close to the O-O distance reported for liquid water (2.85 A).

Reflected shock tube studies of high-temperature rate constants for OH + CH4 --> CH3 + H2O and CH3 + NO2 --> CH3O + NO.

PubMed

Srinivasan, N K; Su, M-C; Sutherland, J W; Michael, J V

2005-03-10

The reflected shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm has been used to study the reactions OH + CH(4) --> CH(3) + H(2)O and CH(3) + NO(2) --> CH(3)O + NO. Over the temperature range 840-2025 K, the rate constants for the first reaction can be represented by the Arrhenius expression k = (9.52 +/- 1.62) x 10(-11) exp[(-4134 +/- 222 K)/T] cm(3) molecule(-1) s(-1). Since this reaction is important in both combustion and atmospheric chemistry, there have been many prior investigations with a variety of techniques. The present results extend the temperature range by 500 K and have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range 195-2025 K. A three-parameter expression describes the rate behavior over this temperature range, k = (1.66 x 10(-18))T(2.182) exp[(-1231 K)/T] cm(3) molecule(-1) s(-1). Previous theoretical studies are discussed, and the present evaluation is compared to earlier theoretical estimates. Since CH(3) radicals are a product of the reaction and could cause secondary perturbations in rate constant determinations, the second reaction was studied by OH radical production from the fast reactions CH(3)O --> CH(2)O + H and H + NO(2) --> OH + NO. The measured rate constant is 2.26 x 10(-11) cm(3) molecule(-1) s(-1) and is not dependent on temperature from 233 to 1700 K within experimental error.

Infrared and reflectron time-of-flight mass spectroscopic study on the synthesis of glycolaldehyde in methanol (CH3OH) and methanol-carbon monoxide (CH3OH-CO) ices exposed to ionization radiation.

PubMed

Maity, Surajit; Kaiser, Ralf I; Jones, Brant M

2014-01-01

We present conclusive evidence on the formation of glycolaldehyde (HOCH2CHO) synthesized within astrophysically relevant ices of methanol (CH3OH) and methanol-carbon monoxide (CH3OH-CO) upon exposure to ionizing radiation at 5.5 K. The radiation induced chemical processes of the ices were monitored on line and in situ via infrared spectroscopy which was complimented by temperature programmed desorption studies post irradiation, utilizing highly sensitive reflectron time-of-flight mass spectrometry coupled with single photon fragment free photoionization (ReTOF-PI) at 10.49 eV. Specifically, glycolaldehyde was observed via the v14 band and further enhanced with the associated frequency shifts of the carbonyl stretching mode observed in irradiated isotopologue ice mixtures. Furthermore, experiments conducted with mixed isotopic ices of methanol-carbon monoxide (13CH3OH-CO, CH3(18)OH-CO, CD3OD-13CO and CH3OH-C18O) provide solid evidence of at least three competing reaction pathways involved in the formation of glycolaldehyde via non-equilibrium chemistry, which were identified as follows: (i) radical-radical recombination of HCO and CH2OH formed via decomposition of methanol--the "two methanol pathway"; (ii) via the reaction of one methanol unit (CH2OH from the decomposition of CH3OH) with one carbon monoxide unit (HCO from the hydrogenation of CO)--the "one methanol, one carbon monoxide pathway"; and (iii) formation via hydrogenation of carbon monoxide resulting in radicals of HCO and CH2OH--the "two carbon monoxide pathway". In addition, temperature programmed desorption studies revealed an increase in the amount of glycolaldehyde formed, suggesting further thermal chemistry of trapped radicals within the ice matrix. Sublimation of glycolaldehyde during the warm up was also monitored via ReTOF-PI and validated via the mutual agreement of the associated isotopic frequency shifts within the infrared band positions and the identical sublimation profiles obtained from the ReTOF spectra and infrared spectroscopy of the corresponding isotopes. In addition, an isomer of glycolaldehyde (ethene-1,2-diol) was tentatively assigned. Confirmation of the identified pathways based on infrared spectroscopy was also obtained from the observed ion signals corresponding to isotopomers of glycolaldehyde. These coupled techniques provide clear, concise evidence of the formation of a complex and astrobiologically important organic, glycolaldehyde, relevant to the icy mantles observed in the interstellar medium.

Evaluated rate constants for selected HCFC's and HFC's with OH and O((sup)1D)

NASA Technical Reports Server (NTRS)

Hampson, Robert F.; Kurylo, Michael J.; Sander, Stanley P.

1990-01-01

The chemistry of HCFC's and HFC's in the troposphere is controlled by reactions with OH in which a hydrogen atom is abstracted from the halocarbon to form water and a halo-alkyl radical. The halo-alkyl radical subsequently reacts with molecular oxygen to form a peroxy radical. The reactions of HCFC's and HFC's with O(exp1D) atoms are unimportant in the troposphere, but may be important in producing active chlorine of OH in the stratosphere. Here, the rate constants for the reactions of OH and O(exp1D) with many HFC's and HCFC's are evaluated. Recommendations are given for the five HCFC's and three HFC's specified by AFEAS as primary alternatives as well as for all other isomers of C1 and C2 HCFC's and HFC's where rate data exist. In addition, recommendations are included for CH3CCl3, CH2Cl2, and CH4.

Radical routes to interstellar glycolaldehyde. The possibility of stereoselectivity in gas-phase polymerization reactions involving CH(2)O and ˙CH(2)OH.

PubMed

Wang, Tianfang; Bowie, John H

2010-10-21

A previous report that the interstellar molecule glycolaldehyde (HOCH(2)CHO) can be made from hydroxymethylene (HOCH:) and formaldehyde has been revisited at the CCSD(T)/6-311++G(3df,2p)//MP2/6-311++G(3df,2p) level of theory. This reaction competes with the formation of acetic acid and methylformate, molecules which have also been detected in interstellar clouds. Other possible modes of formation of glycolaldehyde by radical/radical reactions have been shown to be viable theoretically as follows: HO˙+˙CH2CHO -->HOCH2CHO [ΔG(Γ)(298K)=-303kJ mol⁻¹] HOCH2˙+˙CHO-->HOCH2CHO (-259kJ mol⁻¹). The species in these two processes are known interstellar molecules. Key radicals ˙CH(2)CHO and ˙CH(2)OH in these sequences have been shown to be stable for the microsecond duration of neutralization/reionization experiments in the dual collision cells of a VG ZAB 2HF mass spectrometer. The polymerization reaction HOCH(2)CH˙OH + nCH(2)O → HOCH(2)[CH(OH)](n)˙CHOH (n = 1 to 3) has been studied theoretically and shown to be energetically feasible, as is the cyclization reaction of HOCH(2)[(CH(2)OH)(4)]˙CHOH (in the presence of one molecule of water at the reacting centre) to form glucose. The probability of such a reaction sequence is small even if polymerization were to occur in interstellar ice containing a significant concentration of CH(2)O. The large number of stereoisomers produced by such a reaction sequence makes the formation of a particular sugar, again for example glucose, an inefficient synthesis. The possibility of stereoselectivity occurring during the polymerization was investigated for two diastereoisomers of HOCH(2)[(CHOH)](2)˙CHOH. No significant difference was found in the transition state energies for addition of CH(2)O to these two diastereoisomers, but a barrier difference of 12 kJ mol(-1) was found for the H transfer reactions ˙OCH(2)[(CHOH)](2)CH(2)OH → HOCH(2)[(CHOH)(2)˙CHOH of the two diastereoisomers.

Tunneling effects in the unimolecular decay of (CH 3) 2COO Criegee intermediates to OH radical products

DOE PAGES

Fang, Yi; Barber, Victoria P.; Klippenstein, Stephen J.; ...

2017-04-04

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH 3) 2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer with time-resolved detection of the resultant OH radical products. (CH 3) 2COO is prepared at specific energies in the 3900-4600 cm -1 region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity ofmore » the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH 3) 2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH 3) 2COO to OH products under atmospheric conditions of 276 s -1 at 298 K (high pressure limit). Furthermore, thermal unimolecular decay of (CH 3) 2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.« less

Tunneling effects in the unimolecular decay of (CH 3) 2COO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Barber, Victoria P.; Klippenstein, Stephen J.

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH 3) 2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer with time-resolved detection of the resultant OH radical products. (CH 3) 2COO is prepared at specific energies in the 3900-4600 cm -1 region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity ofmore » the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH 3) 2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH 3) 2COO to OH products under atmospheric conditions of 276 s -1 at 298 K (high pressure limit). Furthermore, thermal unimolecular decay of (CH 3) 2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.« less

Reactions of inorganic free radicals with liver protecting drugs

NASA Astrophysics Data System (ADS)

György, I.; Blázovics, A.; Fehér, J.; Földiák, G.

Liver protecting drugs, silibinin, a flavonolignane, and the dihydroquinoline derivates, CH 402 and MTDQ-DA, were shown to inhibit processes in which enzymatically or non-enzymatically generated free radicals were involved. Inorganic free radicals (N 3, (SCN) -2, OH, Trp, CO -2, O -2) produced by pulse radiolysis readily react with the compounds, which transform into exceptionally long-lived, unreactive transients. Time evolution of the UV and visible spectra indicate that oxidising radicals form a phenoxyl type radical from silibinin, while OH forms an adduct by attacking, simultaneously, at various sites of the molecule. Superoxide radicals reduce silibinin and oxidise CH 402 and MTDQ-DA. It is concluded that the drugs might exhibit antioxidant behavior in living systems.

Laboratory spectroscopy of methoxymethanol in the millimeter-wave range

NASA Astrophysics Data System (ADS)

Motiyenko, Roman A.; Margulès, Laurent; Despois, Didier; Guillemin, Jean-Claude

2018-02-01

Methoxymethanol, CH3OCH2OH is a very interesting candidate for detection in the interstellar medium since it can be formed in the recombination reaction between two radicals considered as intermediates in methanol formation: CH3O (already detected in the ISM) and CH2OH.

Kinetics of the reduction of cobalt(III) amine complexes by 1-hydroxy-1-methylethyl radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kusaba, K.; Ogino, Hiroshi; Bakac, A.

1989-03-08

In order to better understand the rate constants for the reduction of several cobalt complexes by 1-hydroxy-1-methylene radicals ({sup {sm bullet}}C(CH{sub 3}){sub 2}OH), the reactions of {sup {sm bullet}}(CH{sub 3}){sub 2}OH with several cobalt(III) complexes of bidentate amines have been studied. The Marcus-Hush theory was deemed the most appropriate for analysis of the kinetic data. The correlation between the kinetics of the reduction of the Co(III) amines by C(CH{sub 3}){sub 2}OH and the reduction of the first d-d band for Co(III) complexes is discussed. 21 refs., 2 figs., 1 tab.

FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms.

PubMed

Moreno, A; Gallego-Iniesta, M P; Taccone, R; Martín, M P; Cabañas, B; Salgado, M S

2014-10-01

Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298 ± 2 K) and atmospheric pressure (708 ± 8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm(3) molecule(-1) s(-1)): (3.27 ± 0.33) × 10(-11) and (4.43 ± 0.42) × 10(-11), for CH3CH═CHC(O)OCH3 and (CH3)2CH═CHC(O)OCH3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N2 and air were used as the bath gases. The following rate coefficients were obtained (in cm(3) molecule(-1) s(-1)): k3 (CH2═CHC(O)O(CH2)5CH3 + Cl) = (3.31 ± 0.31) × 10(-10), k4(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + Cl) = (3.46 ± 0.31) × 10(-10), k5(CH2═CHC(O)O(CH2)5CH3 + OH) = (2.28 ± 0.23) × 10(-11), and k6(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + OH) = (2.74 ± 0.26) × 10(-11). The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in -C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming.

Measuring Atmospheric Free Radicals Using Chemical Amplification

DTIC Science & Technology

1988-05-01

CH 3Br, H2S, and SO2 [Logan et al., 1981]. Recently, the OH radical has been determined as the dominant loss mechanism for isoprene and monoterpenes ...W. Heaps, D. Philen, and T. McGee, Bondary Layer Measurements of the OH Radical in the Vicinity of an Isolated Power Plant Plume: SO2 and NO2

A theoretical study of the decomposition of gold (I) complexes

NASA Astrophysics Data System (ADS)

Tossell, J. A.

1998-04-01

Structures, energetics and excitation energies are calculated for the gold (I) complexes CH 3Au, (CH 3) 2Au -, CH 3AuOH 2, CH 3AuPH 3 and PH 3AuCl at the Hartree-Fock and MP2 levels of theory, and for CH 3AuP(CH 3) 3, CH 3AuP(OH) 3 and Au 3Cl 3 at the HF level. The lowest-energy neutral triplet state of each 2-coordinate compound dissociates into either two or three radical species (always including the CH 3 radical), with the exception of (CH 3) 2Au - which shows only slight Au-C bond elongation. In contrast, the doublet anion states dissociate neutral ligands, like PH 3, but do not dissociate CH 3. These results indicate that gold (I) chemical vapor deposition processes must involve excited states of the neutrals rather than their anions.

Ab Initio Chemical Kinetics for the CH3 + O((3)P) Reaction and Related Isomerization-Decomposition of CH3O and CH2OH Radicals.

PubMed

Xu, Z F; Raghunath, P; Lin, M C

2015-07-16

The kinetics and mechanism of the CH3 + O reaction and related isomerization-decomposition of CH3O and CH2OH radicals have been studied by ab initio molecular orbital theory based on the CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVTZ, CCSD/aug-cc-pVDZ, and G2M//B3LYP/6-311+G(3df,2p) levels of theory. The predicted potential energy surface of the CH3 + O reaction shows that the CHO + H2 products can be directly generated from CH3O by the TS3 → LM1 → TS7 → LM2 → TS4 path, in which both LM1 and LM2 are very loose and TS7 is roaming-like. The result for the CH2O + H reaction shows that there are three low-energy barrier processes including CH2O + H → CHO + H2 via H-abstraction and CH2O + H → CH2OH and CH2O + H → CH3O by addition reactions. The predicted enthalpies of formation of the CH2OH and CH3O radicals at 0 K are in good agreement with available experimental data. Furthermore, the rate constants for the forward and some key reverse reactions have been predicted at 200-3000 K under various pressures. Based on the new reaction pathway for CH3 + O, the rate constants for the CH2O + H and CHO + H2 reactions were predicted with the microcanonical variational transition-state/Rice-Ramsperger-Kassel-Marcus (VTST/RRKM) theory. The predicted total and individual product branching ratios (i.e., CO versus CH2O) are in good agreement with experimental data. The rate constant for the hydrogen abstraction reaction of CH2O + H has been calculated by the canonical variational transition-state theory with quantum tunneling and small-curvature corrections to be k(CH2O + H → CHO + H2) = 2.28 × 10(-19) T(2.65) exp(-766.5/T) cm(3) molecule(-1) s(-1) for the 200-3000 K temperature range. The rate constants for the addition giving CH3O and CH2OH and the decomposition of the two radicals have been calculated by the microcanonical RRKM theory with the time-dependent master equation solution of the multiple quantum well system in the 200-3000 K temperature range at 1 Torr to 100 atm. The predicted rate constants are in good agreement with most of the available data.

Direct production of OH radicals upon CH overtone activation of (CH{sub 3}){sub 2}COO Criegee intermediates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fang; Beames, Joseph M.; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2014-12-21

Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH{sub 3}){sub 2}COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol{sup −1}) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features,more » indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X{sup 2}Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH{sub 3}){sub 2}COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH{sub 3}CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].« less

On the Formation of the C2H6O Isomers Ethanol (C2H5OH) and Dimethyl Ether (CH3OCH3) in Star-forming Regions

NASA Astrophysics Data System (ADS)

Bergantini, Alexandre; Maksyutenko, Pavlo; Kaiser, Ralf I.

2017-06-01

The structural isomers ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3) were detected in several low-, intermediate-, and high-mass star-forming regions, including Sgr B2, Orion, and W33A, with the relative abundance ratios of ethanol/dimethyl ether varying from about 0.03 to 3.4. Until now, no experimental data regarding the formation mechanisms and branching ratios of these two species in laboratory simulation experiments could be provided. Here, we exploit tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) to detect and analyze the production of complex organic molecules (COMs) resulting from the exposure of water/methane (H2O/CH4) ices to energetic electrons. The main goal is to understand the formation mechanisms in star-forming regions of two C2H6O isomers: ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3). The results show that the experimental branching ratios favor the synthesis of ethanol versus dimethyl ether (31 ± 11:1). This finding diverges from the abundances observed toward most star-forming regions, suggesting that production routes on interstellar grains to form dimethyl ether might be missing; alternatively, ethanol can be overproduced in the present simulation experiments, such as via radical-radical recombination pathways involving ethyl and hydroxyl radicals. Finally, the PI-ReTOF-MS data suggest the formation of methylacetylene (C3H4), ketene (CH2CO), propene (C3H6), vinyl alcohol (CH2CHOH), acetaldehyde (CH3CHO), and methyl hydroperoxide (CH3OOH), in addition to ethane (C2H6), methanol (CH3OH), and CO2 detected from infrared spectroscopy. The yield of all the confirmed species is also determined.

Lanthanide chelates of (bis)-hydroxymethyl-substituted DTTA with potential application as contrast agents in magnetic resonance imaging.

PubMed

Silvério, Sara; Torres, Susana; Martins, André F; Martins, José A; André, João P; Helm, Lothar; Prata, M Isabel M; Santos, Ana C; Geraldes, Carlos F G C

2009-06-28

A novel bis-hydroxymethyl-substituted DTTA chelator N'-Bz-C(4,4')-(CH(2)OH)(2)-DTTA () and its DTPA analogue C(4,4')-(CH(2)OH)(2)-DTPA () were synthesized and characterized. A variable-temperature (1)H NMR spectroscopy study of the solution dynamics of their diamagnetic (La) and paramagnetic (Sm, Eu) Ln(3+) complexes showed them to be rigid when compared with analogous Ln(3+)-DTTA and Ln(3+)-DTPA complexes, as a result of their C(4,4')-(CH(2)OH)(2) ligand backbone substitution. The parameters that govern the water (1)H relaxivity of the [Gd()(H(2)O)(2)](-) and [Gd()(H(2)O)](2-) complexes were obtained by (17)O and (1)H NMR relaxometry. While the relaxometric behaviour of the [Gd()(H(2)O)](2-) complex is very similar to the parent [Gd(DTPA)(H(2)O)](2-) system, the [Gd()(H(2)O)(2)](-) complex displays higher relaxivity, due to the presence of two inner sphere water molecules and an accelerated, near optimal water exchange rate. The [Gd()(H(2)O)(2)](-) complex interacts weakly with human serum albumin (HSA), and its fully bound relaxivity is limited by slow water exchange, as monitored by (1)H NMR relaxometry. This complex interacts weakly with phosphate, but does not form ternary complexes with bidentate bicarbonate and l-lactate anions, indicating that the two inner-sphere water molecules of the [Gd()(H(2)O)(2)](-) complex are not located in adjacent positions in the coordination sphere of the Gd(3+) ion. The transmetallation reaction rate of [Gd()(H(2)O)(2)](-) with Zn(2+) in phosphate buffer solution (pH 7.0) was measured to be similar to that of the backbone unsubstituted [Gd(DTTA-Me)(H(2)O)(2)](-), but twice faster than for [Gd(DTPA-BMA)(H(2)O)]. The in vivo biodistribution studies of the (153)Sm(3+)-labelled ligand () in Wistar rats reveal slow blood elimination and short term fixation in various organs, indicating some dissociation. The bis-hydroxymethyl-substituted DTTA skeleton can be seen as a new lead for the synthesis of high relaxivity contrast agents, although its low thermodynamic and kinetic stability will limit its use to in vitro and animal studies.

Exploring the potential for spatio-temporal mapping of VOC-OH reactions from column measurements of CH2O and NO2

NASA Astrophysics Data System (ADS)

Valin, L. C.; Fiore, A. M.; Chance, K.; Nowlan, C. R.; Gonzalez Abad, G.; Browne, E. C.

2014-12-01

Reactions of OH with volatile organic compounds (VOC) such as CH4 and isoprene produce formaldehyde (CH2O). The concentration of OH and the chemistry of peroxy radicals, a reactive intermediate of VOC + OH reactions, depend strongly on the concentration of NOx. Here, we investigate the influence of NOx on the formation of CH2O in an isoprene-rich atmosphere (Martin Lake Power Plant, NE Texas) and in a "background" atmosphere (Navajo Power Plant, N Arizona) using conceptual models and the WRF-Chem regional chemistry-transport model alongside satellite-based (Aura-OMI) and flight-based (ARCTAS) measurements. In the conceptual model, the enhancement of CH2O in an NO2 plume is large and depends on the magnitude of the OH enhancement, the lifetime of the parent VOC, the concentration of intermediate oxidation products, and the impact of NOx on the branching ratios of peroxy radicals. Preliminary analysis of WRF-Chem results supports these findings. For a large point source of NOx in a low NOx-background, the enhancement of the CH2O concentration in the NOx plume is more than two times that of the surrounding region in both the isoprene-rich and the "background" WRF-Chem simulations. Furthermore, the spatial correlation of OH and CH2O in these simulated plumes suggests that simultaneous measurement of CH2O and NO2 offers the potential to better constrain the processes affecting the reaction of VOC with OH, and thus the factors controlling O3 production and the NOx lifetime. The precision of UV/Visible spectrometers planned for future geostationary missions, such as TEMPO, suggest that the routine measurement of these relationships will be possible.

Rate coefficients for the gas-phase reaction of the hydroxyl radical with CH2=CHF and CH2=CF2.

PubMed

Baasandorj, Munkhbayar; Knight, Gary; Papadimitriou, Vassileios C; Talukdar, Ranajit K; Ravishankara, A R; Burkholder, James B

2010-04-08

Rate coefficients, k, for the gas-phase reaction of the OH radical with CH(2)=CHF (k(1)) and CH(2)=CF(2) (k(2)) were measured under pseudo-first-order conditions in OH using pulsed laser photolysis to produce OH and laser-induced fluorescence (PLP-LIF) to detect it. Rate coefficients were measured over a range of temperature (220-373 K) and bath gas pressure (20-600 Torr; He, N(2)). The rate coefficients were found to be independent of pressure. The measured rate coefficient for reaction 1 at room temperature was k(1)(296 K) = (5.18 +/- 0.50) x 10(-12) cm(3) molecule(-1) s(-1), independent of pressure, and the temperature dependence is given by the Arrhenius expression k(1)(T) = (1.75 +/- 0.20) x 10(-12) exp[(316 +/- 25)/T] cm(3) molecule(-1) s(-1); the rate coefficients for reaction 2 were k(2)(296 K) = (2.79 +/- 0.25) x 10(-12) cm(3) molecule(-1) s(-1) and k(2)(T) = (1.75 +/- 0.20) x 10(-12) exp[(140 +/- 20)/T] cm(3) molecule(-1) s(-1). The quoted uncertainties are 2sigma (95% confidence level) and include estimated systematic errors. The fall-off parameters for reaction 2 of k(infinity) = 3 x 10(-12) cm(3) molecule(-1) s(-1) and k(0)(296 K) = 1.8 x 10(-28) cm(6) molecule(-2) s(-1) with F(c) = 0.6 reproduce the room temperature data obtained in this study combined with the low pressure rate coefficient data from Howard (J. Chem. Phys. 1976, 65, 4771). OH radical formation was observed for reactions 1 and 2 in the presence of O(2), and the mechanism was investigated using (18)OH and OD rate coefficient measurements with CH(2)=CHF and CH(2)=CF(2) over a range of temperature (260-373 K) and pressure (20-100 Torr, He). Quantum chemical calculations using density functional theory (DFT) were used to determine the geometries and energies of the reactants and adducts formed in reactions 1 and 2 and the peroxy radicals formed following the addition of O(2). The atmospheric lifetimes of CH(2)=CHF and CH(2)=CF(2) due to loss by reaction with OH are approximately 2 and 4 days, respectively. Infrared absorption spectra of CH(2)=CHF and CH(2)=CF(2) were measured, and global warming potentials (GWP) values of 0.7 for CH(2)=CHF and 0.9 for CH(2)=CF(2) were obtained for the 100 year time horizon.

Mechanistic and kinetic study of the CH3CO + O2 reaction.

PubMed

Hou, Hua; Li, Aixiao; Hu, Hongyi; Li, Yuzhen; Li, Hui; Wang, Baoshan

2005-06-08

Potential-energy surface of the CH3CO + O2 reaction has been calculated by ab initio quantum chemistry methods. The geometries were optimized using the second-order Moller-Plesset theory (MP2) with the 6-311G(d,p) basis set and the coupled-cluster theory with single and double excitations (CCSD) with the correlation consistent polarized valence double zeta (cc-pVDZ) basis set. The relative energies were calculated using the Gaussian-3 second-order Moller-Plesset theory with the CCSD/cc-pVDZ geometries. Multireference self-consistent-field and MP2 methods were also employed using the 6-311G(d,p) and 6-311++G(3df,2p) basis sets. Both addition/elimination and direct abstraction mechanisms have been investigated. It was revealed that acetylperoxy radical [CH3C(O)OO] is the initial adduct and the formation of OH and alpha-lactone [CH2CO2(1A')] is the only energetically accessible decomposition channel. The other channels, e.g., abstraction, HO2 + CH2CO, O + CH3CO2, CO + CH3O2, and CO2 + CH3O, are negligible. Multichannel Rice-Ramsperger-Kassel-Marcus theory and transition state theory (E-resolved) were employed to calculate the overall and individual rate coefficients and the temperature and pressure dependences. Fairly good agreement between theory and experiments has been obtained without any adjustable parameters. It was concluded that at pressures below 3 Torr, OH and CH2CO2(1A') are the major nascent products of the oxidation of acetyl radicals, although CH2CO2(1A') might either undergo unimolecular decomposition to form the final products of CH2O + CO or react with OH and Cl to generate H2O and HCl. The acetylperoxy radicals formed by collisional stabilization are the major products at the elevated pressures. In atmosphere, the yield of acetylperoxy is nearly unity and the contribution of OH is only marginal.

The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde. [photochemical reactions in stratosphere

NASA Technical Reports Server (NTRS)

Osif, T. L.

1976-01-01

An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.

A flash photolysis resonance fluorescence investigation of the reaction OH + CH3CCl3 yields H2O + CH2CCl3. [in troposphere

NASA Technical Reports Server (NTRS)

Kurylo, M. J.; Anderson, P. C.; Klais, O.

1979-01-01

The absolute rate constant for the reaction OH + CH3CCl3 yields H2O + CH2CCl3 was determined by the flash photolysis resonance fluorescence method from 253 to 363K. The use of the Arrhenius equation with atmospheric observational data on methyl chloroform nearly doubles the predicted tropospheric OH reaction sink strength for the removal of atmospheric gases whose lifetimes are controlled by OH. The increased use of methyl chloroform instead of the restricted trichloroethylene focused attention to its role in stratospheric ozone depletion, producing modeling analyses to determine the amount of released methyl chloroform which reaches the stratosphere. Since the primary atmospheric loss of CH3CCl3 is considered by reaction with OH radicals, these data are used to compute an average tropospheric OH concentration and the strength of the 'global tropospheric OH reaction sink'.

Formation of interstellar methanol ice prior to the heavy CO freeze-out stage

NASA Astrophysics Data System (ADS)

Qasim, D.; Chuang, K.-J.; Fedoseev, G.; Ioppolo, S.; Boogert, A. C. A.; Linnartz, H.

2018-04-01

Context. The formation of methanol (CH3OH) on icy grain mantles during the star formation cycle is mainly associated with the CO freeze-out stage. Yet there are reasons to believe that CH3OH also can form at an earlier period of interstellar ice evolution in CO-poor and H2O-rich ices. Aims: This work focuses on CH3OH formation in a H2O-rich interstellar ice environment following the OH-mediated H-abstraction in the reaction, CH4 + OH. Experimental conditions are systematically varied to constrain the CH3OH formation yield at astronomically relevant temperatures. Methods: CH4, O2, and hydrogen atoms are co-deposited in an ultrahigh vacuum chamber at 10-20 K. OH radicals are generated by the H + O2 surface reaction. Temperature programmed desorption - quadrupole mass spectrometry (TPD-QMS) is used to characterize CH3OH formation, and is complemented with reflection absorption infrared spectroscopy (RAIRS) for CH3OH characterization and quantitation. Results: CH3OH formation is shown to be possible by the sequential surface reaction chain, CH4 + OH → CH3 + H2O and CH3 + OH → CH3OH at 10-20 K. This reaction is enhanced by tunneling, as noted in a recent theoretical investigation Lamberts et al. (2017, A&A, 599, A132). The CH3OH formation yield via the CH4 + OH route versus the CO + H route is approximately 20 times smaller for the laboratory settings studied. The astronomical relevance of the new formation channel investigated here is discussed.

Formation of formic acid and organic peroxides in the ozonolysis of ethene with added water vapour

NASA Astrophysics Data System (ADS)

Horie, Osamu; Neeb, Peter; Limbach, Stefan; Moortgat, Geert K.

1994-07-01

Ozonolysis of C2H4 was carried out in a 580 l glass reaction vessel at 1-5 ppm reactant concentrations, with added water vapour. Under dry conditions ([H2O]0 = 0.5 ppm), HCHO, CO, CO2, (CHO)2O (formic acid anhydride), H2O2, and CH3OOH were identified as the reaction products. Under wet conditions ([H2O]0 = 2 × 104 ppm), HCOOH yields approaching ca. 20% of the converted C2H4, were observed, while no (CHO)2O was formed. Hydroxymethyl hydroperoxide, HOCH2OOH, was observed as the major peroxide, and found to be formed only in the presence of water vapour. Direct reactions of H2O vapour with the excited CH2OO* radicals and with stabilized CH2OO radicals are postulated to explain the formation of HCOOH and HOCH2OOH in the presence of water vapour, respectively.

Laboratory Study of the OH + Permethylsiloxane (L2, L3, D3, and D4) Reaction Rate Coefficients Between 240 and 370 K

NASA Astrophysics Data System (ADS)

Burkholder, J. B.; Bernard, F.; Papadimitriou, V. C.

2016-12-01

The atmospheric chemistry of organosiloxanes has recently been implicated in the formation of new particles as well as regional and indoor air quality. Methylsiloxanes with Si<6 are relatively volatile compounds with either linear or cyclic molecular structures. Methylsiloxanes are found in consumer goods such as cosmetics, textiles, health care and household products and in industrial applications as solvents and lubricants. They are released into the atmosphere during manufacturing, use, and disposal and have been observed in the atmosphere in ppb levels in certain locations. However, the fundamental chemical properties of this class of compounds, particularly their reactivity with the OH radical, are presently not fully characterized. In this work, the temperature dependence of the rate coefficients for the OH radical reaction with the simplest linear (L2 and L3) and cyclic (D3 and D4) siloxanes were measured: OH + (CH3)3SiOSi(CH3)3 = Products L2OH + [(CH3)3SiO]2Si(CH3)2 = Products L3OH + [-Si(CH3)2O-]3 = Products D3OH + [-Si(CH3)2O-]4 = Products D4OH rate coefficients were measured under pseudo-first conditions in OH over the temperature range 240-370 K using a pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique and at 296 K using a relative rate method. The present results are compared with available literature data where possible and discrepancies are discussed. The results from this work will be discussed in terms of the atmospheric lifetimes of these methylsiloxanes and the reactivity trends for this class of compound.

Mechanism and kinetics of the atmospheric degradation of 2-formylcinnamaldehyde with O3 and hydroxyl OH radicals - a theoretical study

NASA Astrophysics Data System (ADS)

Thangamani, D.; Shankar, R.; Vijayakumar, S.; Kolandaivel, P.

2016-10-01

In the present investigation, the reaction mechanism and kinetics of 2-formylcinnamaldehyde (2-FC) with O3 and hydroxyl OH radicals were studied. The reaction of 2-FC with O3 radical are initiated by the formation of primary ozonide, whereas the reaction of 2-FC with the hydroxyl OH radical are initiated by two different ways: (1). H-atom abstraction by hydroxyl OH radical from the -CHO and -CH = CHCHO group of 2-FC (2). Hydroxyl OH addition to the -CH = CHCHO group to the ring-opened 2-FC. These reactions lead to the formation of an alkyl radical. The reaction pathways corresponding to the reactions between 2-FC with O3 and hydroxyl OH radicals have been analysed using density functionals of B3LYP and M06-2X level of methods with the 6-31+G(d,p) basis set. Single-point energy calculations for the most favourable reactive species are determined by B3LYP/6-311++G(d,p) and CCSD(T)/6-31+G(d,p) levels of theory. From the obtained results, the hydroxyl OH addition at C8 position of 2-FC are most favourable than the C9 position of 2-FC. The subsequent reactions of the alkyl radicals, formed from the hydroxyl OH addition at C8 position, are analysed in detail. The individual and overall rate constant for the most favourable reactions are calculated by canonical variational transition theory with small-curvature tunnelling corrections over the temperature range of 278-350 K. The calculated theoretical rate constants are in good agreement with the available experimental data. The Arrhenius plot of the rate constants with the temperature are fitted and the atmospheric lifetimes of the 2-FC with hydroxyl OH radical reaction in the troposphere calculate for the first time, which can be applied to the study on the atmospheric implications. The condensed Fukui function has been verified for the most favourable reaction sites. This study can be regarded as an attempt to investigate the O3-initiated and hydroxyl OH-initiated reaction mechanisms of 2-FC in the atmosphere.

The reaction of peroxy radicals with OH: rate constants and HO2 yields

NASA Astrophysics Data System (ADS)

Fittschen, C. M.; Assaf, E.; Schoemaecker, C.; Vereecken, L.

2017-12-01

Peroxy radicals, RO2, are key species in the atmosphere. They are formed from a reaction of OH radicals with hydrocarbon: RH + OH + O2 → RO2 + H2O In polluted environments, RO2 radicals react predominantly with NO, leading to formation of NO2 and eventually through photolysis of NO2 to formation of O3. At low NOx concentrations such as in the marine boundary layer or the background troposphere, the lifetime of RO2 radicals increases and other reaction pathways become competitive. Atmospheric chemistry models have considered until recently only the self- and cross reaction with other RO2 radicals or with HO2 radicals as the major fate for RO2 radicals under low NOx conditions. Recently, the rate constants for the reaction of peroxy radicals with OH radicals RO2 + OH → products has been measured for CH3O2 [1, 2] and C2H5O2 [3] and it was shown to become competitive to other sinks [4]. However, in order to evaluate the impact of this so far neglected sink for peroxy radicals on the composition of remote atmospheres, the reaction products must be known. A recently improved experimental set-up combining laser photolysis with two simultaneous cw-CRDS detections in the near IR allowing for a time resolved, absolute quantification of OH and RO2 radicals has been used for a further investigation of this class of reactions. High-repetition rate LIF is used for determining relative OH profiles. For CH3O2 radicals, HO2 has been determined as major product recently [5]. Currently, we study the next larger perxoy, C2H5O2, using different radical precursors (C2H5I, (COCl)2/C2H6, XeF2/C2H6) and also deuterated C2D5I in order to elucidate the product yield. Preliminary results show a much lower HO2 yield for C2H5O2 compared to CH3O2. The most recent results will be presented at the conference. [1] A. Bossolasco, E. Faragó, C. Schoemaecker, and C. Fittschen, CPL, 593, 7, (2014). [2] E. Assaf, B. Song, A. Tomas, C. Schoemaecker, C. Fittschen, JPC A, 120, 8923 (2016) [3] Eszter Faragó, Coralie Schoemaecker, Bela Viskolcz, and Christa Fittschen, CPL, 619, 196, (2015). [4] Christa Fittschen, Lisa Whalley, and Dwayne Heard, EST, 118, 7700, (2014). [5] E. Assaf, L. Sheps, L. Whalley, D. Heard, A. Tomas, C. Schoemaecker, C. Fittschen, EST, 51, 2170 (2017)

On-Chip Electrophoresis in Supported Lipid Bilayer Membranes Achieved Using Low Potentials

PubMed Central

2013-01-01

A micro supported lipid bilayer (SLB) electrophoresis method was developed, which functions at low potentials and appreciable operating times. To this end, (hydroxymethyl)-ferrocene (FcCH2OH) was employed to provide an electrochemical reaction at the anode and cathode at low applied potential to avoid electrolysis of water. The addition of FcCH2OH did not alter the SLB characteristics or affect biomolecule function, and pH and temperature variations and bubble formation were eliminated. Applying potentials of 0.25–1.2 V during flow gave homogeneous electrical fields and a fast, reversible, and strong build-up of a charged dye-modified lipid in the direction of the oppositely charged electrode. Moreover, streptavidin mobility could be modulated. This method paves the way for further development of analytical devices. PMID:24345193

Formation of ethylene glycol and other complex organic molecules in star-forming regions

NASA Astrophysics Data System (ADS)

Rivilla, V. M.; Beltrán, M. T.; Cesaroni, R.; Fontani, F.; Codella, C.; Zhang, Q.

2017-02-01

Context. The detection of complex organic molecules related with prebiotic chemistry in star-forming regions allows us to investigate how the basic building blocks of life are formed. Aims: Ethylene glycol (CH2OH)2 is the simplest sugar alcohol and the reduced alcohol of the simplest sugar glycoladehyde (CH2OHCHO). We study the molecular abundance and spatial distribution of (CH2OH)2, CH2OHCHO and other chemically related complex organic species (CH3OCHO, CH3OCH3, and C2H5OH) towards the chemically rich massive star-forming region G31.41+0.31. Methods: We analyzed multiple single-dish (Green Bank Telescope and IRAM 30 m) and interferometric (Submillimeter Array) spectra towards G31.41+0.31, covering a range of frequencies from 45 to 258 GHz. We fitted the observed spectra with a local thermodynamic equilibrium (LTE) synthetic spectra, and obtained excitation temperatures and column densities. We compared our findings in G31.41+0.31 with the results found in other environments, including low- and high-mass star-forming regions, quiescent clouds and comets. Results: We report for the first time the presence of the aGg' conformer of (CH2OH)2 towards G31.41+0.31, detecting more than 30 unblended lines. We also detected multiple transitions of other complex organic molecules such as CH2OHCHO, CH3OCHO, CH3OCH3, and C2H5OH. The high angular resolution images show that the (CH2OH)2 emission is very compact, peaking towards the maximum of the 1.3 mm continuum. These observations suggest that low abundance complex organic molecules, like (CH2OH)2 or CH2OHCHO, are good probes of the gas located closer to the forming stars. Our analysis confirms that (CH2OH)2 is more abundant than CH2OHCHO in G31.41+0.31, as previously observed in other interstellar regions. Comparing different star-forming regions we find evidence of an increase of the (CH2OH)2/CH2OHCHO abundance ratio with the luminosity of the source. The CH3OCH3/CH3OCHO and (CH2OH)2/C2H5OH ratios are nearly constant with luminosity. We also find that the abundance ratios of pairs of isomers (CH2OHCHO/CH3OCHO and C2H5OH/CH3OCH3) decrease with the luminosity of the sources. Conclusions: The most likely explanation for the behavior of the (CH2OH)2/CH2OHCHO ratio is that these molecules are formed by different chemical formation routes not directly linked, although different formation and destruction efficiencies in the gas phase cannot be ruled out. The most likely formation route of (CH2OH)2 is by combination of two CH2OH radicals on dust grains. We also favor that CH2OHCHO is formed via the solid-phase dimerization of the formyl radical HCO. The interpretation of the observations also suggests a chemical link between CH3OCHO and CH3OCH3, and between (CH2OH)2 and C2H5OH. The behavior of the abundance ratio C2H5OH/CH3OCH3 with luminosity may be explained by the different warm-up timescales in hot cores and hot corinos. The reduced spectra (ASCII files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A59

Formation of a Criegee intermediate in the low-temperature oxidation of dimethyl sulfoxide.

PubMed

Asatryan, Rubik; Bozzelli, Joseph W

2008-04-07

Dimethyl sulfoxide (DMSO) is the major sulfur-containing constituent of the Marine Boundary Layer. It is a significant source of H2SO4 aerosol/particles and methane sulfonic acid via atmospheric oxidation processes, where the mechanism is not established. In this study, several new, low-temperature pathways are revealed in the oxidation of DMSO using CBS-QB3 and G3MP2 multilevel and B3LYP hybrid density functional quantum chemical methods. Unlike analogous hydrocarbon peroxy radicals the chemically activated DMSO peroxy radical, [CH3S(=O)CH2OO*]*, predominantly undergoes simple dissociation to a methylsulfinyl radical CH3S*(=O) and a Criegee intermediate, CH2OO, with the barrier to dissociation 11.3 kcal mol(-1) below the energy of the CH3S(=O)CH2* + O2 reactants. The well depth for addition of O2 to the CH3S(=O)CH2 precursor radical is 29.6 kcal mol(-1) at the CBS-QB3 level of theory. We believe that this reaction may serve an important role in atmospheric photochemical and irradiated biological (oxygen-rich) media where formation of initial radicals is facilitated even at lower temperatures. The Criegee intermediate (carbonyl oxide, peroxymethylene) and sulfinyl radical can further decompose, resulting in additional chain branching. A second reaction channel important for oxidation processes includes formation (via intramolecular H atom transfer) and further decomposition of hydroperoxide methylsulfoxide radical, *CH2S(=O)CH2OOH over a low barrier of activation. The initial H-transfer reaction is similar and common in analogous hydrocarbon radical + O2 reactions; but the subsequent very low (3-6 kcal mol(-1)) barrier (14 kcal mol(-1) below the initial reagents) to beta-scission products is not common in HC systems. The low energy reaction of the hydroperoxide radical is a beta-scission elimination of *CH2S(=O)CH2OOH into the CH2=S=O + CH2O + *OH product set. This beta-scission barrier is low, because of the delocalization of the *CH2 radical center through the -S(=O) group, to the -CH2OOH fragment in the transition state structure. The hydroperoxide methylsulfoxide radical can also decompose via a second reaction channel of intramolecular OH migration, yielding formaldehyde and a sulfur-centered hydroxymethylsulfinyl radical HOCH2S*(=O). The barrier of activation relative to initial reagents is 4.2 kcal mol(-1). Heats of formation for DMSO, DMSO carbon-centered radical and Criegee intermediate are evaluated at 298 K as -35.97 +/- 0.05, 13.0 +/- 0.2 and 25.3 +/- 0.7 kcal mol(-1) respectively using isodesmic reaction analysis. The [CH3S*(=O) + CH2OO] product set is shown to form a van der Waals complex that results in O-atom transfer reaction and the formation of new products CH3SO2* radical and CH2O. Proper orientation of the Criegee intermediate and methylsulfinyl radical, as a pre-stabilized pre-reaction complex, assist the process. The DMSO radical reaction is also compared to that of acetonyl radical.

The gas phase origin of complex organic molecules precursors in prestellar cores

NASA Astrophysics Data System (ADS)

Bacmann, A.; Faure, A.

2015-05-01

Complex organic molecules (COMs) have long been observed in the warm regions surrounding nascent protostars. The recent discovery of oxygen-bearing COMs like methyl formate or dimethyl ether in prestellar cores (Bacmann et al. [2]), where gas and dust temperatures rarely exceed 10-15 K, has challenged the previously accepted models according to which COM formation relied on the diffusion of heavy radicals on warm (˜30 K) grains. Following these detections, new questions have arisen: do non-thermal processes play a role in increasing radical mobility or should new gas-phase routes be explored? The radicals involved in the formation of the aforementioned COMs, HCO and CH3O represent intermediate species in the grain-surface synthesis of methanol which proceeds via successive hydrogenations of CO molecules in the ice. We present here observations of methanol and its grain-surface precursors HCO, H2CO, CH3O in a sample of prestellar cores and derive their relative abundances. We find that the relative abundances HCO:H2CO:CH3O:CH3OH are constant across the core sample, close to 10:100:1:100. Our results also show that the amounts of HCO and CH3O are consistent with a gas-phase synthesis of these species from H2CO and CH3OH via radical-neutral or ion-molecule reactions followed by dissociative recombinations. Thus, while grain chemistry is necessary to explain the abundances of the parent volatile CH3OH, and possibly H2CO, the reactive species HCO and CH3O might be daughter molecules directly produced in the gas-phase.

Photochemistry of formaldoxime−nitrous acid complexes in an argon matrix: identification of formaldoxime nitrite.

PubMed

Golec, Barbara; Bil, Andrzej; Mielke, Zofia

2009-08-27

We have studied the structure and photochemistry of the formaldoxime−nitrous acid system (CH2NOH−HONO) by help of FTIR matrix isolation spectroscopy and ab initio methods. The MP2/6-311++G(2d,2p) calculations show stability of six isomeric CH2NOH···HONO complexes. The FTIR spectra evidence formation of two hydrogen bonded complexes in an argon matrix whose structures are determined by comparison of the experimental spectra with the calculated ones for the six stable complexes. In the matrix there is present the most stable cyclic complex with two O−H···N bonds; a strong bond is formed between the OH group of HONO and the N atom of CH2NOH and the weaker one between the OH group of CH2NOH and the N atom of HONO. In the other complex present in the matrix the OH group of formaldoxime is attached to the OH group of HONO forming an O−H···O bond. The irradiation of the CH2NOH···HONO complexes with the filtered output of the mercury lamp (λ > 345 nm) leads to the formation of formaldoxime nitrite, CH2NONO, and its two isomeric complexes with water. The main product is the CH2NONO···H2O complex in which water is hydrogen bonded to the N atom of the C═N group. The identity of the photoproducts is confirmed by both FTIR spectroscopy and MP2 or QCISD(full) calculations with the 6-311++G(2d,2p) basis set. The intermediate in this reaction is iminoxyl radical that is formed by abstraction of hydrogen atom from formaldoxime OH group by an OH radical originating from HONO photolysis.

Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

DOE PAGES

Welz, Oliver; Savee, John D.; Osborn, David L.; ...

2014-07-04

The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH 3) 2CCHCH 2OH) and isoprenol (3-methyl-3-buten-1-ol, CH 2C(CH 3)CH 2CH 2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant productsmore » arising from QOOH chemistry are observed. These results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O 2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O 2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O 2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO 2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.« less

High-temperature shock tube and modeling studies on the reactions of methanol with D-atoms and CH3-radicals.

PubMed

Peukert, S L; Michael, J V

2013-10-10

The shock tube technique has been used to study the hydrogen abstraction reactions D + CH3OH → CH2O + H + HD (A) and CH3 + CH3OH → CH2O + H + CH4 (B). For reaction A, the experiments span a T-range of 1016 K ≤ T ≤ 1325 K, at pressures 0.25 bar ≤ P ≤ 0.46 bar. The experiments on reaction B, CH3 + CH3OH, cover a T-range of 1138 K ≤ T ≤ 1270 K, at pressures around 0.40 bar. Reflected shock tube experiments, monitoring the depletion of D-atoms by applying D-atom atomic resonance absorption spectrometry (ARAS), were performed on reaction A using gas mixtures of C2D5I and CH3OH in Kr bath gas. C2D5I was used as precursor for D-atoms. For reaction B, reflected shock tube experiments monitoring H-atom formation with H-ARAS, were carried out using gas mixtures of diacetyl ((CH3CO)2) and CH3OH in Kr bath gas. (CH3CO)2 was used as the source of CH3-radicals. Detailed reaction models were assembled to fit the D-atom and H-atom time profiles in order to obtain experimental rate constants for reactions A and B. Total rate constants from the present experiments on D + CH3OH and CH3 + CH3OH can be represented by the Arrhenius equations kA(T) = 1.51 × 10(-10) exp(-3843 K/T) cm(3) molecules(-1) s(-1) (1016 K ≤ T ≤ 1325 K) and kB(T) = 9.62 × 10(-12) exp(-7477 K/T) cm(3) molecules(-1) s(-1) (1138 K ≤ T ≤ 1270 K). The experimentally obtained rate constants were compared with available rate data from the literature. The results from quantum chemical studies on reaction A were found to be in good agreement with the present results. The present work represents the first direct experimental study on these bimolecular reactions at combustion temperatures and is important to the high-temperature oxidation of CH3OH.

Part 1: Antiplasmodial, cytotoxic, radical scavenging and antioxidant activities of Thai plants in the family Acanthaceae.

PubMed

Charoenchai, Panarat; Vajrodaya, Srunya; Somprasong, Winai; Mahidol, Chulabhorn; Ruchirawat, Somsak; Kittakoop, Prasat

2010-11-01

Crude extracts (CH(2)Cl(2) and MeOH) of 20 plants in the family Acanthaceae were screened for their antiplasmodial, cytotoxic, antioxidant, and radical scavenging activities. These plants included Asystasia nemorum, Barleria cristata, B. strigosa, Dicliptera burmanni, Eranthemum tetragonum, Hygrophila ringens, Justicia balansae, J. procumbens, Lepidagathis incurva, Peristrophe lanceolaria, Phaulopsis dorsiflora, Ruellia kerrii, Strobilanthes auriculata, S. corrugata, S. cusia, S. dimorphotricha, S. karensium, S. maxwellii, S. pateriformis, and S. brandisii. CH(2)Cl(2) extracts of A. nemorum, S. corrugata, S. cusia, S. maxwellii, S. pateriformis, and S. brandisii, as well as MeOH extracts of J. balansae and J. procumbens, showed antiplasmodial activity with IC(50) values of 10-100 µg/mL. CH(2)Cl(2) extracts of nine plants including D. burmanni, H. ringens, J. balansae, J. procumbens, L. incurva, P. lanceolaria, P. dorsiflora, S. corrugata, and S. maxwellii showed cytotoxic activity with IC(50) values of 3.5-46.0 µg/mL. MeOH extracts (at 100 µg/mL) of R. kerrii and S. auriculata could effectively scavenge DPPH free radicals (82-83% inhibition) and superoxide anion radicals (79% and 88% inhibition). In the ORAC antioxidant assay, MeOH extracts of B. cristata, J. procumbens, R. kerrii, and S. auriculata exhibited activity with ORAC units of 3.1-3.9. © Georg Thieme Verlag KG Stuttgart · New York.

Experimental and Computational Study fo CH, CH*, and OH* in an Axisymmetric Laminar Diffusion Flame

NASA Technical Reports Server (NTRS)

Walsh, K. T.

1998-01-01

In this study, we extend the results of previous combined numerical and experimental investigations of an axisymmetric laminar diffusion flame in which difference Raman spectroscopy, laser-induced fluorescence (LIF), and a multidimensional flame model were used to generate profiles of the temperature and major and minor species. A procedure is outlined by which the number densities of ground-state CH (X(sup 2)II) excited-state CH (A(sup 2)Delta, denoted CH*), and excited-state OH (A(sup 2)Sigma, denoted OH*) are measured and modeled. CH* and OH* number densities are deconvoluted from line-of-sight flame-emission measurements. Ground-state CH is measured using linear LIF. The computations are done with GRI Mech 2.11 as well as an alternate hydrocarbon mechanism. In both cases, additional reactions for the production and consumption of CH* and OH* are added from recent kinetic studies. Collisional quenching and spontaneous emission are responsible for the de-excitation of the excited-state radicals. As with our previous investigations, GRI Mech 2.11 continues to produce very good agreement with the overall flame length observed in the experiments, while significantly under predicting the flame lift-off height. The alternate kinetic scheme is much more accurate in predicting lift-off height but overpredicts the over-all flame length. Ground-state CH profiles predicted with GRI Mech 2.11 are in excellent agreement with the corresponding measurements, regarding both spatial distribution and absolute concentration (measured at 4 ppm) of the CH radical. Calculations of the excited-state species show reasonable agreement with the measurements as far as spatial distribution and overall characteristics are concerned. For OH*, the measured peak mole fraction, 1.3 x 10(exp -8), compared well with computed peaks, while the measured peak level for CH*, 2 x 10(exp -9), was severely underpredicted by both kinetic schemes, indicating that the formation and destruction kinetics associated with excited-state species in flames require further research.

Reactions of O/1D/ with methane and ethane.

NASA Technical Reports Server (NTRS)

Lin, C.-L.; Demore, W. B.

1973-01-01

Mixtures of nitrous oxide and methane and mixtures of nitrous oxide and ethane were photolyzed with 1849-A light. The reaction products were analyzed chromatographically. It was found that the reaction of the excited atomic oxygen with methane gives mainly CH3 and OH radicals as initial products, along with about 9% of formaldehyde and molecular hydrogen. The reaction of the excited atomic oxygen with ethane gives C2H5, OH, CH3 and CH2OH as major initial products, with only a few per cent of molecular hydrogen.

Thermal decomposition of ethanol. 4. Ab initio chemical kinetics for reactions of H atoms with CH3CH2O and CH3CHOH radicals.

PubMed

Xu, Z F; Xu, Kun; Lin, M C

2011-04-21

The potential energy surfaces of H-atom reactions with CH(3)CH(2)O and CH(3)CHOH, two major radicals in the decomposition and oxidation of ethanol, have been studied at the CCSD(T)/6-311+G(3df,2p) level of theory with geometric optimization carried out at the BH&HLYP/6-311+G(3df,2p) level. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated ethanol molecule have been considered for both reactions. The rate constants for both reactions have been calculated at 100-3000 K and 10(-4) Torr to 10(3) atm Ar pressure by microcanonical VTST/RRKM theory with master equation solution for all accessible product channels. The results show that the major product channel of the CH(3)CH(2)O + H reaction is CH(3) + CH(2)OH under atmospheric pressure conditions. Only at high pressure and low temperature, the rate constant for CH(3)CH(2)OH formation by collisonal deactivation becomes dominant. For CH(3)CHOH + H, there are three major product channels; at high temperatures, CH(3)+CH(2)OH production predominates at low pressures (P < 100 Torr), while the formation of CH(3)CH(2)OH by collisional deactivation becomes competitive at high pressures and low temperatures (T < 500 K). At high temperatures, the direct hydrogen abstraction reaction producing CH(2)CHOH + H(2) becomes dominant. Rate constants for all accessible product channels in both systems have been predicted and tabulated for modeling applications. The predicted value for CH(3)CHOH + H at 295 K and 1 Torr pressure agrees closely with available experimental data. For practical modeling applications, the rate constants for the thermal unimolecular decomposition of ethanol giving key accessible products have been predicted; those for the two major product channels taking place by dehydration and C-C breaking agree closely with available literature data.

Reaction CH3 + OH studied over the 294-714 K temperature and 1-100 bar pressure ranges.

PubMed

Sangwan, Manuvesh; Chesnokov, Evgeni N; Krasnoperov, Lev N

2012-08-30

Reaction of methyl radicals with hydroxyl radicals, CH(3) + OH → products (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 294-714 K temperature and 1-100 bar pressure ranges (bath gas He). Methyl radicals were produced by photolysis of acetone at 193.3 nm. Hydroxyl radicals were generated in reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N(2)O at 193.3 nm, with H(2)O. Temporal profiles of CH(3) were recorded via absorption at 216.4 nm using xenon arc lamp and a spectrograph; OH radicals were monitored via transient absorption of light from a dc discharge H(2)O/Ar low pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light inside the reactor was determined by an accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study indicate that the rate constant of reaction 1 is pressure independent within the studied pressure and temperature ranges and has slight negative temperature dependence, k(1) = (1.20 ± 0.20) × 10(-10)(T/300)(-0.49) cm(3) molecule(-1) s(-1).

Astronomical masers and lasers

NASA Astrophysics Data System (ADS)

Townes, C. H.

1997-12-01

A brief account is given of the discovery of the astronomical maser and laser effects in OH radicals and in molecules of water (H2O), carbon monoxide and dioxide (CO and CO2), ammonia (NH3), methyl alcohol (CH3OH), formaldehyde (CH2O), and silicon oxide (SiO). A detailed table is given of all the currently known molecular stimulated-emission lines.

Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marques, Carla S.T.; Barreta, Luiz G.; Sbampato, Maria E.

In this study, nitric oxide laser-saturated fluorescence (LSF) measurements were acquired from premixed ethanol flames at atmospheric pressure in a burner. NO-LSF experimental profiles for fuel-rich premixed ethanol flames ({phi} = 1.34 and {phi} = 1.66) were determined through the excitation/detection scheme of the Q{sub 2}(26.5) rotational line in the A{sup 2}{sigma}{sup +} - X{sup 2}{pi} (0,0) vibronic band and {gamma}(0,1) emission band. A calibration procedure by NO doping into the flame was applied to establish the NO concentration profiles in these flames. Chemiluminescent emission measurements in the (0, 0) vibronic emission bands of the OH{sup *} (A{sup 2}{sigma}{sup +}more » - X{sup 2}{pi}) and CH{sup *}(A{sup 2}{delta} - X{sup 2}{pi}) radicals were also obtained with high spatial and spectral resolution for fuel-rich premixed ethanol flames to correlate them with NO concentrations. Experimental chemiluminescence profiles and the ratios of the integrated areas under emission spectra (A{sub CH*}/A{sub CH*}(max.) and A{sub CH*}/A{sub OH*}) were determined. The relationships between chemiluminescence and NO concentrations were established along the premixed ethanol flames. There was a strong connection between CH{sup *} radical chemiluminescence and NO formation and the prompt-NO was identified as the governing mechanism for NO production. The results suggest the optimum ratio of the chemiluminescence of two radicals (A{sub CH*}/A{sub OH*}) for NO diagnostic purposes. (author)« less

On reaction kinetics and atmospheric lifetimes of CF3CFHCF3 and CF3CH2Br

NASA Technical Reports Server (NTRS)

Nelson, D. D., Jr.; Zahniser, M. S.; Kolb, C. E.

1993-01-01

The rate constants for the reaction of the OH radical with CF3CFHCF3 and with CF3CH2Br have been measured as a function of temperature using the discharge flow technique with laser induced fluorescence detection of the OH radicals. The temperature dependent rate coefficients are well described by a simple Arrhenius expression, k(T) = A exp(E/(RT)). For the reaction of OH with CF3CFHCF3 we find A = 3.7 x 10 exp -13 cu cm/molecules/s and E/R = 1615 K; for the reaction of OH with CF3CH2Br we report A = 1.4 x 10 exp -12 cu cm/molecule/s and E/R = 1350 K. These Arrhenius parameters imply rate coefficients at 277 K of 1.09 x 10 exp -15 cu cm/molecule/s for CF3CFHCF3 and 1.06 x 10 exp -14 cu cm/molecule/s for CF3CH2Br. We find atmospheric lifetimes for CF3CFHCH3 and CF3CH2Br of 42 years and 4.1 years, respectively. We also estimate the steady state ozone depletion potential (ODP) of the brominated species relative to CFCl3 as about 0.84 using a semiempirical model.

Synthesis and structural features of U VI and V IV chelate complexes with (hhmmbH)Cl·H 2O [hhmmb = {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide], a new Schiff base ligand derived from vitamin B6

NASA Astrophysics Data System (ADS)

Back, Davi Fernando; Ballin, Marco Aurélio; de Oliveira, Gelson Manzoni

2009-10-01

The Schiff base ligand {3-hydroxyl-5-(hydroxymethyl)-2-methylpyridine-4-yl-methylene}benzohydrazide hydrochloride monohydrated {(hhmmbH)Cl·H 2O} ( 1) was prepared by reaction of pyridoxine hydrochloride with benzoic acid hydrazide. The reaction of 1 with [VO(acac) 2] and triethylamine yields the neutral vanadium IV complex [VO 2(hhmmb)]·Py ( 2), with a distorted quadratic pyramidal configuration. The Schiff base 1 reacts also with UO 2(NO 3) 2·6H 2O and triethylamine under deprotonation giving the uranium VI cationic complexes [UO 2(hhmmb)(H 2O)Cl] + ( 3) and [UO 2(hhmmb)(CH 3OH)Cl] + ( 4), both showing the classical pentagonal bipyrimidal geometry of UO22+ complexes. The structural features of all compounds are discussed.

A Mechanistical Study on the Formation of Dimethyl Ether (CH3OCH3) and Ethanol (CH3CH2OH) in Methanol-containing Ices and Implications for the Chemistry of Star-forming Regions

NASA Astrophysics Data System (ADS)

Bergantini, Alexandre; Góbi, Sándor; Abplanalp, Matthew J.; Kaiser, Ralf I.

2018-01-01

The underlying formation mechanisms of complex organic molecules (COMs)—in particular, structural isomers—in the interstellar medium (ISM) are largely elusive. Here, we report new experimental findings on the role of methanol (CH3OH) and methane (CH4) ices in the synthesis of two C2H6O isomers upon interaction with ionizing radiation: ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3). The present study reproduces the interstellar abundance ratios of both species with ethanol to dimethyl ether branching ratios of (2.33 ± 0.14):1 suggesting that methanol and methane represents the key precursor to both isomers within interstellar ices. Exploiting isotopic labeling combined with reflectron time-of-flight mass spectrometry (Re-TOF-MS) after isomer selective vacuum ultra-violet (VUV) photoionization of the neutral molecules, we also determine the formation mechanisms of both isomers via radical–radical recombination versus carbene (CH2) insertion with the former pathway being predominant. Formation routes to higher molecular weight reaction products such as ethylene glycol (HOCH2CH2OH), dimethyl peroxide (CH3OOCH3), and methoxymethanol (CH3OCH2OH) are discussed briefly as well.

Theoretical study on the reaction mechanism of CH 4 with CaO

NASA Astrophysics Data System (ADS)

Yang, Hua-Qing; Hu, Chang-Wei; Qin, Song

2006-11-01

The reaction pathways and energetics for the reaction of methane with CaO are discussed on the singlet spin state potential energy surface at the B3LYP/6-311+G(2df,2p) and QCISD/6-311++G(3df,3pd)//B3LYP/6-311+G(2df,2p) levels of theory. The reaction of methane with CaO is proposed to proceed in the following reaction pathways: CaO + CH 4 → CaOCH 4 → [TS] → CaOH + CH 3, CaO + CH 4 → OCaCH 4 → [TS] → HOCaCH 3 → CaOH + CH 3 or [TS] → CaCH 3OH → Ca + CH 3OH, and OCaCH 4 → [TS] → HCaOCH 3 → CaOCH 3 + H or [TS] → CaCH 3OH → Ca + CH 3OH. The gas-phase methane-methanol conversion by CaO is suggested to proceed via two kinds of important reaction intermediates, HOCaCH 3 and HCaOCH 3, and the reaction pathway via the hydroxy intermediate (HOCaCH 3) is energetically more favorable than the other one via the methoxy intermediate (HCaOCH 3). The hydroxy intermediate HOCaCH 3 is predicted to be the energetically most preferred configuration in the reaction of CaO + CH 4. Meanwhile, these three product channels (CaOH + CH 3, CaOCH 3 + H and Ca + CH 3OH) are expected to compete with each other, and the formation of methyl radical is the most preferable pathway energetically. On the other hand, the intermediates HCaOCH 3 and HOCaCH 3 are predicted to be the energetically preferred configuration in the reaction of Ca + CH 3OH, which is precisely the reverse reaction of methane hydroxylation.

CH3CO + O2 + M (M = He, N2) Reaction Rate Coefficient Measurements and Implications for the OH Radical Product Yield.

PubMed

Papadimitriou, Vassileios C; Karafas, Emmanuel S; Gierczak, Tomasz; Burkholder, James B

2015-07-16

The gas-phase CH3CO + O2 reaction is known to proceed via a chemical activation mechanism leading to the formation of OH and CH3C(O)OO radicals via bimolecular and termolecular reactive channels, respectively. In this work, rate coefficients, k, for the CH3CO + O2 reaction were measured over a range of temperature (241-373 K) and pressure (0.009-600 Torr) with He and N2 as the bath gas and used to characterize the bi- and ter-molecular reaction channels. Three independent experimental methods (pulsed laser photolysis-laser-induced fluorescence (PLP-LIF), pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS), and a very low-pressure reactor (VLPR)) were used to characterize k(T,M). PLP-LIF was the primary method used to measure k(T,M) in the high-pressure regime under pseudo-first-order conditions. CH3CO was produced by PLP, and LIF was used to monitor the OH radical bimolecular channel reaction product. CRDS, a complementary high-pressure method, measured k(295 K,M) over the pressure range 25-600 Torr (He) by monitoring the temporal CH3CO radical absorption following its production via PLP in the presence of excess O2. The VLPR technique was used in a relative rate mode to measure k(296 K,M) in the low-pressure regime (9-32 mTorr) with CH3CO + Cl2 used as the reference reaction. A kinetic mechanism analysis of the combined kinetic data set yielded a zero pressure limit rate coefficient, kint(T), of (6.4 ± 4) × 10(-14) exp((820 ± 150)/T) cm(3) molecule(-1) s(-1) (with kint(296 K) measured to be (9.94 ± 1.3) × 10(-13) cm(3) molecule(-1) s(-1)), k0(T) = (7.39 ± 0.3) × 10(-30) (T/300)(-2.2±0.3) cm(6) molecule(-2) s(-1), and k∞(T) = (4.88 ± 0.05) × 10(-12) (T/300)(-0.85±0.07) cm(3) molecule(-1) s(-1) with Fc = 0.8 and M = N2. A He/N2 collision efficiency ratio of 0.60 ± 0.05 was determined. The phenomenological kinetic results were used to define the pressure and temperature dependence of the OH radical yield in the CH3CO + O2 reaction. The present results are compared with results from previous studies and the discrepancies are discussed.

Formation of OH radicals in the gas phase ozonolysis of alkenes: the unexpected role of carbonyl oxides

NASA Astrophysics Data System (ADS)

Gutbrod, Roland; Schindler, Ralph N.; Kraka, Elfi; Cremer, Dieter

1996-04-01

According to CCSD(T)/TZ + 2P calculations, the decomposition of carbonyl oxide, H 2COO to HCO and OH radicals is unlikely in view of an activation enthalpy ΔΔHf0(298) of 31 kcal/mol. However, for dimethylcarbonyl oxide there is a low energy rearrangement mode ( ΔΔHf0(298): 14.4 kca/mol) which involves a H atom of ghe methyl group and which leads to a hydroperoxy methyl ethene intermediate, which in turn can decompose to OH and CH 2COCH 3 radicals ( ΔΔHf0(298): 23 kcal/mol). In the gas phase ozonolysis of alkyl substituted alkenes the formation of OH radicals is the most likely process. This has important consequences for the chemistry of the atmosphere.

Molecule searches in Comet Kohoutek /1973f/ at microwave frequencies

NASA Technical Reports Server (NTRS)

Mango, S. A.; Johnston, K. J.; Chui, M. F.; Cheung, A. C.; Matsakis, D.

1974-01-01

Nine transitions of the possible parent molecules H2O, NH3, CH3OH and N2O as well as the OH radical were searched for in Comet Kohoutek (1973f) in the frequency range 22.2-25.2 GHz. These molecules were not detected, but the upper limits for the optical depth, mean column density and the production rate are derived for each of the molecules. These results are discussed and compared with the reported detections of HCN and CH3CN emission and OH absorption.

Deuterium Substitution used as a Tool for Investigating Mechanisms of Gas-Phase Free-Radical Reactions

NASA Technical Reports Server (NTRS)

Wine, P. H.; Hynes, A. J.; Nicovich, J. M.

1997-01-01

Results are presented and discussed for a number of gas phase free radical reactions where H/D isotope effects provide valuable mechanistic insights. The cases considered are (1) the reactions of OH, NO3, and Cl with atmospheric reduced sulfur compounds, (2) the reactions of OH and OD with CH3CN and CD3CN, and (3) the reactions of alkyl radicals with HBr and DBr.

Detection methods for atoms and radicals in the gas phase

NASA Astrophysics Data System (ADS)

Hack, W.

This report lists atoms and free radicals in the gas phase which are of interest for environmental and flame chemistry and have been detected directly. The detection methods which have been used are discussed with respect to their range of application, specificity and sensitivity. In table 1, detection methods for the five atoms of group IV (C, Si, Ge, Sn, Pb) and about 60 radicals containing at least one atom of group IV are summarized (CH, Cd, Cf, CC1, CBr, Cn, Cs, CSe, CH2, CD2, Chf, Cdf, CHC1, CHBr, CF2, CC12, CBr2, CFC1, CFBr, CH3, CD3, CF3, CH2F, CH2C1, CH2Br, CHF2, CHC12, CHBr2, Hco, Fco, CH30, CD30, CH2OH, CH3S, Nco, CH4N, CH302, CF302; C2, C2N, C2H, C20, C2HO, C2H3, C2F3, C2H5, C2HsO, C2H4OH, CH3CO, CD3CO, C2H3O, C2H502, CH3COO2, C2H4N, C2H6N, C3; Si, SiF, SiF2, SiO, SiC, Si2; Ge, GeC, GeO, GeF, GeF2, GeCl2, Sn, SnF, SnO, SnF2, Pb, PbF, PbF2, PbO, PbS). In table 2 detection methods for about 25 other atoms and 60 radicals are listed: (H, D, O, O2, Oh, Od, HO2, DO2, F, Ci, Br, I, Fo, Cio, BrO, Io, FO2, C1O2, Li, Na, K, Rb, Cs, N, N3, Nh, Nd, Nf, Nci, NBr, NH2, ND2, Nhd, Nhf, NF2, NC12, N2H3, No, NO2, NO3, Hno, Dno, P, Ph, Pd, Pf, Pci, PH2, PD2, PF2, Po, As, AsO, AsS, Sb, Bi, S, S2, Sh, Sd, Sf, SF2, So, Hso, Dso, Sn, Se, Te, Se2, SeH, SeD, SeF, SeO, SeS, SeN, TeH, TeO, Bh, BH2, Bo, Bn, B02, Cd, Hg, UF5). The tables also cite some recent kinetic applications of the various methods.

Calculated hyperfine coupling constants for 5,5-dimethyl-1-pyrroline N-oxide radical products in water and benzene

NASA Astrophysics Data System (ADS)

Nardali, Ş.; Ucun, F.; Karakaya, M.

2017-11-01

The optimized structures of some radical adducts of 5,5-dimethyl-1-pyrroline N-oxide were computed by different methods on ESR spectra. As trapped radicals, H, N3, NH2, CH3, CCl3, OOH in water and F, OH, CF3, CH2OH, OC2H5 in benzene solutions were used. The calculated isotropic hyperfine coupling constants of all the trapped radicals were compared with the corresponding experimental data. The hyperfine coupling constant due to the β proton of the nitroxide radical was seen to be consist with the McConnel's relation αβ = B 0 + B 1cos2θ and, to be effected with the opposite spin density of oxygen nucleus bonded to the nitrogen. It was concluded that in hyperfine calculations the DFT(B3PW91)/LanL2DZ level is superior computational quantum model relative to the used other level. Also, the study has been enriched by the computational of the optimized geometrical parameters, the hyper conjugative interaction energies, the atomic charges and spin densities for all the radical adducts.

Gas phase kinetics of the OH + CH3CH2OH reaction at temperatures of the interstellar medium (T = 21-107 K).

PubMed

Ocaña, A J; Blázquez, S; Ballesteros, B; Canosa, A; Antiñolo, M; Albaladejo, J; Jiménez, E

2018-02-21

Ethanol, CH 3 CH 2 OH, has been unveiled in the interstellar medium (ISM) by radioastronomy and it is thought to be released into the gas phase after the warm-up phase of the grain surface, where it is formed. Once in the gas phase, it can be destroyed by different reactions with atomic and radical species, such as hydroxyl (OH) radicals. The knowledge of the rate coefficients of all these processes at temperatures of the ISM is essential in the accurate interpretation of the observed abundances. In this work, we have determined the rate coefficient for the reaction of OH with CH 3 CH 2 OH (k(T)) between 21 and 107 K by employing the pulsed and continuous CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, which means Reaction Kinetics in a Uniform Supersonic Flow) technique. The pulsed laser photolysis technique was used for generating OH radicals, whose time evolution was monitored by laser induced fluorescence. An increase of approximately 4 times was observed for k(21 K) with respect to k(107 K). With respect to k(300 K), the OH-reactivity at 21 K is enhanced by two orders of magnitude. The obtained T-expression in the investigated temperature range is k(T) = (2.1 ± 0.5) × 10 -11 (T/300 K) -(0.71±0.10) cm 3 molecule -1 s -1 . In addition, the pressure dependence of k(T) has been investigated at several temperatures between 21 K and 90 K. No pressure dependence of k(T) was observed in the investigated ranges. This may imply that this reaction is purely bimolecular or that the high-pressure limit is reached at the lowest total pressure experimentally accessible in our system. From our results, k(T) at usual IS temperatures (∼10-100 K) is confirmed to be very fast. Typical rate coefficients can be considered to range within about 4 × 10 -11 cm 3 molecule -1 s -1 at 100 K and around 1 × 10 -10 cm 3 molecule -1 s -1 at 20 K. The extrapolation of k at the lowest temperatures of the dense molecular clouds of ISM is also discussed in this paper.

Gas phase kinetics of the OH + CH3CH2OH reaction at temperatures of the interstellar medium (T = 21-10^7 K)

NASA Astrophysics Data System (ADS)

Ocaña, A. J.; Blázquez, S.; Ballesteros, B.; Canosa, A.; Antiñolo, M.; Albaladejoab, J.; Jiménez, E.

2018-02-01

Ethanol, CH3CH2OH, has been unveiled in the interstellar medium (ISM) by radioastronomy and it is thought to be released into the gas phase after the warm-up phase of the grain surface, where it is formed. Once in the gas phase, it can be destroyed by different reactions with atomic and radical species, such as hydroxyl (OH) radicals. The knowledge of the rate coefficients of all these processes at temperatures of the ISM is essential in the accurate interpretation of the observed abundances. In this work, we have determined the rate coefficient for the reaction of OH with CH3CH2OH (k(T)) between 21 and 10^7 K by employing the pulsed and continuous CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, which means Reaction Kinetics in a Uniform Supersonic Flow) technique. The pulsed laser photolysis technique was used for generating OH radicals, whose time evolution was monitored by laser induced fluorescence. An increase of approximately 4 times was observed for k(21 K) with respect to k(10^7 K). With respect to k(300 K), the OH-reactivity at 21 K is enhanced by two orders of magnitude. The obtained T-expression in the investigated temperature range is k(T) = (2.1 ± 0.5) × 10^-11 (T/300 K)-(0.71±0.10) cm^3 molecule^-1 s^-1. In addition, the pressure dependence of k(T) has been investigated at several temperatures between 21 K and 90 K. No pressure dependence of k(T) was observed in the investigated ranges. This may imply that this reaction is purely bimolecular or that the high-pressure limit is reached at the lowest total pressure experimentally accessible in our system. From our results, k(T) at usual IS temperatures (˜10-100 K) is confirmed to be very fast. Typical rate coefficients can be considered to range within about 4 × 10^-11 cm^3 molecule^-1 s^-1 at 100 K and around 1 × 10^-10 cm^3 molecule^-1 s^-1 at 20 K. The extrapolation of k at the lowest temperatures of the dense molecular clouds of ISM is also discussed in this paper.

Ab initio rate constants from hyperspherical quantum scattering: Application to H+C2H6 and H+CH3OH

NASA Astrophysics Data System (ADS)

Kerkeni, Boutheïna; Clary, David C.

2004-10-01

The dynamics and kinetics of the abstraction reactions of H atoms with ethane and methanol have been studied using a quantum mechanical procedure. Bonds being broken and formed are treated with explicit hyperspherical quantum dynamics. The ab initio potential energy surfaces for these reactions have been developed from a minimal number of grid points (average of 48 points) and are given by analytical functionals. All the degrees of freedom except the breaking and forming bonds are optimized using the second order perturbation theory method with a correlation consistent polarized valence triple zeta basis set. Single point energies are calculated on the optimized geometries with the coupled cluster theory and the same basis set. The reaction of H with C2H6 is endothermic by 1.5 kcal/mol and has a vibrationally adiabatic barrier of 12 kcal/mol. The reaction of H with CH3OH presents two reactive channels: the methoxy and the hydroxymethyl channels. The former is endothermic by 0.24 kcal/mol and has a vibrationally adiabatic barrier of 13.29 kcal/mol, the latter reaction is exothermic by 7.87 kcal/mol and has a vibrationally adiabatic barrier of 8.56 kcal/mol. We report state-to-state and state-selected cross sections together with state-to-state rate constants for the title reactions. Thermal rate constants for these reactions exhibit large quantum tunneling effects when compared to conventional transition state theory results. For H+CH3OH, it is found that the CH2OH product is the dominant channel, and that the CH3O channel contributes just 2% at 500 K. For both reactions, rate constants are in good agreement with some measurements.

Adventures on the C 3H 5O potential energy surface: OH+propyne, OH+allene and related reactions

DOE PAGES

Zádor, Judit; Miller, James A.

2014-06-25

We mapped out the stationary points and the corresponding conformational space on the C 3H 5O potential energy surface relevant for the OH + allene and OH + propyne reactions systematically and automatically using the KinBot software at the UCCSD(T)-F12b/cc-pVQZ-F12//M06-2X/6-311++G(d,p) level of theory. We used RRKM-based 1-D master equations to calculate pressure- and temperature-dependent, channel-specific phenomenological rate coefficients for the bimolecular reactions propyne + OH and allene + OH, and for the unimolecular decomposition of the CH 3CCHOH, CH 3C(OH)CH, CH 2CCH 2OH, CH 2C(OH)CH 2 primary adducts, and also for the related acetonyl, propionyl, 2-methylvinoxy, and 3-oxo-1-propyl radicals. Themore » major channel of the bimolecular reactions at high temperatures is the formation propargyl + H 2O, which makes the title reactions important players in soot formation at high temperatures. However, below ~1000 K the chemistry is more complex, involving the competition of stabilization, isomerization and dissociation processes. We found that the OH addition to the central carbon of allene has a particularly interesting and complex pressure dependence, caused by the low-lying exit channel to form ketene + CH 3 bimolecular products. In this study, we compared our results to a wide range of experimental data and assessed possible uncertainties arising from certain aspects of the theoretical framework.« less

Hydrogen Radicals, Nitrogen Radicals, and the Production of Ozone in the Middle and Upper Troposphere

NASA Technical Reports Server (NTRS)

Bui, T. P.

1997-01-01

The concentrations of hydrogen radicals, OH and HO2, in the middle and upper troposphere were measured simultaneously with those of NO, O3,CO, H20, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field.

Thermodynamic properties (enthalpy, bond energy, entropy, and heat capacity) and internal rotor potentials of vinyl alcohol, methyl vinyl ether, and their corresponding radicals.

PubMed

da Silva, Gabriel; Kim, Chol-Han; Bozzelli, Joseph W

2006-06-29

Vinyl alcohols (enols) have been discovered as important intermediates and products in the oxidation and combustion of hydrocarbons, while methyl vinyl ethers are also thought to occur as important combustion intermediates. Vinyl alcohol has been detected in interstellar media, while poly(vinyl alcohol) and poly(methyl vinyl ether) are common polymers. The thermochemical property data on these vinyl alcohols and methyl vinyl ethers is important for understanding their stability, reaction paths, and kinetics in atmospheric and thermal hydrocarbon-oxygen systems. Enthalpies , entropies , and heat capacities (C(p)()(T)) are determined for CH(2)=CHOH, C(*)H=CHOH, CH(2)=C(*)OH, CH(2)=CHOCH(3), C(*)H=CHOCH(3), CH(2)=C(*)OCH(3), and CH(2)=CHOC(*)H(2). Molecular structures, vibrational frequencies, , and C(p)(T) are calculated at the B3LYP/6-31G(d,p) density functional calculation level. Enthalpies are also determined using the composite CBS-Q, CBS-APNO, and G3 methods using isodesmic work reactions to minimize calculation errors. Potential barriers for internal rotors are calculated at the B3LYP/6-31G(d,p) level and used to determine the hindered internal rotational contributions to entropy and heat capacity. The recommended ideal gas phase values calculated in this study are the following (in kcal mol(-1)): -30.0, -28.9 (syn, anti) for CH(2)=CHOH; -25.6, -23.9 for CH(2)=CHOCH(3); 31.3, 33.5 for C(*)H=CHOH; 27.1 for anti-CH(2)=C(*)OH; 35.6, 39.3 for C(*)H=CHOCH(3); 33.5, 32.2 for CH(2)=C(*)OCH(3); 21.3, 22.0 for CH(2)=CHOC(*)H(2). Bond dissociation energies (BDEs) and group additivity contributions are also determined. The BDEs reveal that the O-H, O-CH(3), C-OH, and C-OCH(3) bonds in vinyl alcohol and methyl vinyl ether are similar in energy to those in the aromatic molecules phenol and methyl phenyl ether, being on average around 3 kcal mol(-1) weaker in the vinyl systems. The keto-enol tautomerization enthalpy for the interconversion of vinyl alcohol to acetaldehyde is determined to be -9.7 kcal mol(-1), while the activation energy for this reaction is calculated as 55.9 kcal mol(-1); this is the simplest keto-enol tautomerization and is thought to be important in the reactions of vinyl alcohol. Formation of the formyl methyl radical (vinoxy radical/vinyloxy radical) from both vinyl alcohol and methyl vinyl ether is also shown to be important, and its reactions are discussed briefly.

Experimental evidence for glycolaldehyde and ethylene glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Cuppen, H. M.; Ioppolo, S.; Lamberts, T.; Linnartz, H.

2015-04-01

This study focuses on the formation of two molecules of astrobiological importance - glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - by surface hydrogenation of CO molecules. Our experiments aim at simulating the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing become dominant. It is shown that along with the formation of H2CO and CH3OH - two well-established products of CO hydrogenation - also molecules with more than one carbon atom form. The key step in this process is believed to be the recombination of two HCO radicals followed by the formation of a C-C bond. The experimentally established reaction pathways are implemented into a continuous-time random-walk Monte Carlo model, previously used to model the formation of CH3OH on astrochemical time-scales, to study their impact on the solid-state abundances in dense interstellar clouds of glycolaldehyde and ethylene glycol.

Interannual Variability and Trends of CH4, CO and OH Using the Computationally-Efficient CH4-CO-OH (ECCOH) Module

NASA Technical Reports Server (NTRS)

Elshorbany, Yasin F.; Duncan, Bryan N.; Strode, Sarah A.; Wang, James S.; Kouatchou, Jules

2015-01-01

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG). Its 100-year global warming potential (GWP) is 34 times larger than that for carbon dioxide. The 100-year integrated GWPof CH4 is sensitive to changes in hydroxyl radical (OH) levels.Oxidation of CH4 and carbon monoxide (CO) by OH is the main loss process, thus affecting the oxidizing capacity of the atmosphere and contributing to the global ozone background. Limitations of using archived, monthly OH fields for studies of methane's and COs evolution are that feedbacks of the CH4-CO-OH system on methane, CO and OH are not captured. In this study, we employ the computationally Efficient CH4-CO-OH (ECCOH) module (Elshorbany et al., 2015) to investigate the nonlinear feedbacks of the CH4-CO-OH system on the interannual variability and trends of the CH4, CO, OH system.

The Description and Validation of a Computationally-Efficient CH4-CO-OH (ECCOHv1.01) Chemistry Module for 3D Model Applications

NASA Technical Reports Server (NTRS)

Elshorbany, Yasin F.; Duncan, Bryan N.; Strode, Sarah A.; Wang, James S.; Kouatchou, Jules

2016-01-01

We present the Efficient CH4-CO-OH (ECCOH) chemistry module that allows for the simulation of the methane, carbon monoxide, and hydroxyl radical (CH4-CO- OH) system, within a chemistry climate model, carbon cycle model, or Earth system model. The computational efficiency of the module allows many multi-decadal sensitivity simulations of the CH4-CO-OH system, which primarily determines the global atmospheric oxidizing capacity. This capability is important for capturing the nonlinear feedbacks of the CH4-CO-OH system and understanding the perturbations to methane, CO, and OH, and the concomitant impacts on climate. We implemented the ECCOH chemistry module in the NASA GEOS-5 atmospheric global circulation model (AGCM), performed multiple sensitivity simulations of the CH4-CO-OH system over 2 decades, and evaluated the model output with surface and satellite data sets of methane and CO. The favorable comparison of output from the ECCOH chemistry module (as configured in the GEOS- 5 AGCM) with observations demonstrates the fidelity of the module for use in scientific research.

Evaluating Effects of H2O and overhead O3 on Global Mean Tropospheric OH Concentration

NASA Technical Reports Server (NTRS)

Nicely, Julie M.; Salawitch, R.J.; Canty, T.; Lang, Chang; Duncan, Bryan; Liang, Qing; Oman, Luke David; Stolarski, Richard S.; Waugh, Darryn

2012-01-01

The oxidizing capacity of the troposphere is controlled, to a large extent, by the abundance of hydroxyl radical (OH). The global mean concentration of OH, [OH]GLOBAL, inferred from measurements of methyl chloroform, has remained relatively constant during the past several decades, despite rising levels of CH4 that should have led to a steady decline. Here we examine other factors that may have affected [OH]GLOBAL, such as the overhead burden of stratospheric O3 and tropospheric H2O, using global OH fields from the GEOS-CHEM Chemistry-Climate Model. Our analysis suggests these factors may have contributed a positive trend to [OH]GLOBAL large enough to counter the decrease due to CH4.

On the Formation of the C{sub 2}H{sub 6}O Isomers Ethanol (C{sub 2}H{sub 5}OH) and Dimethyl Ether (CH{sub 3}OCH{sub 3}) in Star-forming Regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergantini, Alexandre; Maksyutenko, Pavlo; Kaiser, Ralf I., E-mail: ralfk@hawaii.edu

The structural isomers ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}) were detected in several low-, intermediate-, and high-mass star-forming regions, including Sgr B2, Orion, and W33A, with the relative abundance ratios of ethanol/dimethyl ether varying from about 0.03 to 3.4. Until now, no experimental data regarding the formation mechanisms and branching ratios of these two species in laboratory simulation experiments could be provided. Here, we exploit tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) to detect and analyze the production of complex organic molecules (COMs) resulting from the exposure of water/methane (H{sub 2}O/CH{sub 4}) ices to energetic electrons.more » The main goal is to understand the formation mechanisms in star-forming regions of two C{sub 2}H{sub 6}O isomers: ethanol (CH{sub 3}CH{sub 2}OH) and dimethyl ether (CH{sub 3}OCH{sub 3}). The results show that the experimental branching ratios favor the synthesis of ethanol versus dimethyl ether (31 ± 11:1). This finding diverges from the abundances observed toward most star-forming regions, suggesting that production routes on interstellar grains to form dimethyl ether might be missing; alternatively, ethanol can be overproduced in the present simulation experiments, such as via radical–radical recombination pathways involving ethyl and hydroxyl radicals. Finally, the PI-ReTOF-MS data suggest the formation of methylacetylene (C{sub 3}H{sub 4}), ketene (CH{sub 2}CO), propene (C{sub 3}H{sub 6}), vinyl alcohol (CH{sub 2}CHOH), acetaldehyde (CH{sub 3}CHO), and methyl hydroperoxide (CH{sub 3}OOH), in addition to ethane (C{sub 2}H{sub 6}), methanol (CH{sub 3}OH), and CO{sub 2} detected from infrared spectroscopy. The yield of all the confirmed species is also determined.« less

Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths

NASA Astrophysics Data System (ADS)

Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

2014-06-01

Photodissociation pathways of nitromethane following π → π* electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH3 and NO2 (2B2) is formed by direct dissociation from the S1 state. Important pathways involving S1 and S0 states for production of various dissociation products CH3NO + O (1D), CH3O(X2E) + NO (X2Π), CH2NO + OH, and CH2O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH3NO2, the OH radical roaming in OH dissociation from CH2N(O)(OH), and the NO roaming in NO dissociation from CH3ONO.

Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths.

PubMed

Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

2014-06-28

Photodissociation pathways of nitromethane following π → π(*) electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH3 and NO2 ((2)B2) is formed by direct dissociation from the S1 state. Important pathways involving S1 and S0 states for production of various dissociation products CH3NO + O ((1)D), CH3O(X(2)E) + NO (X(2)Π), CH2NO + OH, and CH2O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH3NO2, the OH radical roaming in OH dissociation from CH2N(O)(OH), and the NO roaming in NO dissociation from CH3ONO.

Quantum Chemical Study of CH3 + O2 Combustion Reaction System: Catalytic Effects of Additional CO2 Molecule.

PubMed

Masunov, Artëm E; Wait, Elizabeth; Vasu, Subith S

2017-08-03

The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO 2 concentrations. Here, we investigate potential energy surfaces of the four elementary reactions in the CH 3 + O 2 reactive system in the presence of one CO 2 molecule. In the case of reaction CH 3 + O 2 → CH 2 O + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ∼2.2 kcal/mol. Alternatively, covalently bonded CO 2 may form a six-membered ring transition state and reduce the activation barrier by ∼0.6 kcal/mol. In case of reaction CH 3 + O 2 → CH 3 O + O (R2 channel), covalent participation of CO 2 lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH 3 + O 2 → CHO + H 2 O (R3 channel) with covalent participation of CO 2 , the activation barrier is lowered by 0.5 kcal/mol. The reaction CH 2 O + OH → CHO + H 2 O (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO 2 . These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO 2 medium.

Thermal Decomposition of Potential Ester Biofuels. Part I: Methyl Acetate and Methyl Butanoate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porterfield, Jessica P.; Bross, David H.; Ruscic, Branko

2017-06-09

Two methyl esters have been examined as models for the pyrolysis of biofuels. Dilute samples (0.06 - 0.13%) of methyl acetate (CH 3COOCH 3) and methyl butanoate (CH 3CH 2CH 2COOCH 3) were entrained in (He, Ar) carrier gas and decomposed in a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from the methyl esters were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures in the pulsed micro-reactor were roughly 20 Torr and residence times through the reactors were approximately 25 - 150 µs. Reactor temperatures ofmore » 300 – 1600 K were explored. Decomposition of CH 3COOCH 3 commences at 1000 K and the initial products are (CH 2=C=O and CH 3OH). As the micro-reactor is heated to 1300 K, a mixture of (CH 2=C=O and CH 3OH, CH 3, CH 2=O, H, CO, CO 2) appears. The thermal cracking of CH 3CH 2CH 2COOCH 3 begins at 800 K with the formation of (CH 3CH 2CH=C=O, CH 3OH). By 1300 K, the pyrolysis of methyl butanoate yields a complex mixture of (CH 3CH 2CH=C=O, CH 3OH, CH 3, CH 2=O, CO, CO 2, CH 3CH=CH 2, CH 2CHCH 2, CH 2=C=CH 2, HCCCH 2, CH 2=C=C=O, CH 2=CH 2, HCΞCH, CH 2=C=O). Based on the results from the thermal cracking of methyl acetate and methyl butanoate, we predict several important decomposition channels for the pyrolysis of fatty acid methyl esters, R CH 2-COOCH 3. The lowest energy fragmentation will be a 4-center elimination of methanol to form the ketene, RCH=C=O. At higher temperatures, concerted fragmentation to radicals will ensue to produce a mixture of species: (RCH 2 + CO 2 + CH 3) and (RCH 2 + CO + CH 2=O + H). Thermal cracking of the β C-C bond of the methyl ester will generate the radicals (R and H) as well as CH 2=C=O + CH 2=O. The thermochemistry of methyl acetate and its fragmentation products have been obtained via the Active Thermochemical Tables (ATcT) approach, resulting in Δ fH 298(CH 3COOCH 3) = -98.7 ± 0.2 kcal mol -1, Δ fH 298(CH 3CO 2) = -45.7 ± 0.3 kcal mol -1, and Δ fH 298(COOCH 3) = -38.3 ± 0.4 kcal mol -1.« less

First evidence for the production of OH radicals by carbonyl oxides in solution phase A DFT investigation

NASA Astrophysics Data System (ADS)

Cremer, Dieter; Kraka, Elfi; Sosa, Carlos

2001-03-01

Dimesitylketone O-oxide ( 1) rearranges in solution to yield the alcohol 2-methylhydroxy-pentamethylbenzophenone ( 5) and dimesitylketone ( 6). DFT-B3LYP/cc-pVTZ calculations reveal that H migration from an o-methyl group to the terminal O atom of the COO unit of 1 rather than the isomerization of 1 is energetically the most favorable process. Calculated activation enthalpies (gas phase: 12.8 kcal/mol; CH 3CN solution: 12.4 kcal/mol) are in excellent agreement with measured activation enthalpies (CFCl 3 solution: 13.2±0.2 kcal/mol; CH 3CN solution: 12.5±0.3 kcal/mol). The hydroperoxide formed by H migration decomposes to a OH and a benzyl radical. Recombination in the solvent cage leads to alcohol 5 while diffusion of OH out of the solvent cage yields 6.

Synthesis, structure and magnetic study of a novel mixed-valent Co(II)10Co(III)4 shield constructed by mixed pyridine-alcoholate ligands.

PubMed

Peng, Yan; Tian, Chong-Bin; Zhang, Hua-Bin; Li, Zhi-Hua; Lin, Ping; Du, Shao-Wu

2012-04-28

A novel tetradecanuclear mixed-valent cobalt cluster, formulated as [Co(II)(10)Co(III)(4)(OH)(2)O(6)(hmp)(10)(pdm)(4)(CH(3)OH)(2)]·5H(2)O (1), was obtained using mixed ligands of 2-(hydroxymethyl)pyridine (hmpH) and 2,6-pyridinedimethanol (pdmH(2)). The cobalt ions in 1 are connected by ten chelating hmp(-) ligands, four tris-chelating pdm(2-) ligands and six μ(3)-oxide/hydroxide anions, forming a unique shield-like planar structure that is rarely observed for Co-based clusters. Compound 1 displays slight frequency dependence at static zero field below 4.5 K, suggesting that it might be a single molecule magnet (SMM). This journal is © The Royal Society of Chemistry 2012

A new method for speciated CH3O2 radical detection and HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) studies of the CH3O2 self-reaction

NASA Astrophysics Data System (ADS)

Onel, Lavinia; Brennan, Alexander; Seakins, Paul W.; Whalley, Lisa; Heard, Dwayne

2016-04-01

A new method has been developed for the speciated detection of CH3O2 radicals by FAGE (Fluorescence Assay by Gas Expansion) by titrating CH3O2 to CH3O by reaction with added NO and then detecting the resultant CH3O by LIF (laser induced fluorescence). The limit of detection of the technique is ˜108 cm-3 CH3O2 for a unity signal-to-noise ratio and 5 min averaging time. The method has been used for time monitoring of CH3O2 during its self-reaction within HIRAC at 1 bar and room temperature to determine a preliminary value of the rate coefficient of 4.2 × 10-13 cm3 s-1, which lies in the range of the previous results, (2.7 - 5.2) × 10-13 cm3 s-1.1 In addition to detection of CH3O2, products of the CH3O2 self-reaction were also observed for the two reaction channels over a range of temperatures from 260 - 320 K: (a) 2CH3O2 → CH2O + CH3OH; (b) 2CH3O2 → 2CH3O + O2, namely HO2 radicals (from reaction of CH3O + O2) and formaldehyde monitored by FAGE and formaldehyde and methanol observed by FTIR. A good agreement has been obtained between the FTIR and FAGE measurements of CH2O which increased to ˜ 2 ppmv over the experiments. Using the concentrations of CH3OH and CH2O, the branching ratio for channel (a) at room temperature has been determined as ra = 0.66 ± 0.06. The result is in very good agreement with the value recommended in the review of Tyndall et al.2 of ra = 0.63 ± 0.06. No temperature dependence of ra has been observed from 296 K to 321 K. 1. http://iupac.pole-ether.fr/ 2. G. S. Tyndall et al., J. Geophys. Res. 106, 12157 (2001).

Geraniol (2,6-dimethyl-2,6-octadien-8-ol) reactions with ozone and OH radical: Rate constants and gas-phase products

NASA Astrophysics Data System (ADS)

Forester, Crystal D.; Ham, Jason E.; Wells, J. R.

The bimolecular rate constants, kOH+geraniol, (231±58)×10 -12 cm 3 molecule -1 s -1 and k+geraniol, (9.3±2.3)×10 -16 cm 3 molecule -1 s -1, were measured using the relative rate technique for the reaction of the hydroxyl radical (OH) and ozone (O 3) with 2,6-dimethyl-2,6-octadien-8-ol (geraniol) at (297±3) K and 1 atmosphere total pressure. To more clearly define part of geraniol's indoor environment degradation mechanism, the products of the geraniol+OH and geraniol+O 3 reactions were also investigated. The identified geraniol+OH and geraniol+O 3 reaction products were: acetone, hydroxyacetaldehyde (glycolaldehyde, HC( dbnd O)CH 2OH), ethanedial (glyoxal, HC( dbnd O)C( dbnd O)H), and 2-oxopropanal (methylglyoxal, CH 3C( dbnd O)C( dbnd O)H). The use of derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to propose 4-oxopentanal as the other major geraniol+OH and geraniol+O 3 reaction product. The elucidation of this other reaction product was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible geraniol+OH and geraniol+O 3 reaction mechanisms based on previously published volatile organic compound+OH and volatile organic compound+O 3 gas-phase reaction mechanisms.

Photodissociation dynamics of nitromethane at 226 and 271 nm at both nanosecond and femtosecond time scales.

PubMed

Guo, Y Q; Bhattacharya, A; Bernstein, E R

2009-01-08

Photodissociation of nitromethane has been investigated for decades both theoretically and experimentally; however, as a whole picture, the dissociation dynamics for nitromethane are still not clear, although many different mechanisms have been proposed. To make a complete interpretation of these different mechanisms, photolysis of nitromethane at 226 and 271 nm under both collisional and collisionless conditions is investigated at nanosecond and femtosecond time scales. These two laser wavelengths correspond to the pi* <-- pi and pi* <-- n excitations of nitromethane, respectively. In nanosecond 226 nm (pi* <-- pi) photolysis experiments, CH(3) and NO radicals are observed as major products employing resonance enhanced multiphoton ionization techniques and time-of-flight mass spectrometry. Additionally, OH and CH(3)O radicals are weakly observed as dissociation products employing laser induced fluorescence spectroscopy; the CH(3)O product is only observed under collisional conditions. In femtosecond 226 nm experiments, CH(3), NO(2), and NO products are observed. These results confirm that rupture of C-N bond should be the main primary process for the photolysis of nitromethane after the pi* <-- pi excitation at 226 nm, and the NO(2) molecule should be the precursor of the observed NO product. Formation of the CH(3)O radical after the recombination of CH(3) and NO(2) species under collisional conditions rules out a nitro-nitrite isomerization mechanism for the generation of CH(3)O and NO from pi pi* CH(3)NO(2). The OH radical formation for pi pi* CH(3)NO(2) should be a minor dissociation channel because of the weak OH signal in both nanosecond and femtosecond (nonobservable) experiments. Single color femtosecond pump-probe experiments at 226 nm are also employed to monitor the dynamics of the dissociation of nitromethane after the pi* <-- pi excitation. Because of the ultrafast dynamics of product formation at 226 nm, the pump-probe transients for the three dissociation products are measured as an autocorrelation of the laser pulse, indicating the dissociation of nitromethane in the pi pi* excited state is faster than the laser pulse duration (180 fs). In nanosecond 271 nm (pi* <-- n) photolysis experiments, pump-probe experiments are performed to detect potential dissociation products, such as CH(3), NO(2), CH(3)O, and OH; however, none of them is observed. In femtosecond 271 nm laser experiments, the nitromethane parent ion is observed with major intensity, together with CH(3), NO(2), and NO fragment ions with only minor intensities. Pump-probe transients for both nitromethane parent and fragment ions at 271 nm excitation and 406.5 nm ionization display a fast exponential decay with a constant time of 36 fs, which we suggest to be the lifetime of the excited n pi* state of nitromethane. Combined with the 271 nm nanosecond pump-probe experiments, in which none of the CH(3), NO(2), CH(3)O, or OH fragment is observed, we suggest that all the fragment ions generated in 271 nm femtosecond laser experiments are derived from the parent ion, and dissociation of nitromethane from the n pi* excited electronic state does not occur in a supersonic molecular beam under collisionless conditions.

Photodissociation dynamics of the simplest alkyl peroxy radicals, CH 3OO and C 2H 5OO, at 248 nm

DOE PAGES

Sullivan, Erin N.; Nichols, Bethan; Neumark, Daniel M.

2018-01-28

The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CH 3OO) and ethyl peroxy C 2H 5OO , are investigated using fast beam photofragment translational spectroscopy. A fast beam of CH3OO- or C2H5OO- anions is photodetached to generate neutral radicals that are subsequently dissociated using 248 nm photons. The coincident detection of the photofragment positions and arrival times allows for the determination of mass, translational energy, and angular distributions for both two-body and three-body dissociation events. CH3OO exhibits repulsive O loss resulting in the formation of O(1D) + CH3O with high translational energy release. Minor two-body channels leadingmore » to OH + CH2O and CH3O + O(3P) formation are also detected. In addition, small amounts of H + O(3P) + CH2O are observed and attributed to O loss followed by CH3O dissociation. C2H5OO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(1D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O2 + C2H5 and HO2 + C2H4 are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, C2H5OO dissociation yields a three-body product channel, CH3 + O(3P) + CH2O, for which the proposed mechanism is repulsive O loss followed by the dissociation of C2H5O over a barrier. These results are compared to a recent study of tert-butyl peroxy (t-BuOO) in which 248 nm excitation results in three-body dissociatio n and ground state two-body dissociation but no O(1D) production.« less

Photodissociation dynamics of the simplest alkyl peroxy radicals, CH 3OO and C 2H 5OO, at 248 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, Erin N.; Nichols, Bethan; Neumark, Daniel M.

The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CH 3OO) and ethyl peroxy C 2H 5OO , are investigated using fast beam photofragment translational spectroscopy. A fast beam of CH3OO- or C2H5OO- anions is photodetached to generate neutral radicals that are subsequently dissociated using 248 nm photons. The coincident detection of the photofragment positions and arrival times allows for the determination of mass, translational energy, and angular distributions for both two-body and three-body dissociation events. CH3OO exhibits repulsive O loss resulting in the formation of O(1D) + CH3O with high translational energy release. Minor two-body channels leadingmore » to OH + CH2O and CH3O + O(3P) formation are also detected. In addition, small amounts of H + O(3P) + CH2O are observed and attributed to O loss followed by CH3O dissociation. C2H5OO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(1D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O2 + C2H5 and HO2 + C2H4 are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, C2H5OO dissociation yields a three-body product channel, CH3 + O(3P) + CH2O, for which the proposed mechanism is repulsive O loss followed by the dissociation of C2H5O over a barrier. These results are compared to a recent study of tert-butyl peroxy (t-BuOO) in which 248 nm excitation results in three-body dissociatio n and ground state two-body dissociation but no O(1D) production.« less

A model of CO-CH4 global transport/chemistry. I - Chemistry model

NASA Technical Reports Server (NTRS)

Peters, L. K.; Kitada, T.

1980-01-01

A simplified chemistry model was developed to incorporate the CO-CH4 chemistry into the global transport model of these compounds. CO is important because of its effects on atmospheric chemistry and is partly responsible for controlling the hydroxyl radical (OH) concentration in the troposphere. The model includes the photodissociation rate coefficients expressed as functions of solar zenith angle and altitude, and it was applied to determine the sensitivity of the OH concentration to trace gaseous species, such as NOx, O3, and H2O. Also, the concentrations and diurnal variations of OH and HO2, and the contribution of individual reactions to OH generation and consumption were calculated.

Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isegawa, Miho; Liu, Fengyi; Morokuma, Keiji

2014-06-28

Photodissociation pathways of nitromethane following π → π{sup *} electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH{sub 3} and NO{sub 2} ({sup 2}B{sub 2}) is formed by direct dissociation from the S{sub 1} state. Importantmore » pathways involving S{sub 1} and S{sub 0} states for production of various dissociation products CH{sub 3}NO + O ({sup 1}D), CH{sub 3}O(X{sup 2}E) + NO (X{sup 2}Π), CH{sub 2}NO + OH, and CH{sub 2}O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH{sub 3}NO{sub 2}, the OH radical roaming in OH dissociation from CH{sub 2}N(O)(OH), and the NO roaming in NO dissociation from CH{sub 3}ONO.« less

Kinetic study of the reaction of the hydroxyl radical (OH) with methyl ethyl ketone (2-butanone) and its deuterated isotopomers at low pressure

NASA Astrophysics Data System (ADS)

Liljegren, J. A.; Stevens, P. S.

2012-12-01

Methyl ethyl ketone (2-butanone) in the atmosphere comes from a variety of sources. It is produced commercially as an industrial ketone. It can be formed as a result of the OH or Cl-initiated oxidation of C4-C6 alkanes, primarily n-butane, or from the reaction of some alkenes with OH or O3. Biogenic sources include direct emissions from certain plants as well as emissions from decaying plant matter. Methyl ethyl ketone is removed from the atmosphere primarily by its reaction with OH. A product of this reaction includes acetaldehyde, which is a hazardous air pollutant, can further react to produce peroxy acetyl nitrate (PAN), and can be a significant source of free radicals to the atmosphere. The absolute rate constant for the reaction of OH with methyl ethyl ketone has been measured as a function of temperature at low pressure using discharge-flow techniques coupled with laser induced fluorescence (LIF) detection of OH. In addition, measurements of the rate constants for the reactions of OH with two deuterated isotopomers of methyl ethyl ketone, including CD3C(O)CH2CH3 and CH3C(O)CD2CD3, will be presented to gain a better understanding of the mechanism for this reaction. Theoretical studies of the potential energy surface for this reaction suggest that the reaction proceeds through the formation of a hydrogen-bonded pre-reactive complex, similar to that of several other atmospherically relevant oxygenated VOCs such as acetone, acetic acid, and hydroxyacetone.

Assessing thermochemical data

NASA Astrophysics Data System (ADS)

Holmes, John L.; Aubry, Christiane; Wang, Xian

2007-11-01

This paper describes, with examples, a critical assessment of thermochemical data for some small molecules and free radicals. The available heats of formation, [Delta]fH° (all 298 K values). for simple alkyl hydroperoxides and di-alkyl peroxides were compared and new data are provided. The [Delta]fH° values, all ±5 kJ/mol, are: CH3OOH, -135; CH3CH2OOH, -168; n-C3H7OOH, -189; s-C3H7OOH, -205; t-C4H9OOH, -240; CH3OOCH3, -132; CH3CH2OOCH3, -165; C2H5OOC2H5, -198; n-C3H7OOn-C3H7, -240; s-C3H7OOs-C3H7, -272; t-C4H9OOt-C4H9, -342. These are consistent with established O-O bond dissociation energies and with additivity considerations. [Delta]fH° values for the corresponding alkoxy radicals are also addressed. A similar survey was applied to the homologous n-alkyl aldehydes, C2 to C8, for which recommended [Delta]fH° values, all ±1.5 kJ/mol, are: -166.5, -189, -207.5, -227, -248, -268 and -289, respectively. Particular attention was given to [Delta]fH°(CH3CO) = -10.3 ± 1.8 kJ/mol. The current NIST WebBook datum, [Delta]fH°(CS) = 280.3 kJ/mol, is arguably the best value, being consistent with related thermochemical data. Finally the [Delta]fH° values for the allylic free radicals CH2CHCH2, 174 ± 3 kJ/mol, CH2CHCH(OH), 4.5 ± 4 kJ/mol, and (CH2CH)2C(OH), 37 ± 4 kJ/mol, derived from experimental data and results of computational chemistry are described, together with some related homolytic bond strengths.

Importance of sulfate radical anion formation and chemistry in heterogeneous OH oxidation of sodium methyl sulfate, the smallest organosulfate

DOE PAGES

Kwong, Kai Chung; Chim, Man Mei; Davies, James F.; ...

2018-02-27

Organosulfates are important organosulfur compounds present in atmospheric particles. While the abundance, composition, and formation mechanisms of organosulfates have been extensively investigated, it remains unclear how they transform and evolve throughout their atmospheric lifetime. To acquire a fundamental understanding of how organosulfates chemically transform in the atmosphere, this study investigates the heterogeneous OH radical-initiated oxidation of sodium methyl sulfate (CH 3SO 4Na) droplets, the smallest organosulfate detected in atmospheric particles, using an aerosol flow tube reactor at a high relative humidity (RH) of 85%. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (direct analysis in real time,more » DART) coupled with a high-resolution mass spectrometer showed that neither functionalization nor fragmentation products are detected. Instead, the ion signal intensity of the bisulfate ion (HSO 4 -) has been found to increase significantly after OH oxidation. We postulate that sodium methyl sulfate tends to fragment into a formaldehyde (CH 2O) and a sulfate radical anion (SO 4 .-) upon OH oxidation. The formaldehyde is likely partitioned back to the gas phase due to its high volatility. The sulfate radical anion, similar to OH radical, can abstract a hydrogen atom from neighboring sodium methyl sulfate to form the bisulfate ion, contributing to the secondary chemistry. Kinetic measurements show that the heterogeneous OH reaction rate constant, k, is (3.79 ± 0.19) × 10 -13cm 3molecule -1s -1 with an effective OH uptake coefficient, γ eff, of 0.17 ± 0.03. While about 40% of sodium methyl sulfate is being oxidized at the maximum OH exposure (1.27 × 10 12molecule cm -3s), only a 3% decrease in particle diameter is observed. This can be attributed to a small fraction of particle mass lost via the formation and volatilization of formaldehyde. Overall, we firstly demonstrate that the heterogeneous OH oxidation of an organosulfate can lead to the formation of sulfate radical anion and produce inorganic sulfate. Fragmentation processes and sulfate radical anion chemistry play a key role in determining the compositional evolution of sodium methyl sulfate during heterogeneous OH oxidation.« less

Importance of sulfate radical anion formation and chemistry in heterogeneous OH oxidation of sodium methyl sulfate, the smallest organosulfate

NASA Astrophysics Data System (ADS)

Chung Kwong, Kai; Chim, Man Mei; Davies, James F.; Wilson, Kevin R.; Nin Chan, Man

2018-02-01

Organosulfates are important organosulfur compounds present in atmospheric particles. While the abundance, composition, and formation mechanisms of organosulfates have been extensively investigated, it remains unclear how they transform and evolve throughout their atmospheric lifetime. To acquire a fundamental understanding of how organosulfates chemically transform in the atmosphere, this work investigates the heterogeneous OH radical-initiated oxidation of sodium methyl sulfate (CH3SO4Na) droplets, the smallest organosulfate detected in atmospheric particles, using an aerosol flow tube reactor at a high relative humidity (RH) of 85 %. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (direct analysis in real time, DART) coupled with a high-resolution mass spectrometer showed that neither functionalization nor fragmentation products are detected. Instead, the ion signal intensity of the bisulfate ion (HSO4-) has been found to increase significantly after OH oxidation. We postulate that sodium methyl sulfate tends to fragment into a formaldehyde (CH2O) and a sulfate radical anion (SO4 ṡ -) upon OH oxidation. The formaldehyde is likely partitioned back to the gas phase due to its high volatility. The sulfate radical anion, similar to OH radical, can abstract a hydrogen atom from neighboring sodium methyl sulfate to form the bisulfate ion, contributing to the secondary chemistry. Kinetic measurements show that the heterogeneous OH reaction rate constant, k, is (3.79 ± 0.19) × 10-13 cm3 molecule-1 s-1 with an effective OH uptake coefficient, γeff, of 0.17 ± 0.03. While about 40 % of sodium methyl sulfate is being oxidized at the maximum OH exposure (1.27 × 1012 molecule cm-3 s), only a 3 % decrease in particle diameter is observed. This can be attributed to a small fraction of particle mass lost via the formation and volatilization of formaldehyde. Overall, we firstly demonstrate that the heterogeneous OH oxidation of an organosulfate can lead to the formation of sulfate radical anion and produce inorganic sulfate. Fragmentation processes and sulfate radical anion chemistry play a key role in determining the compositional evolution of sodium methyl sulfate during heterogeneous OH oxidation.

Importance of sulfate radical anion formation and chemistry in heterogeneous OH oxidation of sodium methyl sulfate, the smallest organosulfate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwong, Kai Chung; Chim, Man Mei; Davies, James F.

Organosulfates are important organosulfur compounds present in atmospheric particles. While the abundance, composition, and formation mechanisms of organosulfates have been extensively investigated, it remains unclear how they transform and evolve throughout their atmospheric lifetime. To acquire a fundamental understanding of how organosulfates chemically transform in the atmosphere, this study investigates the heterogeneous OH radical-initiated oxidation of sodium methyl sulfate (CH 3SO 4Na) droplets, the smallest organosulfate detected in atmospheric particles, using an aerosol flow tube reactor at a high relative humidity (RH) of 85%. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (direct analysis in real time,more » DART) coupled with a high-resolution mass spectrometer showed that neither functionalization nor fragmentation products are detected. Instead, the ion signal intensity of the bisulfate ion (HSO 4 -) has been found to increase significantly after OH oxidation. We postulate that sodium methyl sulfate tends to fragment into a formaldehyde (CH 2O) and a sulfate radical anion (SO 4 .-) upon OH oxidation. The formaldehyde is likely partitioned back to the gas phase due to its high volatility. The sulfate radical anion, similar to OH radical, can abstract a hydrogen atom from neighboring sodium methyl sulfate to form the bisulfate ion, contributing to the secondary chemistry. Kinetic measurements show that the heterogeneous OH reaction rate constant, k, is (3.79 ± 0.19) × 10 -13cm 3molecule -1s -1 with an effective OH uptake coefficient, γ eff, of 0.17 ± 0.03. While about 40% of sodium methyl sulfate is being oxidized at the maximum OH exposure (1.27 × 10 12molecule cm -3s), only a 3% decrease in particle diameter is observed. This can be attributed to a small fraction of particle mass lost via the formation and volatilization of formaldehyde. Overall, we firstly demonstrate that the heterogeneous OH oxidation of an organosulfate can lead to the formation of sulfate radical anion and produce inorganic sulfate. Fragmentation processes and sulfate radical anion chemistry play a key role in determining the compositional evolution of sodium methyl sulfate during heterogeneous OH oxidation.« less

Role of atmospheric oxidation in recent methane growth

PubMed Central

Rigby, Matthew; Montzka, Stephen A.; Prinn, Ronald G.; White, James W. C.; Young, Dickon; Lunt, Mark F.; Ganesan, Anita L.; Manning, Alistair J.; Simmonds, Peter G.; Salameh, Peter K.; Harth, Christina M.; Mühle, Jens; Weiss, Ray F.; Fraser, Paul J.; Steele, L. Paul; McCulloch, Archie; Park, Sunyoung

2017-01-01

The growth in global methane (CH4) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH4 sink, in the recent CH4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH3CCl3), which is lost primarily through reaction with OH, to estimate OH levels as well as CH3CC3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH4/12CH4 ratio and the recent growth in C2H6. Our approach indicates that significant OH-related uncertainties in the CH4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered. PMID:28416657

Self-assembly of 2-aldehyde-8-hydroxyquinolinate-based lanthanide complexes and NIR luminescence

NASA Astrophysics Data System (ADS)

Zhang, Meiqi; Li, Hongfeng; Chen, Peng; Sun, Wenbin; Zhang, Lei; Yan, Pengfei

2015-02-01

Self-assembly reaction of 2-aldehyde-8-hydroxyquinoline, tris(hydroxymethyl)aminomethane and LnCl3ṡ6H2O affords a series of mononuclear lanthanide complexes Ce(baho)2·Et2O (1) (H2baho = 2,8-bis(2-(8-hydroxylquinolinyl))-1-aza-5-hydroxymethyl-3,7-dioxabicyclo[3.3.0]octane), Dy(nhm)2Cl·0.5H2O (2) and Ln(nhm)2Cl·0.5C6H14 (Ln = Ho (3), Er (4), Yb (5) and Hnhm = N-(2-(8-hydroxylquinolinyl)methylene)(trishydroxymethyl)methylamine. The crystal structures have been determined by X-ray crystallographic analysis, and the tetravalence of Ce in 1 has been proven by XPS. Interestingly, the positive charge of Ce4+ ion in 1 is neutralized by two deprotonated baho2- ligands, while two deprotonated nhm- ligands and one Cl- compensate the positive charge of Ln3+ ions in 2-5. Complex 5 exhibit essential NIR luminescence of Yb3+ ion with lifetime of 17.64 μs in solid and 9.96 μs in CH3OH solution.

Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raston, Paul L.; Obi, Emmanuel I.; Douberly, Gary E.

Here, the entrance channel complex in the exothermic OH + CH 4 → H 2O + CH 3 reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j CH4 = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same formore » all internal rotation states; however, subband origins are found to decrease with increasing j CH4. Measurements of deuterated complexes have also been made (OD–CH 4, OH–CD 4, and OD–CD 4), the relative linewidths of which provide information about the flow of vibrational energy in the complexes; vibrational lifetime broadening is prominent for OH–CH 4 and OD–CD 4, for which the excited OX stretching state has a nearby CY 4 stretching fundamental (X, Y = H or D).« less

Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets

DOE PAGES

Raston, Paul L.; Obi, Emmanuel I.; Douberly, Gary E.

2017-09-22

Here, the entrance channel complex in the exothermic OH + CH 4 → H 2O + CH 3 reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j CH4 = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same formore » all internal rotation states; however, subband origins are found to decrease with increasing j CH4. Measurements of deuterated complexes have also been made (OD–CH 4, OH–CD 4, and OD–CD 4), the relative linewidths of which provide information about the flow of vibrational energy in the complexes; vibrational lifetime broadening is prominent for OH–CH 4 and OD–CD 4, for which the excited OX stretching state has a nearby CY 4 stretching fundamental (X, Y = H or D).« less

Ab Initio Kinetics of Hydrogen Abstraction from Methyl Acetate by Hydrogen, Methyl, Oxygen, Hydroxyl, and Hydroperoxy Radicals.

PubMed

Tan, Ting; Yang, Xueliang; Krauter, Caroline M; Ju, Yiguang; Carter, Emily A

2015-06-18

The kinetics of hydrogen abstraction by five radicals (H, O((3)P), OH, CH3, and HO2) from methyl acetate (MA) is investigated theoretically in order to gain further understanding of certain aspects of the combustion chemistry of biodiesels, such as the effect of the ester moiety. We employ ab initio quantum chemistry methods, coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) and multireference averaged coupled pair functional theory (MRACPF2), to predict chemically accurate reaction energetics. Overall, MRACPF2 predicts slightly higher barrier heights than CCSD(T) for MA + H/CH3/O/OH, but slightly lower barrier heights for hydrogen abstraction by HO2. Based on the obtained reaction energies, we also report high-pressure-limit rate constants using transition state theory (TST) in conjunction with the separable-hindered-rotor approximation, the variable reaction coordinate TST, and the multi-structure all-structure approach. The fitted modified Arrhenius expressions are provided over a temperature range of 250 to 2000 K. The predictions are in good agreement with available experimental results. Abstractions from both of the methyl groups in MA are expected to contribute to consumption of the fuel as they exhibit similar rate coefficients. The reactions involving the OH radical are predicted to have the highest rates among the five abstracting radicals, while those initiated by HO2 are expected to be the lowest.

Quantifying the causes of differences in tropospheric OH within global models

NASA Astrophysics Data System (ADS)

Nicely, Julie M.; Salawitch, Ross J.; Canty, Timothy; Anderson, Daniel C.; Arnold, Steve R.; Chipperfield, Martyn P.; Emmons, Louisa K.; Flemming, Johannes; Huijnen, Vincent; Kinnison, Douglas E.; Lamarque, Jean-François; Mao, Jingqiu; Monks, Sarah A.; Steenrod, Stephen D.; Tilmes, Simone; Turquety, Solene

2017-02-01

The hydroxyl radical (OH) is the primary daytime oxidant in the troposphere and provides the main loss mechanism for many pollutants and greenhouse gases, including methane (CH4). Global mean tropospheric OH differs by as much as 80% among various global models, for reasons that are not well understood. We use neural networks (NNs), trained using archived output from eight chemical transport models (CTMs) that participated in the Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport Model Intercomparison Project (POLMIP), to quantify the factors responsible for differences in tropospheric OH and resulting CH4 lifetime (τCH4) between these models. Annual average τCH4, for loss by OH only, ranges from 8.0 to 11.6 years for the eight POLMIP CTMs. The factors driving these differences were quantified by inputting 3-D chemical fields from one CTM into the trained NN of another CTM. Across all CTMs, the largest mean differences in τCH4 (ΔτCH4) result from variations in chemical mechanisms (ΔτCH4 = 0.46 years), the photolysis frequency (J) of O3 → O(1D) (0.31 years), local O3 (0.30 years), and CO (0.23 years). The ΔτCH4 due to CTM differences in NOx (NO + NO2) is relatively low (0.17 years), although large regional variation in OH between the CTMs is attributed to NOx. Differences in isoprene and J(NO2) have negligible overall effect on globally averaged tropospheric OH, although the extent of OH variations due to each factor depends on the model being examined. This study demonstrates that NNs can serve as a useful tool for quantifying why tropospheric OH varies between global models, provided that essential chemical fields are archived.

UV Photodesorption of Methanol in Pure and CO-rich Ices: Desorption Rates of the Intact Molecule and of the Photofragments

NASA Astrophysics Data System (ADS)

Bertin, Mathieu; Romanzin, Claire; Doronin, Mikhail; Philippe, Laurent; Jeseck, Pascal; Ligterink, Niels; Linnartz, Harold; Michaut, Xavier; Fillion, Jean-Hugues

2016-02-01

Wavelength-dependent photodesorption rates have been determined using synchrotron radiation for condensed pure and mixed methanol ice in the 7-14 eV range. The VUV photodesorption of intact methanol molecules from pure methanol ices is found to be of the order of 10-5 molecules/photon, that is two orders of magnitude below what is generally used in astrochemical models. This rate gets even lower (<10-6 molecules/photon) when the methanol is mixed with CO molecules in the ices. This is consistent with a picture in which photodissociation and recombination processes are at the origin of intact methanol desorption from pure CH3OH ices. Such low rates are explained by the fact that the overall photodesorption process is dominated by the desorption of the photofragments CO, CH3, OH, H2CO, and CH3O/CH2OH, whose photodesorption rates are given in this study. Our results suggest that the role of the photodesorption as a mechanism to explain the observed gas phase abundances of methanol in cold media is probably overestimated. Nevertheless, the photodesorption of radicals from methanol-rich ices may stand at the origin of the gas phase presence of radicals such as CH3O, therefore, opening new gas phase chemical routes for the formation of complex molecules.

Dissociative photoionization mechanism of methanol isotopologues (CH3OH, CD3OH, CH3OD and CD3OD) by iPEPICO: energetics, statistical and non-statistical kinetics and isotope effects.

PubMed

Borkar, Sampada; Sztáray, Bálint; Bodi, Andras

2011-07-28

The dissociative photoionization of energy selected methanol isotopologue (CH(3)OH, CD(3)OH, CH(3)OD and CD(3)OD) cations was investigated using imaging Photoelectron Photoion Coincidence (iPEPICO) spectroscopy. The first dissociation is an H/D-atom loss from the carbon, also confirmed by partial deuteration. Somewhat above 12 eV, a parallel H(2)-loss channel weakly asserts itself. At photon energies above 15 eV, in a consecutive hydrogen molecule loss to the first H-atom loss, the formation of CHO(+)/CDO(+) dominates as opposed to COH(+)/COD(+) formation. We see little evidence for H-atom scrambling in these processes. In the photon energy range corresponding to the B[combining tilde] and C[combining tilde] ion states, a hydroxyl radical loss appears yielding CH(3)(+)/CD(3)(+). Based on the branching ratios, statistical considerations and ab initio calculations, this process is confirmed to take place on the first electronically excited Ã(2)A' ion state. Uncharacteristically, internal conversion is outcompeted by unimolecular dissociation due to the apparently weak Renner-Teller-like coupling between the X[combining tilde] and the à ion states. The experimental 0 K appearance energies of the ions CH(2)OH(+), CD(2)OH(+), CH(2)OD(+) and CD(2)OD(+) are measured to be 11.646 ± 0.003 eV, 11.739 ± 0.003 eV, 11.642 ± 0.003 eV and 11.737 ± 0.003 eV, respectively. The E(0)(CH(2)OH(+)) = 11.6454 ± 0.0017 eV was obtained based on the independently measured isotopologue results and calculated zero point effects. The 0 K heat of formation of CH(2)OH(+), protonated formaldehyde, was determined to be 717.7 ± 0.7 kJ mol(-1). This yields a 0 K heat of formation of CH(2)OH of -11.1 ± 0.9 kJ mol(-1) and an experimental 298 K proton affinity of formaldehyde of 711.6 ± 0.8 kJ mol(-1). The reverse barrier to homonuclear H(2)-loss from CH(3)OH(+) is determined to be 36 kJ mol(-1), whereas for heteronuclear H(2)-loss from CH(2)OH(+) it is found to be 210 kJ mol(-1). This journal is © the Owner Societies 2011

The fate of the hydroxyl radical in the earth's primitive atmosphere and implications for the production of molecular oxygen

NASA Technical Reports Server (NTRS)

Vander Wood, T. B.; Thiemens, M. H.

1980-01-01

Behavior of the hydroxyl radical produced by the photolysis of water vapor in the earth's early atmosphere is examined. Because of the substantial OH radical reactivity with trace species (CO, HCl, SO2, H2S, NH3, and CH4) the formation of molecular oxygen may be prevented, even at a trace species mixing ratio. The photolysis rate of H2O, with corrections for hydrogen exospheric escape, is capable of describing the oxidation of the atmosphere and crust but may not be used to determine the rate of molecular oxygen generation without consideration of the various OH-trace species reactions.

(CH3)3COOH (tert-butyl hydroperoxide): OH reaction rate coefficients between 206 and 375 K and the OH photolysis quantum yield at 248 nm.

PubMed

Baasandorj, Munkhbayar; Papanastasiou, Dimitrios K; Talukdar, Ranajit K; Hasson, Alam S; Burkholder, James B

2010-10-14

Rate coefficients, k, for the gas-phase reaction of the OH radical with (CH(3))(3)COOH (tert-butyl hydroperoxide) were measured as a function of temperature (206-375 K) and pressure (25-200 Torr (He, N(2))). Rate coefficients were measured under pseudo-first-order conditions using pulsed laser photolysis to produce OH and laser induced fluorescence (PLP-LIF) to measure the OH temporal profile. Two independent methods were used to determine the gas-phase infrared cross sections of (CH(3))(3)COOH, absolute pressure and chemical titration, that were used to determine the (CH(3))(3)COOH concentration in the LIF reactor. The temperature dependence of the rate coefficients is described, within the measurement precision, by the Arrhenius expression k(1)(T) = (7.0 ± 1.0) × 10(-13) exp[(485 ± 20)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (3.58 ± 0.54) × 10(-12) cm(3) molecule(-1) s(-1). The uncertainties are 2σ (95% confidence level) and include estimated systematic errors. UV absorption cross sections of (CH(3))(3)COOH were determined at 185, 214, 228, and 254 nm and over the wavelength range 210-300 nm. The OH quantum yield following the 248 nm pulsed laser photolysis of (CH(3))(3)COOH was measured relative to the OH quantum yields of H(2)O(2) and HNO(3) using PLP-LIF and found to be near unity.

Reaction of Pentanol isomers with OH radical – A theoretical perspective

NASA Astrophysics Data System (ADS)

Aazaad, Basheer; Lakshmipathi, Senthilkumar

2018-05-01

The stability of all the three isomeric forms of Pentanol has been examined with relative energy analysis. Even though 2-Pentanol is predicted to be most stable isomeric form, all the three isomeric forms undergo hydrogen atom abstraction reaction with OH radical. Among the proposed 18 different hydrogen atom abstraction reaction, the abstraction from CH2 and CH functional group is found to be a favourable reactive site with low energy barrier in M06-2X/6-311+G(d,p) level of theory. Wiberg bond order analysis shows all the abstraction reactions are concreted but not synchronic in nature. Using force analysis, the calculated work done of individual reaction regions illustrates that structural rearrangements drive the reaction with higher contribution to the energy barrier. The rate constant calculated at M06-2X method for the most favourable reaction is well matched with available experimental data. Using the reported atmospheric OH concentration (1 × 106 molecules/cm3), the life time of 1-Pentanol, 2-Pentanol and 3-Pentanol has calculated to be 18.66, 0.36 and 2.86 days, respectively.

Detecting a Quasi-stable Imine Species on the Reaction Pathway of SHV-1 β-Lactamase and 6β-(Hydroxymethyl)penicillanic Acid Sulfone

PubMed Central

2015-01-01

For the class A β-lactamase SHV-1, the kinetic and mechanistic properties of the clinically used inhibitor sulbactam are compared with the sulbactam analog substituted in its 6β position by a CH2OH group (6β-(hydroxymethyl)penicillanic acid). The 6β substitution improves both in vitro and microbiological inhibitory properties of sulbactam. Base hydrolysis of both compounds was studied by Raman and NMR spectroscopies and showed that lactam ring opening is followed by fragmentation of the dioxothiazolidine ring leading to formation of the iminium ion within 3 min. The iminium ion slowly loses a proton and converts to cis-enamine (which is a β-aminoacrylate) in 1 h for sulbactam and in 4 h for 6β-(hydroxymethyl) sulbactam. Rapid mix–rapid freeze Raman spectroscopy was used to follow the reactions between the two sulfones and SHV-1. Within 23 ms, a 10-fold excess of sulbactam was entirely hydrolyzed to give a cis-enamine product. In contrast, the 6β-(hydroxymethyl) sulbactam formed longer-lived acyl–enzyme intermediates that are a mixture of imine and enamines. Single crystal Raman studies, soaking in and washing out unreacted substrates, revealed stable populations of imine and trans-enamine acyl enzymes. The corresponding X-ray crystallographic data are consonant with the Raman data and also reveal the role played by the 6β-hydroxymethyl group in retarding hydrolysis of the acyl enzymes. The 6β-hydroxymethyl group sterically hinders approach of the water molecule as well as restraining the side chain of E166 that facilitates hydrolysis. PMID:25536850

Gas-phase kinetics study of reaction of OH radical with CH3NHNH2 by second-order multireference perturbation theory.

PubMed

Sun, Hongyan; Zhang, Peng; Law, Chung K

2012-05-31

The gas-phase kinetics of H-abstraction reactions of monomethylhydrazine (MMH) by OH radical was investigated by second-order multireference perturbation theory and two-transition-state kinetic model. It was found that the abstractions of the central and terminal amine H atoms by the OH radical proceed through the formation of two hydrogen bonded preactivated complexes with energies of 6.16 and 5.90 kcal mol(-1) lower than that of the reactants, whereas the abstraction of methyl H atom is direct. Due to the multireference characters of the transition states, the geometries and ro-vibrational frequencies of the reactant, transition states, reactant complexes, and product complexes were optimized by the multireference CASPT2/aug-cc-pVTZ method, and the energies of the stationary points of the potential energy surface were refined at the QCISD(T)/CBS level via extrapolation of the QCISD(T)/cc-pVTZ and QCISD(T)/cc-pVQZ energies. It was found that the abstraction reactions of the central and two terminal amine H atoms of MMH have the submerged energy barriers with energies of 2.95, 2.12, and 1.24 kcal mol(-1) lower than that that of the reactants respectively, and the abstraction of methyl H atom has a real energy barrier of 3.09 kcal mol(-1). Furthermore, four MMH radical-H(2)O complexes were found to connect with product channels and the corresponding transition states. Consequently, the rate coefficients of MMH + OH for the H-abstraction of the amine H atoms were determined on the basis of a two-transition-state model, with the total energy E and angular momentum J conserved between the two transition-state regions. In units of cm(3) molecule(-1) s(-1), the rate coefficient was found to be k(1) = 3.37 × 10(-16)T(1.295) exp(1126.17/T) for the abstraction of the central amine H to form the CH(3)N(•)NH(2) radical, k(2) = 2.34 × 10(-17)T(1.907) exp(1052.26/T) for the abstraction of the terminal amine H to form the trans-CH(3)NHN(•)H radical, k(3) = 7.41 × 10(-20)T(2.428) exp(1343.20/T) for the abstraction of the terminal amine H to form the cis-CH(3)NHN(•)H radical, and k(4) = 9.13 × 10(-21)T(2.964) exp(-114.09/T) for the abstraction of the methyl H atom to form the C(•)H(2)NHNH(2) radical, respectively. Assuming that the rate coefficients are additive, the total rate coefficient of these theoretical predictions quantitatively agrees with the measured rate constant at temperatures of 200-650 K, with no adjustable parameters.

Infrared absorption spectra of partially deuterated methoxy radicals CH2DO and CHD2O isolated in solid para-hydrogen.

PubMed

Haupa, Karolina A; Johnson, Britta A; Sibert, Edwin L; Lee, Yuan-Pern

2017-10-21

The investigation of partially deuterated methoxy radicals is important because the symmetry lowering from C 3v to C s provides new insights into the couplings between rovibronic states via Jahn-Teller and spin-orbit interactions. The vibrational spectrum of the partially deuterated methoxy radical CH 2 DO in a matrix of p-H 2 has been recorded. This species was prepared by irradiating a p-H 2 matrix containing deuterated d 1 -nitritomethane (CH 2 DONO) at 3.3 K with laser light at 355 nm. The identification of the radical is based on the photochemical behavior of the precursor and comparison of observed vibrational wavenumbers and infrared (IR) intensities with those predicted from a refined quartic, curvilinear, internal coordinate force field calculated with the coupled-cluster singles and doubles with perturbative triples/cc-pVTZ method. CH 2 DO reacts with H 2 with a rate coefficient (3.5 ± 1.0) × 10 -3 s -1 . Predominantly c-CHDOH and a negligibly small amount of t-CHDOH were produced. This stereoselectivity results from the reaction H + C s -CH 2 DOH, which was demonstrated by an additional experiment on irradiation of a CH 2 DOH/Cl 2 /p-H 2 matrix with ultraviolet and IR light to induce the H + CH 2 DOH reaction; only c-CHDOH was observed from this experiment. Even though the energies of transition states and products for the formation of c-CHDOH and t-CHDOH differ by only ∼10 cm -1 , the selective formation of c-CHDOH can be explained by tunneling of the hydrogen atom via an optimal tunneling path. Similarly, the vibronic spectrum for the partially deuterated specie d 2 -methoxy radical (CHD 2 O) was obtained upon irradiation of d 2 -nitritomethane (CHD 2 ONO) at 355 nm. Lines associated with the fundamental vibrational modes were observed and assigned; line positions agree with theoretically predicted vibrational wavenumbers. CHD 2 O reacts with H 2 with a rate coefficient (6.0 ± 1.4) × 10 -3 s -1 ; CD 2 OH was produced as a major product because the barrier for the formation of CHDOH from H + CHD 2 OH is greater by ∼400 cm -1 . Rate coefficients of the decays of CH 3 O, CH 2 DO, CHD 2 O, and CD 3 O and their corresponding potential energy surfaces are compared.

Infrared absorption spectra of partially deuterated methoxy radicals CH2DO and CHD2O isolated in solid para-hydrogen

NASA Astrophysics Data System (ADS)

Haupa, Karolina A.; Johnson, Britta A.; Sibert, Edwin L.; Lee, Yuan-Pern

2017-10-01

The investigation of partially deuterated methoxy radicals is important because the symmetry lowering from C3v to Cs provides new insights into the couplings between rovibronic states via Jahn-Teller and spin-orbit interactions. The vibrational spectrum of the partially deuterated methoxy radical CH2DO in a matrix of p-H2 has been recorded. This species was prepared by irradiating a p-H2 matrix containing deuterated d1-nitritomethane (CH2DONO) at 3.3 K with laser light at 355 nm. The identification of the radical is based on the photochemical behavior of the precursor and comparison of observed vibrational wavenumbers and infrared (IR) intensities with those predicted from a refined quartic, curvilinear, internal coordinate force field calculated with the coupled-cluster singles and doubles with perturbative triples/cc-pVTZ method. CH2DO reacts with H2 with a rate coefficient (3.5 ± 1.0) × 10-3 s-1. Predominantly c-CHDOH and a negligibly small amount of t-CHDOH were produced. This stereoselectivity results from the reaction H + Cs-CH2DOH, which was demonstrated by an additional experiment on irradiation of a CH2DOH/Cl2/p-H2 matrix with ultraviolet and IR light to induce the H + CH2DOH reaction; only c-CHDOH was observed from this experiment. Even though the energies of transition states and products for the formation of c-CHDOH and t-CHDOH differ by only ˜10 cm-1, the selective formation of c-CHDOH can be explained by tunneling of the hydrogen atom via an optimal tunneling path. Similarly, the vibronic spectrum for the partially deuterated specie d2-methoxy radical (CHD2O) was obtained upon irradiation of d2-nitritomethane (CHD2ONO) at 355 nm. Lines associated with the fundamental vibrational modes were observed and assigned; line positions agree with theoretically predicted vibrational wavenumbers. CHD2O reacts with H2 with a rate coefficient (6.0 ± 1.4) × 10-3 s-1; CD2OH was produced as a major product because the barrier for the formation of CHDOH from H + CHD2OH is greater by ˜400 cm-1. Rate coefficients of the decays of CH3O, CH2DO, CHD2O, and CD3O and their corresponding potential energy surfaces are compared.

Competing 1πσ* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.

PubMed

Hadden, David J; Roberts, Gareth M; Karsili, Tolga N V; Ashfold, Michael N R; Stavros, Vasilios G

2012-10-14

Deactivation of excited electronic states through coupling to dissociative (1)πσ* states in heteroaromatic systems has received considerable attention in recent years, particularly as a mechanism that contributes to the ultraviolet (UV) photostability of numerous aromatic biomolecules and their chromophores. Recent studies have expanded upon this work to look at more complex species, which involves understanding competing dynamics on two different (1)πσ* potential energy surfaces (PESs) localized on different heteroatom hydride coordinates (O-H and N-H bonds) within the same molecule. In a similar spirit, the work presented here utilizes ultrafast time-resolved velocity map ion imaging to study competing dissociation pathways along (1)πσ* PESs in mequinol (p-methoxyphenol), localized at O-H and O-CH(3) bonds yielding H atoms or CH(3) radicals, respectively, over an excitation wavelength range of 298-238 nm and at 200 nm. H atom elimination is found to be operative via either tunneling under a conical intersection (CI) (298 ≥ λ ≥ 280 nm) or ultrafast internal conversion through appropriate CIs (λ ≤ 245 nm), both of which provide mechanisms for coupling onto the dissociative state associated with the O-H bond. In the intermediate wavelength range of 280 ≥ λ ≥ 245 nm, mediated H atom elimination is not observed. In contrast, we find that state driven CH(3) radical elimination is only observed in the excitation range 264 ≥ λ ≥ 238 nm. Interpretation of these experimental results is guided by: (i) high level complete active space with second order perturbation theory (CASPT2) calculations, which provide 1-D potential energy cuts of the ground and low lying singlet excited electronic states along the O-H and O-CH(3) bond coordinates; and (ii) calculated excitation energies using CASPT2 and the equation-of-motion coupled cluster with singles and doubles excitations (EOM-CCSD) formalism. From these comprehensive studies, we find that the dynamics along the O-H coordinate generally mimic H atom elimination previously observed in phenol, whereas O-CH(3) bond fission in mequinol appears to present notably different behavior to the CH(3) elimination dynamics previously observed in anisole (methoxybenzene).

Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer.

PubMed

Anglada, Josep M; Crehuet, Ramon; Adhikari, Sarju; Francisco, Joseph S; Xia, Yu

2018-02-14

Hydropersulfides (RSSH) are highly reactive as nucleophiles and hydrogen atom transfer reagents. These chemical properties are believed to be key for them to act as antioxidants in cells. The reaction involving the radical species and the disulfide bond (S-S) in RSSH, a known redox-active group, however, has been scarcely studied, resulting in an incomplete understanding of the chemical nature of RSSH. We have performed a high-level theoretical investigation on the reactions of the hydroxyl radical (˙OH) toward a set of RSSH (R = -H, -CH 3 , -NH 2 , -C(O)OH, -CN, and -NO 2 ). The results show that S-S cleavage and H-atom abstraction are the two competing channels. The electron inductive effect of R induces selective ˙OH substitution at one sulfur atom upon S-S cleavage, forming RSOH and ˙SH for the electron donating groups (EDGs), whereas producing HSOH and ˙SR for the electron withdrawing groups (EWGs). The H-Atom abstraction by ˙OH follows a classical hydrogen atom transfer (hat) mechanism, producing RSS˙ and H 2 O. Surprisingly, a proton-coupled electron transfer (pcet) process also occurs for R being an EDG. Although for RSSH having EWGs hat is the leading channel, S-S cleavage can be competitive or even dominant for the EDGs. The overall reactivity of RSSH toward ˙OH attack is greatly enhanced with the presence of an EDG, with CH 3 SSH being the most reactive species found in this study (overall rate constant: 4.55 × 10 12 M -1 s -1 ). Our results highlight the complexity in RSSH reaction chemistry, the extent of which is closely modulated by the inductive effect of the substituents in the case of the oxidation by hydroxyl radicals.

Glyceryl ether sulfonates for use in oil recovery fluids and processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCoy, D.R.

1984-08-21

Petroleum may be recovered from petroleum containing formations having high salinity by injecting into the formation an aqueous fluid containing an effective amount of a surface active agent characterized by the formula: R/sub 1/(OCH/sub 2/CH(OH)CH/sub 2/) /SUB m/ (R/sub 2/) /SUB n/ OR/sub 3/SO/sub 3/X wherein R/sub 1/ is an alkyl or alkylaryl radical, m is an integer of from 1 to 10, R/sub 2/ is an ethoxy radical and/or 1,2-propoxy radical, n is an integer of from 0 to 10, R/sub 3/ is an ethylene or 1,3-propylene radical, X is a sodium, potassium or ammonium cation; and driving themore » fluid through the formation and thereby displacing and recovering petroleum from the formation.« less

Temperature Dependent Rate Coefficients for the Gas-Phase Reaction of the OH Radical with Linear (L2, L3) and Cyclic (D3, D4) Permethylsiloxanes.

PubMed

Bernard, François; Papanastasiou, Dimitrios K; Papadimitriou, Vassileios C; Burkholder, James B

2018-05-03

Permethylsiloxanes are emitted into the atmosphere during production and use as personal care products, lubricants, and cleaning agents. The predominate atmospheric loss process for permethylsiloxanes is expected to be via gas-phase reaction with the OH radical. In this study, rate coefficients, k(T), for the OH radical gas-phase reaction with the two simplest linear and cyclic permethylsiloxanes were measured using a pulsed laser photolysis-laser induced fluorescence technique over the temperature range of 240-370 K and a relative rate method at 294 K: hexamethyldisiloxane ((CH 3 ) 3 SiOSi(CH 3 ) 3 , L 2 ), k 1 ; octamethyltrisiloxane ([(CH 3 ) 3 SiO] 2 Si(CH 3 ) 2 , L 3 ), k 2 ; hexamethylcyclotrisiloxane ([-Si(CH 3 ) 2 O-] 3 , D 3 ), k 3 ; and octamethylcyclotetrasiloxane ([-Si(CH 3 ) 2 O-] 4 , D 4 ), k 4 . The obtained k(294 K) values and temperature-dependence expressions for the 240-370 K temperature range are (cm 3 molecule -1 s -1 , 2σ absolute uncertainties): k 1 (294 K) = (1.28 ± 0.08) × 10 -12 , k 1 ( T) = (1.87 ± 0.18) × 10 -11 exp(-(791 ± 27)/ T); k 2 (294 K) = (1.72 ± 0.10) × 10 -12 , k 2 ( T) = 1.96 × 10 -13 (T/298) 4.34 exp(657/ T); k 3 (294 K) = (0.82 ± 0.05) × 10 -12 , k 3 ( T) = (1.29 ± 0.19) × 10 -11 exp(-(805 ± 43)/ T); and k 4 (294 K) = (1.12 ± 0.10) × 10 -12 , k 4 ( T) = (1.80 ± 0.26) × 10 -11 exp(-(816 ± 43)/ T). The cyclic molecules were found to be less reactive than the analogous linear molecule with the same number of -CH 3 groups, while the linear and cyclic permethylsiloxane reactivity both increase with the increasing number of CH 3 - groups. The present results are compared with previous rate coefficient determinations where available. The permethylsiloxanes included in this study are atmospherically short-lived compounds with estimated atmospheric lifetimes of 11, 8, 17, and 13 days, respectively.

Chemical Feedback From Decreasing Carbon Monoxide Emissions

NASA Astrophysics Data System (ADS)

Gaubert, B.; Worden, H. M.; Arellano, A. F. J.; Emmons, L. K.; Tilmes, S.; Barré, J.; Martinez Alonso, S.; Vitt, F.; Anderson, J. L.; Alkemade, F.; Houweling, S.; Edwards, D. P.

2017-10-01

Understanding changes in the burden and growth rate of atmospheric methane (CH4) has been the focus of several recent studies but still lacks scientific consensus. Here we investigate the role of decreasing anthropogenic carbon monoxide (CO) emissions since 2002 on hydroxyl radical (OH) sinks and tropospheric CH4 loss. We quantify this impact by contrasting two model simulations for 2002-2013: (1) a Measurement of the Pollution in the Troposphere (MOPITT) CO reanalysis and (2) a Control-Run without CO assimilation. These simulations are performed with the Community Atmosphere Model with Chemistry of the Community Earth System Model fully coupled chemistry climate model with prescribed CH4 surface concentrations. The assimilation of MOPITT observations constrains the global CO burden, which significantly decreased over this period by 20%. We find that this decrease results to (a) increase in CO chemical production, (b) higher CH4 oxidation by OH, and (c) 8% shorter CH4 lifetime. We elucidate this coupling by a surrogate mechanism for CO-OH-CH4 that is quantified from the full chemistry simulations.

Methanol Formation via Oxygen Insertion Chemistry in Ices

NASA Astrophysics Data System (ADS)

Bergner, Jennifer B.; Öberg, Karin I.; Rajappan, Mahesh

2017-08-01

We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or nonexistent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O2 within a mixture of O2:CH4 and observe efficient production of CH3OH via O(1D) insertion. CH3OH growth curves are fit with a kinetic model, and we observe no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH4: ˜65% of insertions lead to CH3OH, with the remainder leading instead to H2CO formation. There is no evidence for CH3 or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH3OH formation from O2 and CH4 diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.

Deriving Global OH Abundance and Atmospheric Lifetimes for Long-Lived Gases: A Search for CH3CCl3 Alternatives

NASA Astrophysics Data System (ADS)

Liang, Qing; Chipperfield, Martyn P.; Fleming, Eric L.; Abraham, N. Luke; Braesicke, Peter; Burkholder, James B.; Daniel, John S.; Dhomse, Sandip; Fraser, Paul J.; Hardiman, Steven C.; Jackman, Charles H.; Kinnison, Douglas E.; Krummel, Paul B.; Montzka, Stephen A.; Morgenstern, Olaf; McCulloch, Archie; Mühle, Jens; Newman, Paul A.; Orkin, Vladimir L.; Pitari, Giovanni; Prinn, Ronald G.; Rigby, Matthew; Rozanov, Eugene; Stenke, Andrea; Tummon, Fiona; Velders, Guus J. M.; Visioni, Daniele; Weiss, Ray F.

2017-11-01

An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone recovery. As the atmospheric mixing ratios of methyl chloroform (CH3CCl3) (MCF), the commonly used OH reference gas, approaches zero, it is important to find alternative approaches to infer atmospheric OH abundance and variability. The lack of global bottom-up emission inventories is the primary obstacle in choosing a MCF alternative. We illustrate that global emissions of long-lived trace gases can be inferred from their observed mixing ratio differences between the Northern Hemisphere (NH) and Southern Hemisphere (SH), given realistic estimates of their NH-SH exchange time, the emission partitioning between the two hemispheres, and the NH versus SH OH abundance ratio. Using the observed long-term trend and emissions derived from the measured hemispheric gradient, the combination of HFC-32 (CH2F2), HFC-134a (CH2FCF3, HFC-152a (CH3CHF2), and HCFC-22 (CHClF2), instead of a single gas, will be useful as a MCF alternative to infer global and hemispheric OH abundance and trace gas lifetimes. The primary assumption on which this multispecies approach relies is that the OH lifetimes can be estimated by scaling the thermal reaction rates of a reference gas at 272 K on global and hemispheric scales. Thus, the derived hemispheric and global OH estimates are forced to reconcile the observed trends and gradient for all four compounds simultaneously. However, currently, observations of these gases from the surface networks do not provide more accurate OH abundance estimate than that from MCF.

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

DOE PAGES

Nguyen, Tran B.; Bates, Kelvin H.; Crounse, John D.; ...

2015-06-12

Methacryloyl peroxynitrate (MPAN), the acyl peroxynitrate of methacrolein, has been suggested to be an important secondary organic aerosol (SOA) precursor from isoprene oxidation. Yet, the mechanism by which MPAN produces SOA through reaction with the hydroxyl radical (OH) is unclear. We systematically evaluate three proposed mechanisms in controlled chamber experiments and provide the first experimental support for the theoretically-predicted lactone formation pathway from the MPAN + OH reaction, producing hydroxymethyl-methyl-α-lactone (HMML). The decomposition of the MPAN–OH adduct yields HMML + NO 3 (~75%) and hydroxyacetone + CO + NO 3 (~25%), out-competing its reaction with atmospheric oxygen. The production ofmore » other proposed SOA precursors, e.g., methacrylic acid epoxide (MAE), from MPAN and methacrolein are negligible (<2%). Furthermore, we show that the beta-alkenyl moiety of MPAN is critical for lactone formation. Alkyl radicals formed cold via H-abstraction by OH do not decompose to HMML, even if they are structurally identical to the MPAN–OH adduct. The SOA formation from HMML, from polyaddition of the lactone to organic compounds at the particle interface or in the condensed phase, is close to unity under dry conditions. However, the SOA yield is sensitive to particle liquid water and solvated ions. In hydrated inorganic particles, HMML reacts primarily with H 2O to produce the monomeric 2-methylglyceric acid (2MGA) or with aqueous sulfate and nitrate to produce the associated organosulfate and organonitrate, respectively. 2MGA, a tracer for isoprene SOA, is semivolatile and its accommodation in aerosol water decreases with decreasing pH. Conditions that enhance the production of neutral 2MGA suppress SOA mass from the HMML channel. In conclusion, considering the liquid water content and pH ranges of ambient particles, 2MGA will exist largely as a gaseous compound in some parts of the atmosphere.« less

Clumped isotope effects during OH and Cl oxidation of methane

NASA Astrophysics Data System (ADS)

Whitehill, Andrew R.; Joelsson, Lars Magnus T.; Schmidt, Johan A.; Wang, David T.; Johnson, Matthew S.; Ono, Shuhei

2017-01-01

A series of experiments were carried out to determine the clumped (13CH3D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH was produced from the reaction of O(1D) (from O3 photolysis) with H2O, and Cl was from photolysis of Cl2. Samples were taken from the reaction cell and analyzed for methane (12CH4, 12CH3D, 13CH4, 13CH3D) isotopologue ratios using tunable infrared laser direct absorption spectroscopy. Measured kinetic isotope effects for singly substituted species were consistent with previous experimental studies. For doubly substituted methane, 13CH3D, the observed kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13C and deuterium substituted species (i.e., 13,2KIE = 13KIE × 2KIE). The deviation from this relationship is 0.3‰ ± 1.2‰ and 3.5‰ ± 0.7‰ for OH and Cl oxidation, respectively. This is consistent with model calculations performed using quantum chemistry and transition state theory. The OH and Cl reactions enrich the residual methane in the clumped isotopologue in open system reactions. In a closed system, however, this effect is overtaken by the large D/H isotope effect, which causes the residual methane to become anti-clumped relative to the initial methane. Based on these results, we demonstrate that oxidation of methane by OH, the predominant oxidant for tropospheric methane, will only have a minor (∼0.3‰) impact on the clumped isotope signature (Δ13CH3D, measured as a deviation from a stochastic distribution of isotopes) of tropospheric methane. This paper shows that Δ13CH3D will provide constraints on methane source strengths, and predicts that Δ12CH2D2 can provide information on methane sink strengths.

The Gaseous Phase as a Probe of the Astrophysical Solid Phase Chemistry

NASA Astrophysics Data System (ADS)

Abou Mrad, Ninette; Duvernay, Fabrice; Isnard, Robin; Chiavassa, Thierry; Danger, Grégoire

2017-09-01

In support of space missions and spectroscopic observations, laboratory experiments on ice analogs enable a better understanding of organic matter formation and evolution in astrophysical environments. Herein, we report the monitoring of the gaseous phase of processed astrophysical ice analogs to determine if the gaseous phase can elucidate the chemical mechanisms and dominant reaction pathways occurring in the solid ice subjected to vacuum ultra-violet (VUV) irradiation at low temperature and subsequently warmed. Simple (CH3OH), binary (H2O:CH3OH, CH3OH:NH3), and ternary ice analogs (H2O:CH3OH:NH3) were VUV-processed and warmed. The evolution of volatile organic compounds in the gaseous phase shows a direct link between their relative abundances in the gaseous phase, and the radical and thermal chemistries modifying the initial ice composition. The correlation between the gaseous and solid phases may play a crucial role in deciphering the organic composition of astrophysical objects. As an example, possible solid compositions of the comet Lovejoy are suggested using the abundances of organics in its comae.

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

NASA Astrophysics Data System (ADS)

Vinayakumar, C. K.; Dey, G. R.; Kishore, K.; Moorthy, P. N.

1996-12-01

Reactions of e aq-, H-atoms, OH, (CH 3) 2COH, and CO 2- radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.

Global average concentration and trend for hydroxyl radicals deduced from ALE/GAGE trichloroethane (methyl chloroform) data for 1978-1990

NASA Technical Reports Server (NTRS)

Prinn, R.; Cunnold, D.; Simmonds, P.; Alyea, F.; Boldi, R.; Crawford, A.; Fraser, P.; Gutzler, D.; Hartley, D.; Rosen, R.

1992-01-01

An optimal estimation inversion scheme is utilized with atmospheric data and emission estimates to determined the globally averaged CH3CCl3 tropospheric lifetime and OH concentration. The data are taken from atmospheric measurements from surface stations of 1,1,1-trichloroethane and show an annual increase of 4.4 +/- 0.2 percent. Industrial emission estimates and a small oceanic loss rate are included, and the OH concentration for the same period (1978-1990) are incorporated at 1.0 +/- 0.8 percent/yr. The positive OH trend is consistent with theories regarding OH and ozone trends with respect to land use and global warming. Attention is given to the effects of the ENSO on the CH3CCl3 data and the assumption of continuing current industrial anthropogenic emissions. A novel tropical atmospheric tracer-transport mechanism is noted with respect to the CH3CCl3 data.

Interaction of tertiary phosphines with lignin-type, alpha,beta-unsaturated aldehydes in water.

PubMed

Moiseev, Dmitry V; Patrick, Brian O; James, Brian R; Hu, Thomas Q

2007-10-29

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, lignin chromophores, such as the alpha,beta-unsaturated aromatic aldehydes, sinapaldehyde, coniferylaldehyde, and coumaraldehyde, were reacted with the tertiary phosphines R2R'P [R = R' = Me, Et, (CH2)3OH, iPr, cyclo-C6H11, (CH2)2CN; R = Me or Et, R' = Ph; R = Ph, R' = Me, m-NaSO3-C6H4] in water at room temperature under argon. In all cases, initial nucleophilic attack of the phosphine occurs at the activated C=C bond to form a zwitterionic monophosphonium species. With the phosphines PR3 [R = Me, Et, (CH2)3OH] and with R2R'P (R = Me or Et, R' = Ph), the zwitterion undergoes self-condensation to give a bisphosphonium zwitterion that can react with aqueous HCl to form the corresponding dichloride salts (as a mixture of R,R- and S,S-enantiomers); X-ray structures are presented for the bisphosphonium chlorides synthesized from the Et3P and Me3P reactions with sinapaldehyde. With the more bulky phosphines, iPr3P, MePPh2, (cyclo-C6H11)3P, and Na[Ph2P(m-SO3-C6H4)], only an equilibrium of the monophosphonium zwitterion with the reactant aldehyde is observed. The weakly nucleophilic [NC(CH2)2]3P does not react with sinapaldehyde. An analysis of some exceptional 1H NMR data within the prochiral phosphorus centers of the bisphosphonium chlorides is also presented.

Heterospin systems constructed from [Cu2Ln]3+ and [Ni(mnt)2]1-,2- Tectons: First 3p-3d-4f complexes (mnt = maleonitriledithiolato).

PubMed

Madalan, Augustin M; Avarvari, Narcis; Fourmigué, Marc; Clérac, Rodolphe; Chibotaru, Liviu F; Clima, Sergiu; Andruh, Marius

2008-02-04

New heterospin complexes have been obtained by combining the binuclear complexes [{Cu(H(2)O)L(1)}Ln(O(2)NO)(3)] or [{CuL(2)}Ln(O(2)NO)(3)] (L(1) = N,N'-propylene-di(3-methoxysalicylideneiminato); L(2) = N,N'-ethylene-di(3-methoxysalicylideneiminato); Ln = Gd(3+), Sm(3+), Tb(3+)), with the mononuclear [CuL(1)(2)] and the nickel dithiolene complexes [Ni(mnt)(2)](q)- (q = 1, 2; mnt = maleonitriledithiolate), as follows: (1)infinity[{CuL(1)}(2)Ln(O(2)NO){Ni(mnt)(2)}].Solv.CH(3)CN (Ln = Gd(3+), Solv = CH(3)OH (1), Ln = Sm(3+), Solv = CH(3)CN (2)) and [{(CH(3)OH)CuL(2)}(2)Sm(O(2)NO)][Ni(mnt)(2)] (3) with [Ni(mnt)2]2-, [{(CH(3)CN)CuL(1)}(2)Ln(H(2)O)][Ni(mnt)(2)]3.2CH(3)CN (Ln = Gd(3+) (4), Sm(3+) (5), Tb(3+) (6)), and [{(CH(3)OH)CuL(2)}{CuL(2)}Gd(O(2)NO){Ni(mnt)(2)}][Ni(mnt)(2)].CH(2)Cl(2) (7) with [Ni(mnt))(2]*-. Trinuclear, almost linear, [CuLnCu] motifs are found in all the compounds. In the isostructural 1 and 2, two trans cyano groups from a [Ni(mnt)2]2- unit bridge two trimetallic nodes through axial coordination to the Cu centers, thus leading to the establishment of infinite chains. 3 is an ionic compound, containing discrete [{(CH(3)OH)CuL(2)}(2)Sm(O(2)NO)](2+) cations and [Ni(mnt)(2)](2-) anions. Within the series 4-6, layers of discrete [CuLnCu](3+) motifs alternate with stacks of interacting [Ni(mnt)(2)](*-) radical anions, for which two overlap modes, providing two different types of stacks, can be disclosed. The strength of the intermolecular interactions between the open-shell species is estimated through extended Hückel calculations. In compound 7, [Ni(mnt)(2)](*-) radical anions coordinate group one of the Cu centers of a trinuclear [Cu(2)Gd] motif through a CN, while discrete [Ni(mnt)(2)](*-) units are also present, overlapping in between, but also with the coordinated ones. Furthermore, the [Cu(2)Gd] moieties dimerize each other upon linkage by two nitrato groups, both acting as chelate toward the gadolinium ion from one unit and monodentate toward a Cu ion from the other unit. The magnetic properties of the gadolinium-containing complexes have been determined. Ferromagnetic exchange interactions within the trinuclear [Cu(2)Gd] motifs occur. In the compounds 4 and 7, the [Ni(mnt)(2)](*-) radical anions contribution to the magnetization is clearly observed in the high-temperature regime, and most of it vanishes upon temperature decrease, very likely because of the rather strong antiferromagnetic exchange interactions between the open-shell species. The extent of the exchange interaction in the compound 7, which was found to be antiferromagnetic, between the coordinated Cu center and the corresponding [Ni(mnt)(2)](*-) radical anion, bearing mostly a 3p spin type, was estimated through CASSCF/CASPT2 calculations. Compound 6 exhibits a slow relaxation of the magnetization.

Mechanism of Ethane Destruction in Dielectric Barrier Discharge in Air: Detailed Elementary Reaction Model and Experiment

NASA Astrophysics Data System (ADS)

Krasnoperov, Lev; Modenese, Camila; Krishtopa, Larisa

2006-10-01

Free radical destruction mechanism was extended by inclusion of reactions of excited and ionic species. The mechanism consists of 935 reactions of 85 neutral species, 9 excited states and 38 ions. The reactions include 9 initiation processes in streamers, 66 processes involving excited states and 83 reactions involving ions. The reactant, the final products as well as the major intermediates of the destruction of ethane in air in corona discharge were identified and quantified Carbon dioxide (CO2), water (H2O), formaldehyde (H2CO), acetaldehyde (CH3CHO), methanol (CH3OH), ethanol (C2H5OH), formic acid (HCOOH), acetic acid (CH3COOH), methyl nitrate (CH3ONO2) and ethyl nitrate (C2H5ONO2) were identified among the major destruction products. The destruction efficiency predicted by the mechanism is in good agreement with the experiment, the major contribution is being due to the ionization transfer reactions. Reactions of excited species play but only a minor role. The product spectrum is consistent with the subsequent low temperature free radical reactions complicated by the presence of ozone and nitrogen oxides. The generic reaction mechanism for other organic as well as inorganic compounds is discussed.

Changes in Global Tropospheric OH Expected as a Result of Climate Change Over the Last Several Decades

NASA Technical Reports Server (NTRS)

Nicely, Julie M.; Salawitch, Ross J.; Canty, Timothy P.; Douglass, Anne R.; Duncan, Bryan N.; Lang, C.; Liang, Qing; Oman, Luke D.; Rodriguez, Jose M.; Stolarksi, Richard;

Experimental and Estimated Rate Constants for the Reactions of Hydroxyl Radicals with Several Halocarbons

NASA Technical Reports Server (NTRS)

DeMore, W.B.

1996-01-01

Relative rate experiments are used to measure rate constants and temperature dependencies of the reactions of OH with CH3F (41), CH2FCl (31), CH2BrCl (30B1), CH2Br2 (3OB2), CHBr3 (2OB3), CF2BrCHFCl (123aBl(alpha)), and CF2ClCHCl2 (122). Rate constants for additional compounds of these types are estimated using an empirical rate constant estimation method which is based on measured rate constants for a wide range of halocarbons. The experimental data are combined with the estimated and previously reported rate constants to illustrate the effects of F, Cl, and Br substitution on OH rate constants for a series of 19 halomethanes and 25 haloethanes. Application of the estimation technique is further illustrated for some higher hydrofluorocarbons (HFCs), including CHF2CF2CF2CF2H (338pcc), CF3CHFCHFCF2CF3 (43-10mee), CF3CH2CH2CF3 (356ffa), CF3CH2CF2CH2CF3 (458mfcf), CF3CH2CHF2 (245fa), and CF3CH2CF2CH3 (365mfc). The predictions are compared with literature data for these compounds.

Quantifying the Causes of Differences in Tropospheric OH Within Global Models

NASA Technical Reports Server (NTRS)

Nicely, Julie M.; Salawitch, Ross J.; Canty, Timothy; Anderson, Daniel C.; Arnold, Steve R.; Chipperfield, Martyn P.; Emmons, Louisa K.; Flemming, Johannes; Huijnen, Vincent; Kinnison, Douglas E.;

Atmospheric degradation mechanisms of hydrogen containing chlorofluorocarbons (HCFC) and fluorocarbons (HFC)

NASA Technical Reports Server (NTRS)

Zellner, Reinhard

1990-01-01

The current knowledge of atmospheric degradation of hydrogen containing chlorofluorocarbons (HCFC 22 (CHClF2), HCFC 123 (CHCl2CF3), HCFC 124 (CHClFCF3), HCFC 141b (CFCl2CH3), HCFC 142b (CF2ClCH3)) and fluorocarbons (HFC 125 (CHF2CF3), HFC 134a (CH2FCF3), HFC 152a (CHF2CH3)) is assessed. Except for the initiation reaction by OH radicals, there are virtually no experimental data available concerning the subsequent oxidative breakdown of these molecules. However, from an analogy to the degradation mechanisms of simple alkanes, some useful guidelines as to the expected intermediates and final products can be derived. A noteable exception from this analogy, however, appears for the oxi-radicals. Here, halogen substitution induces new reaction types (C-Cl and C-C bond ruptures) which are unknown to the unsubstituted analogues and which modify the nature of the expected carbonyl products. Based on an evaluation of these processes using estimated bond strength data, the following simplified rules with regards to the chlorine content of the HCFC's may be deduced: (1) HCFC's containing one chlorine atom such as 22 and 142b seem to release their chlorine content essentially instantaneous with the initial attack on the parent by OH radicals, and for HCFC 124, such release is apparently prevented; (2) HCFC's such as 123 and 141b with two chlorine atoms are expected to release only one of these instantaneously; and the second chlorine atom may be stored in potentially long-lived carbonyl compounds such as CF3CClO or CClFO.

Methanol Formation via Oxygen Insertion Chemistry in Ices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergner, Jennifer B.; Öberg, Karin I.; Rajappan, Mahesh

We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or nonexistent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O{sub 2} within a mixture of O{sub 2}:CH{sub 4} and observe efficient production of CH{sub 3}OH via O({sup 1}D) insertion. CH{sub 3}OH growth curves are fit with a kinetic model, and we observemore » no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH{sub 4}: ∼65% of insertions lead to CH{sub 3}OH, with the remainder leading instead to H{sub 2}CO formation. There is no evidence for CH{sub 3} or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH{sub 3}OH formation from O{sub 2} and CH{sub 4} diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.« less

Organic Molecules in Oxygen-Rich Circumstellar Envelopes: Methanol and Hydrocarbons

NASA Technical Reports Server (NTRS)

Charnley, S. B.; Tielens, A. G. G. M.; Kress, M. E.

1995-01-01

The existence of anomalously high abundances of gaseous CH4 has been invoked to explain the unexpectedly high abundances of the carbon-bearing molecules HCN and H2CO in the outflows from O-rich red giants. We have modelled the chemistry that proceeds in the outer envelope when CH4 is injected from the inner envelope. We find that photolysis by the interstellar radiation field drives an ion-neutral chemistry which produces several organic molecules. The calculated abundances of CH3OH, C2H and C2 can be comparable to those calculated for H2CO and HCN. Species such as C2H4, C2H2 and CH3CN can also be abundant. A search for CH3OH and C2H in several O-rich outflows known to exhibit strong HCN emission is needed. As it derives entirely from the CH4 photochain, is insensitive to the envelope temperature distribution, and has accessible transitions at millimetre wavelengths, the detection of the C2H radical would provide further indirect support for the presence of the hypothesized methane.

Enhanced Oxidation Capacity from Photolytic HOx/NOx Recycling: Implications for CH4 Growth

NASA Astrophysics Data System (ADS)

Madronich, S.

2017-12-01

Oxidation by OH radicals converts many emitted compounds (CO, CH4, VOCs as well as NOx, SO2, HCFCs, and others) to more soluble forms that can be removed rapidly from the atmosphere, e.g., by deposition. In a chemically stable atmosphere (without runaway concentration growth) the rate of OH production must generally exceed the emission rates of the reduced compounds, but secondary chemistry complicates OH budgets. If emission rates (e.g., E for CH4) increase, OH concentrations can either decrease or increase depending on NOx conditions, causing a non-linear dependence of CH4 concentrations on its emissions, [CH4] Ef where f, the methane feedback factor, is currently estimated in global 3d models to be 1.3-1.4. This feature is robust among models, and can be reproduced in simpler box models with the canonical Ox-HOx-NOx chemistry, in which global OH is increased by NOx emissions and decreased by CO, CH4, and VOC emissions. Scenarios with lower NOx emissions but higher CH4 emissions point to substantially lower global oxidation capacity in the future. Several newly hypothesized processes have attracted attention in recent years, including the photolytic recycling of OH from biogenic VOCs, and the photolysis of particulate nitrates to regenerate NOx. The latter process could be particularly significant in regions far from NOx emissions, where low NOx levels are more efficient at generating O3 and OH. To the extent that these processes do occur, they may provide some buffering of global OH against CH4 variations (f nearer 1), and more generally against anthropogenic perturbations. However, critical measurements from both lab and field are needed to assess the importance of these proposed processes.

1H NMR studies of the 5-(hydroxymethyl)-2'-deoxyuridine containing TF1 binding site.

PubMed

Pasternack, L B; Bramham, J; Mayol, L; Galeone, A; Jia, X; Kearns, D R

1996-07-15

The pyrimidine base 5-(hydroxymethyl)-2'-deoxyuridine (HmU) is a common nucleotide in SPO1 phage DNA. Numerous transcriptional proteins bind HmU-containing DNA preferentially implicating a regulatory function of HmU. We have investigated the conformation and dynamics of d-(5'-CHmUCHmUACACGHmUGHmUAGAG-OH-3')2 (HmU-DNA). This oligonucleotide mimics the consensus sequence of Transcription Factor 1 (TF1). The HmU-DNA was compared to the thymine-containing oligonucleotide. NOESY and DQF COSY spectroscopy provided resonance assignments of nonexchangeable and exchangeable protons, intranucleotide, internucleotide and intrastrand proton-proton distances, and dihedral angle constraints. Methylene protons of the hydroxymethyl group are nonequivalent protons and the hydroxymethyl group is not freely rotating. The hydroxymethyl group adopts a specific orientation with the OH group oriented on the 3' side of the plane of the base. Analysis of imino proton resonances and NOEs indicates additional end base pair fraying and a temperature-induced transition to a conformation in which the internal HmU-A base pairs are disrupted or have reduced lifetimes. Orientation of the hydroxymethyl group indicates the presence of internucleotide intrastrand hydrogen bonding between the HmU12C5 hydroxyl group and A13. All sugars in both DNAs show a C2'endo conformation (typical of B-DNA).

Deep tunneling in the unimolecular decay of CH 3CHOO Criegee intermediates to OH radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yi; Liu, Fang; Barber, Victoria P.

Unimolecular decay of Criegee intermediates produced in alkene ozonolysis is known to be a significant source of OH radicals in the troposphere. In this work, unimolecular decay of the methyl-substituted Criegee intermediate, syn-CH 3CHOO, to OH products is shown to occur at energies significantly below the transition state barrier for a 1,4 hydrogen transfer that leads to these products [Y. Fang et al., J. Chem. Phys. 144, 061102 (2016)]. The rate of appearance of OH products arising from tunneling through the barrier is obtained through direct time-domain measurements following the vibrational activation of syn-CH 3CHOO. IR excitation of syn-CH 3CHOOmore » at energies nearly 2000 cm -1 below the barrier is achieved through combination bands involving CH stretch and another lower frequency mode, and the resultant OH products are detected by UV laser-induced fluorescence. The observed syn-CH 3CHOO combination bands in the 4100–4350 cm -1 region are identified by comparison with the computed IR absorption spectrum. The experimental decay rates are found to be ca. 106 s -1 in this deep tunneling regime, which is approximately 100-times slower than that in the vicinity of the barrier.The experimental results are consistent with statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical decay rates with tunneling through the barrier, and notable deviations may originate from the sparsity in the density of states for syn-CH 3CHOO at lower energies. Thermal unimolecular decay of syn-CH 3CHOO is predicted to have significant contribution from microcanonical rates at energies that are much below the barrier.« less

The Description and Validation of a Computationally-Efficient CH4-CO-OH (ECCOH) Module for 3D Model Applications

NASA Technical Reports Server (NTRS)

Elshorbany, Yasin F.; Duncan, Bryan N.; Strode, Sarah A.; Wang, James S.; Kouatchou, Jules

2015-01-01

We present the Efficient CH4-CO-OH Module (ECCOH) that allows for the simulation of the methane, carbon monoxide and hydroxyl radical (CH4-CO-OH cycle, within a chemistry climate model, carbon cycle model, or earth system model. The computational efficiency of the module allows many multi-decadal, sensitivity simulations of the CH4-CO-OH cycle, which primarily determines the global tropospheric oxidizing capacity. This capability is important for capturing the nonlinear feedbacks of the CH4-CO-OH system and understanding the perturbations to relatively long-lived methane and the concomitant impacts on climate. We implemented the ECCOH module into the NASA GEOS-5 Atmospheric Global Circulation Model (AGCM), performed multiple sensitivity simulations of the CH4-CO-OH system over two decades, and evaluated the model output with surface and satellite datasets of methane and CO. The favorable comparison of output from the ECCOH module (as configured in the GEOS-5 AGCM) with observations demonstrates the fidelity of the module for use in scientific research.

Atmospheric Degradation Initiated by OH Radicals of the Potential Foam Expansion Agent, CF3(CF2)2CH═CH2 (HFC-1447fz): Kinetics and Formation of Gaseous Products and Secondary Organic Aerosols.

PubMed

Jiménez, Elena; González, Sergio; Cazaunau, Mathieu; Chen, Hui; Ballesteros, Bernabé; Daële, Véronique; Albaladejo, José; Mellouki, Abdelwahid

2016-02-02

The assessment of the atmospheric impact of the potential foam expansion agent, CF3(CF2)2CH═CH2 (HFC-1447fz), requires the knowledge of its degradation routes, oxidation products, and radiative properties. In this paper, the gas-phase reactivity of HFC-1447fz with OH radicals is presented as a function of temperature, obtaining kOH (T = 263-358 K) = (7.4 ± 0.4) × 10(-13)exp{(161 ± 16)/T} (cm(3)·molecule(-1)·s(-1)) (uncertainties: ±2σ). The formation of gaseous oxidation products and secondary organic aerosols (SOAs) from the OH + HFC-1447fz reaction was investigated in the presence of NOx at 298 K. CF3(CF2)2CHO was observed at low- and high-NOx conditions. Evidence of SOA formation (ultrafine particles in the range 10-100 nm) is reported with yields ranging from 0.12 to 1.79%. In addition, the absolute UV (190-368 nm) and IR (500-4000 cm(-1)) absorption cross-sections of HFC-1447fz were determined at room temperature. No appreciable absorption in the solar actinic region (λ > 290 nm) was observed, leaving the removal by OH radicals as the main atmospheric loss process for HFC-1447fz. The major contribution of the atmospheric loss of HFC-1447fz is due to OH reaction (84%), followed by ozone (10%) and chlorine atoms (6%). Correction of the instantaneous radiative efficiency (0.36 W m(-2)·ppbv(-1)) with the relatively short lifetime of HFC-1447fz (ca. 8 days) implies that its global warming potential at a time horizon of 100 year is negligible (0.19) compared to that of HCFC-141b (782) and to that of modern foam-expansion blowing agents (148, 882, and 804 for HFC-152a, HFC-245fa and HFC-365mfc, respectively).

High-level theoretical characterization of the vinoxy radical (•CH2CHO) + O2 reaction

NASA Astrophysics Data System (ADS)

Weidman, Jared D.; Allen, Ryan T.; Moore, Kevin B.; Schaefer, Henry F.

2018-05-01

Numerous processes in atmospheric and combustion chemistry produce the vinoxy radical (•CH2CHO). To understand the fate of this radical and to provide reliable energies needed for kinetic modeling of such processes, we have examined its reaction with O2 using highly reliable theoretical methods. Utilizing the focal point approach, the energetics of this reaction and subsequent reactions were obtained using coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] extrapolated to the complete basis set limit. These extrapolated energies were appended with several corrections including a treatment of full triples and connected quadruple excitations, i.e., CCSDT(Q). In addition, this study models the initial vinoxy radical + O2 reaction for the first time with multireference methods. We predict a barrier for this reaction of approximately 0.4 kcal mol-1. This result agrees with experimental findings but is in disagreement with previous theoretical studies. The vinoxy radical + O2 reaction produces a 2-oxoethylperoxy radical which can undergo a number of unimolecular reactions. Abstraction of a β-hydrogen (a 1,4-hydrogen shift) and dissociation back to reactants are predicted to be competitive to each other due to their similar barriers of 21.2 and 22.3 kcal mol-1, respectively. The minimum-energy β-hydrogen abstraction pathway produces a hydroperoxy radical (QOOH) that eventually decomposes to formaldehyde, CO, and •OH. Two other unimolecular reactions of the peroxy radical are α-hydrogen abstraction (38.7 kcal mol-1 barrier) and HO2• elimination (43.5 kcal mol-1 barrier). These pathways lead to glyoxal + •OH and ketene + HO2• formation, respectively, but they are expected to be uncompetitive due to their high barriers.

Investigation of the antioxidant and radical scavenging activities of some phenolic Schiff bases with different free radicals.

PubMed

Marković, Zoran; Đorović, Jelena; Petrović, Zorica D; Petrović, Vladimir P; Simijonović, Dušica

2015-11-01

The antioxidant properties of some phenolic Schiff bases in the presence of different reactive particles such as (•)OH, (•)OOH, (CH2=CH-O-O(•)), and (-•)O2 were investigated. The thermodynamic values, ΔH BDE, ΔH IP, and ΔH PA, were used for this purpose. Three possible mechanisms for transfer of hydrogen atom, concerted proton-electron transfer (CPET), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) were considered. These mechanisms were tested in solvents of different polarity. On the basis of the obtained results it was shown that SET-PT antioxidant mechanism can be the dominant mechanism when Schiff bases react with radical cation, while SPLET and CPET are competitive mechanisms for radical scavenging of hydroxy radical in all solvents under investigation. Examined Schiff bases react with the peroxy radicals via SPLET mechanism in polar and nonpolar solvents. The superoxide radical anion reacts with these Schiff bases very slowly.

Global modelling of the total OH reactivity: investigations on the "missing" OH sink and its atmospheric implications

NASA Astrophysics Data System (ADS)

Ferracci, Valerio; Heimann, Ines; Abraham, N. Luke; Pyle, John A.; Archibald, Alexander T.

2018-05-01

The hydroxyl radical (OH) plays a crucial role in the chemistry of the atmosphere as it initiates the removal of most trace gases. A number of field campaigns have observed the presence of a missing OH sink in a variety of regions across the planet. A comparison of direct measurements of the OH loss frequency, also known as total OH reactivity (kOH), with the sum of individual known OH sinks (obtained via the simultaneous detection of species such as volatile organic compounds and nitrogen oxides) indicates that, in some cases, up to 80 % of kOH is unaccounted for. In this work, the UM-UKCA chemistry-climate model was used to investigate the wider implications of the missing reactivity on the oxidising capacity of the atmosphere. Simulations of the present-day atmosphere were performed and the model was evaluated against an array of field measurements to verify that the known OH sinks were reproduced well, with a resulting good agreement found for most species. Following this, an additional sink was introduced to simulate the missing OH reactivity as an emission of a hypothetical molecule, X, which undergoes rapid reaction with OH. The magnitude and spatial distribution of this sink were underpinned by observations of the missing reactivity. Model runs showed that the missing reactivity accounted for on average 6 % of the total OH loss flux at the surface and up to 50 % in regions where emissions of the additional sink were high. The lifetime of the hydroxyl radical was reduced by 3 % in the boundary layer, whilst tropospheric methane lifetime increased by 2 % when the additional OH sink was included. As no OH recycling was introduced following the initial oxidation of X, these results can be interpreted as an upper limit of the effects of the missing reactivity on the oxidising capacity of the troposphere. The UM-UKCA simulations also allowed us to establish the atmospheric implications of the newly characterised reactions of peroxy radicals (RO2) with OH. Whilst the effects of this chemistry on kOH were minor, the reaction of the simplest peroxy radical, CH3O2, with OH was found to be a major sink for CH3O2 and source of HO2 over remote regions at the surface and in the free troposphere. Inclusion of this reaction in the model increased tropospheric methane lifetime by up to 3 %, depending on its product branching. Simulations based on the latest kinetic and product information showed that this reaction cannot reconcile models with observations of atmospheric methanol, in contrast to recent suggestions.

Diagnostic studies of H2 Ar N2 microwave plasmas containing methane or methanol using tunable infrared diode laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Hempel, F.; Davies, P. B.; Loffhagen, D.; Mechold, L.; Röpcke, J.

2003-11-01

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and nine stable molecules, CH4, CH3OH, C2H2, C2H4, C2H6, NH3, HCN, CH2O and C2N2, in H2-Ar-N2 microwave plasmas containing up to 7% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbon precursor molecules varied between 20% and 97%. The methyl radical concentration was found to be in the range 1012-1013 molecules cm-3. By analysing the temporal development of the molecular concentrations under static conditions it was found that HCN and NH3 are the final products of plasma chemical conversion. The fragmentation rates of methane and methanol (RF(CH4) = (2-7) × 1015 molecules J-1, RF(CH3OH) = (6-9) × 1015 molecules J-1) and the respective conversion rates to methane, hydrogen cyanide and ammonia (RCmax(CH4) = 1.2 × 1015 molecules J-1, RCmax(HCN) = 1.3 × 1015 molecules J-1, RCmax(NH3) = 1 × 1014 molecules J-1) have been determined for different hydrogen to nitrogen concentration ratios. An extensive model of the chemical reactions involved in the H2-N2-Ar-CH4 plasma has been developed. Model calculations were performed by including 22 species, 145 chemical reactions and appropriate electron impact dissociation rate coefficients. The results of the model calculations showed satisfactory agreement between calculated and measured concentrations. The most likely main chemical pathways involved in these plasmas are discussed and an appropriate reaction scheme is proposed.

Radiolysis of poly(acrylic acid) in aqueous solution

NASA Astrophysics Data System (ADS)

Ulanski, Piotr; Bothe, Eberhard; Hildenbrand, Knut; Rosiak, Janusz M.; von Sonntag, Clemens

1995-02-01

Poly(acrylic acid), PAA, reacts with OH-radicals yielding -CHCH(CO 2H)- (β-radicals) and -CH 2C(CO 2H)- (α-radicals) in a ratio of approximately 2:1. This estimate is based on pulse radiolysis data where the absorption spectrum of the PAA-radicals was compared with the spectra of α-radicals from model systems. The β-radicals convert slowly into α-radicals ( k = 0.7 s -1 at pH 10). This process has also been observed by ESR. At PAA-concentrations of 10 -2 mol dm -3 chain scission dominates over other competing reactions except at low pH. The rate of chain scission was followed by pulse conductometry and in the pH range 7-9 k = 4 × 10 -2s -1 was observed. Oxygen reacts with PAA-radicals with k = 3.1 × 10 8 dm 3 mol -1 s -1 at pH 3.5 and k = 1.0 × 10 8 dm 3 mol -1 s -1 at pH 10. The corresponding peroxyl radicals undergo slow intramolecular H-transfer yielding a UV-absorbing product whose properties are that of 1,3-diketones.

Observation of hydroxymethyl hydroperoxide in a reaction system containing CH{sub 2}OO and water vapor through pure rotational spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakajima, Masakazu; Endo, Yasuki, E-mail: endo@bunshi.c.u-tokyo.ac.jp

Pure rotational transitions of hydroxymethyl hydroperoxide (HMHP) were observed in the discharged plasma of a CH{sub 2}I{sub 2}/O{sub 2}/water gas mixture, where the water complex with the simplest Criegee intermediate CH{sub 2}OO has been identified [M. Nakajima and Y. Endo, J. Chem. Phys. 140, 134302 (2014)]. Isotope experiments using heavy water support that the currently observed HMHP molecule was produced by the reaction of CH{sub 2}OO with water vapor. The observed species was identified as the most stable conformer with the help of quantum chemical calculations. We also clarified that productions of formic acid and dioxirane are promoted by themore » existence of water vapor in the discharged reaction system.« less

The Gaseous Phase as a Probe of the Astrophysical Solid Phase Chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abou Mrad, Ninette; Duvernay, Fabrice; Isnard, Robin

2017-09-10

In support of space missions and spectroscopic observations, laboratory experiments on ice analogs enable a better understanding of organic matter formation and evolution in astrophysical environments. Herein, we report the monitoring of the gaseous phase of processed astrophysical ice analogs to determine if the gaseous phase can elucidate the chemical mechanisms and dominant reaction pathways occurring in the solid ice subjected to vacuum ultra-violet (VUV) irradiation at low temperature and subsequently warmed. Simple (CH{sub 3}OH), binary (H{sub 2}O:CH{sub 3}OH, CH{sub 3}OH:NH{sub 3}), and ternary ice analogs (H{sub 2}O:CH{sub 3}OH:NH{sub 3}) were VUV-processed and warmed. The evolution of volatile organic compoundsmore » in the gaseous phase shows a direct link between their relative abundances in the gaseous phase, and the radical and thermal chemistries modifying the initial ice composition. The correlation between the gaseous and solid phases may play a crucial role in deciphering the organic composition of astrophysical objects. As an example, possible solid compositions of the comet Lovejoy are suggested using the abundances of organics in its comae.« less

Mass spectrometric measurement of hydrogen isotope fractionation for the reactions of chloromethane with OH and Cl

NASA Astrophysics Data System (ADS)

Keppler, Frank; Bahlmann, Enno; Greule, Markus; Schöler, Heinz Friedrich; Wittmer, Julian; Zetzsch, Cornelius

2018-05-01

Chloromethane (CH3Cl) is an important provider of chlorine to the stratosphere but detailed knowledge of its budget is missing. Stable isotope analysis is a potentially powerful tool to constrain CH3Cl flux estimates. The largest degree of isotope fractionation is expected to occur for deuterium in CH3Cl in the hydrogen abstraction reactions with its main sink reactant tropospheric OH and its minor sink reactant Cl atoms. We determined the isotope fractionation by stable hydrogen isotope analysis of the fraction of CH3Cl remaining after reaction with hydroxyl and chlorine radicals in a 3.5 m3 Teflon smog chamber at 293 ± 1 K. We measured the stable hydrogen isotope values of the unreacted CH3Cl using compound-specific thermal conversion isotope ratio mass spectrometry. The isotope fractionations of CH3Cl for the reactions with hydroxyl and chlorine radicals were found to be -264±45 and -280±11 ‰, respectively. For comparison, we performed similar experiments using methane (CH4) as the target compound with OH and obtained a fractionation constant of -205±6 ‰ which is in good agreement with values previously reported. The observed large kinetic isotope effects are helpful when employing isotopic analyses of CH3Cl in the atmosphere to improve our knowledge of its atmospheric budget.

ArF laser photodissociation dynamics of hydroxyacetone: LIF observation of OH and its reaction rate with the parent

NASA Astrophysics Data System (ADS)

Chowdhury, Pradyot K.; Upadhyaya, Hari P.; Naik, Prakash D.; Mittal, Jai P.

2002-01-01

Upon photoexcitation at 193 nm, hydroxyacetone dissociation appears to give CH 3 and COCH 2OH radicals as primary products, and the latter undergoes further dissociation to OH and ketene. Real time LIF observation of OH formation shows a dissociation rate of COCH 2OH as (4.6±0.5)×10 6 s-1. There is no significant population (<1%) in excited vibrational levels of OH ( X2Π) observed. The rotational state distribution has a Boltzmann temperature of the OH photofragment 380±40 K. Doppler spectroscopy shows an average translational energy with the OH photofragment as 3.6±1.3 kcal mol-1. The bimolecular rate constant for OH + hydroxyacetone is (2.8±0.2)×10 -12 cm3 molecule-1 s-1.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Chong-Wen; Simmie, John M.; Pitz, William J.

Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO 2, and CH 3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds truemore » for HO 2 radicals. We also determined the subsequent β-scission of the radicals formed, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit.« less

Numerical evaluation of equivalence ratio measurement using OH{sup *} and CH{sup *} chemiluminescence in premixed and non-premixed methane-air flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panoutsos, C.S.; Hardalupas, Y.; Taylor, A.M.K.P.

This work presents results from detailed chemical kinetics calculations of electronically excited OH (A{sup 2}{sigma}, denoted as OH{sup *}) and CH (A{sup 2}{delta}, denoted as CH{sup *}) chemiluminescent species in laminar premixed and non-premixed counterflow methane-air flames, at atmospheric pressure. Eight different detailed chemistry mechanisms, with added elementary reactions that account for the formation and destruction of the chemiluminescent species OH{sup *} and CH{sup *}, are studied. The effects of flow strain rate and equivalence ratio on the chemiluminescent intensities of OH{sup *}, CH{sup *} and their ratio are studied and the results are compared to chemiluminescent intensity ratio measurementsmore » from premixed laminar counterflow natural gas-air flames. This is done in order to numerically evaluate the measurement of equivalence ratio using OH{sup *} and CH{sup *} chemiluminescence, an experimental practise that is used in the literature. The calculations reproduced the experimental observation that there is no effect of strain rate on the chemiluminescent intensity ratio of OH{sup *} to CH{sup *}, and that the ratio is a monotonic function of equivalence ratio. In contrast, the strain rate was found to have an effect on both the OH{sup *} and CH{sup *} intensities, in agreement with experiment. The calculated OH{sup *}/CH{sup *} values showed that only five out of the eight mechanisms studied were within the same order of magnitude with the experimental data. A new mechanism, proposed in this work, gave results that agreed with experiment within 30%. It was found that the location of maximum emitted intensity from the excited species OH{sup *} and CH{sup *} was displaced by less than 65 and 115 {mu}m, respectively, away from the maximum of the heat release rate, in agreement with experiments, which is small relative to the spatial resolution of experimental methods applied to combustion applications, and, therefore, it is expected that intensity from the OH{sup *} and CH{sup *} excited radicals can be used to identify the location of the reaction zone. Calculations of the OH{sup *}/CH{sup *} intensity ratio for strained non-premixed counterflow methane-air flames showed that the intensity ratio takes different values from those for premixed flames, and therefore has the potential to be used as a criterion to distinguish between premixed and non-premixed reaction in turbulent flames. (author)« less

Characterization of starch polymorphic structures using vibrational sum frequency generation spectroscopy.

PubMed

Kong, Lingyan; Lee, Christopher; Kim, Seong H; Ziegler, Gregory R

2014-02-20

The polymorphic structures of starch were characterized with vibrational sum frequency generation (SFG) spectroscopy. The noncentrosymmetry requirement of SFG spectroscopy allows for the detection of the ordered domains without spectral interferences from the amorphous phase and also the distinction of the symmetric elements among crystalline polymorphs. The V-type amylose was SFG-inactive due to the antiparallel packing of single helices in crystal unit cells, whereas the A- and B-type starches showed strong SFG peaks at 2904 cm(-1) and 2952-2968 cm(-1), which were assigned to CH stretching of the axial methine group in the ring and CH2 stretching of the exocyclic CH2OH side group, respectively. The CH2/CH intensity ratios of the A- and B-type starches are significantly different, indicating that the conformation of hydroxymethyl groups in these two polymorphs may be different. Cyclodextrin inclusion complexes were also analyzed as a comparison to the V-type amylose and showed that the head-to-tail and head-to-head stacking patterns of cyclodextrin molecules govern their SFG signals and peak positions. Although the molecular packing is different between V-type amylose and cyclodextrin inclusion complexes, both crystals show the annihilation of SFG signals when the functional group dipoles are arranged pointing in opposite directions.

Role of water and carbonates in photocatalytic transformation of CO{sub 2} to CH{sub 4} on titania.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrijevic, N. M.; Vijayan, B. K.; Poluektov, O. G.

Using the electron paramagnetic resonance technique, we have elucidated the multiple roles of water and carbonates in the overall photocatalytic reduction of carbon dioxide to methane over titania nanoparticles. The formation of H atoms (reduction product) and {center_dot}OH radicals (oxidation product) from water, and CO{sub 3}{sup -} radical anions (oxidation product) from carbonates, was detected in CO{sub 2}-saturated titania aqueous dispersion under UV illumination. Additionally, methoxyl, {center_dot}OCH{sub 3}, and methyl, {center_dot}CH{sub 3}, radicals were identified as reaction intermediates. The two-electron, one-proton reaction proposed as an initial step in the reduction of CO{sub 2} on the surface of TiO{sub 2} ismore » supported by the results of first-principles calculations.« less

Role of Water and Carbonates in Photocatalytic Transformation of CO2 to CH4 on Titania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrijevic, Nada; Vijayan, Baiju K.; Poluektov, Oleg G.

Using the electron paramagnetic resonance technique, we have elucidated the multiple roles of water and carbonates in the overall photocatalytic reduction of carbon dioxide to methane over titania nanoparticles. The formation of H atoms (reduction product) and {sm_bullet}OH radicals (oxidation product) from water, and CO{sub 3}{sup -} radical anions (oxidation product) from carbonates, was detected in CO{sub 2}-saturated titania aqueous dispersion under UV illumination. Additionally, methoxyl, {sm_bullet}OCH{sub 3}, and methyl, {sm_bullet}CH{sub 3}, radicals were identified as reaction intermediates. The two-electron, one-proton reaction proposed as an initial step in the reduction of CO{sub 2}, on the surface of TiO{sub 2}, ismore » supported by the results of first-principles calculations.« less

CH3OCH3 in Orion-KL: a striking similarity with HCOOCH3

NASA Astrophysics Data System (ADS)

Brouillet, N.; Despois, D.; Baudry, A.; Peng, T.-C.; Favre, C.; Wootten, A.; Remijan, A. J.; Wilson, T. L.; Combes, F.; Wlodarczak, G.

2013-02-01

Context. Orion-KL is a remarkable, nearby star-forming region where a recent explosive event has generated shocks that could have released complex molecules from the grain mantles. Aims: A comparison of the distribution of the different complex molecules will help in understanding their formation and constraining the chemical models. Methods: We used several data sets from the Plateau de Bure Interferometer to map the dimethyl ether emission with different arcsec spatial resolutions and different energy levels (from Eup = 18 to 330 K) to compare with our previous methyl formate maps. Results: Our data show remarkable similarity between the dimethyl ether (CH3OCH3) and the methyl formate (HCOOCH3) distributions even on a small scale (1.8″ × 0.8″ or ~500 AU). This long suspected similarity, seen from both observational and theoretical arguments, is demonstrated with unprecedented confidence, with a correlation coefficient of maps ~0.8. Conclusions: A common precursor is the simplest explanation of our correlation. Comparisons with previous laboratory work and chemical models suggest the major role of grain surface chemistry and a recent release, probably with little processing, of mantle molecules by shocks. In this case the CH3O radical produced from methanol ice would be the common precursor (whereas ethanol, C2H5OH, is produced from the radical CH2OH). The alternative gas phase scheme, where protonated methanol CH3OH+2 is the common precursor to produce methyl formate and dimethyl ether through reactions with HCOOH and CH3OH, is also compatible with our data. Our observations cannot yet definitely allow a choice between the different chemical processes, but the tight correlation between the distributions of HCOOCH3 and CH3OCH3 strongly contrasts with the different behavior we observe for the distributions of ethanol and formic acid. This provides a very significant constraint on models. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Mechanistic and kinetic investigation on OH-initiated oxidation of tetrabromobisphenol A.

PubMed

He, Maoxia; Li, Xin; Zhang, Shiqing; Sun, Jianfei; Cao, Haijie; Wang, Wenxing

2016-06-01

Detailed mechanism of the OH-initiated transformation of tetrabromobisphenol A (TBBPA) has been investigated by quantum chemical methods in this paper. Abstraction reactions of hydrogen atoms from the OH groups and CH3 groups of TBBPA are the dominant pathways of the initial reactions. The produced phenolic-type radical and alkyl-type radical may transfer to 4,4'-(ethene-1,1-diyl)bis(2,6-dibromophenol), 4-acetyl-2,6-dibromophenol and 2,6-dibromobenzoquinone at high temperature. In water, major products are 2,6-dibromo-p-hydroquinone, 4-isopropylene-2,6-dibromophenol and 4-(2-hydroxyisopropyl)-2,6-dibromophenol resulting from the addition reactions. Total rate constants of the initial reaction are 1.02 × 10(-12) cm(3) molecule(-1) s(-1) in gas phase and 1.93 × 10(-12) cm(3) molecule(-1) s(-1) in water at 298 K. Copyright © 2016 Elsevier Ltd. All rights reserved.

Bimetallo-radical carbon-hydrogen bond activation of methanol and methane.

PubMed

Cui, Weihong; Zhang, X Peter; Wayland, Bradford B

2003-04-30

Carbon-hydrogen bond cleavage reactions of CH3OH and CH4 by a dirhodium(II) diporphyrin complex with a m-xylyl tether (.Rh(m-xylyl)Rh.(1)) are reported. Kinetic-mechanistic studies show that the substrate reactions are bimolecular and occur through the use of two Rh(II) centers in the molecular unit of 1. Second-order rate constants (T = 296 K) for the reactions of 1 with methanol (k(CH3OH) = 1.45 x 10-2 M-1 s-1) and methane (k(CH4) = 0.105 M-1 s-1) show a clear kinetic preference for the methane activation process. The methanol and methane reactions with 1 have large kinetic isotope effects (k(CH3OH)/k(CD3OD) = 9.7 +/- 0.8, k(CH4)/k(CD4) = 10.8 +/- 1.0, T = 296 K), consistent with a rate-limiting step of C-H bond homolysis through a linear transition state. Activation parameters for reaction of 1 with methanol (DeltaH = 15.6 +/- 1.0 kcal mol-1; DeltaS = -14 +/- 5 cal K-1 mol-1) and methane (DeltaH = 9.8 +/- 0.5 kcal mol-1; DeltaS = -30 +/- 3 cal K-1 mol-1) are reported.

The atmospheric degradation of methyl isocyanate (CH3NCO), a toxic substance

NASA Astrophysics Data System (ADS)

Papanastasiou, D. K.; Bernard, F.; Burkholder, J. B.

2016-12-01

Alkyl isocyanates (R-NCO), as well as isocyanic acid (HNCO), are toxic substances that are emitted into the atmosphere during incomplete combustion of biomass and also formed as products in the atmospheric photooxidation of nitrogen-containing organic species. For example, methyl isocyanate (MIC, CH3NCO) is formed in the atmospheric photochemical transformation of methylisothiocyanate (CH3NCS), a widely used soil fumigant, as well as in the atmospheric photooxidation of amides, such as N-methylformamide. MIC is of particular interest to society because of the possible exposure to this toxic trace compound (recommended exposure limit is 0.02 ppm) in the aftermath of fumigation. Although, there are limited observations of atmospheric MIC (mostly nearby agricultural/fumigation activities) the possibility of emission from combustion processes, such as wildfires, warrants future study. The atmospheric lifetime and fate (gas phase and heterogeneous chemistry) of CH3NCO are presently not well characterized with only a single study of the OH + CH3NCO reaction rate coefficient available in the literature. Additional results from fundamental laboratory studies regarding the major atmospheric degradation pathways of MIC are needed for input to air quality, health, and environmental impact studies. In this study, the reaction of CH3NCO with OH radicals was investigated using pulsed laser photolysis coupled with laser induced fluorescence detection of the OH radical. The rate coefficients, k(OH+CH3NCO), were determined over a range of temperature (295-375 K) and pressure (40-100 Torr, He). The present results are in significant disagreement with the recently published relative rate study. A relative rate kinetic method was also used in this study for comparison and the problems associated with these measurements will be discussed. The atmospheric lifetime of MIC with respect to its gas-phase reaction with OH radicals is estimated to be 85 days, which implies the possibility for long-range transport. In addition, the UV absorption spectrum of CH3NCO at 295 K was measured between 185 and 260 nm and UV photolysis is considered to be a relatively minor atmospheric loss process. The importance of gas phase and heterogeneous removal processes for CH3NCO and the atmospheric degradation mechanism will be discussed.

Calculations of Electron Transport through Radicals

NASA Astrophysics Data System (ADS)

Smeu, Manuel; Dilabio, Gino

2010-03-01

Organic radicals are of interest in molecular electronics because a singly occupied molecular orbital (SOMO) would have a higher energy than its doubly occupied analog, suggesting they might make better conductors. The unpaired electron present in a radical leads to degeneracy splitting in other energy levels and such molecules may act as spin filters. Our study employs first principles transport calculations that are performed using a combination of density functional theory and a non-equilibrium Green's function technique. The conductance of 1,4-benzenediamine (BDA) molecules bridging two Au electrodes was modeled. These molecules were substituted in the 2-position with: -CH3, -NH2, and -OH; as well as with their radical analogs: -CH2, -NH, and -O, all of which have π-type SOMOs. The conductance of a radical with a σ-type SOMO was also calculated from a BDA molecule with the H atom in the 2-position removed. Comparing the transmission spectra for these species will yield insight into the nature of electron transport through radicals vs. transport through their reduced form as well as the nature of transport through π- and σ-type molecular orbitals.

Energetics of the O-H bond and of intramolecular hydrogen bonding in HOC6H4C(O)Y (Y = H, CH3, CH2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds.

PubMed

Bernardes, Carlos E S; Minas da Piedade, Manuel E

2008-10-09

The energetics of the phenolic O-H bond in a series of 2- and 4-HOC 6H 4C(O)Y (Y = H, CH3, CH 2CH=CH2, C[triple bond]CH, CH2F, NH2, NHCH 3, NO2, OH, OCH3, OCN, CN, F, Cl, SH, and SCH3) compounds and of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y, was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-hydroxybenzaldehyde (2HBA), 4-hydroxybenzaldehyde (4HBA), 2'-hydroxyacetophenone (2HAP), 2-hydroxybenzamide (2HBM), and 4-hydroxybenzamide (4HBM), at 298.15 K, were determined by micro- or macrocombustion calorimetry. The corresponding enthalpies of vaporization or sublimation were also measured by Calvet drop-calorimetry and Knudsen effusion measurements. The combination of the obtained experimental data led to Delta f H m (o)(2HBA, g) = -238.3 +/- 2.5 kJ.mol (-1), DeltafHm(o)(4HBA, g) = -220.3 +/- 2.0 kJ.mol(-1), Delta f H m (o)(2HAP, g) = -291.8 +/- 2.1 kJ.mol(-1), DeltafHm(o)(2HBM, g) = -304.8 +/- 1.5 kJ.mol (-1), and DeltafHm(o) (4HBM, g) = -278.4 +/- 2.4 kJ.mol (-1). These values, were used to assess the predictions of the B3LYP/6-31G(d,p), B3LYP/6-311+G(d,p), B3LYP/aug-cc-pVDZ, B3P86/6-31G(d,p), B3P86/6-311+G(d,p), B3P86/aug-cc-pVDZ, and CBS-QB3 methods, for the enthalpies of a series of isodesmic gas phase reactions. In general, the CBS-QB3 method was able to reproduce the experimental enthalpies of reaction within their uncertainties. The B3LYP/6-311+G(d,p) method, with a slightly poorer accuracy than the CBS-QB3 approach, achieved the best performance of the tested DFT models. It was further used to analyze the trends of the intramolecular O...H hydrogen bond in 2-HOC 6H 4C(O)Y evaluated by the ortho-para method and to compare the energetics of the phenolic O-H bond in 2- and 4-HOC 6H 4C(O)Y compounds. It was concluded that the O-H bond "strength" is systematically larger for 2-hydroxybenzoyl than for the corresponding 4-hydroxybenzoyl isomers mainly due to the presence of the intramolecular O...H hydrogen bond in the 2-isomers. The observed differences are, however, significantly dependent on the nature of the substituent Y, in particular, when an intramolecular H-bond can be present in the radical obtained upon cleavage of the O-H bond.

Phase diagram calculations and high pressure Raman spectroscopy studies of organic "plastic crystal" thermal energy storage materials

NASA Astrophysics Data System (ADS)

Chellappa, Raja S.

This dissertation presents the phase diagram calculations and high pressure Raman spectroscopy studies on organic "plastic crystal" thermal storage materials. The organic "plastic crystals" that were studied include pentaerythritol [PE:C(CH 2OH)4], neopentylglycol [NPG:(CH3)2C(CH 2OH)2], tris(hydroxymethyl)-aminomethane [TRIS:(NH2 )C(CH2OH)3], and 2-amino-2-methyl-1,3-propanediol [AMPL: (NH2)(CH3)C(CH2OH)2]. Thermodynamic optimization of the experimental data of AMPL-NPG and PE-AMPL binary system was performed and the calculated phase diagrams are presented. A preliminary calculated phase diagram of the TRIS-NPG binary system is also presented. A thorough reevaluation of the existing calorimetric and x-ray diffraction data of the PE-AMPL binary system is also presented. This analysis resulted in the correct interpretation of the phase boundaries and a revised phase diagram has been drawn. The results of high pressure Raman spectroscopy experiments on neopentylglycol and pentaerythritol presented. The phase transformation pressures were determined by analyzing the frequency shifts as a function of pressure as well as the changes in the internal modes of vibration for these compounds. A simplified assignment of the vibrational modes for NPG at ambient pressure is presented. The results indicate experiments were carried out using Diamond Anvil Cell (DAC) and the pressure induced transformations were studied by Raman spectroscopy. In NPG, a phase transition occurs at ˜3.6 GPa from Phase I (Monoclinic) to Phase II (unknown structure). In PE, the proposed phase transformation pressures are ˜4.8 GPa (Phase I to Phase II), ˜6.9 GPa (Phase II to Phase III), ˜9.5 GPa (Phase III to Phase IV), and ˜15 GPa (Phase IV to Amorphous). The results of a critical assessment of the vapor pressure data of solid metal carbonyls. The vapor pressure data of Chromium Carbonyl (Cr(CO)6), Tungsten Carbonyl (W(CO)6 ), Osmium Carbonyl (Os3(CO)12), Molybdenum Carbonyl (MO(CO)6). Rhenium Carbonyl (Re2(CO)10), and Manganese Carbonyl (Mn(CO)5) were assessed using the "Oonk Methodology". The sublimation properties using the assessed data (Delta subGo,DeltasubH o and Deltasub Cop,m ) of these compounds have been evaluated and a discussion on the mutual consistency of various data sets for each compound over a wide range of temperature is also presented.

Conversion of 3-imidazoline-3-oxide nitroxyl radicals into nitronylnitroxyl radicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grigor'ev, I.A.; Shchukin, G.I.; Khramtsov, V.V.

1986-04-20

Continuing the studies of the effect of the pH of the medium on the EPR spectra of nitroxyl radicals (NR) containing acid-base functional groups at a distance of 2-3 sigma-bonds from the radical center, they have examined the EPR spectra of NR, which contain OH groups in the 2-position of the heterocycle. It is assumed that deprotonation of the OH group is accompanied by changes in the hfc constant a/sub N//sup 1/ and the g-factor. At pH values greater than or equal to 12, however, the EPR spectra of aqueous solutions of radicals undergo irreversible changes from a triplet tomore » a more complex multiplet, similar to the spectra of nitronylnitroxyl radicals. The EPR spectra of these solutions remain unchanged over periods of several days. The spectra have a quintet structure, with further splitting into four or three components. When similar experiments are carried out in D/sub 2/O, the additional hfs disappear as a result of deuterium exchange in the CH/sub 2/ and CH/sub 3/ groups of the radicals. A simulation of the EPR spectra was carried out, assuming splitting into two N nuclei (a/sub N//sup 1/ and a/sub N//sup 3/), with three or two equivalent H. This resulted in complete agreement between the calculated and experimental spectra. In order to assign the nitrogen hfc constants, they synthesized radicals containing the N/sup 15/ isotope in the 3-position of the imidazole ring. Comparison of the results of simulations of the EPR spectra enabled unambiguous assignments of the hfc constants a/sub N//sup 1/ and a/sub N//sup 3/ to be made.« less

Radiation and quantum chemical studies of chalcone derivatives.

PubMed

Gaikwad, P; Priyadarsini, K I; Naumov, S; Rao, B S M

2010-08-05

The reactions of oxidizing radicals ((*)OH, Br(2)(*-), and SO(4)(*-)) with -OH-, -CH(3)-, or -NH(2)-substituted indole chalcones and hydroxy benzenoid chalcones were studied by radiation and quantum chemical methods. The (*)OH radical was found to react by addition at diffusion-controlled rates (k = 1.1-1.7 x 10(10) dm(3) mol(-1) s(-1)), but Br(2)(*-) radical reacted by 2 orders of magnitude lower. Quantum chemical calculations at the B3LYP/6-31+G(d,p) level of theory have shown that the (C2-OH)(*), (C11-OH)(*), and (C10-OH)(*) adducts of the indole chalcones and the (C7-OH)(*) and (C8-OH)(*) adducts of the hydroxy benzenoid chalcones are more stable with DeltaH = -39 to -28 kcal mol(-1) and DeltaG = -32 to -19 kcal mol(-1). This suggests that (*)OH addition to the alpha,beta-unsaturated bond is a major reaction channel in both types of chalcones and is barrierless. The stability and lack of dehydration of the (*)OH adducts arise from two factors: strong frontier orbital interaction due to the low energy gap between interacting orbitals and the negligible Coulombic repulsion due to small absolute values of Mulliken charges. The transient absorption spectrum measured in the (*)OH radical reaction with all the indole chalcone derivatives exhibited a maximum at 390 nm, which is in excellent agreement with the computed value (394 nm). The formation of three phenolic products under steady-state radiolysis is in line with the three stable (*)OH adducts predicted by theory. Independent of the substituent, identical spectra (lambda(max) = 330-360 and approximately 580 nm) were obtained on one-electron oxidation of the three indole chalcones. MO calculations predict the deprotonation from the -NH group is more efficient than from the substituent due to the larger electron density on the N1 atom forming the chalcone indolyl radical. Its reduction potential was determined to be 0.56 V from the ABTS(*-)/ABTS(2-) couple. In benzenoid chalcones, the (*)OH adduct spectrum is characterized by a peak at 270 nm and a broad maximum centered in the range 430-450 nm with an intense bleaching at 340 nm. The spectrum formed by electron transfer in these derivatives with lambda(max) = 280 and 380 nm (epsilon(280) = 5000 dm(3) mol(-1) cm(-1) and epsilon(380) = 700 dm(3) mol(-1) cm(-1)) was assigned to its phenoxyl radical. Our pulse radiolysis experiments in combination with quantum chemical calculations demonstrate that chalcones are efficient scavengers of damaging oxyl radicals.

Toward the Development of a Fundamentally Based Chemical Model for Cyclopentanone: High-Pressure-Limit Rate Constants for H Atom Abstraction and Fuel Radical Decomposition

DOE PAGES

Zhou, Chong-Wen; Simmie, John M.; Pitz, William J.; ...

2016-08-25

Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO 2, and CH 3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds truemore » for HO 2 radicals. We also determined the subsequent β-scission of the radicals formed, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit.« less

Low-energy (<20 eV) and high-energy (1000 eV) electron-induced methanol radiolysis of astrochemical interest

NASA Astrophysics Data System (ADS)

Sullivan, Kristal K.; Boamah, Mavis D.; Shulenberger, Katie E.; Chapman, Sitara; Atkinson, Karen E.; Boyer, Michael C.; Arumainayagam, Christopher R.

2016-07-01

We report the first infrared study of the low-energy (<20 eV) electron-induced reactions of condensed methanol. Our goal is to simulate processes which occur when high-energy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor of several prebiotic species, is relatively abundant. The interactions of high-energy radiation, such as cosmic rays (Emax ˜ 1020 eV), with matter produce large numbers of low-energy secondary electrons, which are known to initiate radiolysis reactions in the condensed phase. Using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS), we have investigated low-energy (5-20 eV) and high-energy (˜1000 eV) electron-induced reactions in condensed methanol (CH3OH). IRAS has the benefit that it does not require thermal processing prior to product detection. Using IRAS, we have found evidence for the formation of ethylene glycol (HOCH2CH2OH), formaldehyde (CH2O), dimethyl ether (CH3OCH3), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and the hydroxyl methyl radical (·CH2OH) upon both low-energy and high-energy electron irradiation of condensed methanol at ˜85 K. Additionally, TPD results, presented herein, are similar for methanol films irradiated with both 1000 eV and 20 eV electrons. These IRAS and TPD findings are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. Moreover, methoxymethanol (CH3OCH2OH) could serve as a tracer molecule for electron-induced reactions in the interstellar medium. The results of experiments such as ours may provide a fundamental understanding of how complex organic molecules are synthesized in cosmic ices.

Rate and pathways for the reaction of OH with the biogenic p-cymene, an alkylated aromatic

NASA Astrophysics Data System (ADS)

Strekowski, R.; Rayez, M.-T.; Rayez, J.-C.; Zetzsch, C.

2009-04-01

Aromatics are known to contribute strongly to tropospheric formation of ozone, and p-cymene (4-isopropyltoluene) is one of only a few biogenic, volatile aromatic hydrocarbons. In spite of its symmetry, this molecule (CH3 - °-CH(CH3)2) has a multitude of potential pathways of its reaction with OH radicals. Addition of OH is well-known to be the predominating primary step in the tropospheric transformation of aromatic hydrocarbons. The addition is expected to occur preferably at a non-occupied position, where four positions are available: two equivalent ones ortho to the methyl group and two equivalent ones ortho to the isopropyl group. Furthermore, various C-H bonds (4 aromatic and 10 aliphatic) are available for abstraction, leading to benzyl-type radicals in two cases. The present study combines theoretical calculations with kinetic experiments in the gas phase. The theoretical calculations are based on electronic quantum chemistry DFT method for the investigation of the possible pathways in the potential energy surface of the reaction. The experiments are carried out by the flash photolysis/resonance fluorescence technique. OH radicals are produced by pulsed vacuum-UV photolysis of H2O (> 115 nm) in the presence of p-cymene in a slow flow of He as carrier gas. Their pseudo-first-order decays are monitored by resonance fluorescence, storing the photon counts by multichannel scaling in a PC and accumulating 50 decays each; see Koch et al. (2007) for details of the technique and evaluation of data. The temperature was varied between room temperature (295 K) and 345K, the He pressure was 250 mbar, and the level of p-cymene was increased stepwise, up to 3 x 1013 molecules/cm3. The decays of OH were observed to be exponential at room temperature, becoming clearly biexponential at higher temperatures, thus indicating reversible addition of OH according to the equilibration OH + p-cymene ⇔ p-cymene-OH (1, -1) These reactions might be accompanied by various abstraction channels, summarized as OH + p-cymene ⇒ alkylbenzyl + H2O (2) A value of 1.4 x 10-11 cm3 s-1 at 295 K is obtained for the sum k1 + k2, in good agreement with a value of 1.51 x 10-11 cm3 s-1determined by Corchnoy and Atkinson (1990) in a smog chamber at 295 K. The sum k1 + k2 decreases slightly with increasing temperature, falling below 10-11 cm3 s-1 at 345 K. The Arrhenius plot reveals a curved behaviour with a negative activation energy, approximately 1 x 10-12 exp (60 K/T) cm3 s-1. The biexponential behaviour corresponds to an apparent equilibrium constant of k1/k-1 = 8 x 10-25 exp [(-8500 ± 400) K/T] cm3 s-1. On the other hand, the bond energy of OH in the adduct can hardly be obtained from this biexponential behaviour alone since the abstraction of H atoms from the alkyl groups of p-cymene can be estimated to contribute markedly. Extrapolating the respective abstraction channels of toluene and the xylenes to two methyl substituents would yield k2= 1.6 x 10-18 T2exp (-38 K/T) cm3 s-1 (Atkinson, 1989). This amounts to 1.2x10-12 cm3 s-1 at 295 K (about 9% of the observed reactivity) and 1.7x10-12 cm3 s-1 at 345K (>17% of the observed reactivity) and does not even take the possibly largerreactivity of the isopropyl group (as compared to CH3) into account. The abstraction channel has been found to predominate in the analogous reaction of atomic Cl with p-cymene (Finlayson-Pitts et al, 1999), and further experiments by other methods are required to clarify the reaction channels for OH radicals. References Atkinson, R. (1989) Kinetics and Mechanisms of the Gas-Phase Reactions of the Hydroxyl Radical with Organic Compounds. J. Phys. Chem. Ref. Data, Monograph 1, Am. Chem. Soc./Am. Inst. Phys./NIST, p. 229. Corchnoy, S.B., Atkinson, R. (1990) Kinetics of the gas-phase reactions of OH and NO3 radicals with 2-Carene, 1,8-CineoIe, p-Cymene, and Terpinolene. Environ. Sci. Technol. 24, 1497-1502. Finlayson-Pitts, B. J., Keoshian, C.J., Buehler, B., Ezell, A.A. (1999) Kinetics of reaction of chlorine atoms with some biogenic organics. Int . J. Chem. Kinet. 31, 491-499. Koch, R., Knispel, R. Elend, M., Siese, M., Zetzsch, C. (2007) Consecutive reactions of aromatic-OH adducts with NO, NO2 and O2: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline. Atmos. Chem. Phys. 7, 2057-2071.

Experimental and theoretical understanding of the gas phase oxidation of atmospheric amides with OH radicals: kinetics, products, and mechanisms.

PubMed

Borduas, Nadine; da Silva, Gabriel; Murphy, Jennifer G; Abbatt, Jonathan P D

2015-05-14

Atmospheric amides have primary and secondary sources and are present in ambient air at low pptv levels. To better assess the fate of amides in the atmosphere, the room temperature (298 ± 3 K) rate coefficients of five different amides with OH radicals were determined in a 1 m(3) smog chamber using online proton-transfer-reaction mass spectrometry (PTR-MS). Formamide, the simplest amide, has a rate coefficient of (4.44 ± 0.46) × 10(-12) cm(3) molec(-1) s(-1) against OH, translating to an atmospheric lifetime of ∼1 day. N-methylformamide, N-methylacetamide and propanamide, alkyl versions of formamide, have rate coefficients of (10.1 ± 0.6) × 10(-12), (5.42 ± 0.19) × 10(-12), and (1.78 ± 0.43) × 10(-12) cm(3) molec(-1) s(-1), respectively. Acetamide was also investigated, but due to its slow oxidation kinetics, we report a range of (0.4-1.1) × 10(-12) cm(3) molec(-1) s(-1) for its rate coefficient with OH radicals. Oxidation products were monitored and quantified and their time traces were fitted using a simple kinetic box model. To further probe the mechanism, ab initio calculations are used to identify the initial radical products of the amide reactions with OH. Our results indicate that N-H abstractions are negligible in all cases, in contrast to what is predicted by structure-activity relationships. Instead, the reactions proceed via C-H abstraction from alkyl groups and from formyl C(O)-H bonds when available. The latter process leads to radicals that can readily react with O2 to form isocyanates, explaining the detection of toxic compounds such as isocyanic acid (HNCO) and methyl isocyanate (CH3NCO). These contaminants of significant interest are primary oxidation products in the photochemical oxidation of formamide and N-methylformamide, respectively.

Investigation of flame structure and burning intensity of partially premixed methane enrichment of syngas using OH-PLIF and kinetic simulation

NASA Astrophysics Data System (ADS)

Pu, Ge; Huang, Beibei; Zhang, Xun; Du, Jiantai; Zhu, Tuanhui; Chen, Bei

2018-05-01

Various experiments were conducted to study the combustion characteristics of partially premixed methane enrichment of syngas by using the OH-PLIF technique. Experiments were conducted on a co-flow burner, and the methane concentration (XCH4 = CH4/(H2+CO+CH4)) was varied from 0 to 20%, the overall equivalence ratio was varied from 0.4 to 1.2 and the inner equivalence ratio was varied from 1.5 to 3.5. Kinetic simulation was conducted by using OPPDIF module of CHEMKIN-Pro software. Results show that an increase in XCH4 and ϕoverall weakens the OH signal intensity. Adding methane into the fuel greatly increases the height of the inner flame front, and the increase of methane concentration has a negative effect on flame propagation speed. Meanwhile, simulation results remain consistent with the experiments. The main OH radical production reaction changes from R46: H+HO2 = 2OH to R38: H+O2 = O+OH when methane concentration contained in the fuel mixture increases. Sensitivity analysis also indicates that reaction which plays a dominant effect on temperature changes with the increase of methane concentration.

The products of the thermal decomposition of CH{sub 3}CHO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasiliou, AnGayle; National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401; Piech, Krzysztof M.

2011-07-07

We have used a heated 2 cm x 1 mm SiC microtubular ({mu}tubular) reactor to decompose acetaldehyde: CH{sub 3}CHO +{Delta}{yields} products. Thermal decomposition is followed at pressures of 75-150 Torr and at temperatures up to 1675 K, conditions that correspond to residence times of roughly 50-100 {mu}s in the {mu}tubular reactor. The acetaldehyde decomposition products are identified by two independent techniques: vacuum ultraviolet photoionization mass spectroscopy (PIMS) and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. Besides CH{sub 3}CHO, we have studied three isotopologues, CH{sub 3}CDO, CD{sub 3}CHO, and CD{sub 3}CDO. We have identified the thermal decomposition productsmore » CH{sub 3} (PIMS), CO (IR, PIMS), H (PIMS), H{sub 2} (PIMS), CH{sub 2}CO (IR, PIMS), CH{sub 2}=CHOH (IR, PIMS), H{sub 2}O (IR, PIMS), and HC{identical_to}CH (IR, PIMS). Plausible evidence has been found to support the idea that there are at least three different thermal decomposition pathways for CH{sub 3}CHO; namely, radical decomposition: CH{sub 3}CHO +{Delta}{yields} CH{sub 3}+[HCO]{yields} CH{sub 3}+ H + CO; elimination: CH{sub 3}CHO +{Delta}{yields} H{sub 2}+ CH{sub 2}=C=O; isomerization/elimination: CH{sub 3}CHO +{Delta}{yields}[CH{sub 2}=CH-OH]{yields} HC{identical_to}CH + H{sub 2}O. An interesting result is that both PIMS and IR spectroscopy show compelling evidence for the participation of vinylidene, CH{sub 2}=C:, as an intermediate in the decomposition of vinyl alcohol: CH{sub 2}=CH-OH +{Delta}{yields}[CH{sub 2}=C:]+ H{sub 2}O {yields} HC{identical_to}CH + H{sub 2}O.« less

A novel assessment of the role of the methyl radical and water formation channel in the CH3OH + H reaction.

PubMed

Sanches-Neto, Flávio O; Coutinho, Nayara D; Carvalho-Silva, Valter H

2017-09-20

A number of experimental and theoretical papers accounted almost exclusively for two channels in the reaction of atomic hydrogen with methanol: H-abstraction from the methyl (R1) and hydroxyl (R2) functional groups. Recently, several astrochemical studies claimed the importance of another channel for this reaction, which is crucial for kinetic simulations related to the abundance of molecular constituents in planetary atmospheres: methyl radical and water formation (R3 channel). Here, motivated by the lack of and uncertainties about the experimental and theoretical kinetic rate constants for the third channel, we developed first-principles Car-Parrinello molecular dynamics thermalized at two significant temperatures - 300 and 2500 K. Furthermore, the kinetic rate constant of all three channels was calculated using a high-level deformed-transition state theory (d-TST) at a benchmark electronic structure level. d-TST is shown to be suitable for describing the overall rate constant for the CH 3 OH + H reaction (an archetype of the moderate tunnelling regime) with the precision required for practical applications. Considering the experimental ratios at 1000 K, k R1 /k R2 ≈ 0.84 and k R1 /k R3 ≈ 15-40, we provided a better estimate when compared with previous theoretical work: 7.47 and 637, respectively. The combination of these procedures explicitly demonstrates the role of the third channel in a significant range of temperatures and indicates its importance considering the thermodynamic control to estimate methyl radical and water formation. We expect that these results can help to shed new light on the fundamental kinetic rate equations for the CH 3 OH + H reaction.

Thermal Decomposition of Methyl Acetate (CH_3COOCH_3) in a Flash-Pyrolysis Micro-Reactor

NASA Astrophysics Data System (ADS)

Porterfield, Jessica P.; Bross, David H.; Ruscic, Branko; Thorpe, James H.; Nguyen, Thanh Lam; Baraban, Joshua H.; Stanton, John F.; Daily, John W.; Ellison, Barney

2017-06-01

The thermal decomposition of methyl acetate (CH_3COOCH_3) has been studied in a set of flash pyrolysis micro-reactors. Samples were diluted to (0.06 - 0.13%) in carrier gases (He, Ar) and subjected to temperatures of 300 - 1600 K at roughly 20 Torr. After residence times of approximately 25 - 150 μseconds, the unimolecular pyrolysis products were detected by vacuum ultraviolet photoionization mass spectrometry at 10.487 eV (118.2 nm). Complementary product identification was provided by matrix isolation infrared spectroscopy. Decomposition began at 1000 K with the observation of (CH_2=C=O, CH_3OH), products of a four centered rearrangement with a Δ_{rxn}H_{298} = 39.1 ± 0.2 kcal mol^{-1}. As the micro-reactor was heated to 1300 K, a mixture of (CH_2=C=O, CH_3OH, CH_3, CH_2=O, H, CO, CO_2) appeared. A new novel pathway is calculated in which both methyl groups leave behind CO_2 simultaneously, Δ_{rxn}H_{298} = 74.5 ± 0.4 kcal mol^{-1}. This pathway is in contrast to step-wise loss of methyl radical, which can go in two ways: Δ_{rxn}H_{298} (CH_3COOCH_3 → CH_3 + COOCH_3) = 95.4 ± 0.4 kcal mol^{-1}, Δ_{rxn}H_{298} (CH_3COOCH_3 → CH_3COO + CH_3) = 88.0 ± 0.3 kcal mol^{-1}.

Formation of Glycerol through Hydrogenation of CO Ice under Prestellar Core Conditions

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Chuang, K.-J.; Ioppolo, S.; Qasim, D.; van Dishoeck, E. F.; Linnartz, H.

2017-06-01

Observational studies reveal that complex organic molecules (COMs) can be found in various objects associated with different star formation stages. The identification of COMs in prestellar cores, I.e., cold environments in which thermally induced chemistry can be excluded and radiolysis is limited by cosmic rays and cosmic-ray-induced UV photons, is particularly important as this stage sets up the initial chemical composition from which ultimately stars and planets evolve. Recent laboratory results demonstrate that molecules as complex as glycolaldehyde and ethylene glycol are efficiently formed on icy dust grains via nonenergetic atom addition reactions between accreting H atoms and CO molecules, a process that dominates surface chemistry during the “CO freeze-out stage” in dense cores. In the present study we demonstrate that a similar mechanism results in the formation of the biologically relevant molecule glycerol—HOCH2CH(OH)CH2OH—a three-carbon-bearing sugar alcohol necessary for the formation of membranes of modern living cells and organelles. Our experimental results are fully consistent with a suggested reaction scheme in which glycerol is formed along a chain of radical-radical and radical-molecule interactions between various reactive intermediates produced upon hydrogenation of CO ice or its hydrogenation products. The tentative identification of the chemically related simple sugar glyceraldehyde—HOCH2CH(OH)CHO—is discussed as well. These new laboratory findings indicate that the proposed reaction mechanism holds much potential to form even more complex sugar alcohols and simple sugars.

Hydrogen atom abstraction from aldehydes - OH + H2CO and O + H2CO

NASA Technical Reports Server (NTRS)

Dupuis, M.; Lester, W. A., Jr.

1984-01-01

The essential features of the potential energy surfaces governing hydrogen abstraction from formaldehyde by oxygen atom and hydroxyl radical have been characterized with ab inito multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) wave functions. The results are consistent with a very small activation energy for the OH + H2CO reaction, and an activation energy of a few kcal/mol for the O + H2CO reaction. In the transition state structure of both systems, the attacking oxygen atom is nearly collinear with the attacked CH bond.

Paramagnetic species on catalytic surfaces--DFT investigations into structure sensitivity of the hyperfine coupling constants.

PubMed

Sojka, Zbigniew; Pietrzyk, Piotr

2004-05-01

Structure sensitivity of the hyperfine coupling constants was investigated by means of DFT calculations for selected surface paramagnetic species. A *CH2OH radical trapped on silica and intrazeolite copper nitrosyl adducts encaged in ZSM-5 were taken as the examples. The surface of amorphous silica was modeled with a [Si5O8H10] cluster, whereas the zeolite hosting sites were epitomized by [Si4AlO5(OH)10]- cluster. Three different coordination modes of the *CH2OH radical were considered and the isotropic 13C and 1H hyperfine constants of the resultant van der Waals complexes, calculated with B3LYP/6-311G(d), were discussed in terms of the angular deformations caused by hydrogen bonds with the cluster. The magnetic parameters of the eta1-N[CuNO]11 and eta1-O[CuNO]11 linkage isomers were calculated at the BPW91/LanL2DZ and 6-311G(df) level. For the most stable eta1-N adduct a clear dependence of the spin density distribution within the Cu-NO moiety on changes in the Cu-N-O angle and the Cu-N bond distance was observed and accounted for by varying spin polarization and delocalization contributions.

Rate constant for the reaction of OH with CH3CCl2F (HCFC-141b) determined by relative rate measurements with CH4 and CH3CCl3

NASA Technical Reports Server (NTRS)

Huder, Karin; Demore, William B.

1993-01-01

Determination of accurate rate constants for OH abstraction is of great importance for the calculation of lifetimes for HCFCs and their impact on the atmosphere. For HCFC-141b there has been some disagreement in the literature for absolute measurements of this rate constant. In the present work rate constant ratios for HCFC-141b were measured at atmospheric pressure in the temperature range of 298-358 K, with CH4 and CH3CCl3 as reference gases. Ozone was photolyzed at 254 nm in the presence of water vapor to produce OH radicals. Relative depletions of 141b and the reference gases were measured by FTIR. Arrhenius expressions for 141b were derived from each reference gas and found to be in good agreement with each other. The combined expression for HCFC-141b which we recommend is 1.4 x 10 exp -12 exp(-1630/T) with k at 298 K being 5.9 x 10 exp -15 cu cm/molec-s. This value is in excellent agreement with the JPL 92-20 recommendation.

UV PHOTODESORPTION OF METHANOL IN PURE AND CO-RICH ICES: DESORPTION RATES OF THE INTACT MOLECULE AND OF THE PHOTOFRAGMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bertin, Mathieu; Doronin, Mikhail; Philippe, Laurent

2016-02-01

Wavelength-dependent photodesorption rates have been determined using synchrotron radiation for condensed pure and mixed methanol ice in the 7–14 eV range. The VUV photodesorption of intact methanol molecules from pure methanol ices is found to be of the order of 10{sup −5} molecules/photon, that is two orders of magnitude below what is generally used in astrochemical models. This rate gets even lower (<10{sup −6} molecules/photon) when the methanol is mixed with CO molecules in the ices. This is consistent with a picture in which photodissociation and recombination processes are at the origin of intact methanol desorption from pure CH{sub 3}OHmore » ices. Such low rates are explained by the fact that the overall photodesorption process is dominated by the desorption of the photofragments CO, CH{sub 3}, OH, H{sub 2}CO, and CH{sub 3}O/CH{sub 2}OH, whose photodesorption rates are given in this study. Our results suggest that the role of the photodesorption as a mechanism to explain the observed gas phase abundances of methanol in cold media is probably overestimated. Nevertheless, the photodesorption of radicals from methanol-rich ices may stand at the origin of the gas phase presence of radicals such as CH{sub 3}O, therefore, opening new gas phase chemical routes for the formation of complex molecules.« less

Peptide affinity labels for thrombin and other trypsin-like proteases

DOEpatents

Shaw, Elliott N.; Kettner, Charles A.

1982-03-09

A peptide affinity label of the formula (I): ##STR1## wherein X is a radical capable of acting as a leaving group in a nucleophilic substitution reaction; A is an aromatic amino acid residue; B is H, or a C.sub.1 -C.sub.4 alkyl group, or aryl; Y is selected from the group consisting of hydrogen, aroyl, C.sub.1 -C.sub.6 acyl, and Q--(A)--.sub.n, wherein Q=hydrogen, aroyl, or C.sub.1 -C.sub.6 acyl, n=1-10, A is an amino acid residue selected from the aliphatic, hydroxy-containing, carboxylic acid group, and amide-thereof-containing, aromatic, sulfur-containing and imino-containing amino acids; and wherein J is selected from the group consisting of --CH.sub.2 --, --CH.sub.2 --CH.sub.2 --,--CH.sub.2 --CH.sub.2 --CH.sub.2 --, --CH.dbd.CH-- and --CH(OH)--CH.sub.2. The affinity label is useful for irreversibly inactivating thrombin and trypsin-like enzymes and may be used as a potential anticlotting agent.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mount, G.H.; Harder, J.W.

The determination of the concentration of the hydroxyl radical in the troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. Described here are experiments located at Fritz Peak Observatory, Colorado, that measure of OH concentration to a sensitivity limit of about 5 X 10{sup 5} cm{sup {minus}3} (0.025 pptv) with absolute error approximately {+-}30% and, simultaneously, measure the concentrations of H{sub 2}O, SO{sub 2}, CH{sub 2}O, NO{sub 2}, NO{sub 3}, HONO, O{sub 3}, and other trace gases in the troposphere that affect OH concentration to provide a test of photochemical theories of OH formationmore » and destruction. An informal OH intercomparison campaign that occurred at Fritz Peak in 1991 and the 1993 Tropospheric OH Photochemistry Experiment are discussed. 33 refs., 14 figs., 2 tabs.« less

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

NASA Astrophysics Data System (ADS)

Butscher, Teddy; Duvernay, Fabrice; Danger, Grégoire; Chiavassa, Thierry

2016-09-01

Surface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (COMs) observed in several astrophysical regions and cometary environments. We present new laboratory experiments on the low-temperature solid state formation of complex organic molecules - glycolaldehyde, ethylene glycol, and polyoxymethylene - through radical-induced reactivity from VUV photolysis of formaldehyde in water-free and water-dominated ices. Radical reactivity and endogenous formation of COMs were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (TPD) using a quadripole mass spectrometer. We show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. It experimentally confirms the role of thermal diffusion in radical reactivity. We propose a new pathway for formaldehyde polymerisation induced by HCO radicals that might explain some observations made by the Ptolemy instrument on board the Rosetta lander Philae. In addition, our results seem to indicate that H-atom additions on H2CO proceed preferentially through CH2OH intermediate radicals rather than the CH3O radical.

Weakly Bound Free Radicals in Combustion: "Prompt" Dissociation of Formyl Radicals and Its Effect on Laminar Flame Speeds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Labbe, Nicole J.; Sivaramakrishnan, Raghu; Goldsmith, C. Franklin

2016-01-07

Weakly bound free radicals have low-dissociation thresholds such that at high temperatures, timescales for dissociation and collisional relaxation become comparable, leading to significant dissociation during the vibrational-rotational relaxation process. Here we characterize this “prompt” dissociation of formyl (HCO), an important combustion radical, using direct dynamics calculations for OH + CH2O and H + CH2O (key HCO-forming reactions). For all other HCO-forming reactions, presumption of a thermal incipient HCO distribution was used to derive prompt dissociation fractions. Inclusion of these theoretically derived HCO prompt dissociation fractions into combustion kinetics models provides an additional source for H-atoms that feeds chain branching reactions.more » Simulations using these updated combustion models are therefore shown to enhance flame propagation in 1,3,5-trioxane and acetylene. The present results suggest that HCO prompt dissociation should be included when simulating flames of hydrocarbons and oxygenated molecules and that prompt dissociations of other weakly bound radicals may also impact combustion simulations« less

Reactions of OH radicals with 2-methyl-1-butyl, neopentyl and 1-hexyl nitrates. Structure-activity relationship for gas-phase reactions of OH with alkyl nitrates: An update

NASA Astrophysics Data System (ADS)

Bedjanian, Yuri; Morin, Julien; Romanias, Manolis N.

2018-05-01

The kinetics of the reactions 2-methyl-1-butyl (2M1BNT), neopentyl (NPTNT) and 1-hexyl nitrates (1HXNT) with OH radicals has been studied using a low pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo-first order conditions from kinetics of OH consumption in excess of nitrates. The overall rate coefficients, k2M1BNT = 1.54 × 10-14 (T/298)4.85 exp (1463/T) (T = 278-538 K), kNPTNT = 1.39 × 10-14 (T/298)4.89 exp (1189/T) (T = 278-500 K) and k1HXNT = 2.23 × 10-13 (T/298)2.83 exp (853/T) cm3molecule-1s-1 (T = 306-538 K) (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium. The yield of trimethylacetaldehyde ((CH3)3CCHO), resulting from the abstraction by OH of an α-hydrogen atom in neopentyl nitrate, followed by α-substituted alkyl radical decomposition, was determined as 0.31 ± 0.06 at T = 298 K. The calculated tropospheric lifetimes of 2M1BNT, NPTNT and 1HXNT indicate that reaction of these nitrates with OH represents an important sink of these compounds in the atmosphere. Based on the available kinetic data, we have updated the structure-activity relationship (SAR) for reactions of alkyl nitrates with OH at T = 298 K. Good agreement (within 20%) is obtained between experimentally measured rate constants (total and that for H-atom abstraction from α carbon) and those calculated from SAR using new substituents factors for almost all the experimental data available.

Ambient formaldehyde and its contributing factor to ozone and OH radical in a rural area

NASA Astrophysics Data System (ADS)

Xiaoyan, Wang; Huixiang, Wang; Shaoli, Wang

2010-06-01

Formaldehyde (HCHO), as well as correlative pollutants was measured from 1 to 31 July in 2007 at Mazhuang, a rural site located in the east of China. Gaseous HCHO was scrubbed from the air with an acidic 2,4-dinitrophenylhydrazine (DNPH) solution, which leaded to the reaction of HCHO with DNPH and produced a stable product, 2,4-dinitrophenylhydrazone, followed by online analysis by high-performance liquid chromatography (HPLC) coupled with Ultraviolet detector. During the observation period, mixing ratios of HCHO ranged from 0.2 ppbv to 6.2 ppbv, with an average of 1.5 ± 0.67 ppbv. HCHO shows an evident diurnal variation, the maximum appeared during 12:00-14:00. The average concentration diurnal variations of measured HCHO, ozone (O 3), Methylhydroperoxides (MHP, CH 3OOH), hydrogen peroxide (H 2O 2), nitrogen oxides (NO x) and meteorological parameters were compared. The similar variations of HCHO, O 3 and radiation imply that photo-oxidation of hydrocarbons might be the major source for HCHO. Based on the maximum incremental reactivity (MIR) coefficient of HCHO, the calculation shows that HCHO contributes about 20% to total observed O 3 during the study period. In order to compare the contributions of O 3, HCHO and HONO to OH radical, photolysis rate parameters ( J-values) of the three compounds were calculated by the Tropospheric Ultraviolet and Visible (TUV) Radiation Model (4.4 version). Based on the comparison, this study reaches the conclusion that O 3 is the dominant source of OH radical at Mazhuang. This study also uses P(HCHO)/P(O 3) which represents the ratio of contrbutions of HCHO and O 3 to OH radical, to discuss the action of HCHO in OH radical soucers. The result shows that P(HCHO)/P(O 3) is 12.5% on average, with the maximum of 21.0% at 13:00 P.M. and minimum of 7.5% before 9:00 A.M. and after 17:00 P.M..Therefore HCHO is also an important source of OH radical and cannot be ignored.

Intramolecular hydrogen bonding in malonaldehyde and its radical analogues.

PubMed

Lin, Chen; Kumar, Manoj; Finney, Brian A; Francisco, Joseph S

2017-09-28

High level Brueckner doubles with triples correction method-based ab initio calculations have been used to investigate the nature of intramolecular hydrogen bonding and intramolecular hydrogen atom transfer in cis-malonaldehyde (MA) and its radical analogues. The radicals considered here are the ones that correspond to the homolytic cleavage of C-H bonds in cis-MA. The results suggest that cis-MA and its radical analogues, cis-MA RS , and cis-MA RA , both exist in planar geometry. The calculated intramolecular O-H⋯O=C bond in cis-MA is shorter than that in the radical analogues. The intramolecular hydrogen bond in cis-MA is stronger than in its radicals by at least 3.0 kcal/mol. The stability of a cis-malonaldehyde radical correlates with the extent of electron spin delocalization; cis-MA RA , in which the radical spin is more delocalized, is the most stable MA radical, whereas cis-MA RS , in which the radical spin is strongly localized, is the least stable radical. The natural bond orbital analysis indicates that the intramolecular hydrogen bonding (O⋯H⋯O) in cis-malonaldehyde radicals is stabilized by the interaction between the lone pair orbitals of donor oxygen and the σ * orbital of acceptor O-H bond (n → σ * OH ). The calculated barriers indicate that the intramolecular proton transfer in cis-MA involves 2.2 kcal/mol lower barrier than that in cis-MA RS .

Further investigation into maple syrup yields 3 new lignans, a new phenylpropanoid, and 26 other phytochemicals.

PubMed

Li, Liya; Seeram, Navindra P

2011-07-27

Maple syrup is made by boiling the sap collected from certain maple ( Acer ) species. During this process, phytochemicals naturally present in tree sap are concentrated in maple syrup. Twenty-three phytochemicals from a butanol extract of Canadian maple syrup (MS-BuOH) had previously been reported; this paper reports the isolation and identification of 30 additional compounds (1-30) from its ethyl acetate extract (MS-EtOAc) not previously reported from MS-BuOH. Of these, 4 compounds are new (1-3, 18) and 20 compounds (4-7, 10-12, 14-17, 19, 20, 22-24, 26, and 28-30) are being reported from maple syrup for the first time. The new compounds include 3 lignans and 1 phenylpropanoid: 5-(3″,4″-dimethoxyphenyl)-3-hydroxy-3-(4'-hydroxy-3'-methoxybenzyl)-4-(hydroxymethyl)dihydrofuran-2-one (1), (erythro,erythro)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (2), (erythro,threo)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (3), and 2,3-dihydroxy-1-(3,4- dihydroxyphenyl)-1-propanone (18), respectively. In addition, 25 other phenolic compounds were isolated including (threo,erythro)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (4), (threo,threo)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (5), threo-guaiacylglycerol-β-O-4'-dihydroconiferyl alcohol (6), erythro-1-(4-hydroxy-3-methoxyphenyl)-2-[4-(3-hydroxypropyl)-2,6-dimethoxyphenoxy]-1,3-propanediol (7), 2-[4-[2,3-dihydro-3-(hydroxymethyl)-5-(3-hydroxypropyl)-7-methoxy-2-benzofuranyl]-2,6-dimethoxyphenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (8), acernikol (9), leptolepisol D (10), buddlenol E (11), (1S,2R)-2-[2,6-dimethoxy-4-[(1S,3aR,4S,6aR)-tetrahydro-4-(4-hydroxy-3,5-dimethoxyphenyl)-1H,3H-furo[3,4-c]furan-1-yl]phenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (12), syringaresinol (13), isolariciresinol (14), icariside E4 (15), sakuraresinol (16), 1,2-diguaiacyl-1,3-propanediol (17), 2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (19), 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)propan-1-one (20), dihydroconiferyl alcohol (21), 4-acetylcatechol (22), 3',4',5'-trihydroxyacetophenone (23), 3,4-dihydroxy-2-methylbenzaldehyde (24), protocatechuic acid (25), 4-(dimethoxymethyl)pyrocatechol (26), tyrosol (27), isofraxidin (28), and 4-hydroxycatechol (29). One sesquiterpene, phaseic acid (30), which is a known metabolite of the phytohormone abscisic acid, was also isolated from MS-EtOAc. The antioxidant activities of MS-EtOAc (IC(50) = 75.5 μg/mL) and the pure isolates (IC(50) ca. 68-3000 μM) were comparable to that of vitamin C (IC(50) = 40 μM) and the synthetic commercial antioxidant butylated hydroxytoluene (IC(50) = 3000 μM), in the diphenylpicrylhydrazyl radical scavenging assay. The current study advances scientific knowledge of maple syrup constituents and suggests that these diverse phytochemicals may impart potential health benefits to this natural sweetener.

Further Investigation Into Maple Syrup Yields Three New Lignans, a New Phenylpropanoid, and Twenty-Six Other Phytochemicals

PubMed Central

LI, LIYA; SEERAM, NAVINDRA P.

2011-01-01

Maple syrup is made by boiling the sap collected from certain maple (Acer) species. During this process, phytochemicals naturally present in tree sap are concentrated in maple syrup. We previously reported 23 phytochemicals from a butanol extract of Canadian maple syrup (MS-BuOH). Here we report the isolation and identification of 30 additional compounds (1–30) from its ethyl acetate extract (MS-EtOAc) not previously reported from MS-BuOH. Of these, 4 compounds are new (1–3, 18) and 20 compounds (4–7, 10–12, 14–17, 19–20, 22–24, 26, 28–30) are being reported from maple syrup for the first time. The new compounds include 3 lignans and 1 phenylpropanoid: 5-(3″,4″-dimethoxyphenyl)-3-hydroxy-3-(4′-hydroxy-3′-methoxybenzyl)-4-hydroxymethyl-dihydrofuran-2-one (1), (erythro, erythro)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (2), (erythro, threo)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (3) and 2,3-dihydroxy-1-(3,4-dihydroxyphenyl)-1-propanone (18), respectively. In addition, 25 other phenolic compounds were isolated including (threo, erythro)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (4), (threo, threo)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (5), threo-guaiacylglycerol-β-O-4′-dihydroconiferyl alcohol (6), erythro-1-(4-hydroxy-3-methoxyphenyl)-2-[4-(3-hydroxypropyl)-2,6-dimethoxyphenoxy]-1,3-propanediol (7), 2-[4-[2,3-dihydro-3-(hydroxymethyl)-5-(3-hydroxypropyl)-7-methoxy-2-benzofuranyl]-2,6-dimethoxyphenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (8), acernikol (9), leptolepisol D (10), buddlenol E (11), (1S,2R)-2-[2,6-dimethoxy-4-[(1S,3aR,4S,6aR)-tetrahydro-4-(4-hydroxy-3,5-dimethoxyphenyl)-1H,3H-furo[3,4-c]furan-1-yl]phenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (12), syringaresinol (13), isolariciresinol (14), icariside E4 (15), sakuraresinol (16), 1,2-diguaiacyl-1,3-propanediol (17), 2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (19), 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)propan-1-one (20), dihydroconiferyl alcohol (21), 4-acetylcatechol (22), 3′,4′,5′-trihydroxyacetophenone (23), 3,4-dihydroxy-2-methylbenzaldehyde (24), protocatechuic acid (25), 4-(dimethoxymethyl)-pyrocatechol (26), tyrosol (27), isofraxidin (28) and 4-hydroxycatechol (29). One sesquiterpene, phaseic acid (30), which is a known metabolite of the phytohormone, abscisic acid, was also isolated from MS-EtOAc. The antioxidant activities of MS-EtOAc (IC50 = 75.5 μg/mL), and the pure isolates (IC50 ca. 68–3000 μM) were comparable to vitamin C (IC50 = 40 μM) and the synthetic commercial antioxidant, butylated hydroxytoluene (IC50 = 3000 μM), in the diphenylpicrylhydrazyl radical scavenging assay. The current study advances scientific knowledge of maple syrup constituents and suggest that these diverse phytochemicals may impart potential health benefits to this natural sweetener. PMID:21675726

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent.

PubMed

Postils, Verònica; Company, Anna; Solà, Miquel; Costas, Miquel; Luis, Josep M

2015-09-08

The reaction mechanisms for alkane hydroxylation catalyzed by non-heme Fe(V)O complexes presented in the literature vary from rebound stepwise to concerted highly asynchronous processes. The origin of these important differences is still not completely understood. Herein, in order to clarify this apparent inconsistency, the hydroxylation of a series of alkanes (methane and substrates bearing primary, secondary, and tertiary C-H bonds) through a Fe(V)O species, [Fe(V)(O)(OH)(PyTACN)](2+) (PyTACN = 1-(2'-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane), has been computationally examined at the gas phase and in acetonitrile solution. The initial breaking of the C-H bond can occur via hydrogen atom transfer (HAT), leading to an intermediate where there is an interaction between the radical substrate and [Fe(IV)(OH)2(PyTACN)](2+), or through hydride transfer to form a cationic substrate interacting with the [Fe(III)(OH)2(PyTACN)](+) species. Our calculations show the following: (i) except for methane in the rest of the alkanes studied, the intermediate formed by R(+) and [Fe(III)(OH)2(PyTACN)](+) is more stable than that involving the alkyl radical and the [Fe(IV)(OH)2(PyTACN)](2+) complex; (ii) in spite of (i), the first step of the reaction mechanism for all substrates is a HAT instead of hydride abstraction; (iii) the HAT is the rate-determining step for all analyzed cases; and (iv) the barrier for the HAT decreases along methane → primary → secondary → tertiary carbon. The second part of the reaction mechanism corresponds to the rebound process. Therefore, the stereospecific hydroxylation of alkane C-H bonds by non-heme Fe(V)(O) species occurs through a rebound stepwise mechanism that resembles that taking place at heme analogues. Finally, our study also shows that, to properly describe alkane hydroxylation processes mediated by Fe(V)O species, it is essential to consider the solvent effects during geometry optimizations. The use of gas-phase geometries explains the variety of mechanisms for the hydroxylation of alkanes reported in the literature.

Species and temperature measurements of methane oxidation in a nanosecond repetitively pulsed discharge

PubMed Central

Lefkowitz, Joseph K; Guo, Peng; Rousso, Aric; Ju, Yiguang

2015-01-01

Speciation and temperature measurements of methane oxidation during a nanosecond repetitively pulsed discharge in a low-temperature flow reactor have been performed. Measurements of temperature and formaldehyde during a burst of pulses were made on a time-dependent basis using tunable diode laser absorption spectroscopy, and measurements of all other major stable species were made downstream of a continuously pulsed discharge using gas chromatography. The major species for a stoichiometric methane/oxygen/helium mixture with 75% dilution are H2O, CO, CO2, H2, CH2O, CH3OH, C2H6, C2H4 and C2H2. A modelling tool to simulate homogeneous plasma combustion kinetics is assembled by combining the ZDPlasKin and CHEMKIN codes. In addition, a kinetic model for plasma-assisted combustion (HP-Mech/plasma) of methane, oxygen and helium mixtures has been assembled to simulate the measurements. Predictions can accurately capture reactant consumption as well as production of the major product species. However, significant disagreement is found for minor species, particularly CH2O and CH3OH. Further analysis revealed that the plasma-activated low-temperature oxidation pathways, particularly those involving CH3O2 radical reactions and methane reactions with O(1D), are responsible for this disagreement. PMID:26170433

Constraining the global bromomethane budget from carbon stable isotopes

NASA Astrophysics Data System (ADS)

Bahlmann, Enno; Wittmer, Julian; Greule, Markus; Zetzsch, Cornelius; Seifert, Richard; Keppler, Frank

2016-04-01

Despite intense research in the last two decades, the global bromomethane (CH3Br) budget remains unbalanced with the known sinks exceeding the known sources by about 25%. The reaction with OH is the largest sink for CH3Br. We have determined the kinetic isotope effects for the reactions of CH3Br with the OH and Cl radical in order to better constrain the global CH3Br budget from an isotopic perspective. The isotope fractionation experiments were performed at 20±1°C in a 3500 L Teflon smog-chamber with initial CH3Br mixing ratios of about 2 and 10 ppm and perflourohexane (25 ppb) as internal standard. Atomic chlorine (Cl) was generated via photolysis of molecular chlorine (Cl2) using a solar simulator with an actinic flux comparable to that of the sun in mid-summer in Germany. OH radicals were generated via the photolysis of ozone (O3) at 253.7 nm in the presence of water vapor (RH = 70%).The mixing ratios of CH3Br, and perflourohexane were monitored by GC-MS with a time resolution of 15 minutes throughout the experiments. From each experiment 10 to 15 sub samples were taken in regular time intervals for subsequent carbon isotope ratio determinations by GC-IRMS performed at two independent laboratories in parallel. We found a kinetic isotope effect (KIE) of 17.6±3.3‰ for the reaction of CH3Br with OH and a KIE of 9.8±1.4 ‰ for the reaction with Cl*. We used these fractionation factors along with new data on the isotopic composition of CH3Br in the troposphere (-34±7‰) and the surface ocean (-26±7‰) along with reported source signatures, to constrain the unknown source from an isotopic perspective. The largest uncertainty in estimating the isotopic composition of the unknown source arises from the soil sink. Microbial degradation in soils is the second largest sink and assigned with a large fractionation factors of about 50‰. However, field experiments revealed substantially smaller apparent fractionation factors ranging from 11 to 22‰. In addition, simple model studies suggest that the soil uptake of CH3Br and hence its isotopic effect is largely controlled by diffusion resulting in an even smaller apparent isotopic fractionation. As a consequence, the estimated source signature for the unknown source is discussed with respect to the assumptions made for the soil sink.

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

NASA Astrophysics Data System (ADS)

Porterfield, Jessica P.; Nguyen, Thanh Lam; Baraban, Joshua H.; Buckingham, Grant; Troy, Tyler; Kostko, Oleg; Ahmed, Musahid; Stanton, John F.; Daily, John W.; Ellison, Barney

2016-06-01

he thermal decomposition of cyclohexanone (C_6H10=O) has been studied in a set of flash-pyrolysis micro-reactors. Samples of C_6H10=O were first observed to decompose at 1200 K. Short residence times of 100 μsec and dilution of samples (<0.1%) isolate unimolecular decomposition. Products were identified by tunable VUV photoionization mass spectroscopy, photoionization appearance thresholds, and complementary matrix infrared absorption spectroscopy. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways pictured to the right. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C_6H_9OH), is followed by retro-Diels-Alder cleavage to CH_2=CH_2 and CH_2=C(OH)-CH=CH_2. Further isomerization of CH_2=C(OH)CH=CH_2 to methyl vinyl ketone (CH_3COCH=CH_2, MVK) was also observed. Photoionization spectra identified both enols, C_6H_9OH and CH=C(OH)CH=CH_2, and the ionization threshold of C_6H_9OH was measured to be 8.2 ± 0.1 eV. At 1200 K, the products of cyclohexanone pyrolysis were found to be: C_6H_9OH, CH_2=C(OH)CH=CH_2, MVK, CH_2CHCH_2, CO, CH_2=C=O, CH_3, CH_2=C=CH_2, CH_2=CH-CH=CH_2, CH_2=CHCH_2CH_3, CH_2=CH_2, and HCCH.

Importance of tunneling in H-abstraction reactions by OH radicals. The case of CH4 + OH studied through isotope-substituted analogs

NASA Astrophysics Data System (ADS)

Lamberts, T.; Fedoseev, G.; Kästner, J.; Ioppolo, S.; Linnartz, H.

2017-03-01

We present a combined experimental and theoretical study focussing on the quantum tunneling of atoms in the reaction between CH4 and OH. The importance of this reaction pathway is derived by investigating isotope substituted analogs. Quantitative reaction rates needed for astrochemical models at low temperature are currently unavailable both in the solid state and in the gas phase. Here, we study tunneling effects upon hydrogen abstraction in CH4 + OH by focusing on two reactions: CH4 + OD → CH3 + HDO and CD4 + OH → CD3 + HDO. The experimental study shows that the solid-state reaction rate RCH4 + OD is higher than RCD4 + OH at 15 K. Experimental results are accompanied by calculations of the corresponding unimolecular and bimolecular reaction rate constants using instanton theory taking into account surface effects. For the work presented here, the unimolecular reactions are particularly interesting as these provide insight into reactions following a Langmuir-Hinshelwood process. The resulting ratio of the rate constants shows that the H abstraction (kCH4 + OD) is approximately ten times faster than D-abstraction (kCD4 + OH) at 65 K. We conclude that tunneling is involved at low temperatures in the abstraction reactions studied here. The unimolecular rate constants can be used by the modeling community as a first approach to describe OH-mediated abstraction reactions in the solid phase. For this reason we provide fits of our calculated rate constants that allow the inclusion of these reactions in models in a straightforward fashion.

Ab Initio Theoretical Studies on the Kinetics of Hydrogen Abstraction Type Reactions of Hydroxyl Radicals with CH3CCl2F and CH3CClF2

NASA Astrophysics Data System (ADS)

Saheb, Vahid; Maleki, Samira

2018-03-01

The hydrogen abstraction reactions from CH3Cl2F (R-141b) and CH3CClF2 (R-142b) by OH radicals are studied theoretically by semi-classical transition state theory. The stationary points for the reactions are located by using KMLYP density functional method along with 6-311++G(2 d,2 p) basis set and MP2 method along with 6-311+G( d, p) basis set. Single-point energy calculations are performed by the CBS-Q and G4 combination methods on the geometries optimized at the KMLYP/6-311++G(2 d,2 p) level of theory. Vibrational anharmonicity coefficients, x ij , which are needed for semi-classical transition state theory calculations, are computed at the KMLYP/6-311++G(2 d,2 p) and MP2/6-311+G( d, p) levels of theory. The computed barrier heights are slightly sensitive to the quantum-chemical method. Thermal rate coefficients are computed over the temperature range from 200 to 2000 K and they are shown to be in accordance with available experimental data. On the basis of the computed rate coefficients, the tropospheric lifetime of the CH3CCl2F and CH3CClF2 are estimated to be about 6.5 and 12.0 years, respectively.

Effects of reactant rotation on the dynamics of the OH + CH4 → H2O + CH3 reaction: a six-dimensional study.

PubMed

Song, Hongwei; Li, Jun; Jiang, Bin; Yang, Minghui; Lu, Yunpeng; Guo, Hua

2014-02-28

The dynamics of the hydrogen abstraction reaction between methane and hydroxyl radical is investigated using an initial state selected time-dependent wave packet method within a six-dimensional model. The ab initio calibrated global potential energy surface of Espinosa-García and Corchado was used. Integral cross sections from several low-lying rotational states of both reactants have been obtained using the centrifugal sudden and J-shifting approximations. On the empirical potential energy surface, the rotational excitation of methane has little effect on the reaction cross section, but excited rotational states of OH inhibit the reactivity slightly. These results are rationalized with the newly proposed sudden vector projection model.

van der Waals forces and confinement in carbon nanopores: Interaction between CH 4, COOH, NH 3, OH, SH and single-walled carbon nanotubes

DOE PAGES

Weck, Philippe F.; Kim, Eunja; Wang, Yifeng

2016-04-13

Interactions between CH 4, COOH, NH 3, OH, SH and armchair (n,n)(n=4,7,14) and zigzag (n,0)(n=7,12,25) single-walled carbon nanotubes (SWCNTs) have been systematically investigated within the framework of dispersion-corrected density functional theory (DFT-D2). Endohedral and exohedral molecular adsorption on SWCNT walls is energetically unfavorable or weak, despite the use of C 6/r 6 pairwise London-dispersion corrections. The effects of pore size and chirality on the molecule/SWCNTs interaction were also assessed. Furthermore, chemisorption of COOH, NH 3, OH and SH at SWCNT edge sites was examined using a H-capped (7,0) SWCNT fragment and its impact on electrophilic, nucleophilic and radical attacks wasmore » predicted by means of Fukui functions.« less

A new mechanism-based inhibitor of photosynthetic water oxidation: Acetone hydrazone. I. Equilibrium reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tso, J.; Dismukes, G.C.; Petrouleas, V.

1990-08-21

The process of photosynthetic water oxidation has been investigated by using a new type of water oxidation inhibitor, the alkyl hydrazones. Acetone hydrazone (AceH), (CH{sub 3}){sub 2}CNNH{sub 2}, inhibits water oxidation by a mechanism that is analogous to that of NH{sub 2}OH. This involves binding to the water-oxidizing complex (WOC), followed by photoreversible reduction of manganese (loss of the S{sub 1} {yields} S{sub 2} reaction). At higher AceH concentrations the S{sub 1} state is reduced in the dark and Mn is released, albeit to a lesser extent than with NH{sup 2}OH. Following extraction of Mn, AceH is able to donatemore » electrons rapidly to the reaction center tyrosine radical Z{sup +} ({sup 161}Tyr-D{sub 1} protein), more slowly to a reaction center radical C{sup +}, and not at all to the dark-stable tyrosine radical D{sup +} ({sup 160}Tyr-D{sub 2} protein) which must be sequestered in an inaccessible site. Unexpectedly, Cl{sup {minus}} was found not to interfere or compete with AceH for binding to the WOC in the S{sub 1} state, in contrast to the reported rate of binding of N,N-dimethylhydroxylamine (CH{sub 3}){sub 2}NOH. The authors interpret the latter behavior as due to ionic screening of the thylakoid membrane, rather than a specific Cl site involved in water oxidation. AceH appears not to bind to the acceptor side of PSII as evidenced by normal EPR signals both for Q{sub A}{sup {minus}}Fe(II), the primary electron acceptor, and for the oxidized Fe(III) acceptor (Q{sub 400} species), in contrast to that observed with NH{sub 2}OH. AceH can be oxidized in solution by a variety of oxidants including Mn(III) to form a reactive diazo intermediate, (CH{sub 3}){sub 2}CNN, which reacts with carbonyl compounds. Oxidation to this diazo intermediate is postulated to be responsible for inhibition of the WOC.« less

A Competitive Kinetics Study of the Reaction of Cl with CS2 in Air at 298 K

NASA Technical Reports Server (NTRS)

Wallington, Timothy J.; Andino, Jean M.; Potts, Alan R.; Wine, Paul H.

1997-01-01

The relative rate technique has been used to investigate the kinetics of the reaction of Cl atoms with carbon disulfide, CS2, at 700 Torr total pressure of air at 298 K. The decay rate of CS2 was measured relative to CH4, CH3Cl and CHF2CL. For experiments using CH4 and CH3Cl references, the decay rate of CS2 was dependent on the ratio of the concentration of the reference to that of CS2. We ascribe this behavior to the generation of OH radicals in the system leading to complicated secondary chemistry. From experiments using CHF2Cl we are able to assign an upper limit of 4 x 10(exp -15) cu cm/(molecule s) for the overall reaction, Cl + CS2 yields products.

Peptide affinity labels for thrombin and other trypsin-like proteases

DOEpatents

Shaw, E.N.; Kettner, C.A.

1982-03-09

A peptide affinity label is disclosed of the formula (I): as given in the patent wherein X is a radical capable of acting as a leaving group in a nucleophilic substitution reaction; A is an aromatic amino acid residue; B is H, or a C[sub 1]--C[sub 4] alkyl group, or aryl; Y is selected from the group consisting of hydrogen, aroyl, C[sub 1]--C[sub 6] acyl, and Q--(A)--[sub n], wherein Q = hydrogen, aroyl, or C[sub 1]--C[sub 6] acyl, n = 1--10, A is an amino acid residue selected from the aliphatic, hydroxy-containing, carboxylic acid group, and amide-thereofcontaining, aromatic, sulfur-containing and imino-containing amino acids; and wherein J is selected from the group consisting of --CH[sub 2]--, --CH[sub 2]--CH[sub 2]--, --CH[sub 2]--CH[sub 2]--CH[sub 2]--, --CH[double bond]CH-- and --CH(OH)--CH[sub 2]. The affinity label is useful for irreversibly inactivating thrombin and trypsin-like enzymes and may be used as a potential anticlotting agent. 2 figs.

Oxidation mechanisms of CF2Br2 and CH2Br2 induced by air nonthermal plasma.

PubMed

Schiorlin, Milko; Marotta, Ester; Dal Molin, Marta; Paradisi, Cristina

2013-01-02

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, -dc, or +pulsed high voltage.. The two bromomethanes CF(2)Br(2) and CH(2)Br(2) were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO(2) and CO in the case of CH(2)Br(2), CO(2) and F(2)C ═ O in the case of CF(2)Br(2). F(2)C ═ O is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO(2) and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO(3) and N(2)O. Ozone, an important product of air NTP, was never detected in experiments with CF(2)Br(2) and CH(2)Br(2) because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF(2)Br(2) reacts in air NTP via a common intermediate, the CF(2)Br radical. The possible reactions leading to this radical are discussed, including, for -dc activation, charge exchange with O(2)(-), a species detected by APCI mass spectrometry.

[Study on the Emission Spectrum of Hydrogen Production with Microwave Discharge Plasma in Ethanol Solution].

PubMed

Sun, Bing; Wang, Bo; Zhu, Xiao-mei; Yan, Zhi-yu; Liu, Yong-jun; Liu, Hui

2016-03-01

Hydrogen is regarded as a kind of clean energy with high caloricity and non-pollution, which has been studied by many experts and scholars home and abroad. Microwave discharge plasma shows light future in the area of hydrogen production from ethanol solution, providing a new way to produce hydrogen. In order to further improve the technology and analyze the mechanism of hydrogen production with microwave discharge in liquid, emission spectrum of hydrogen production by microwave discharge plasma in ethanol solution was being studied. In this paper, plasma was generated on the top of electrode by 2.45 GHz microwave, and the spectral characteristics of hydrogen production from ethanol by microwave discharge in liquid were being studied using emission spectrometer. The results showed that a large number of H, O, OH, CH, C2 and other active particles could be produced in the process of hydrogen production from ethanol by microwave discharge in liquid. The emission spectrum intensity of OH, H, O radicals generated from ethanol is far more than that generated from pure water. Bond of O-H split by more high-energy particles from water molecule was more difficult than that from ethanol molecule, so in the process of hydrogen production by microwave discharge plasma in ethanol solution; the main source of hydrogen was the dehydrogenation and restructuring of ethanol molecules instead of water decomposition. Under the definite external pressure and temperature, the emission spectrum intensity of OH, H, O radicals increased with the increase of microwave power markedly, but the emission spectrum intensity of CH, C2 active particles had the tendency to decrease with the increase of microwave power. It indicated that the number of high energy electrons and active particles high energy electron energy increased as the increase of microwave power, so more CH, C2 active particles were split more thoroughly.

Atmospheric chemical reactions of monoethanolamine initiated by OH radical: mechanistic and kinetic study.

PubMed

Xie, Hong-Bin; Li, Chao; He, Ning; Wang, Cheng; Zhang, Shaowen; Chen, Jingwen

2014-01-01

Monoethanolamine (MEA) is a benchmark and widely utilized solvent in amine-based postcombustion CO2 capture (PCCC), a leading technology for reducing CO2 emission from fossil fuel power plants. The large-scale implementation of PCCC would lead to inevitable discharges of amines to the atmosphere. Therefore, understanding the kinetics and mechanisms of the transformation of representative amine MEA in the atmosphere is of great significance for risk assessment of the amine-based PCCC. In this study, the H-abstraction reaction of MEA with ·OH, and ensuing reactions of produced MEA-radicals, including isomerization, dissociation, and bimolecular reaction MEA-radicals+O2, were investigated by quantum chemical calculation [M06-2X/aug-cc-pVTZ//M06-2X/6-311++G(d,p)] and kinetic modeling. The calculated overall rate constant [(7.27 × 10(-11)) cm(3) molecule(-1) s(-1)] for H-abstraction is in excellent agreement with the experimental value [(7.02 ± 0.46) × 10(-11) cm(3) molecule(-1) s(-1)]. The results show that the product branching ratio of NH2CH2 · CHOH (MEA-β) (43%) is higher than that of NH2 · CHCH2OH (MEA-α) (39%), clarifying that MEA-α is not an exclusive product. On the basis of the unveiled reaction mechanisms of MEA-radicals + O2, the proton transfer reaction mass spectrometry signal (m/z 60.044), not recognized in the experiment, was identified.

Atmospheric lifetimes and ozone depletion potentials of methyl bromide (CH3Br) and dibromomethane (CH2Br2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mellouki, A.; Talukdar, R.K.; Schmoltner, A.

The rate coefficients for the reactions of OH radical with CH3Br and CH2Br2 were measured as functions of temperature using the laser photolysis - laser induced fluorescence method. This data was incorporated into a semiempirical model (Solomon et al., 1992) and a 2D model to calculate the steady-state ozone depletion potentials (ODP) and atmospheri lifetimes, tau, with greatly improved accuracy as compared to earlier studies. The calculated ODPs and tau are 0.65 and 1.7 years and 0.17 and 0.41 years for CH3Br and CH2Br2, respectively, using the semiempirical model. These lifetimes agree well with those calculated using a 2D model.more » This study better quantifies the ODPs and tau of these species which are needed inputs for discussion of possible regulation of human emissions currently under international considerations. 29 refs.« less

Theoretical prediction of the mechanistic pathways and kinetics of methylcyclohexane initiated by OH radicals

NASA Astrophysics Data System (ADS)

Begum, Saheen Shehnaz; Deka, Ramesh Chandra; Gour, Nand Kishor

2018-06-01

In this manuscript, we have systematically depicted the theoretical prediction of H-absorption from methylcyclohexane initiated by OH radical. For this we have performed dual-level of quantum chemical calculations on the gas-phase reactions between methylcyclohexane (MCH) and OH radical. Geometry optimisation and vibrational frequency calculations have been performed at BHandHLYP/6-311G(d,p) level of theory along with energetic calculations at coupled cluster CCSD(T) method using the same basis set. All the stationary points of titled reaction have been located on the potential energy surface. It has also been found that the H-abstraction takes place from -CH site of MCH, which is the minimum energy pathway than others. The rate constant was calculated using canonical transition state theory for MCH with OH radical and is found to be 3.27 × 10-12 cm3 molecule-1 s-1, which is in sound agreement with reported experimental data. The atmospheric lifetime of MCH and branching ratios of the reaction channels are also reported in the manuscript.

Direct Dynamics Simulation of Dissociation of the [CH3--I--OH]- Ion-Molecule Complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Jing; McClellan, Miranda; Sun, Rui

Direct dynamics simulations were used to study dissociation of the [CH3--I--OH]- complex ion, which was observed in a previous study of the OH- + CH3I gas phase reaction (J. Phys. Chem. A 2013, 117, 7162). Restricted B97-1 simulations were performed to study dissociation at 65, 75 and 100 kcal/mol and the [CH3--I--OH]- ion dissociated exponentially, in accord with RRKM theory. For these energies the major dissociation products are CH3I + OH-, CH2I- + H2O, and CH3OH + I-. Unrestricted B97-1 and restricted and unrestricted CAM-B3LYP simulations were also performed at 100 kcal/mol to compare with the restricted B97-1 results. Themore » {CH3I + OH-}:{CH2I- + H2O}:{CH3OH + I-} product ratio is 0.72 : 0.15 : 0.13, 0.81 : 0.05 : 0.14, 0.71 : 0.19 : 0.10 , and 0.83 : 0.13 : 0.04 for the restricted B97-1, unrestricted B97-1, restricted CAM-B3LYP, and unrestricted CAM-B3LYP simulations, respectively. Other product channels found are CH2 + I- + H2O, CH2 + I-(H2O), CH4 + IO-, CH3 - + IOH, and CH3 + IOH-. The CH3 - + IOH singlet products are only given by the restricted B97-1 simulation and the lower energy CH3 + IOH- doublet products are only formed by the unrestricted B97-1 simulation. Also studied were the direct and indirect atomic-level mechanisms for forming CH3I + OH-, CH2I- + H2O, and CH3OH + I-. The majority of CH3I + OH- were formed through a direct mechanism. For both CH2I- + H2O and CH3OH + I-, the direct mechanism is overall more important than the indirect mechanisms, with the round-about like mechanism the most important indirect mechanism at high excitation energies. Mechanism comparisons between the B97-1 and CAM-B3LYP simulations showed that formation of the CH3OH---I- complex is favored for the B97-1 simulations, while formation of the HO----HCH2I complex is favored for the CAM-B3LYP simulations. The unrestricted simulations give a higher percentage of indirect mechanisms than the restricted simulations. The possible role of the self-interaction error in the simulations is also discussed. The work presented here gives a detailed picture of the [CH3--I--OH]- dissociation dynamics, and is very important for unraveling the role of [CH3--I--OH]- in the dynamics of the OH-(H2O)n=1,2 + CH3I reactions.« less

Direct Determination of the Rate Coefficient for the Reaction of OH Radicals with Monoethanol Amine (MEA) from 296 to 510 K.

PubMed

Onel, L; Blitz, M A; Seakins, P W

2012-04-05

Monoethanol amine (H2NCH2CH2OH, MEA) has been proposed for large-scale use in carbon capture and storage. We present the first absolute, temperature-dependent determination of the rate coefficient for the reaction of OH with MEA using laser flash photolysis for OH generation, monitoring OH removal by laser-induced fluorescence. The room-temperature rate coefficient is determined to be (7.61 ± 0.76) × 10(-11) cm(3) molecule(-1) s(-1), and the rate coefficient decreases by about 40% by 510 K. The temperature dependence of the rate coefficient is given by k1= (7.73 ± 0.24) × 10(-11)(T/295)(-(0.79±0.11)) cm(3) molecule(-1) s(-1). The high rate coefficient shows that gas-phase processing in the atmosphere will be competitive with uptake onto aerosols.

Sonochemiluminescence of lucigenin: Evidence of superoxide radical anion formation by ultrasonic irradiation

NASA Astrophysics Data System (ADS)

Matsuoka, Masanori; Takahashi, Fumiki; Asakura, Yoshiyuki; Jin, Jiye

2016-07-01

The sonochemiluminescence (SCL) behavior of lucigenin (Luc2+) has been studied in aqueous solutions irradiated with 500 kHz ultrasound. Compared with the SCL of a luminol system, a tremendously increased SCL intensity is observed from 50 µM Luc2+ aqueous solution (pH =11) when small amounts of coreactants such as 2-propanol coexist. It is shown that SCL intensity strongly depends on the presence of dissolved gases such as air, O2, N2, and Ar. The highest SCL intensity is obtained in an O2-saturated solution, indicating that molecular oxygen is required to generate SCL. Since SCL intensity is quenched completely in the presence of superoxide dismutase (SOD), an enzyme that can catalyze the disproportionation of O2 •-, the generation of O2 •- in the ultrasonic reaction field is important in the SCL of Luc2+. In this work, the evidence of O2 •- production is examined by a spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as the fluorescent probe. The results indicate that the yield of O2 •- is markedly increased in the O2-saturated solutions when a small amount of 2-propanol coexists, which is consistent with the results of SCL measurements. 2-Propanol in the interfacial region of a cavitation bubble reacts with a hydroxyl radical (•OH) to form a 2-propanol radical, CH3C•(OH)CH3, which can subsequently react with dissolved oxygen to generate O2 •-. The most likely pathways for SCL as well as the spatial distribution of SCL in a microreactor are discussed in this study.

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

DOE PAGES

Porterfield, Jessica P.; Nguyen, Thanh Lam; Baraban, Joshua H.; ...

2015-11-30

Here, the thermal decomposition of cyclohexanone (C 6H 10=O) has been studied in a set of flash-pyrolysis microreactors. Decomposition of the ketone was observed when dilute samples of C 6H 10=O were heated to 1200 K in a continuous flow microreactor. Pyrolysis products were detected and identified by tunable VUV photoionization mass spectroscopy and by photoionization appearance thresholds. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures were roughly 100 Torr, and contact times with the microreactors were roughly 100 μs. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways, all of whichmore » open roughly simultaneously. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C 6H 9OH), is followed by retro-Diels–Alder cleavage to CH 2=CH 2 and CH 2=C(OH)–CH=CH 2. Further isomerization of CH 2=C(OH)–CH=CH 2 to methyl vinyl ketone (CH 3CO–CH=CH 2, MVK) was also observed. Photoionization spectra identified both enols, C 6H 9OH and CH 2=C(OH)–CH=CH 2, and the ionization threshold of C 6H 9OH was measured to be 8.2 ± 0.1 eV. Coupled cluster electronic structure calculations were used to establish the energetics of MVK. The heats of formation of MVK and its enol were calculated to be Δ fH 298(cis-CH 3CO–CH=CH 2) = -26.1 ± 0.5 kcal mol –1 and Δ fH 298(s-cis-1-CH 2=C(OH)–CH=CH 2) = -13.7 ± 0.5 kcal mol –1. The reaction enthalpy Δ rxnH 298(C 6H 10=O → CH 2=CH 2 + s-cis-1-CH 2=C(OH)–CH=CH 2) is 53 ± 1 kcal mol –1 and Δ rxnH 298(C 6H 10=O → CH 2=CH 2 + cis-CH 3CO–CH=CH 2) is 41 ± 1 kcal mol –1. At 1200 K, the products of cyclohexanone pyrolysis were found to be C 6H 9OH, CH 2=C(OH)–CH=CH 2, MVK, CH 2CHCH 2, CO, CH 2=C=O, CH 3, CH 2=C=CH 2, CH 2=CH–CH=CH 2, CH 2=CHCH 2CH 3, CH 2=CH 2, and HC≡CH.« less

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

NASA Technical Reports Server (NTRS)

Wennberg, P. O.; Hanisco, T. F.; Jaegle, L.; Jacob, D. J.; Hintsa, E. J.; Lanzendorf, E. J.; Anderson, J. G.; Gao, R.-S.; Keim, E. R.; Donnelly, S. G.;

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

NASA Technical Reports Server (NTRS)

Wennberg, P. O.; Hanisco, T. F.; Jaegle, L.; Jacob, D. J.; Hintsa, E. J.; Lanzendorf, E. J.; Anderson, J. G.; Gao, R.-S.; Keim, E. R.; Donnelly, S. G.;

Computational Study of Interstellar Glycine Formation Occurring at Radical Surfaces of Water-ice Dust Particles

NASA Astrophysics Data System (ADS)

Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

2012-07-01

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH• radical and H3O+ surface defects. The coupling of incoming CO molecules with the surface OH• radicals on the ice clusters yields the formation of the COOH• radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol-1 and -22 kcal mol-1, respectively. The COOH• radicals couple with incoming NH=CH2 molecules (experimentally detected in the ISM) to form the NHCH2COOH• radical glycine through energy barriers of 12 kcal mol-1, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H3O+ is present, one proton may be barrierless transferred to NH=CH2 to give NH2=CH2 +. This latter may react with the COOH• radical to give the NH2CH2COOH+• glycine radical cation which can then be transformed into the NH2CHC(OH)2 +• species (the most stable form of glycine in its radical cation state) or into the NH2CHCOOH• neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H3O+ ions to facilitate chemical processes by proton transfer (i.e., acting as acidic catalysts) is highlighted, and plausible ways of their formation at the water-ice surface in the ISM are also discussed.

Rotational and translational effects in collisions of electronically excited diatomic hydrides

NASA Technical Reports Server (NTRS)

Crosley, David R.

1988-01-01

Collisional quenching and vibrational energy proceed competitively with rotational energy transfer for several excited states of the diatomic radicals OH, NH, and CH. This occurs for a wide variety of molecular collision partners. This phenomenon permits the examination of the influence of rotational motion on the collision dynamics of these theoretically tractable species. Measurements can also be made as a function of temperature, i.e., collision velocity. In OH (sup 2 sigma +), both vibrational transfer and quenching are found to decrease with an increase in rotational level, while quenching decreases with increasing temperature. This behavior indicates that for OH, anisotropic attractive forces govern the entrance channel dynamics for these collisions. The quenching of NH (sup 3 pi sub i) by many (although not all) collision partners also decreases with increasing rotational and translational energy, and NH (sup 1 pi) behaves much like OH (sup 2 sigma +). However, the quenching of CH (sup 2 delta) appears to decrease with increasing rotation but increases with increasing temperature, suggesting in this case anisotropic forces involving a barrier or repulsive wall. Such similarities and differences should furnish useful comparisons with both simple and detailed theoretical pictures of the appropriate collision dynamics.

[Spectroscopic Diagnosis of Two-Dimensional Distribution of OH Radicals in Wire-Plate Pulsed Corona Discharge Reactor].

PubMed

Jiang, Jian-ping; Luo, Zhong-yang; Xuan, Jian-yong; Zhao, Lei; Fang, Meng-xiang; Gao, Xiang

2015-10-01

Pulsed corona discharge in atmosphere has been widely regarded as an efficient flue gas treatment technology for the generation of active radical species, such as the OH radicals. The spatial distribution of OH radicals generated by pulsed corona discharge plays an important role in decomposing pollutants. The two-dimensional (2-D) distribution of OH radicals of positive wire--plate pulsed corona discharge was detected using laser-induced fluorescence (LIF). The influence of relative humidity (RH) and oxygen concentration on the 2-D distribution of OH radicals were investigated. The results indicated that the 2-D distribution of OH radicals was characterized by a fan-shaped distribution from the wire electrode to plate electrode, and both the maximum values of vertical length and horizontal width of the fan area was less than 1 cm. The 2-D distribution area of OH radicals increased significantly with increasing the RH and the optimum condition was 65% RH. The optimal level of the oxygen concentration for the 2-D distribution area of OH radicals was 2%. The process of OH radical generation and 2-D distribution area of OH radicals were significantly interfered when the oxygen concentration was larger than 15%. The total quenching rate coefficients for different RH values and oxygen concentration in this study were used to calculate the fluorescence yield of OH radical. The fluorescence yield, which is the ratio between the emission rate (Einstein coefficient) and the sum of the emission rate and quenching rate, was used to normalize the 2-D distribution area of OH radicals. The fluorescence yield of OH radical decreased with increasing the RH and oxygen concentration linearly and rapidly. It was also found that compared with the RH, the influence of the oxygen concentration had more notable effect on the fluorescence yield of OH radical and 2-D distribution area of OH radicals.

Rate constants and temperature dependences for the reactions of hydroxyl radical with several halogenated methanes, ethanes, and propanes by relative rate measurements

NASA Technical Reports Server (NTRS)

Hsu, K.-J.; DeMore, W. B.

1995-01-01

Rate constants of 15 OH reactions with halogen-substituted alkanes, C1 to C3, were studied using a relative rate technique in the temperature range 283-403 K. Compounds studied were CHF2Cl (22), CHF2Br (22B), CH3F (41), CH2F2 (32), CHF3 (23), CHClFCCl2F (122a), CHCl2CF3 (123), CHClFCF3 (124), CH3CF3 (143a), CH3CH2F (161), CF3CHFCF3 (227ea), CF3CH2CF3 (236fa), CF3CHFCHF2 (236ea), and CHF2CF2CH2F (245ca). Using CH4, CH3CCl3, CF3CF2H, and C2H6 as primary reference standards (JPL 92-20 rate constants), absolute rate constants are derived. Results are in good agreement with previous experimental results for six of the compounds studied, including CHF2Cl, CHF2Br, CH2F2, CH3CF3, CHFClCFCl2, and CF3CHFCF3. For the remainder the relative rate constants are lower than those derived from experiments in which OH loss was used to measure the reaction rate. Comparisons of the derived Arrhenius A factors with previous literature transition-state calculations show order of magnitude agreement in most cases. However, the experimental A factors show a much closer proportionality to the number of H atoms in the molecule than is evident from the transition state calculations. For most of the compounds studied, an A factor of (8 +/- 3)E-13 cm(exp 3)/(molecule s) per C-H bond is observed. A new measurement of the ratio k(CH3CCl3)/k(CH4) is reported that is in good agreement with previous data.

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor.

PubMed

Porterfield, Jessica P; Nguyen, Thanh Lam; Baraban, Joshua H; Buckingham, Grant T; Troy, Tyler P; Kostko, Oleg; Ahmed, Musahid; Stanton, John F; Daily, John W; Ellison, G Barney

2015-12-24

The thermal decomposition of cyclohexanone (C6H10═O) has been studied in a set of flash-pyrolysis microreactors. Decomposition of the ketone was observed when dilute samples of C6H10═O were heated to 1200 K in a continuous flow microreactor. Pyrolysis products were detected and identified by tunable VUV photoionization mass spectroscopy and by photoionization appearance thresholds. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures were roughly 100 Torr, and contact times with the microreactors were roughly 100 μs. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways, all of which open roughly simultaneously. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C6H9OH), is followed by retro-Diels-Alder cleavage to CH2═CH2 and CH2═C(OH)-CH═CH2. Further isomerization of CH2═C(OH)-CH═CH2 to methyl vinyl ketone (CH3CO-CH═CH2, MVK) was also observed. Photoionization spectra identified both enols, C6H9OH and CH2═C(OH)-CH═CH2, and the ionization threshold of C6H9OH was measured to be 8.2 ± 0.1 eV. Coupled cluster electronic structure calculations were used to establish the energetics of MVK. The heats of formation of MVK and its enol were calculated to be ΔfH298(cis-CH3CO-CH═CH2) = -26.1 ± 0.5 kcal mol(-1) and ΔfH298(s-cis-1-CH2═C(OH)-CH═CH2) = -13.7 ± 0.5 kcal mol(-1). The reaction enthalpy ΔrxnH298(C6H10═O → CH2═CH2 + s-cis-1-CH2═C(OH)-CH═CH2) is 53 ± 1 kcal mol(-1) and ΔrxnH298(C6H10═O → CH2═CH2 + cis-CH3CO-CH═CH2) is 41 ± 1 kcal mol(-1). At 1200 K, the products of cyclohexanone pyrolysis were found to be C6H9OH, CH2═C(OH)-CH═CH2, MVK, CH2CHCH2, CO, CH2═C═O, CH3, CH2═C═CH2, CH2═CH-CH═CH2, CH2═CHCH2CH3, CH2═CH2, and HC≡CH.

Ionizing radiation and tritium transmutation both cause formation of 5-hydroxymethyl-2'-deoxyuridine in cellular DNA.

PubMed Central

Teebor, G W; Frenkel, K; Goldstein, M S

1984-01-01

HeLa cells grown in the presence of [methyl-3H]thymidine contained large amounts of 5-hydroxymethyl-2'-deoxyuridine (HMdU) in their DNA. When the cells were grown in [6-3H]thymidine and their DNA was labeled to the same specific activity, no HMdU was present. When such [6-3H]thymidine-labeled cells were exposed to increasing amounts of gamma-radiation, small but increasing amounts of HMdU were formed in their DNA. This indicates that HMdU can be formed in DNA by two distinct mechanisms. The first is the result of the transmutation of 3H to 3He (beta decay) in the methyl group of thymidine, leading to formation of a carbocation. This short-lived ion reacts with hydroxide ions of water, yielding the hydroxymethyl group. HMdU that is formed by this mechanism is formed at the rate of beta decay of 3H. It appears only in [methyl-3H]thymidine residues and is present in the DNA of both nonirradiated and gamma-irradiated cells. The second mechanism is the result of the radiolysis of water caused by ionizing radiation. The resultant radical species, particularly hydroxyl radicals, may react with many sites on DNA. When the methyl group of thymine is attacked by hydroxyl radicals, the hydroxymethyl group is formed. The formation of HMdU by this mechanism was detected only when [6-3H]thymidine-labeled cells were used, since transmutation of 3H in position 6 of thymine cannot yield HMdU. PMID:6582490

Ionizing radiation and tritium transmutation both cause formation of 5-hydroxymethyl-2'-deoxyuridine in cellular DNA.

PubMed

Teebor, G W; Frenkel, K; Goldstein, M S

1984-01-01

HeLa cells grown in the presence of [methyl-3H]thymidine contained large amounts of 5-hydroxymethyl-2'-deoxyuridine (HMdU) in their DNA. When the cells were grown in [6-3H]thymidine and their DNA was labeled to the same specific activity, no HMdU was present. When such [6-3H]thymidine-labeled cells were exposed to increasing amounts of gamma-radiation, small but increasing amounts of HMdU were formed in their DNA. This indicates that HMdU can be formed in DNA by two distinct mechanisms. The first is the result of the transmutation of 3H to 3He (beta decay) in the methyl group of thymidine, leading to formation of a carbocation. This short-lived ion reacts with hydroxide ions of water, yielding the hydroxymethyl group. HMdU that is formed by this mechanism is formed at the rate of beta decay of 3H. It appears only in [methyl-3H]thymidine residues and is present in the DNA of both nonirradiated and gamma-irradiated cells. The second mechanism is the result of the radiolysis of water caused by ionizing radiation. The resultant radical species, particularly hydroxyl radicals, may react with many sites on DNA. When the methyl group of thymine is attacked by hydroxyl radicals, the hydroxymethyl group is formed. The formation of HMdU by this mechanism was detected only when [6-3H]thymidine-labeled cells were used, since transmutation of 3H in position 6 of thymine cannot yield HMdU.

Exploring the plasma chemistry in microwave chemical vapor deposition of diamond from C/H/O gas mixtures.

PubMed

Kelly, Mark W; Richley, James C; Western, Colin M; Ashfold, Michael N R; Mankelevich, Yuri A

2012-09-27

Microwave (MW)-activated CH(4)/CO(2)/H(2) gas mixtures operating under conditions relevant to diamond chemical vapor deposition (i.e., X(C/Σ) = X(elem)(C)/(X(elem)(C) + X(elem)(O)) ≈ 0.5, H(2) mole fraction = 0.3, pressure, p = 150 Torr, and input power, P = 1 kW) have been explored in detail by a combination of spatially resolved absorption measurements (of CH, C(2)(a), and OH radicals and H(n = 2) atoms) within the hot plasma region and companion 2-dimensional modeling of the plasma. CO and H(2) are identified as the dominant species in the plasma core. The lower thermal conductivity of such a mixture (cf. the H(2)-rich plasmas used in most diamond chemical vapor deposition) accounts for the finding that CH(4)/CO(2)/H(2) plasmas can yield similar maximal gas temperatures and diamond growth rates at lower input powers than traditional CH(4)/H(2) plasmas. The plasma chemistry and composition is seen to switch upon changing from oxygen-rich (X(C/Σ) < 0.5) to carbon-rich (X(C/Σ) > 0.5) source gas mixtures and, by comparing CH(4)/CO(2)/H(2) (X(C/Σ) = 0.5) and CO/H(2) plasmas, to be sensitive to the choice of source gas (by virtue of the different prevailing gas activation mechanisms), in contrast to C/H process gas mixtures. CH(3) radicals are identified as the most abundant C(1)H(x) [x = 0-3] species near the growing diamond surface within the process window for successful diamond growth (X(C/Σ) ≈ 0.5-0.54) identified by Bachmann et al. (Diamond Relat. Mater.1991, 1, 1). This, and the findings of similar maximal gas temperatures (T(gas) ~2800-3000 K) and H atom mole fractions (X(H)~5-10%) to those found in MW-activated C/H plasmas, points to the prevalence of similar CH(3) radical based diamond growth mechanisms in both C/H and C/H/O plasmas.

Chemical Reactivity of Formaldehyde in FeAlP0{sub 4} Sieve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeom, Young-Hoon; Ulagappan, Nagappan; Frei, Heinz

2001-03-12

Formaldehyde gas loaded into framework Fe aluminophosphate sieve (FeAlP O4-5) at 250 K was found to react with adsorbed H2O, CH3OH, H2O2, or lattice OH groups to yield the corresponding addition product, namely CH2(OH)2, CH3OCH2OH, HO 2CH2OH, or POCH2OH, respectively. Reactions were monitored in situ by static FT-IR spectroscopy, and assignments are based on experiments with CD2=0 and CD3OD. Most efficient was the reaction with H2O2 as indicated by the fact that HO2CH2OH was formed at the exclusion of CH2(OH)2 and POCH2OH when adsorbing formaldehyde onto a sieve loaded with H2O2 and H2O. Methoxymethanol, methanediol, and POCH2OH were stable atmore » 250 K, but dissociated above 0 degrees C under release of formaldehyde. Hydromethyl hydroperoxide disproportionates to formic acid and water. Under 355 nm irradiation in FeAlPO4 sieve, HO2CH2OH was found to undergo efficient photofragmentation.« less

Bond Dissociation Free Energies (BDFEs) of the Acidic H-A Bonds in HA(*)(-) Radical Anions by Three Different Pathways.

PubMed

Zhao, Yongyu; Bordwell, Frederick G.

1996-09-20

Cleavage of radical anions, HA(*)(-), have been considered to give either H(*) + A(-) (path a) or H(-) + A(*) (path b), and factors determining the preferred mode of cleavage have been discussed. It is conceivable that cleavage to give a proton and a radical dianion, HA(*)(-) right harpoon over left harpoon H(+) + A(*)(2)(-) (path c), might also be feasible. A method, based on a thermodynamic cycle, to estimate the bond dissociation free energy (BDFE) by path c has been devised. Comparison of the BDFEs for cleavage of the radical anions derived from 24 nitroaromatic OH, SH, NH, and CH acids by paths a, b, c has shown that path c is favored thermodynamically.

Observation of OH radicals produced by pulsed discharges on the surface of a liquid

NASA Astrophysics Data System (ADS)

Kanazawa, Seiji; Kawano, Hirokazu; Watanabe, Satoshi; Furuki, Takashi; Akamine, Shuichi; Ichiki, Ryuta; Ohkubo, Toshikazu; Kocik, Marek; Mizeraczyk, Jerzy

2011-06-01

The hydroxyl radical (OH) plays an important role in plasma chemistry at atmospheric pressure. OH radicals have a higher oxidation potential compared with other oxidative species such as free radical O, atomic oxygen, hydroperoxyl radical (HO2), hydrogen peroxide(H2O2) and ozone. In this study, surface discharges on liquids (water and its solutions) were investigated experimentally. A pulsed streamer discharge was generated on the liquid surface using a point-to-plane electrode geometry. The primary generation process of OH radicals is closely related to the streamer propagation, and the subsequent secondary process after the discharge has an influence on the chemical reaction. Taking into account the timescale of these processes, we investigated the behavior of OH radicals using two different diagnostic methods. Time evolution of the ground-state OH radicals above the liquid surface after the discharge was observed by a laser-induced fluorescence (LIF) technique. In order to observe the ground-state OH, an OH [A 2∑+(v' = 1) <-- X 2Π(v'' = 0)] system at 282 nm was used. As the secondary process, a portion of OH radicals diffused from gas phase to the liquid surface and dissolved in the liquid. These dissolved OH radicals were measured by a chemical probe method. Terephthalic acid was used as an OH radical trap and fluorescence of the resulting 2-hydroxyterephthalic acid was measured. This paper directly presents visualization of OH radicals over the liquid surface by means of LIF, and indirectly describes OH radicals dissolved in water by means of a chemical method.

Atmospheric fates of Criegee intermediates in the ozonolysis of isoprene.

PubMed

Nguyen, Tran B; Tyndall, Geoffrey S; Crounse, John D; Teng, Alexander P; Bates, Kelvin H; Schwantes, Rebecca H; Coggon, Matthew M; Zhang, Li; Feiner, Philip; Milller, David O; Skog, Kate M; Rivera-Rios, Jean C; Dorris, Matthew; Olson, Kevin F; Koss, Abigail; Wild, Robert J; Brown, Steven S; Goldstein, Allen H; de Gouw, Joost A; Brune, William H; Keutsch, Frank N; Seinfeld, John H; Wennberg, Paul O

2016-04-21

We use a large laboratory, modeling, and field dataset to investigate the isoprene + O3 reaction, with the goal of better understanding the fates of the C1 and C4 Criegee intermediates in the atmosphere. Although ozonolysis can produce several distinct Criegee intermediates, the C1 stabilized Criegee (CH2OO, 61 ± 9%) is the only one observed to react bimolecularly. We suggest that the C4 Criegees have a low stabilization fraction and propose pathways for their decomposition. Both prompt and non-prompt reactions are important in the production of OH (28% ± 5%) and formaldehyde (81% ± 16%). The yields of unimolecular products (OH, formaldehyde, methacrolein (42 ± 6%) and methyl vinyl ketone (18 ± 6%)) are fairly insensitive to water, i.e., changes in yields in response to water vapor (≤4% absolute) are within the error of the analysis. We propose a comprehensive reaction mechanism that can be incorporated into atmospheric models, which reproduces laboratory data over a wide range of relative humidities. The mechanism proposes that CH2OO + H2O (k(H2O)∼ 1 × 10(-15) cm(3) molec(-1) s(-1)) yields 73% hydroxymethyl hydroperoxide (HMHP), 6% formaldehyde + H2O2, and 21% formic acid + H2O; and CH2OO + (H2O)2 (k(H2O)2∼ 1 × 10(-12) cm(3) molec(-1) s(-1)) yields 40% HMHP, 6% formaldehyde + H2O2, and 54% formic acid + H2O. Competitive rate determinations (kSO2/k(H2O)n=1,2∼ 2.2 (±0.3) × 10(4)) and field observations suggest that water vapor is a sink for greater than 98% of CH2OO in a Southeastern US forest, even during pollution episodes ([SO2] ∼ 10 ppb). The importance of the CH2OO + (H2O)n reaction is demonstrated by high HMHP mixing ratios observed over the forest canopy. We find that CH2OO does not substantially affect the lifetime of SO2 or HCOOH in the Southeast US, e.g., CH2OO + SO2 reaction is a minor contribution (<6%) to sulfate formation. Extrapolating, these results imply that sulfate production by stabilized Criegees is likely unimportant in regions dominated by the reactivity of ozone with isoprene. In contrast, hydroperoxide, organic acid, and formaldehyde formation from isoprene ozonolysis in those areas may be significant.

Dry Reforming of Methane in a Gliding Arc Plasmatron: Towards a Better Understanding of the Plasma Chemistry.

PubMed

Cleiren, Emelie; Heijkers, Stijn; Ramakers, Marleen; Bogaerts, Annemie

2017-10-23

Dry reforming of methane (DRM) in a gliding arc plasmatron is studied for different CH 4 fractions in the mixture. The CO 2 and CH 4 conversions reach their highest values of approximately 18 and 10 %, respectively, at 25 % CH 4 in the gas mixture, corresponding to an overall energy cost of 10 kJ L -1 (or 2.5 eV per molecule) and an energy efficiency of 66 %. CO and H 2 are the major products, with the formation of smaller fractions of C 2 H x (x=2, 4, or 6) compounds and H 2 O. A chemical kinetics model is used to investigate the underlying chemical processes. The calculated CO 2 and CH 4 conversion and the energy efficiency are in good agreement with the experimental data. The model calculations reveal that the reaction of CO 2 (mainly at vibrationally excited levels) with H radicals is mainly responsible for the CO 2 conversion, especially at higher CH 4 fractions in the mixture, which explains why the CO 2 conversion increases with increasing CH 4 fraction. The main process responsible for CH 4 conversion is the reaction with OH radicals. The excellent energy efficiency can be explained by the non-equilibrium character of the plasma, in which the electrons mainly activate the gas molecules, and by the important role of the vibrational kinetics of CO 2 . The results demonstrate that a gliding arc plasmatron is very promising for DRM. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational study of the reactions of methanol with the hydroperoxyl and methyl radicals. 1. Accurate thermochemistry and barrier heights.

PubMed

Alecu, I M; Truhlar, Donald G

2011-04-07

The reactions of CH(3)OH with the HO(2) and CH(3) radicals are important in the combustion of methanol and are prototypes for reactions of heavier alcohols in biofuels. The reaction energies and barrier heights for these reaction systems are computed with CCSD(T) theory extrapolated to the complete basis set limit using correlation-consistent basis sets, both augmented and unaugmented, and further refined by including a fully coupled treatment of the connected triple excitations, a second-order perturbative treatment of quadruple excitations (by CCSDT(2)(Q)), core-valence corrections, and scalar relativistic effects. It is shown that the M08-HX and M08-SO hybrid meta-GGA density functionals can achieve sub-kcal mol(-1) agreement with the high-level ab initio results, identifying these functionals as important potential candidates for direct dynamics studies on the rates of these and homologous reaction systems.

The effect of natural iron oxide and oxalic acid on the photocatalytic degradation of isoproturon: a kinetics and analytical study.

PubMed

Boucheloukh, H; Remache, W; Parrino, F; Sehili, T; Mechakra, H

2017-05-17

The photocatalytic degradation of isoproturon, a persistent toxic herbicide, was investigated in the presence of natural iron oxide and oxalic acid and under UV irradiation. The influence of the relevant parameters such as the pH and the iron oxide and oxalic acid concentrations has been studied. The presence of natural iron oxide and oxalic acid in the system effectively allow the degradation of isoproturon, whereas the presence of t-butyl alcohol adversely affects the phototransformation of the target pollutant, thus indicating that an OH radical initiated the degradation mechanism. The degradation mechanism of isoproturon was investigated by means of GC-MS analysis. Oxidation of both the terminal N-(CH 3 ) 2 and isopropyl groups is the initial process leading to N-monodemethylated (NHCH 3 ), N-formyl (N(CH 3 )CHO), and CHCH 3 OH as the main intermediates. The substitution of the isopropyl group by an OH group is also observed as a side process.

A Computational Tale of Two Enzymes: Glycerol Dehydration With or Without B12.

PubMed

Kovačević, Borislav; Barić, Danijela; Babic, Darko; Bilić, Luka; Hanževački, Marko; Sandala, Gregory M; Radom, Leo; Smith, David M

2018-06-12

We present a series of QM/MM calculations aimed at understanding the mechanism of the biological dehydration of glycerol. Strikingly and unusually, this process is catalyzed by two different radical enzymes, one of which is a coenzyme-B 12 - dependent enzyme and the other which is a coenzyme-B 12 - independent enzyme. We show that glycerol dehydration in the presence of the coenzyme-B 12 -dependent enzyme proceeds via a 1,2-OH shift, which benefits from a significant catalytic reduction in the barrier. In contrast, the same reaction in the presence of the coenzyme-B 12 -independent enzyme is unlikely to involve the 1,2-OH shift; instead, a strong preference for direct loss of water from a radical intermediate is indicated. We show that this preference and, ultimately the evolution of such enzymes, is strongly linked with the reactivities of the species responsible for abstracting a hydrogen atom from the substrate. It appears that the hydrogen re-abstraction step involving the product-related radical is fundamental to the mechanistic preference. The unconventional 1,2-OH shift seems to be required to generate a product-related radical of sufficient reactivity to cleave the relatively inactive C-H bond arising from the B 12 cofactor. In the absence of B 12 , it is the relatively weak S-H bond of a cysteine residue that must be homolyzed. Such a transformation is much less demanding and its inclusion apparently enables a simpler overall dehydration mechanism.

Mixing Ratios of CO, CO2, CH4, and Isotope Ratios of Associated 13C, 18O, and 2H in Air Samples from Niwot Ridge, Colorado\\, and Montana de Oro, California, USA (January 2004)

DOE Data Explorer

Tyler, Stanley C. [Department of Earth System Science, University of California, Irvine, CA (USA)

2004-01-01

Air samples from Niwot Ridge, Colorado (41°N, 105°W) and Montaña de Oro, CA (35°N, 121°W) have been collected at approximately semi-monthly to monthly intervals since the mid 1990s. Such time series can provide information about: (1) seasonal cycling of CO, CO2, and CH4 sources and sinks in background air, (2) trends in atmospheric concentrations of CO2 and CH4 and their stable carbon, oxygen, and hydrogen isotopes, (3) the distribution of the hydroxyl (OH) radical in the atmosphere, and (4) the role of the terrestrial biosphere as a source or sink of atmospheric CO2.

Comments on PDF methods

NASA Technical Reports Server (NTRS)

Chen, J.-Y.

1992-01-01

Viewgraphs are presented on the following topics: the grand challenge of combustion engineering; research of probability density function (PDF) methods at Sandia; experiments of turbulent jet flames (Masri and Dibble, 1988); departures from chemical equilibrium; modeling turbulent reacting flows; superequilibrium OH radical; pdf modeling of turbulent jet flames; scatter plot for CH4 (methane) and O2 (oxygen); methanol turbulent jet flames; comparisons between predictions and experimental data; and turbulent C2H4 jet flames.

Desorption induced by solar wind electrons analogs in methanol ice

NASA Astrophysics Data System (ADS)

Bergantini, A. S.; Pilling, Sergio; Andrade, Diana; Boechat-Roberty, Heloisa Maria; Rocco, Maria Luiza M.

2012-07-01

Methanol (CH _{3}OH) has been detected in several environments in space, such as comets, asteroids, grains of interstellar dust and protostars forming regions such as W33A and RAFGL 7009. CH _{3}OH is the most abundant molecule (after H _{2}O) found in solid state in these objects. The action of ionizing agents in such environments induces changes in methanol ice which lead to the formation ionic species, reactive radicals and new compounds. In this experiment, frozen methanol (142 K) was irradiated with an electron beam (energies from 650 to 1500 eV) inside an ultra-high vacuum chamber (˜ 1×10^{-10} mbar), at the Surface Chemistry Laboratory of Federal University of Rio de Janeiro (LaQuiS/ UFRJ). The beam simulates the action of electrons from solar wind in frozen surfaces like as comets, asteroids and moons. Results show the desorption of several new ionized species such as (CH _{3}OH)H ^{+}, H _{2}COH ^{+}, C _{2}H _{3} ^{+}, HCO ^{+}, CO ^{+}, O ^{+}, C ^{+}, H ^{+}. The individual desorbed ion rate was calculated. The determined half-life of frozen methanol in Earth orbit due to the electron bombardment was about 4.2 yr. The ionic desorption rate is an important parameter in surface chemistry, since these parameters are often approximated in chemical evolution models of astrophysical environments, due to the lack of laboratory data.

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

NASA Technical Reports Server (NTRS)

Wennberg, P. O.; Hanisco, T. F.; Jaegle, L.; Jacob, D. J.; Hintsa, E. J.; Lanzendorf, E. J.; Anderson, J. G.; Gao, R.-S.; Keim, E. R.; Donnelly, S. G.;

Thermal decomposition and oxidation of CH3OH.

PubMed

Lee, Pei-Fang; Matsui, Hiroyuki; Xu, Ding-Wei; Wang, Niann-Shiah

2013-01-24

Thermal decomposition of CH(3)OH diluted in Ar has been studied by monitoring H atoms behind reflected shock waves of 100 ppm CH(3)OH + Ar. The total decomposition rate k(1) for CH(3)OH + M → products obtained in this study is expressed as, ln(k(1)/cm(3) molecule(-1) s(-1)) = -(14.81 ± 1.22) - (38.86 ± 1.82) × 10(3)/T, over 1359-1644 K. The present result on k(1) is indicated to be substantially smaller than the extrapolation of the most of the previous experimental data but consistent with the published theoretical results [Faraday Discuss. 2002, 119, 191-205 and J. Phys. Chem. A 2007, 111, 3932-3950]. Oxidation of CH(3)OH has been studied also by monitoring H atoms behind shock waves of (0.35-100) ppm CH(3)OH + (100-400) ppm O(2) + Ar. For the low concentration CH(3)OH (below 10 ppm) + O(2) mixtures, the initial concentration of CH(3)OH is evaluated by comparing evolutions of H atoms in the same concentration of CH(3)OH with addition of 300 ppm H(2) diluted in Ar. The branching fraction for CH(3)OH + Ar → (1)CH(2) + H(2)O + Ar has been quantitatively evaluated from this comparative measurements with using recent experimental result on the yield of H atoms in the reaction of (1,3)CH(2) + O(2) [J. Phys. Chem. A 2012, 116, 9245-9254]; i.e., the branching fraction for the above reaction is evaluated as, φ(1a) = 0.20 ± 0.04 at T = 1880-2050 K, in the 1.3 and 3.5 ppm CH(3)OH + 100 ppm O(2) samples. An extended reaction mechanism for the pyrolysis and oxidation of CH(3)OH is constructed based on the results of the present study combined with the oxidation mechanism of natural gas [GRI-Mech 3.0]; evolution of H atoms can be predicted very well with this new reaction scheme over a wide concentration range for the pyrolysis (0.36-100 ppm CH(3)OH), and oxidation (0.36-100 ppm CH(3)OH + 100/400 ppm O(2)) of methanol.

OH and CH luminescence in opposed flow methane oxy-flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Leo, Maurizio; Saveliev, Alexei; Kennedy, Lawrence A.

Emission spectroscopy is a 2-D nonintrusive diagnostic technique that offers spatially resolved data for combustion optimization and control. The UV and visible chemiluminescence of the excited radicals CH(A{sup 2}{delta},B{sup 2}{sigma}{sup -}) and OH(A{sup 2}{sigma}{sup +}) is studied experimentally and numerically in opposed-flow diffusion flames of methane and oxygen-enriched air. The oxidized oxygen content is varied from 21 to 100% while the range of the studied strain rates spans from 20 to 40 s{sup -1}. The spectrally resolved imaging is obtained by two different methods: scattering through a grating monochromator and interposition of interference filters along the optical path. Absolute measuredmore » chemiluminescence intensities, coupled with a numerical model based on the opposed flow flame code, are used to evaluate the chemical kinetics of the excited species. The predictions of the selected model are in good agreement with the experimental data over the range of the studied flame conditions. (author)« less

Kinetics and products of the OH radical-initiated reaction of 3-methyl-2-butenal.

PubMed

Tuazon, Ernesto C; Aschmann, Sara M; Nishino, Noriko; Arey, Janet; Atkinson, Roger

2005-06-07

Kinetics and products of the gas-phase reaction of OH radicals with 3-methyl-2-butenal [(CH3)2C=CHCHO] have been investigated at room temperature and atmospheric pressure of air. Using a relative rate method with methacrolein as the reference compound, a rate constant for the reaction of OH radicals with 3-methyl-2-butenal of (6.21 +/- 0.18) x 10(-11) cm3 molecule(-1) s(-1) at 296 +/- 2 K was measured, where the indicated error does not include the uncertainty in the rate constant for the methacrolein reference compound. Products of this reaction were investigated using in situ Fourier transform infrared (FT-IR) spectroscopy and solid phase microextraction (SPME) fibers coated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for on-fiber derivatization of carbonyl compounds, with subsequent thermal desorption and analysis by gas chromatography. The products observed and the molar formation yields were: glyoxal, 40 +/- 3%; acetone, 74 +/- 6%; 2-hydroxy-2-methylpropanal, 4.6 +/- 0.7%; CO2, 39% initially, decreasing to 30% at greater extents of reaction; peroxyacyl nitrate(s) [RC(O)OONO2], 5-8%, increasing with the extent of reaction and with the sum of the CO2 and RC(O)OONO2 yields being 38 +/- 6%; and organic nitrates [RONO2], 8.5 +/- 2.3%. The formation of these products is readily explained by a reaction mechanism based on those previously formulated for the corresponding reactions of the alpha,beta-unsaturated aldehydes acrolein, crotonaldehyde and methacrolein. Based on the mechanism proposed, at room temperature H-atom abstraction from the CHO group accounts for 40 +/- 6% of the overall reaction, and OH radical addition to the carbon atoms of the C=C bond accounts for 53 +/- 4% of the overall reaction. Hence 93 +/- 8% of the reaction products and pathways are accounted for.

Theoretical study on the gas-phase reaction mechanism between palladium monoxide and methane.

PubMed

Yang, Hua-Qing; Hu, Chang-Wei; Gao, Chao; Yang, Meng-Yao; Li, Fang-Ming; Li, Cai-Qin; Li, Xiang-Yuan

2011-12-01

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH(2) + H(2)O, whereas the minor channel results in the products Pd + CH(3)OH, CH(2)OPd + H(2), and PdOH + CH(3). The minimum energy reaction pathway for the formation of main products (PdCH(2) + H(2)O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH(3)PdOH and CH(3)Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH(3) PdOH → RS-2-TS1cb → RS-CH(2)Pd(H)OH with the rate constant of k = 1.48 × 10(12) exp(-93,930/RT). For the first C-H bond cleavage, both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) affect the activation energy ΔE(≠), with ΔE(≠)(int) in favor of the direct oxidative insertion. On the other hand, in the PdCH(2) + H(2) O reaction, the main products are Pd + CH(3)OH, and CH(3)PdOH is the energetically preferred intermediate. In the CH(2)OPd + H(2) reaction, the main products are Pd + CH(3)OH with the energetically preferred intermediate H(2)PdOCH(2). In the Pd + CH(3)OH reaction, the main products are CH(2)OPd + H(2), and H(2)PdOCH(2) is the energetically predominant intermediate. The intermediates, PdCH(2), H(2) PdCO, and t-HPdCHO are energetically preferred in the PdC + H(2), PdCO + H(2), and H(2)Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO. Copyright © 2011 Wiley Periodicals, Inc.

Reactions of small organic molecules on silver(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayre, C.R.

1992-01-01

The interaction of two pairs of molecules (1) acetone (CH[sub 3])[sub 2]C=O and isobutylene (CH[sub 3])[sub 2] C=CH[sub 2] and (2) 1,2-propanediol CH[sub 3] CH (OH)CH[sub 2]OH and 1,3-propanediol HOCH[sub 2]CH[sub 2]CH[sub 2]OH with clean and oxygen-activated Ag(110) has been explored to investigate the effects of molecular structure on reactivity. Experimental techniques employed include temperature programmed reaction spectroscopy, isotopic labelling, surface displacement reactions, and electron energy loss spectroscopy. Acetone and isobutylene were studied to explore the relative importance of C=O and C=C bonds in governing the reactivity of structurally similar compounds. Nucleophilic attack by oxygen at the electron-deficient carbonyl carbonmore » in acetone results in reversible formation of the metallacycle (CH[sub 3])[sub 2]COO[sub (a)] at 110 K. Upon heating C-H bond activation by O[sub (a)] occurs near 215 K to yield acetone enolate CH[sub 2]=C(CH[sub 3])O[sub (a)] and evolve H[sub 2]O[sub (g)]. Atomic oxygen activates methyl C-H bonds in isobutylene via an acid-base mechanism. Although the major products are CO[sub 2(g)] and H[sub 2]O[sub (g)], a small amount of (CH[sub 3])[sub 2]C=CH[sub 2(g)] evolves near 310 K. Evidence for the formation of [pi]-2-methylallyl CH[sub 3]C(CH[sub 2])[sub 2(a)] and trimethylenementhane C(CH[sub 2])[sub 3(a)] is presented. The reaction of 1,2-propanediol CH[sub 3] CH(OH)CH[sub 2] OH with oxygen-activated Ag(110) has been compared with that of 1,3-propanediol HOCH[sub 2]CH[sub 2]CH[sub 2]OH to evaluate the effects of varying the position of O-H bonds in both diols to produce the corresponding dialkoxides.« less

Unimolecular thermal decomposition of phenol and d5-phenol: Direct observation of cyclopentadiene formation via cyclohexadienone

NASA Astrophysics Data System (ADS)

Scheer, Adam M.; Mukarakate, Calvin; Robichaud, David J.; Nimlos, Mark R.; Carstensen, Hans-Heinrich; Barney Ellison, G.

2012-01-01

The pyrolyses of phenol and d5-phenol (C6H5OH and C6D5OH) have been studied using a high temperature, microtubular (μtubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy. Gas exiting the heated reactor (375 K-1575 K) is subject to a free expansion after a residence time in the μtubular reactor of approximately 50-100 μs. The expansion from the reactor into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. We find that the initial decomposition steps at the onset of phenol pyrolysis are enol/keto tautomerization to form cyclohexadienone followed by decarbonylation to produce cyclopentadiene; C6H5OH → c-C6H6 = O → c-C5H6 + CO. The cyclopentadiene loses a H atom to generate the cyclopentadienyl radical which further decomposes to acetylene and propargyl radical; c-C5H6 → c-C5H5 + H → HC≡CH + HCCCH2. At higher temperatures, hydrogen loss from the PhO-H group to form phenoxy radical followed by CO ejection to generate the cyclopentadienyl radical likely contributes to the product distribution; C6H5O-H → C6H5O + H → c-C5H5 + CO. The direct decarbonylation reaction remains an important channel in the thermal decomposition mechanisms of the dihydroxybenzenes. Both catechol (o-HO-C6H4-OH) and hydroquinone (p-HO-C6H4-OH) are shown to undergo decarbonylation at the onset of pyrolysis to form hydroxycyclopentadiene. In the case of catechol, we observe that water loss is also an important decomposition channel at the onset of pyrolysis.

Aqueous-phase source of formic acid in clouds

NASA Technical Reports Server (NTRS)

Chameides, W. L.; Davis, D. D.

1983-01-01

The coupled gas- and aqueous-phase cloud chemistry of HCOOH were examined for controlling factors in the acidity of cloud and rainwater. Attention was given to the aqueous OH/HO2 system that yields an OH species that is highly reactive with other species, notably SO2 and the formaldehyde/formic acid complex. A numerical model was developed to simulate the cloud chemistry in the remote troposphere, with considerations given to CH4-CO-NO(x)-O3-H(x)O(y) system. It was determined that aqueous phase OH radicals can produce and destroy formic acid droplets in daylight conditions, as well as control formic acid levels in rainwater. It is sugested that the same types of reactions may be involved in the control of acetic acid and other organic acids.

a Search for the HOCO Radical in the Massive Star-Forming Region Sgr B2(M)

NASA Astrophysics Data System (ADS)

Oyama, Takahiro; Araki, Mitsunori; Takano, Shuro; Kuze, Nobuhiko; Sumiyoshi, Yoshihiro; Tsukiyama, Koichi; Endo, Yasuki

2017-06-01

Despite importance of the origin of life, long lasting challenges to detect the simplest amino acid glycine (H_2NCH_2COOH) in interstellar medium has not been successful. As a preliminary step toward search for glycine, detection of its precursor has received attention. It is considered that glycine is produced by the reaction of the HOCO radical and the aminomethyl radical(CH_2NH_2) on interstellar grain surface: HOCO + CH_2NH_2 → H_2NCH_2COOH. (1) HOCO is produced by the reaction of OH + CO → HOCO and/or HCOOH → HOCO + H. However, HOCO and CH_2NH_2 have not been investigated in interstellar medium. Recently, we determined the accurate molecular constants of HOCO. Thus, accurate rest frequencies were derived from the constants. In the present study, we carried out the observations of HOCO in the massive star-forming region Sgr B2(M), having variety of interstellar molecules, with Nobeyama 45 m radio telescope. Although HOCO could not be detected in Sgr B2(M), the upper limit of the column density was derived to be 9.0× 10^{12} cm^{-2} via the spectrum in the 88 GHz region by the rotational diagram method. If the reaction (1) is a main process of the glycine production in this region, an extremely deep search is needed to detect glycine. T. Oyama et al., J. Chem. Phys. 134, 174303 (2011).

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products

DOE PAGES

Green, Amy M.; Barber, Victoria P.; Fang, Yi; ...

2017-11-06

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH 3CHOO. IR excitation of selectively deuterated syn-CD 3CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn-CD 3CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, whichmore » is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of ~10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. Lastly, at 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn-CH 3CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of ~50.« less

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, Amy M.; Barber, Victoria P.; Fang, Yi

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH 3CHOO. IR excitation of selectively deuterated syn-CD 3CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn-CD 3CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, whichmore » is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of ~10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. Lastly, at 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn-CH 3CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of ~50.« less

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products.

PubMed

Green, Amy M; Barber, Victoria P; Fang, Yi; Klippenstein, Stephen J; Lester, Marsha I

2017-11-21

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH 3 CHOO. IR excitation of selectively deuterated syn -CD 3 CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn -CD 3 CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, which is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of ∼10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. At 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn -CH 3 CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of ∼50.

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products

PubMed Central

Green, Amy M.; Barber, Victoria P.; Fang, Yi; Klippenstein, Stephen J.; Lester, Marsha I.

2017-01-01

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH3CHOO. IR excitation of selectively deuterated syn-CD3CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn-CD3CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, which is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of ∼10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. At 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn-CH3CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of ∼50. PMID:29109292

EPR study of a gamma-irradiated (2-hydroxyethyl)triphenylphosphonium chloride single crystal

NASA Astrophysics Data System (ADS)

Karakaş, E.; Türkkan, E.; Dereli, Ö.; Sayιn, Ü.; Tapramaz, R.

2011-12-01

In this study, gamma-irradiated single crystals of (2-hydroxyethyl)triphenylphosphonium chloride [CH2CH2OH P(C6H5)3Cl] were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature for different orientations in the magnetic field. The single crystals were irradiated with a 60Co-γ-ray source at 0.818 kGy/h for about 36 h. Taking the chemical structure and the experimental spectra of the irradiated single crystal of the title compound into consideration, a paramagnetic species was produced with the unpaired electron delocalized around 31P and several 1H nuclei. The anisotropic hyperfine values due to the 31P nucleus, slightly anisotropic hyperfine values due to the 1H nuclei and the g-tensor of the radical were measured from the spectra. Depending on the molecular structure and measured parameters, three possible radicals were modeled using the B3LYP/6-31+G(d) level of density-functional theory, and EPR parameters were calculated for modeled radicals using the B3LYP/TZVP method/basis set combination. The calculated hyperfine coupling constants were found to be in good agreement with the observed EPR parameters. The experimental and theoretically simulated spectra for each of the three crystallographic axes were well matched with one of the modeled radicals (discussed in the text). We thus identified the radical C˙H2CH2 P(C 6H5)3 Cl as a paramagnetic species produced in a single crystal of the title compound in two magnetically distinct sites. The experimental g-factor and hyperfine coupling constants of the radical were found to be anisotropic, with the isotropic values g iso = 2.0032, ? G, ? G, ? G and ? G for site 1 and g iso=2.0031, ? G, ? G ? G and ? G for site 2.

Inactivation of Bacillus atrophaeus by OH radicals

NASA Astrophysics Data System (ADS)

Ono, Ryo; Yonetamari, Kenta; Tokumitsu, Yusuke; Yonemori, Seiya; Yasuda, Hachiro; Mizuno, Akira

2016-08-01

The inactivation of Bacillus atrophaeus by OH radicals is measured. This study aims to evaluate the bactericidal effects of OH radicals produced by atmospheric-pressure nonthermal plasma widely used for plasma medicine; however, in this study, OH radicals are produced by vacuum ultraviolet (VUV) photolysis of water vapor instead of plasma to allow the production of OH radicals with almost no other reactive species. A 172 nm VUV light from a Xe2 excimer lamp irradiates a He-H2O mixture flowing in a quartz tube to photodissociate H2O to produce OH, H, O, HO2, H2O2, and O3. The produced reactive oxygen species (ROS) flow out of the quartz tube nozzle to the bacteria on an agar plate and cause inactivation. The inactivation by OH radicals among the six ROS is observed by properly setting the experimental conditions with the help of simulations calculating the ROS densities. A 30 s treatment with approximately 0.1 ppm OH radicals causes visible inactivation.

Thermal O-H Bond Activation of Water as Mediated by Heteronuclear [Al2Mg2O5]•+: Evidence for Oxygen-Atom Scrambling.

PubMed

Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schwarz, Helmut

2018-06-25

Mechanistic insight into the thermal O-H bond activation of water by the cubane-like, prototypical heteronuclear oxide cluster [Al 2 Mg 2 O 5 ] •+ has been derived from a combined experimental/computational study. Experiments in the highly diluted gas phase using Fourier transform ion-cyclotron resonance mass spectrometry show that hydrogen-atom abstraction from water by the cluster cation [Al 2 Mg 2 O 5 ] •+ occurs at ambient conditions accompanied by the liberation of an OH • radical. Due to a complete randomization of all oxygen atoms prior to fragmentation about 83% of the oxygen atoms of the hydroxyl radical released originate from the oxide cluster itself. The experimental findings are supported by detailed high-level quantum chemical calculations. The theoretical analysis reveals that the transfer of a formal hydrogen atom from water to the metal-oxide cation can proceed mechanistically via proton- or hydrogen-atom transfer exploiting different active sites of the cluster oxide. In addition to the unprecedented oxygen-atom scrambling, one of the more general and quite unexpected findings concerns the role of spin density at the hydrogen-acceptor oxide atom. While this feature is so crucial for [M-O] + /CH 4 couples, it is much less important in the O-H bond activation of water.

Understanding methane variability from 1980 - 2015 using inversions of methane, δ13C and ethane

NASA Astrophysics Data System (ADS)

Thompson, Rona; Nisbet, Euan

2017-04-01

Atmospheric methane (CH4) increased globally during the 20th century, from a pre-industrial value of approximately 722 ppb to 1773 ppb in 1999. The upward trend, however, was interrupted between 1999 and 2006, when the atmospheric growth rate of CH4 was close to zero. From 2007, atmospheric CH4 started to increase again and, in 2014, the growth rate was substantially faster (12.5 ppb/y) than in any other year since 2007. Changes in the atmospheric growth rate indicate changes in the balance of CH4 sources and sinks, however, the cause of the 1999-2006 stabilization and subsequent rise in atmospheric CH4, and its attribution to different sources is still not fully resolved. Various explanations have been proposed for the pause in the growth, including a reduction in fossil fuel and wetland emissions, and for its renewed increase, such as increasing emissions from wetlands, enteric fermentation, and fossil fuels, as well as a decline in the OH sink. To better constrain the sources and sinks of CH4, we have performed an inversion using the AGAGE 12-box model of the atmosphere using atmospheric observations of CH4, δ13C, and of ethane. Using observations of these 3 atmospheric tracers simultaneously, a stronger constraint is placed on the different sources, as well as the principal atmospheric sink via oxidation by OH. In the model, we account for all emissions grouped into microbial, fossil fuel, biomass burning, landfill and ocean sources, as well as the soil oxidation sink. We also account for the atmospheric sink of CH4 and ethane via oxidation by OH and Cl radicals. The modelled lifetimes of CH4 and ethane were 8.2 years and 1.3 months, respectively. Inversions were also performed in which the OH sink was optimized simultaneously with the emissions. We find that fossil fuel emissions were underestimated in the northern mid to high latitudes in the 1980s but were overestimated from the mid 1990s onwards with respect to the prior (EDGAR-4.2), and that there is no evidence for a recent increase. For microbial emissions, we find an increase in emissions in the northern low and high latitudes from the early 2000s. The inversion also shifts microbial emissions from the northern to the southern low latitudes with respect to the prior (LPX-Bern for wetlands and EDGAR-4.2 for enteric fermentation). Finally, we do not find any evidence for a recent decrease in the OH sink.

The OH-initiated oxidation of atmospheric peroxyacetic acid: Experimental and model studies

NASA Astrophysics Data System (ADS)

Wu, Huihui; Wang, Yin; Li, Huan; Huang, Liubin; Huang, Dao; Shen, Hengqing; Xing, Yanan; Chen, Zhongming

2017-09-01

Peroxyacetic acid (PAA, CH3C(O)OOH) plays an important role in atmospheric chemistry, serving as reactive oxidant and affecting radical recycling. However, previous studies revealed an obvious gap between modelled and observed concentrations of atmospheric PAA, which may be partly ascribed to the uncertainty in the kinetics and mechanism of OH-oxidation. In this study, we measured the rate constant of OH radical reaction with PAA (kPAA+OH) and investigated the products in order to develop a more robust atmospheric PAA chemistry. Using the relative rates technique and employing toluene and meta-xylene as reference compounds, the kPAA+OH was determined to be (9.4-11.9) × 10-12 cm3 molecule-1 s-1 at 298 K and 1 atm, which is about (2.5-3.2) times larger than that parameter used in Master Chemical Mechanism v3.3.1 (MCM v3.3.1) (3.70 × 10-12 cm3 molecule-1 s-1). Incorporation of a box model and MCM v3.3.1 with revised PAA chemistry represented a better simulation of atmospheric PAA observed during Wangdu Campaign 2014, a rural site in North China Plain. It is found that OH-oxidation is an important sink of atmospheric PAA in this rural area, accounting for ∼30% of the total loss. Moreover, the major terminal products of PAA-OH reaction were identified as formaldehyde (HCHO) and formic acid (HC(O)OH). The modelled results show that both primary and secondary chemistry play an important role in the large HCHO and HC(O)OH formation under experimental conditions. There should exist the channel of methyl H-abstraction for PAA-OH reaction, which may also provide routes to HCHO and HC(O)OH formation.

Quantitative isotopic measurements of gas-phase alcohol mixtures using a broadly tunable swept external cavity quantum cascade laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brumfield, B. E.; Phillips, M. C.

A swept-ECQCL is used for broadband IR spectroscopy of isotopic mixtures of CH3OH, CH3OD, CH3CH2OH, and CH3CH2OD in a static gas cell over a wavelength range of 9.5 to 10.4 µm. A weighted least squares fitting approach with quantitative library spectra illustrates that significant spectral congestion does not negatively impact the ability for in situ quantification of large isotopic species in a mixture. The noise equivalent concentrations for CH3OH, CH3OD, CH3CH2OH, and CH3CH2OD are 19 ppbv x m, 28 ppbv x m, 450 ppbv x m, and 330 ppbv x m respectively for a 50 second integration time. Based onmore » the observed NECs, isotopic precisions of 0.07‰ and 0.79‰ for a 50 s integration time are calculated for measurements of the [MeOD]/[MeOH] and [EtOD]/[EtOH] isotope ratios , respectively, for the species concentrations in the gas cell.« less

CuMnOS Nanoflowers with Different Cu+/Cu2+ Ratios for the CO2-to-CH3OH and the CH3OH-to-H2 Redox Reactions

PubMed Central

Chen, Xiaoyun; Abdullah, Hairus; Kuo, Dong-Hau

2017-01-01

A conservative CO2-Methanol (CH3OH) regeneration cycle, to capture and reutilize the greenhouse gas of CO2 by aqueous hydrogenation for industry-useful CH3OH and to convert aqueous CH3OH solution by dehydrogenation for the clean energy of hydrogen (H2), is demonstrated at normal temperature and pressure (NTP) with two kinds of CuMnOS nanoflower catalysts. The [Cu+]-high CuMnOS led to a CH3OH yield of 21.1 mmol·g−1catal.·h−1 in the CuMnOS-CO2-H2O system and the other [Cu+]-low one had a H2 yield of 7.65 mmol·g−1catal.·h−1 in the CuMnOS-CH3OH-H2O system. The successful redox reactions at NTP rely on active lattice oxygen of CuMnOS catalysts and its charge (hole or electron) transfer ability between Cu+ and Cu2+. The CO2-hydrogenated CH3OH in aqueous solution is not only a fuel but also an ideal liquid hydrogen storage system for transportation application. PMID:28117456

CuMnOS Nanoflowers with Different Cu+/Cu2+ Ratios for the CO2-to-CH3OH and the CH3OH-to-H2 Redox Reactions

NASA Astrophysics Data System (ADS)

Chen, Xiaoyun; Abdullah, Hairus; Kuo, Dong-Hau

2017-01-01

A conservative CO2-Methanol (CH3OH) regeneration cycle, to capture and reutilize the greenhouse gas of CO2 by aqueous hydrogenation for industry-useful CH3OH and to convert aqueous CH3OH solution by dehydrogenation for the clean energy of hydrogen (H2), is demonstrated at normal temperature and pressure (NTP) with two kinds of CuMnOS nanoflower catalysts. The [Cu+]-high CuMnOS led to a CH3OH yield of 21.1 mmol·g-1catal.·h-1 in the CuMnOS-CO2-H2O system and the other [Cu+]-low one had a H2 yield of 7.65 mmol·g-1catal.·h-1 in the CuMnOS-CH3OH-H2O system. The successful redox reactions at NTP rely on active lattice oxygen of CuMnOS catalysts and its charge (hole or electron) transfer ability between Cu+ and Cu2+. The CO2-hydrogenated CH3OH in aqueous solution is not only a fuel but also an ideal liquid hydrogen storage system for transportation application.

CuMnOS Nanoflowers with Different Cu+/Cu2+ Ratios for the CO2-to-CH3OH and the CH3OH-to-H2 Redox Reactions.

PubMed

Chen, Xiaoyun; Abdullah, Hairus; Kuo, Dong-Hau

2017-01-24

A conservative CO 2 -Methanol (CH 3 OH) regeneration cycle, to capture and reutilize the greenhouse gas of CO 2 by aqueous hydrogenation for industry-useful CH 3 OH and to convert aqueous CH 3 OH solution by dehydrogenation for the clean energy of hydrogen (H 2 ), is demonstrated at normal temperature and pressure (NTP) with two kinds of CuMnOS nanoflower catalysts. The [Cu + ]-high CuMnOS led to a CH 3 OH yield of 21.1 mmol·g -1 catal.·h -1 in the CuMnOS-CO 2 -H 2 O system and the other [Cu + ]-low one had a H 2 yield of 7.65 mmol·g -1 catal.·h -1 in the CuMnOS-CH 3 OH-H 2 O system. The successful redox reactions at NTP rely on active lattice oxygen of CuMnOS catalysts and its charge (hole or electron) transfer ability between Cu + and Cu 2+ . The CO 2 -hydrogenated CH 3 OH in aqueous solution is not only a fuel but also an ideal liquid hydrogen storage system for transportation application.

A Theoretical Investigation of the Structure and Reactivity of the Molecular Constituents of Oil Sand and Oil Shale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parish, Carol A.

We used a variety of small organic models of asphaltenes to investigate the molecular mechanism for the high temperature decomposition that would take place as part of the oil refinery process. We determined that the decomposition is initiated via four different types of hydrogen migration reactions. According to the energetics of the reactions, the dominant 1,2-H shift mechanism involves two competitive product channels, namely, C 2H 2 + CH 2CS and CS + CH 3CCH. The minor channels include the formation of CS + CH 2CCH 2, H 2S + C 4H 2, HCS + CH 2CCH, CS + CHmore » 2CHCH, H + C 4H 3S, and HS + C 4H 3. We also investigated the alkyl substitution effect by exploring the decomposition pathways of models with alkyl arms. The energetics of such systems were very similar to that for unsubstituted model compounds, which suggests that asphaltene alkylation may not play a significant role in the decomposition of asphaltene compounds. This work was published in the Journal of Physical Chemistry A 2011, 115, 2882-2891. A MECHANISTIC STUDY OF THE 2-THIENYLMETHYL + HO2 RADICAL RECOMBINATION REACTION Radicals are molecules which contain single electrons. They are very reactive. Radical recombination reactions are important in the combustion of fuel oils. Shale oil contains radicals. We used quantum mechanics to explore the reactivity of shale oil model radical compounds. Seventeen product channels corresponding to either addition/elimination or direct hydrogen abstraction were characterized. Direct hydrogen abstraction proceeds via a weakly bonded complex, which leads to 2-methylthiophene, 2-methylene-2,3-dihydrothiophene or 2-methylene-2,5-dihydrothiophene depending upon the 2-thienylmethyl radical reaction site. The addition pathway for the two radical reactants is barrierless with the formation of three adducts, as distinguished by HO 2 reaction at three different sites on the 2-thienylmethyl radical. The addition is exothermic by 37 ~ 55 kcal mol-1 relative to the entrance channel. These excess energies are available to promote further decomposition or rearrangement of the adducts that lead to nascent products such as H, OH, H 2O and CH 2O. The reaction surfaces are characterized by relatively low barriers (most are lower than 10 kcal mol-1). Based upon a careful analysis of the overall barrier heights and reaction exothermicities, the formation of O2, OH and H2O is likely to be an important pathway in the radical recombination reactions of 2-thienylmethyl + HO 2. This work was published in the Journal of Physical Chemistry A, 2011, 115, 14546-14557. REACTION OF THIOPHENE AND METHYLTHIOPHENE WITH SINGLET AND TRIPLET MOLECULAR OXYGEN Mechanisms for the reaction of thiophene and 2-methylthiophene with molecular oxygen on both the triplet and singlet potential energy surfaces (PESs) were investigated using ab initio methods. Thiophene and 2-methylthiophene where shown to react with O 2 via two types of mechanisms; namely, direct hydrogen abstraction and addition/elimination. The barriers for reaction with triplet oxygen are all significantly large (i.e., > 30 kcal mol-1), which indicates that the direct oxidation of thiophene by ground state oxygen might be important only in high temperature processes. Reaction of thiophene with singlet oxygen via a 2+4 cycloaddition leading to endoperoxides is the most favorable channel. Moreover, it was found that alkylation of the thiophene ring (i.e., methyl-substituted thiophene) is capable of lowering the barrier height for the addition pathway. The implication of the current theoretical results may shed new light on the initiation mechanisms for combustion of asphaltenes. This work was published in the Journal of Physical Chemistry A, 2012 116, 4934-4946. JAHN-TELLER STABILIZATION IN POSS CATIONS We have a long standing interest in polyoligomeric silsesquioxane (POSS) molecules. 1-2 These molecules have recently been used as advanced surface coatings for photovoltaic devices and have potential as molecular-based energy storage devices as well as magnetically controllable liquid marbles. 3-5 We have been investigating the small molecule encapsulation properties of POSS and discovered some interesting symmetry breaking processes that need to be better understood in order to use POSS in advanced materials. We have investigated this symmetry breaking mechanism in POSS monocations Si8O12(C(CH3)3)8+ and Si8O12Cl8+, using density functional theory (DFT) and group theory. Under Oh symmetry, these ions possess 2T2g and 2Eg electronic states, respectively, and undergo different symmetry breaking mechanisms. The ground states of Si 8O 12(C(CH 3) 3) 8 + and Si 8O 12Cl 8 + belong to the C 3v and D 4h point groups and are characterized by Jahn-Teller stabilization energies of 3959 and 1328 cm-1, respectively, at the B3LYP/def2-SVP level of theory. The symmetry distortion mechanism in Si 8O 12Cl 8 + is Jahn-Teller type, whereas in Si 8O 12(C(CH 3) 3) 8 + the distortion is a combination of both Jahn-Teller and pseudo-Jahn-Teller effects. The distortion force acting in Si 8O 12(C(CH 3) 3) 8 + is mainly localized on one Si-(tert-butyl) group while in Si 8O 12Cl 8 + it is distributed over the oxygen atoms. The main distortion forces acting on the Si8O12 core arise from the coupling between the electronic state and the vibrational modes; identified as 9t 2g+1e g+3a 2u for the Si 8O 12(C(CH 3) 3) 8 + and 1e g+2e g for Si 8O 12Cl 8 +. This work was published in the Journal of Physical Chemistry A, 2015, 119, 4237-4243.« less

Methane Sensitivity to Perturbations in Tropospheric Oxidizing Capacity

NASA Technical Reports Server (NTRS)

Yegorova, Elena; Duncan, Bryan

2011-01-01

Methane is an important greenhouse gas and has a 25 times greater global warming potential than CO2 on a century timescale. Yet there are considerable uncertainties in the magnitude and variability of its sources and sinks. The response of the coupled non-linear methane-carbon monoxide-hydroxyl radical (OH) system is important in determining the tropospheric oxidizing capacity. Using the NASA Goddard Earth Observing System, Version 5 (GEOS-5) chemistry climate model, we study the response of methane to perturbations of OH and wetland emissions. We use a computationally-efficient option of the GEOS-5 CCM that includes an OH parameterization that accurately represents OH predicted by a full chemical mechanism. The OH parameterization allows for studying non-linear CH4-CO-OH feedbacks in computationally fast sensitivity experiments. We compare our results with surface observations (GMD) and discuss the range of uncertainty in OH and wetland emissions required to bring modeling results in better agreement with surface observations. Our results can be used to improve projections of methane emissions and methane growth.

Signatures of a quantum diffusion limited hydrogen atom tunneling reaction.

PubMed

Balabanoff, Morgan E; Ruzi, Mahmut; Anderson, David T

2017-12-20

We are studying the details of hydrogen atom (H atom) quantum diffusion in highly enriched parahydrogen (pH 2 ) quantum solids doped with chemical species in an effort to better understand H atom transport and reactivity under these conditions. In this work we present kinetic studies of the 193 nm photo-induced chemistry of methanol (CH 3 OH) isolated in solid pH 2 . Short-term irradiation of CH 3 OH at 1.8 K readily produces CH 2 O and CO which we detect using FTIR spectroscopy. The in situ photochemistry also produces CH 3 O and H atoms which we can infer from the post-photolysis reaction kinetics that display significant CH 2 OH growth. The CH 2 OH growth kinetics indicate at least three separate tunneling reactions contribute; (i) reactions of photoproduced CH 3 O with the pH 2 host, (ii) H atom reactions with the CH 2 O photofragment, and (iii) long-range migration of H atoms and reaction with CH 3 OH. We assign the rapid CH 2 OH growth to the following CH 3 O + H 2 → CH 3 OH + H → CH 2 OH + H 2 two-step sequential tunneling mechanism by conducting analogous kinetic measurements using deuterated methanol (CD 3 OD). By performing photolysis experiments at 1.8 and 4.3 K, we show the post-photolysis reaction kinetics change qualitatively over this small temperature range. We use this qualitative change in the reaction kinetics with temperature to identify reactions that are quantum diffusion limited. While these results are specific to the conditions that exist in pH 2 quantum solids, they have direct implications on the analogous low temperature H atom tunneling reactions that occur on metal surfaces and on interstellar grains.

Antioxidant Activity of Magnolol and Honokiol: Kinetic and Mechanistic Investigations of Their Reaction with Peroxyl Radicals.

PubMed

Amorati, Riccardo; Zotova, Julija; Baschieri, Andrea; Valgimigli, Luca

2015-11-06

Magnolol and honokiol, the bioactive phytochemicals contained in Magnolia officinalis, are uncommon antioxidants bearing isomeric bisphenol cores substituted with allyl functions. We have elucidated the chemistry behind their antioxidant activity by experimental and computational methods. In the inhibited autoxidation of cumene and styrene at 303 K, magnolol trapped four peroxyl radicals, with a kinh of 6.1 × 10(4) M(-1) s(-1) in chlorobenzene and 6.0 × 10(3) M(-1) s(-1) in acetonitrile, and honokiol trapped two peroxyl radicals in chlorobenzene (kinh = 3.8 × 10(4) M(-1) s(-1)) and four peroxyl radicals in acetonitrile (kinh = 9.5 × 10(3) M(-1) s(-1)). Their different behavior arises from a combination of intramolecular hydrogen bonding among the reactive OH groups (in magnolol) and of the OH groups with the aromatic and allyl π-systems, as confirmed by FT-IR spectroscopy and DFT calculations. Comparison with structurally related 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, 2-allylphenol, and 2-allylanisole allowed us to exclude that the antioxidant behavior of magnolol and honokiol is due to the allyl groups. The reaction of the allyl group with a peroxyl radical (C-H hydrogen abstraction) proceeds with rate constant of 1.1 M(-1) s(-1) at 303 K. Magnolol and honokiol radicals do not react with molecular oxygen and produce no superoxide radical under the typical settings of inhibited autoxidations.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes.

PubMed

Perez, Evan; Hanley, Cassandra; Koehler, Stephen; Pestok, Jordan; Polonsky, Nevo; Van Stipdonk, Michael

2016-12-01

The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (U VI O 2 2+ ) coordinated by formate or acetate ligands. Anionic complexes containing U VI O 2 2+ and formate ligands fragment by decarboxylation and elimination of CH 2 =O, ultimately to produce an oxo-hydride species [U VI O 2 (O)(H)] - . Cationic species ultimately dissociate to make [U VI O 2 (OH)] + . Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH 3 CO 2 •, with associated reduction of uranyl to U V O 2 + . Subsequent CID steps cause elimination of CO 2 and CH 4 , ultimately to produce [U V O 2 (O)] - . Loss of CH 4 occurs by an intra-complex H + transfer process that leaves U V O 2 + coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH 2 =C=O to leave [U V O 2 (O)] - . Elimination of CH 4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H 2 O. The reactions of other anionic species with gas-phase H 2 O create hydroxyl products, presumably through the elimination of H 2 . Graphical Abstract ᅟ.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

NASA Astrophysics Data System (ADS)

Perez, Evan; Hanley, Cassandra; Koehler, Stephen; Pestok, Jordan; Polonsky, Nevo; Van Stipdonk, Michael

2016-12-01

The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (UVIO2 2+) coordinated by formate or acetate ligands. Anionic complexes containing UVIO2 2+ and formate ligands fragment by decarboxylation and elimination of CH2=O, ultimately to produce an oxo-hydride species [UVIO2(O)(H)]-. Cationic species ultimately dissociate to make [UVIO2(OH)]+. Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH3CO2•, with associated reduction of uranyl to UVO2 +. Subsequent CID steps cause elimination of CO2 and CH4, ultimately to produce [UVO2(O)]-. Loss of CH4 occurs by an intra-complex H+ transfer process that leaves UVO2 + coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH2=C=O to leave [UVO2(O)]-. Elimination of CH4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H2O. The reactions of other anionic species with gas-phase H2O create hydroxyl products, presumably through the elimination of H2.

Heterogeneous processing of biomass burning aerosol proxies by OH radicals for a wide range of OH concentrations and detection of volatilization products

NASA Astrophysics Data System (ADS)

Slade, J. H.; Knopf, D. A.

2012-12-01

Biomass burning aerosol (BBA) constitutes the majority of primary organic aerosol found in the atmosphere, with emission rates comparable to fossil-fuel burning. BBA affects earth's radiative budget directly through absorption and scattering of radiation or indirectly by modifying cloud radiative properties, and impacts air quality. Quantifying BBA source strength and thus its effects on air quality, human health, and climate can be difficult since these organic particles can chemically transform during atmospheric transport, a process also termed aging, due to heterogeneous reactions with oxidants and radicals such as OH. In this work we investigate the reactive uptake of OH radicals by typical BBA compounds that also serve as molecular markers for source apportionment studies. Organic substrates of cellulose pyrolysis products such as levoglucosan (1,6-anhydro-β-glucopyranose, C6H10O5), resin acids such as abietic acid (1-phenanthrenecarboxylic acid, C20H30O2), and lignin decomposition products such as 5-nitroguaiacol (2-methoxy-5-nitrophenol, C7H7NO4) have been exposed to a wide range of OH concentrations (~107-1011 cm-3), in presence of O2 in a rotating wall flow reactor operated at 2-6 mbar coupled to a custom built chemical ionization mass spectrometer (CIMS). OH radicals were generated through H2 dissociation in an Evenson microwave resonant cavity operated at 2.45 GHz followed by reaction with O2 or NO2. In addition, potential volatilization of organic material due to heterogeneous oxidation by OH has been determined in-situ by monitoring the volatile organic compounds using a high resolution-proton transfer reaction-time of flight-mass spectrometer (HR-PTR-ToF-MS). The volatilization studies are conducted at 1 atm and OH is generated by O3 photolysis in the presence of H2O vapor and quantified using a photochemical box model as well as through reaction with a known concentration of isoprene (2-methyl-1,3-butadiene, C5H8). Reactive uptake validation experiments show good agreement with previously derived uptake coefficients for similar OH concentrations including levoglucosan. However, changes in OH concentration by ~4 orders of magnitude results in OH uptake coefficient variations of ~2 orders of magnitude. Higher OH concentration yields lower OH uptake coefficients. Our experiments strongly suggest that the highly reactive OH uptake follows a Langmuir-Hinshelwood type uptake mechanism, i.e. adsorption of OH is followed by reaction with the organic substrate, instead of an Eley-Rideal mechanism in which gas-to-surface collision results in reaction. In other words, surface saturation may play a role at high OH concentrations. Oxidation lifetime estimates for each investigated organic substrate are ~4 days commensurate with wet deposition (~5-10 days). Initial volatilization results indicate the formation of short-chained hydrocarbon species such as acetaldehyde (C2H4O), formic acid (CH2O2), and acetic acid (C2H4O2).

The Distribution, Excitation, and Formation of Cometary Molecules: Methanol, Methyl Cyanide, and Ethylene Glycol

NASA Astrophysics Data System (ADS)

Remijan, Anthony J.; Milam, Stefanie N.; Womack, Maria; Apponi, A. J.; Ziurys, L. M.; Wyckoff, Susan; A'Hearn, M. F.; de Pater, Imke; Forster, J. R.; Friedel, D. N.; Palmer, Patrick; Snyder, L. E.; Veal, J. M.; Woodney, L. M.; Wright, M. C. H.

2008-12-01

We present an interferometric and single-dish study of small organic species toward Comets C/1995 O1 (Hale-Bopp) and C/2002 T7 (LINEAR) using the BIMA interferometer at 3 mm and the ARO 12 m telescope at 2 mm. For Comet Hale-Bopp, both the single-dish and interferometer observations of CH3OH indicate an excitation temperature of 105 +/- 5 K and an average production rate ratio Q(CH3OH)/Q(H2O) ~ 1.3% at ~1 AU. In addition, the aperture synthesis observations of CH3OH suggest a distribution well described by a spherical outflow and no evidence of significant extended emission. Single-dish observations of CH3CN in Comet Hale-Bopp indicate an excitation temperature of 200 +/- 10 K and a production rate ratio of Q(CH3CN)/Q(H2O) ~ 0.017% at ~1 AU. The nondetection of a previously claimed transition of cometary (CH2OH)2 toward Comet Hale-Bopp with the 12 m telescope indicates a compact distribution of emission, D < 9'' (<8500 km). For the single-dish observations of Comet T7 LINEAR, we find an excitation temperature of CH3OH of 35 +/- 5 K and a CH3OH production rate ratio of Q(CH3OH)/Q(H2O) ~ 1.5% at ~0.3 AU. Our data support current chemical models that CH3OH, CH3CN, and (CH2OH)2 are parent nuclear species distributed into the coma via direct sublimation off cometary ices from the nucleus with no evidence of significant production in the outer coma.

Flame Characterization Using a Tunable Solid-State Laser with Direct UV Pumping

NASA Technical Reports Server (NTRS)

Kamal, Mohammed M.; Dubinskii, Mark A.; Misra, Prabhakar

1996-01-01

Tunable solid-state lasers with direct UV pumping, based on d-f transitions of rare earth ions incorporated in wide band-gap dielectric crystals, are reliable sources of laser radiation that are suitable for excitation of combustion-related free radicals. We have employed such a laser for analytical flame characterization utilizing Laser-Induced Fluorescence (LIF) techniques. LIF spectra of alkane-air flames (used for studying combustion processes under normal and microgravity conditions) excited in the region of the A-X (0,0) OH-absorption band have been recorded and found to be both temperature-sensitive and positionally-sensitive. In addition, also clearly noticeable was the sensitivity of the spectra to the specific wavelength used for data registration. The LiCAF:Ce laser shows good prospects for being able to cover the spectral region between 280 and 340 nm and therefore be used excitation of combustion-intermediates such as the hydroxyl OH, methoxy CH30 and methylthio CH3S radicals.

A kinetic study of enhancing effect by phenolic compounds on the hydroxyl radical generation during ozonation.

PubMed

Han, Y H; Ichikawa, K; Utsumi, H

2004-01-01

Ozone decomposition in aqueous solution proceeds through a radical type chain mechanism. These reactions involve the very reactive and catalytic intermediates O2- radical, OH radical, HO2 radical, OH-, H2O2, etc. OH radical is proposed as an important factor in the ozonation of water among them. In the present study, the enhancing effects of several phenolic compounds; phenol, 2-, 3-, 4-monochloro, 2,4-dichloro, 2,4,6-trichlorophenol on OH radical generation were mathematically evaluated using the electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO-OH. The initial velocities of DMPO-OH generation in ozonated water containing phenolic compounds were quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus, which was controlled by homemade software. The initial velocities of DMPO-OH generation increased as a function of the ozone concentration. The relation among ozone concentration, amount of phenolic compounds and the initial velocity (v0) of DMPO-OH generation was mathematically analyzed and the following equation was obtained, v0 (10(-6) M/s) = (A' x [PhOHs (10(-9) M)] + 0.0005) exp (60 x [ozone (10(-9) M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.98.

Radioprotection by Biological Response Modifiers Alone and in Combination with WR-2721

DTIC Science & Technology

1989-01-01

reasons related to cancer therapy rather 247 CH2 OH CH 2OH CH 2 0H H H H OH H OH H OH H OH FI(; . Chemical structure of glucan . a polgl~can consisting...2. GLUCAN : BACKGROUND AND GENERAL IMMUNOLOGIC AND HEMOPOIETIC EFFECTS Glucan (Fig. 1) is a beta -l,3-polyglucose isolated from the inner cell wall of...Adju’an, Therapy. pp. 183- 194. CH iiGOS. M. A led ) Ra%.en Press. New York Ciop. J. K. and AtSTiN. K. F 11985) A beta - glucan inhibitable receptor on human

Observation and modelling of the OH, HO_{2} and RO_{2} radicals at a suburban site of Beijing (Huairou) in winter 2016

NASA Astrophysics Data System (ADS)

Tan, Zhaofeng; Lu, Keding; Ma, Xuefei; Birger, Bohn; Broch, Sebastian; Fuchs, Hendrik; Hofzumahaus, Andreas; Holland, Frank; Li, Xin; Liu, Yuhan; Novelli, Anna; Rohrer, Franz; Shao, Min; Wang, Haichao; Wu, Yusheng; Zeng, Limin; Kiendler-Scharr, Astrid; Wahner, Andreas; Zhang, Yuanhang

2017-04-01

A comprehensive field campaign was carried out in winter 2016 in Huairou, a small town located 60 km northeast of Beijing downtown. Concentrations of OH, HO2and RO2 radicals were measured by a laser induced fluorescence instrument. Radical concentrations were smaller than during summer because of reduced solar radiation. Maximum hourly averaged OH, HO2 and RO2 radical concentrations were (3±2)×106cm-3, (8±6)×107 cm-3 and (7±5)×107 cm-3, respectively. Chemical modulation measurements were applied on a few days showing no significant OH interference for different chemical conditions. HONO and HCHO photolysis were found to be the most important primary source of ROx radicals. OH reactivity, the inverse of the OH radical lifetime, was also measured by a laser-photolysis and laser induced fluorescence instrument. In general, CO and NOx were the dominated OH reactants which contributed more than half of the total OH reactivity. The relative high OH concentrations in polluted episode enabled a fast oxidation of fresh emitted pollutants and the formation of secondary products. The observed radical concentrations were compared with the results from a chemical box model. The model is capable of reproducing radical concentrations in the moderate NOx conditions but has difficulty in both the low and high NOx regimes. The underestimation of RO2 radical concentrations in the high NOx conditions indicate a missing RO2 source.

Spatial distribution of CH3 and CH2 radicals in a methane rf discharge

NASA Astrophysics Data System (ADS)

Sugai, H.; Kojima, H.; Ishida, A.; Toyoda, H.

1990-06-01

Spatial distributions of neutral radicals CH3 and CH2 in a capacitively coupled rf glow discharge of methane were measured by threshold ionization mass spectrometry. A strong asymmetry of the density profile was found for the CH2 radical in the high-pressure (˜100 mTorr) discharge. In addition, comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficient were made to use as inputs to theoretical modeling of radicals in the methane plasma. The model predictions agree substantially with the measured radical distributions.

The effects of complex chemistry on triple flames

NASA Technical Reports Server (NTRS)

Echekki, T.; Chen, J. H.

1996-01-01

The structure, ignition, and stabilization mechanisms for a methanol (CH3OH)-air triple flame are studied using Direct Numerical Simulations (DNS). The methanol (CH3OH)-air triple flame is found to burn with an asymmetric shape due to the different chemical and transport processes characterizing the mixture. The excess fuel, methanol (CH3OH), on the rich premixed flame branch is replaced by more stable fuels CO and H2, which burn at the diffusion flame. On the lean premixed flame side, a higher concentration of O2 leaks through to the diffusion flame. The general structure of the triple point features the contribution of both differential diffusion of radicals and heat. A mixture fraction-temperature phase plane description of the triple flame structure is proposed to highlight some interesting features in partially premixed combustion. The effects of differential diffusion at the triple point add to the contribution of hydrodynamic effects in the stabilization of the triple flame. Differential diffusion effects are measured using two methods: a direct computation using diffusion velocities and an indirect computation based on the difference between the normalized mixture fractions of C and H. The mixture fraction approach does not clearly identify the effects of differential diffusion, in particular at the curved triple point, because of ambiguities in the contribution of carbon and hydrogen atoms' carrying species.

Palladium in Non-Aqueous Solvents. Formation, Stability, and Film Forming Properties.

DTIC Science & Technology

1987-07-14

data reported by Furlong7 in which high valent cations induced flocculation faster than monovalent cations. Addition of water to the colloid induced...reactlons Lf acetone with metal atoms. A number of radiolysis studies -f metal o in water -acetone solutions indicate that organ.c rad 2as ic trinsfer...electrons to the particles which act as electron reservoirs anc "an 7enawe as catalysts for water reduction).2’ (CH ) _OH ’,Ag) ZHA 32 If free radicals

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms.

PubMed

Díaz-de-Mera, Yolanda; Aranda, Alfonso; Bravo, Iván; Rodríguez, Diana; Rodríguez, Ana; Moreno, Elena

2008-10-01

The adverse environmental impacts of chlorinated hydrocarbons on the Earth's ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C-F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF(3)CF(2)CF(2)OCH(3)) (1) and its isomer CF(3)CF(2)CF(2)CH(2)OH (2). Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube-mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266-333 and 298-353 K for reactions of HFE-7000 and CF(3)CF(2)CF(2)CH(2)OH, respectively. The measured room temperature rate constants were k(Cl+CF(3)CF(2)CF(2)OCH(3)) = (1.24 +/- 0.28) x 10(-13) cm(3) molecule(-1) s(-1)and k(Cl+CF(3)CF(2)CF(2)CH(2)OH) = (8.35 +/- 1.63) x 10(-13) cm(3) molecule(-1) s(-1) (errors are 2sigma + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k (1)(266-333 K) = (6.1 +/- 3.8) x 10(-13)exp[-(445 +/- 186)/T] cm(3) molecule(-1) s(-1) and k (2)(298-353 K) = (1.9 +/- 0.7) x 10(-12)exp[-(244 +/- 125)/T] cm(3) molecule(-1) s(-1) (errors are 2sigma). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 +/- 0.38 and 0.97 +/- 0.16 (errors are 2sigma) were obtained for CF(3)CF(2)CF(2)OCH(3) and CF(3)CF(2)CF(2)CH(2)OH, respectively. The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k (1) and k (2), HFE-7000 is significantly less reactive than its isomer C(3)F(7)CH(2)OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of -CF(2)- in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of -CF(2)- without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C(3)H(7)CH(2)OH, respectively. The studied CFCs' substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, tau (Cl) values as low as 2.5 and 0.4 years for HFE-7000 and C(3)H(7)CH(2)OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF(3)CF(2)CF(2)OCH(3), significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure-reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.

Computational Study of the Reactions of Methanol with the Hydroperoxyl and Methyl Radicals. Part I: Accurate Thermochemistry and Barrier Heights

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alecu, I. M.; Truhlar, D. G.

2011-04-07

The reactions of CH 3OH with the HO 2 and CH 3 radicals are important in the combustion of methanol and are prototypes for reactions of heavier alcohols in biofuels. The reaction energies and barrier heights for these reaction systems are computed with CCSD(T) theory extrapolated to the complete basis set limit using correlation-consistent basis sets, both augmented and unaugmented, and further refined by including a fully coupled treatment of the connected triple excitations, a second-order perturbative treatment of quadruple excitations (by CCSDT(2) Q), core–valence corrections, and scalar relativistic effects. It is shown that the M08-HX and M08-SO hybrid meta-GGAmore » density functionals can achieve sub-kcal mol -1 agreement with the high-level ab initio results, identifying these functionals as important potential candidates for direct dynamics studies on the rates of these and homologous reaction systems.« less

Chemical dynamics simulations of the monohydrated OH-(H2O) + CH3I reaction. Atomic-level mechanisms and comparison with experiment

NASA Astrophysics Data System (ADS)

Xie, Jing; Otto, Rico; Wester, Roland; Hase, William L.

2015-06-01

Direct dynamics simulations, with B97-1/ECP/d theory, were performed to study the role of microsolvation for the OH-(H2O) + CH3I reaction. The SN2 reaction dominates at all reactant collision energies, but at higher collision energies proton transfer to form CH2I-, and to a lesser extent CH2I- (H2O), becomes important. The SN2 reaction occurs by direct rebound and stripping mechanisms, and 28 different indirect atomistic mechanisms, with the latter dominating. Important components of the indirect mechanisms are the roundabout and formation of SN2 and proton transfer pre-reaction complexes and intermediates, including [CH3--I--OH]-. In contrast, for the unsolvated OH- + CH3I SN2 reaction, there are only seven indirect atomistic mechanisms and the direct mechanisms dominate. Overall, the simulation results for the OH-(H2O) + CH3IߙSN2 reaction are in good agreement with experiment with respect to reaction rate constant, product branching ratio, etc. Differences between simulation and experiment are present for the SN2 velocity scattering angle at high collision energies and the proton transfer probability at low collision energies. Equilibrium solvation by the H2O molecule is unimportant. The SN2 reaction is dominated by events in which H2O leaves the reactive system as CH3OH is formed or before CH3OH formation. Formation of solvated products is unimportant and participation of the (H2O)CH3OH---I- post-reaction complex for the SN2 reaction is negligible.

Theoretical derivation for reaction rate constants of H abstraction from thiophenol by the H/O radical pool

PubMed Central

Batiha, Marwan; Altarawneh, Mohammednoor; Al-Harahsheh, Mohammad; Altarawneh, Ibrahem; Rawadieh, Saleh

2011-01-01

Reaction and activation energy barriers are calculated for the H abstraction reactions (C6H5SH + X• → C6H5S + XH, X = H, OH and HO2) at the BB1K/GTLarge level of theory. The corresponding reactions with H2S and CH3SH are also investigated using the G3B3 and CBS-QB3 methods in order to demonstrate the accuracy of BB1K functional in finding activation barriers for hydrogen atom transfer reactions. Arrhenius parameters for the title reactions are fitted in the temperature range of 300 K–2000 K. The calculated reaction enthalpies are in good agreement with their corresponding experimental reaction enthalpies. It is found that H abstraction by OH radicals from the thiophenol molecule proceed in a much slower rate in reference to the analogous phenol molecule. ΔfH298o of thiophenoxy radical is calculated to be 63.3 kcal/mol. Kinetic parameters presented herein should be useful in describing the decomposition rate of thiophenol; i.e., one of the major aromatic sulfur carriers, at high temperatures. PMID:22485200

Spatially resolved heat release rate measurements in turbulent premixed flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayoola, B.O.; Kaminski, C.F.; Balachandran, R.

Heat release rate is a fundamental property of great importance for the theoretical and experimental elucidation of unsteady flame behaviors such as combustion noise, combustion instabilities, and pulsed combustion. Investigations of such thermoacoustic interactions require a reliable indicator of heat release rate capable of resolving spatial structures in turbulent flames. Traditionally, heat release rate has been estimated via OH or CH radical chemiluminescence; however, chemiluminescence suffers from being a line-of-sight technique with limited capability for resolving small-scale structures. In this paper, we report spatially resolved two-dimensional measurements of a quantity closely related to heat release rate. The diagnostic technique usesmore » simultaneous OH and CH{sub 2}O planar laser-induced fluorescence (PLIF), and the pixel-by-pixel product of the OH and CH{sub 2}O PLIF signals has previously been shown to correlate well with local heat release rates. Results from this diagnostic technique, which we refer to as heat release rate imaging (HR imaging), are compared with traditional OH chemiluminescence measurements in several flames. Studies were performed in lean premixed ethylene flames stabilized between opposed jets and with a bluff body. Correlations between bulk strain rates and local heat release rates were obtained and the effects of curvature on heat release rate were investigated. The results show that the heat release rate tends to increase with increasing negative curvature for the flames investigated for which Lewis numbers are greater than unity. This correlation becomes more pronounced as the flame gets closer to global extinction.« less

Cooperativity of hydrogen-bonded networks in 7-azaindole(CH3OH)n (n=2,3) clusters evidenced by IR-UV ion-dip spectroscopy and natural bond orbital analysis.

PubMed

Sakota, Kenji; Kageura, Yutaka; Sekiya, Hiroshi

2008-08-07

IR-UV ion-dip spectra of the 7-azaindole (7AI)(CH(3)OH)(n) (n=1-3) clusters have been measured in the hydrogen-bonded NH and OH stretching regions to investigate the stable structures of 7AI(CH(3)OH)(n) (n=1-3) in the S(0) state and the cooperativity of the H-bonding interactions in the H-bonded networks. The comparison of the IR-UV ion-dip spectra with IR spectra obtained by quantum chemistry calculations shows that 7AI(CH(3)OH)(n) (n=1-3) have cyclic H-bonded structures, where the NH group and the heteroaromatic N atom of 7AI act as the proton donor and proton acceptor, respectively. The H-bonded OH stretch fundamental of 7AI(CH(3)OH)(2) is remarkably redshifted from the corresponding fundamental of (CH(3)OH)(2) by 286 cm(-1), which is an experimental manifestation of the cooperativity in H-bonding interaction. Similarly, two localized OH fundamentals of 7AI(CH(3)OH)(3) also exhibit large redshifts. The cooperativity of 7AI(CH(3)OH)(n) (n=2,3) is successfully explained by the donor-acceptor electron delocalization interactions between the lone-pair orbital in the proton acceptor and the antibonding orbital in the proton donor in natural bond orbital (NBO) analyses.

Laser-based measurements of OH in high pressure CH4/air flames

NASA Technical Reports Server (NTRS)

Battles, B. E.; Hanson, R. K.

1991-01-01

Narrow-linewidth laser absorption measurements are reported from which mole fraction and temperature of OH are determined in high-pressure (1-10 atm), lean CH4/air flames. These measurements were made in a new high pressure combustion facility which incorporates a traversable flat flame burner, providing spatially and temporally uniform combustion gases at pressures up to 10 am. A commercially avialable CW ring dye laser was used with an intracavity doubling crystal to provide near-UV single mode output at approximately 306 nm. The UV beam was rapidly scanned over 120 GHz (0.1 sec scan duration) to resolve the absorption lineshape of the A-X (0,0) R1(7)/R1(11) doublet of the OH radical. From the doublet's absorption lineshape, the temperature was determined; and from peak absorption, Beer's Law was employed to find the mole fraction of OH. These data were obtained as a function of height above the flame at various pressures.

Electronic spectroscopy and photodissociation dynamics of Co(2+)-methanol clusters: Co2+ (CH3OH)n (n = 4-7).

PubMed

Thompson, Christopher J; Faherty, Kieron P; Stringer, Kay L; Metz, Ricardo B

2005-03-07

Solvated cluster ions Co2+ (CH3OH)n (n = 4-7) have been produced by electrospray and studied using photofragment spectroscopy. There are notable differences between the photodissociation spectra of these complexes and the analogous water complexes. Co2+ (CH3OH)6 absorbs significantly more strongly than Co2+ (H2O)6. The photodissociation spectra of Co2+ (CH3OH)n (n = 4, 5 and 6) are very similar, which suggests that they share the Co2+ (CH3OH)4 chromophore, with additional solvent molecules in the second shell. In contrast, our earlier studies indicate that Co2+ (H2O)6 is six coordinate, and its spectrum is significantly different from that of Co2+ (H2O)4. The larger clusters Co2+ (CH3OH)n (n = 5-7) dissociate by simple loss of one or more solvent molecules. Larger clusters tend to lose more solvent molecules, especially at higher photon energies. As with the corresponding water cluster, Co2+ (CH3OH)4 photodissociates by proton transfer through a salt-bridge intermediate. This is accompanied by a modest kinetic energy release of 170 kJ mol(-1) and occurs with a lifetime of 145 ns.

Efficient reverse saturable absorption of sol-gel hybrid plasmonic glasses

NASA Astrophysics Data System (ADS)

Lundén, H.; Lopes, C.; Lindgren, M.; Liotta, A.; Chateau, D.; Lerouge, F.; Chaput, F.; Désert, A.; Parola, S.

2017-07-01

Monolithic silica sol-gel glasses doped with platinum(II) acetylide complexes possessing respectively four or six phenylacetylene units (PE2-CH2OH and PE3-CH2OH) in combination with various concentrations of spherical and bipyramidal gold nanoparticles (AuNPs) known to enhance non-linear optical absorption, were prepared and polished to high optical quality. The non-linear absorption of the glasses was measured and compared to glasses doped solely with AuNPs, a platinum(II) acetylide with shorter delocalized structure, or combinations of both. At 532 nm excitation wavelength the chromophore inhibited the non-linear scattering previously found for glasses only doped with AuNPs. The measured non-linear absorption was attributed to reverse saturable absorption from the chromophore, as previously reported for PE2-CH2OH/AuNP glasses. At 600 nm strong nonlinear absorption was observed for the PE3-CH2OH/AuNPs glasses, also attributed to reverse saturable absorption. But contrary to previous findings for PE2-CH2OH/AuNPs, no distinct enhancement of the non-linear absorption for PE3-CH2OH/AuNPs was observed. A numerical population model for PE3-CH2OH was used to give a qualitative explanation of this difference. A stronger linear absorption in PE3-CH2OH would cause the highly absorbing triplet state to populate quicker during the leading edge of the laser pulse and this would in turn reduce the influence from two-photon absorption enhancement from AuNPs.

Alkylating Derivatives of Vitamin D Hormone for Prostate Cancer

DTIC Science & Technology

2006-10-01

Acetic Anhydride / Pyridine/ 40C 1. UV / Toluene 2. EtOH - Reflux TBDMSCl / Imidazole /DMF BrCH2COOH / DCC / DMAP / CH2Cl2 1,25(OH)2D3-3-BE Figure 1...BE OH SO2 OTBDMS OH OTBDMS 1. Liq. SO2 / Reflux 2. TBDMSCl / Imidazole /DMF NaHCO3 / EtOH / Reflux NMO / SeO2 / CH2Cl2 / Reflux OH OTBDMSHO OTHP...containing 200 mg of 25-hydroxyvitamin D3 in a flask fitted with a trap that was cooled with dry ice-acetone (-780C). The yellow solution was refluxed

The thermal decomposition of the benzyl radical in a heated micro-reactor. I. Experimental findings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckingham, Grant T.; Ormond, Thomas K.; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401

2015-01-28

The pyrolysis of the benzyl radical has been studied in a set of heated micro-reactors. A combination of photoionization mass spectrometry (PIMS) and matrix isolation infrared (IR) spectroscopy has been used to identify the decomposition products. Both benzyl bromide and ethyl benzene have been used as precursors of the parent species, C{sub 6}H{sub 5}CH{sub 2}, as well as a set of isotopically labeled radicals: C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}. The combination of PIMS and IR spectroscopy has been used to identify the earliest pyrolysis products from benzyl radical as: C{sub 5}H{submore » 4}=C=CH{sub 2}, H atom, C{sub 5}H{sub 4}—C ≡ CH, C{sub 5}H{sub 5}, HCCCH{sub 2}, and HC ≡ CH. Pyrolysis of the C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2} benzyl radicals produces a set of methyl radicals, cyclopentadienyl radicals, and benzynes that are not predicted by a fulvenallene pathway. Explicit PIMS searches for the cycloheptatrienyl radical were unsuccessful, there is no evidence for the isomerization of benzyl and cycloheptatrienyl radicals: C{sub 6}H{sub 5}CH{sub 2}⇋C{sub 7}H{sub 7}. These labeling studies suggest that there must be other thermal decomposition routes for the C{sub 6}H{sub 5}CH{sub 2} radical that differ from the fulvenallene pathway.« less

Synthesis of ruthenium(II) complexes containing hydroxymethylphosphines and their catalytic activities for hydrogenation of supercritical carbon dioxide.

PubMed

Kayaki, Yoshihito; Shimokawatoko, Yoshiki; Ikariya, Takao

2007-07-09

Ligand substitution of RuCl2[P(C6H5)3]3 and Cp*RuCl(isoprene) (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) complexes with hydroxymethylphosphines was investigated to develop new catalyst systems for CO2 hydrogenation. A reaction of P(C6H5)2CH2OH with RuCl2[P(C6H5)3]3 in CH2Cl2 gave Ru(H)Cl(CO)[P(C6H5)2CH2OH]3 (1), which was characterized by NMR spectroscopy and X-ray crystallographic analysis. An isotope labeling experiment using P(C6H5)213CH2OH indicated that the carbonyl moiety in complex 1 originated from formaldehyde formed by degradation of the hydroxymethylphosphine. Elimination of formaldehyde from PCy2CH2OH (Cy=cyclohexyl) was also promoted by treatment of RuCl2[P(C6H5)3]3 in ethanol to give RuCl2(PHCy2)4 under mild conditions. On the other hand, the substitution reaction using Cp*RuCl(isoprene) with the hydroxymethylphosphine ligands proceeded smoothly with formation of Cp*RuCl(L)2 [2a-2c; L=P(C6H5)2CH2OH, PCy(CH2OH)2, and P(CH2OH)3] in good yields. The isolable hydroxymethylphosphine complexes 1 and 2 efficiently catalyzed the hydrogenative amidation of supercritical carbon dioxide (scCO2) to N,N-dimethylformamide (DMF).

Dynamics and density estimation of hydroxyl radicals in a pulsed corona discharge

NASA Astrophysics Data System (ADS)

Ono, Ryo; Oda, Tetsuji

2002-09-01

Hydroxyl radicals generated by a pulsed corona discharge are measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The discharge with 35 kV voltage and 100 ns pulse current occurs between needle and plate electrodes in H2O/O2/N2 mixture at atmospheric pressure. The density and decay profile of OH radicals are studied. OH radicals decay with time after the discharge with a time constant of about 30-60 µs. The OH density is estimated to be about 7×1014 cm-3 in H2O(2.4%)/N2 mixture 10 µs after the discharge. The OH density is approximately proportional to the energy dissipated in the discharge. The O2 content influences the OH production. When the O2 content is varied in H2O(2.4%)/O2/N2 mixture, the OH density is maximum at an O2 content of 2%. The spatial distribution of OH density shows that OH radicals are produced in the streamers under positive discharge.

Observation and Modelling of the OH, HO2 and RO2 Radicals at a Regional Site of Beijing in Winter 2016.

NASA Astrophysics Data System (ADS)

Tan, Z.; Lu, K.; Ma, X.; Bohn, B.; Hofzumahaus, A.; Broch, S.; Fuchs, H.; Holland, F.; Liu, Y.; Li, X.; Novelli, A.; Rohrer, F.; Wang, H.; Wu, Y.; Shao, M.; Zeng, L.; Kiendler-Scharr, A.; Wahner, A.; Zhang, Y.

2017-12-01

A comprehensive field campaign was carried out in winter 2016 in the campus of UCAS (University of Chinese Academy of Science), located in a small town 60 km northeast of urban Beijing. Concentrations of OH, HO2 and RO2 radicals as well as the total OH reactivity were measured by a laser induced fluorescence instrument. Maximum hourly averaged OH, HO2 and RO2 radical concentrations were (3±2)×106cm-3, (8±6)×107 cm-3 and (7±5)×107 cm-3, respectively. These radical concentrations were smaller than those observed during summer because of the reduced solar radiation. A chemical modulation device to separate atmospheric OH radicals from any interfering species was applied for few days showing negligible interference for both clean and polluted air masses.HONO and HCHO photolysis were found to be the most important primary sources of ROx radicals. CO and NOx were the important OH reactants which contributed more than half of the total OH reactivity. The relative high OH concentrations in polluted episode enabled a fast oxidation of fresh emitted pollutants and the formation of secondary air products. The observed radical concentrations were compared with the results from a chemical box model. The model is capable of reproducing radical concentrations for moderate NOx conditions but larger discrepancies are observed for both low and high NOx regimes for the peroxy radical concentrations. The underestimation of RO2 radical concentrations for high NOx conditions is discussed in the context of recent campaigns.

[Study of emission spectroscopy of OH radicals in pulsed corona discharge].

PubMed

Wei, Bo; Luo, Zhong-Yang; Xu, Fei; Zhao, Lei; Gao, Xiang; Cen, Ke-Fa

2010-02-01

In the present paper, OH radicals generated by pulsed corona discharge in humidified air, N2 and Ar in a needle-plate reactor were measured by emission spectra. With the analysis of the emission spectra, the influence of pulse peak voltage and frequency on OH radical generation was investigated in the three kinds of background gases. The influence of the gas humidity on the generation and the distribution of OH radicals in the electric field was also discussed in detail. The authors studied the influence of the gas humidity on the generation of OH radicals in the electric field by the control of accurate change in humidity, and we also studied the distribution of OH radicals in the electric field in different background gases including humidified air, N2 and Ar by the accurate change in scales. The experiment shows that the output of OH radicals grows as the pulse peak voltage and frequency grow, but the influence of gas humidity on the process of generating OH radicals by pulsed corona discharge depends on the discharge background. The rules of the generation change when the background gases change. As the humidity in the background gases grows, the amount of OH radicals grows in the air, but it grows at first and decreases at last in N2, while it decreases at first and grows at last in Ar. The distribution of OH radical shows a trend of decreasing from the needle-electrode to its circumambience.

Unimolecular Thermal Decomposition of Phenol and d5-Phenol: Direct Observation of Cyclopentadiene Formation via Cyclohexadienone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scheer, A. M.; Mukarakate, C.; Robichaud, D. J.

The pyrolyses of phenol and d{sub 5}-phenol (C{sub 6}H{sub 5}OH and C{sub 6}D{sub 5}OH) have been studied using a high temperature, microtubular ({mu}tubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy. Gas exiting the heated reactor (375 K-1575 K) is subject to a free expansion after a residence time in the {mu}tubular reactor of approximately 50-100 {micro}s. The expansion from the reactor into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. We find that the initial decomposition steps at themore » onset of phenol pyrolysis are enol/keto tautomerization to form cyclohexadienone followed by decarbonylation to produce cyclopentadiene; C{sub 6}H{sub 5}OH {yields} c-C{sub 6}H{sub 6} = O {yields} c-C{sub 5}H{sub 6} + CO. The cyclopentadiene loses a H atom to generate the cyclopentadienyl radical which further decomposes to acetylene and propargyl radical; c-C{sub 5}H{sub 6} {yields} c-C{sub 5}H{sub 5} + H {yields} HC {triple_bond} CH + HCCCH{sub 2}. At higher temperatures, hydrogen loss from the PhO-H group to form phenoxy radical followed by CO ejection to generate the cyclopentadienyl radical likely contributes to the product distribution; C{sub 6}H{sub 5}O-H {yields} C{sub 6}H{sub 5}O + H {yields} c-C{sub 5}H{sub 5} + CO. The direct decarbonylation reaction remains an important channel in the thermal decomposition mechanisms of the dihydroxybenzenes. Both catechol (o-HO-C{sub 6}H{sub 4}-OH) and hydroquinone (p-HO-C{sub 6}H{sub 4}-OH) are shown to undergo decarbonylation at the onset of pyrolysis to form hydroxycyclopentadiene. In the case of catechol, we observe that water loss is also an important decomposition channel at the onset of pyrolysis.« less

Free-radical reactions induced by OH-radical attack on cytosine-related compounds: a study by a method combining ESR, spin trapping and HPLC.

PubMed Central

Hiraoka, W; Kuwabara, M; Sato, F; Matsuda, A; Ueda, T

1990-01-01

Free-radical reactions induced by OH-radical attack on cytosine-related compounds were investigated by a method combining ESR, spin trapping with 2-methyl-2-nitrosopropane and high-performance liquid chromatography (HPLC). Cytidine, 2'-deoxycytidine, cytidine 3'-monophosphate, cytidine 5'-monophosphate, 2'-deoxycytidine 5'-monophosphate and their derivatives, of which 5,6-protons at the base moiety were replaced by deuterons, and polycytidylic acid (poly(C] were employed as samples. OH radicals were generated by X-irradiating an N2O-saturated aqueous solution. Five spin adducts were separated by HPLC. Examination of them by ESR spectroscopy and UV photospectrometry showed that spin adducts assigned to C5 and C6 radicals due to OH addition to the 5,6 double-bond, a deaminated form of the spin adduct derived from a C5 radical due to the cyclization reaction between C5' of the sugar and C6 of the base, and a spin adduct assigned to the C4' radical due to H abstraction by OH radicals were produced. From these results the sites of OH-radical attack and the subsequent radical reactions in cytosine-related compounds were clarified. PMID:2157193

Methanol oxidation on stoichiometric and oxygen-rich RuO2(110).

PubMed

Rai, Rahul; Weaver, Jason F

2017-07-26

We used temperature-programmed reaction spectroscopy (TPRS) to investigate the adsorption and oxidation of methanol on stoichiometric and O-rich RuO 2 (110) surfaces. We find that the complete oxidation of CH 3 OH is strongly preferred on stoichiometric RuO 2 (110) during TPRS for initial CH 3 OH coverages below ∼0.33 ML (monolayer), and that partial oxidation to mainly CH 2 O becomes increasingly favored with increasing CH 3 OH coverage from 0.33 to 1.0 ML. We present evidence that an adsorbed CH 2 O 2 species serves as the key intermediate to complete oxidation and that CH 2 O 2 formation is intrinsically facile but becomes limited by the availability of bridging O-atoms on stoichiometric RuO 2 (110) at initial CH 3 OH coverages above 0.33 ML. We show that methanol molecules adsorbed in excess of 0.33 ML dehydrogenate to mainly CH 2 O and desorb during TPRS, with adsorbed CH 3 O groups mediating the evolution of both CH 2 O and CH 3 OH. We find that O-rich RuO 2 (110) surfaces are also highly active toward methanol oxidation and that selectivity toward the complete oxidation of methanol increases markedly with increasing coverage of on-top O-atoms (O ot ) on RuO 2 (110). Our results demonstrate that CH 3 OH species adsorbed within O ot -rich domains react efficiently during TPRS, in parallel with reaction of CH 3 OH adsorbed initially on cus-Ru sites. The data suggests that the facile hydrogenation of O ot atoms and the resulting desorption of H 2 O at low-temperature (<∼400 K) provides an efficient pathway for restoring reactive O-atoms and thereby promoting complete oxidation of methanol on the O-rich RuO 2 (110) surface.

Destruction of acid gas emissions

DOEpatents

Mathur, Mahendra P.; Fu, Yuan C.; Ekmann, James M.; Boyle, John M.

1991-01-01

A method of destroying NO.sub.x and SO.sub.2 in a combustion gas in disclosed. The method includes generating active species by treating stable moleucles in a high temperature plasma. Ammonia, methane, steam, hydrogen, nitrogen or a combination of these gases can be selected as the stable molecules. The gases are subjected to plasma conditions sufficient to create free radicals, ions or excited atoms such as N, NH, NH.sub.2, OH.sup.-, CH and/or CH.sub.2. These active species are injected into a combustion gas at a location of sufficiently high temperature to maintain the species in active state and permit them to react with NO.sub.x and SO.sub.2. Typically the injection is made into the immediate post-combustion gases at temperatures of 475.degree.-950.degree. C.

Infrared Laser Spectroscopy of the n-PROPYL and i-PROPYL Radicals in Helium Droplets: Significant Bend-Stretch Coupling Revealed in the CH Stretch Region

NASA Astrophysics Data System (ADS)

Moradi, Christopher P.; Douberly, Gary E.; Tabor, Daniel P.; Sibert, Edwin

2016-06-01

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite (CH3(CH2)3ONO) and i-butyl nitrite (CH3CH(CH3)CH2ONO) precursors, respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the C-H stretching region. In addition to three vibrations of n-propyl previously measured in an Ar matrix, we observe many unreported bands between 2800 and 3150 wn, which we attribute to propyl radicals. The C-H stretching modes observed above 2960 wn for both radicals are in excellent agreement with anharmonic frequencies computed using VPT2. Between 2800 and 2960 wn, however, the spectra of n-propyl and i-propyl radicals become quite congested and difficult to assign due to the presence of multiple anharmonic resonances. Computations employing a local mode Hamiltonian reveal the origin of the spectral congestion to be strong coupling between the high frequency C-H stretching modes and the lower frequency bending/scissoring motions. The only significant local coupling is between stretches and bends on the same CH2/CH3 group.

A greenhouse gas source of surprising significance: anthropogenic CO2 emissions from use of methanol in sewage treatment.

PubMed

Willis, John L; Al-Omari, Ahmed; Bastian, Robert; Brower, Bill; DeBarbadillo, Christine; Murthy, Sudhir; Peot, Christopher; Yuan, Zhiguo

2017-05-01

The impact of methanol (CH 3 OH) as a source of anthropogenic carbon dioxide (CO 2 ) in denitrification at wastewater treatment plants (WWTPs) has never been quantified. CH 3 OH is the most commonly purchased carbon source for sewage denitrification. Until recently, greenhouse gas (GHG) reporting protocols consistently ignored the liberation of anthropogenic CO 2 attributable to CH 3 OH. This oversight can likely be attributed to a simplifying notion that CO 2 produced through activated-sludge-process respiration is biogenic because most raw-sewage carbon is un-sequestered prior to entering a WWTP. Instead, a biogenic categorization cannot apply to fossil-fuel-derived carbon sources like CH 3 OH. This paper provides a summary of how CH 3 OH use at DC Water's Blue Plains Advanced Wastewater Treatment Plant (AWTP; Washington, DC, USA) amounts to 60 to 85% of the AWTP's Scope-1 emissions. The United States Environmental Protection Agency and Water Environment Federation databases suggest that CH 3 OH CO 2 likely represents one quarter of all Scope-1 GHG emissions attributable to sewage treatment in the USA. Finally, many alternatives to CH 3 OH use exist and are discussed.

Electron spin resonance of (CO 2 H)CH 2 CH 2 CH(CO 2 H) in irradiated glutaric acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horsfield, A.; Morton, J. R.; Whiffen, D. H.

It is concluded from electron spin resonance spectra that the radical (CO 2 H)CH 2 CH 2 CH(CO 2 H) remains trapped in a glutaric acid crystal after gamma -irradiation. This radical is found in two different conformations. Approximate hyperfine coupling constants are given for each, although exact interpretation is hindered by the overlapping of spectra. Reasons for the formation of the two forms of the radical are discussed.

Rate Constants for the Reactions of OH with CH(sub 3)Cl, CH(sub 2) C1(sub 2), CHC1(sub 3)and CH(sub 3)Br

NASA Technical Reports Server (NTRS)

Hsu, H-J.; DeMore, W.

1994-01-01

Rate constants for the reactions of OH with CH3C1, CH2Cl2, CHCl3 and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH3CHF2)and for CH2Cl2, HFC-161 (CH3CH2F).

A new bipyrrole and some phenolic constituents in prunes (Prunus domestica L.) and their oxygen radical absorbance capacity (ORAC).

PubMed

Kayano, Shin-ichi; Kikuzaki, Hiroe; Ikami, Takao; Suzuki, Tomoo; Mitani, Takahiko; Nakatani, Nobuji

2004-04-01

Isolation and structural elucidation of prune constituents were performed and total 10 compounds were determined by NMR and MS analyses. A novel compound was identified to be 2-(5-hydroxymethyl-2',5'-dioxo-2',3',4',5'-tetrahydro-1'H-1,3'-bipyrrole)carbaldehyde, and 7 phenolic compounds were isolated from prunes for the first time. In addition, antioxidant activity of them was evaluated on the basis of the oxygen radical absorbance capacity (ORAC).

Pyrolysis of the Simplest Carbohydrate, Glycolaldehyde (CHO-CH2OH), and Glyoxal in a Heated Microreactor.

PubMed

Porterfield, Jessica P; Baraban, Joshua H; Troy, Tyler P; Ahmed, Musahid; McCarthy, Michael C; Morgan, Kathleen M; Daily, John W; Nguyen, Thanh Lam; Stanton, John F; Ellison, G Barney

2016-04-14

Both glycolaldehyde and glyoxal were pyrolyzed in a set of flash-pyrolysis microreactors. The pyrolysis products resulting from CHO-CH2OH and HCO-CHO were detected and identified by vacuum ultraviolet (VUV) photoionization mass spectrometry. Complementary product identification was provided by argon matrix infrared absorption spectroscopy. Pyrolysis pressures in the microreactor were about 100 Torr, and contact times with the microreactors were roughly 100 μs. At 1200 K, the products of glycolaldehyde pyrolysis are H atoms, CO, CH2═O, CH2═C═O, and HCO-CHO. Thermal decomposition of HCO-CHO was studied with pulsed 118.2 nm photoionization mass spectrometry and matrix infrared absorption. Under these conditions, glyoxal undergoes pyrolysis to H atoms and CO. Tunable VUV photoionization mass spectrometry provides a lower bound for the ionization energy (IE)(CHO-CH2OH) ≥ 9.95 ± 0.05 eV. The gas-phase heat of formation of glycolaldehyde was established by a sequence of calorimetric experiments. The experimental result is ΔfH298(CHO-CH2OH) = -75.8 ± 1.3 kcal mol(-1). Fully ab initio, coupled cluster calculations predict ΔfH0(CHO-CH2OH) of -73.1 ± 0.5 kcal mol(-1) and ΔfH298(CHO-CH2OH) of -76.1 ± 0.5 kcal mol(-1). The coupled-cluster singles doubles and noniterative triples correction calculations also lead to a revision of the geometry of CHO-CH2OH. We find that the O-H bond length differs substantially from earlier experimental estimates, due to unusual zero-point contributions to the moments of inertia.

Thermochemistry and kinetics for 2-butanone-1-yl radical (CH2·C(═O)CH2CH3) reactions with O2.

PubMed

Sebbar, N; Bozzelli, J W; Bockhorn, H

2014-01-09

Thermochemistry of reactants, intermediates, transition state structures, and products along with kinetics on the association of CH2·C(═O)CH2CH3 (2-butanone-1-yl) with O2 and dissociation of the peroxy adduct isomers are studied. Thermochemical properties are determined using ab initio (G3MP2B3 and G3) composite methods along with density functional theory (B3LYP/6-311g(d,p)). Entropy and heat capacity contributions versus temperature are determined from structures, vibration frequencies, and internal rotor potentials. The CH2·C(═O)CH2CH3 radical + O2 association results in a chemically activated peroxy radical with 27 kcal mol(-1) excess of energy. The chemically activated adduct can react to stabilized peroxy or hydroperoxide alkyl radical adducts, further react to lactones plus hydroxyl radical, or form olefinic ketones and a hydroperoxy radical. Kinetic parameters are determined from the G3 composite methods derived thermochemical parameters, and quantum Rice-Ramsperger-Kassel (QRRK) analysis to calculate k(E) with master equation analysis to evaluate falloff in the chemically activated and dissociation reactions. One new, not previously reported, peroxy chemistry reaction is presented. It has a low barrier path and involves a concerted reaction resulting in olefin formation, H2O elimination, and an alkoxy radical.

Chemical dynamics simulations of the monohydrated OH{sup −}(H{sub 2}O) + CH{sub 3}I reaction. Atomic-level mechanisms and comparison with experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Jing; Hase, William L., E-mail: bill.hase@ttu.edu; Otto, Rico

2015-06-28

Direct dynamics simulations, with B97-1/ECP/d theory, were performed to study the role of microsolvation for the OH{sup −}(H{sub 2}O) + CH{sub 3}I reaction. The S{sub N}2 reaction dominates at all reactant collision energies, but at higher collision energies proton transfer to form CH{sub 2}I{sup −}, and to a lesser extent CH{sub 2}I{sup −} (H{sub 2}O), becomes important. The S{sub N}2 reaction occurs by direct rebound and stripping mechanisms, and 28 different indirect atomistic mechanisms, with the latter dominating. Important components of the indirect mechanisms are the roundabout and formation of S{sub N}2 and proton transfer pre-reaction complexes and intermediates, includingmore » [CH{sub 3}--I--OH]{sup −}. In contrast, for the unsolvated OH{sup −} + CH{sub 3}I S{sub N}2 reaction, there are only seven indirect atomistic mechanisms and the direct mechanisms dominate. Overall, the simulation results for the OH{sup −}(H{sub 2}O) + CH{sub 3}I S{sub N}2 reaction are in good agreement with experiment with respect to reaction rate constant, product branching ratio, etc. Differences between simulation and experiment are present for the S{sub N}2 velocity scattering angle at high collision energies and the proton transfer probability at low collision energies. Equilibrium solvation by the H{sub 2}O molecule is unimportant. The S{sub N}2 reaction is dominated by events in which H{sub 2}O leaves the reactive system as CH{sub 3}OH is formed or before CH{sub 3}OH formation. Formation of solvated products is unimportant and participation of the (H{sub 2}O)CH{sub 3}OH---I{sup −} post-reaction complex for the S{sub N}2 reaction is negligible.« less

Infrared absorption of methanol clusters (CH3OH)n with n = 2-6 recorded with a time-of-flight mass spectrometer using infrared depletion and vacuum-ultraviolet ionization.

PubMed

Han, Hui-Ling; Camacho, Cristopher; Witek, Henryk A; Lee, Yuan-Pern

2011-04-14

We investigated IR spectra in the CH- and OH-stretching regions of size-selected methanol clusters, (CH(3)OH)(n) with n = 2-6, in a pulsed supersonic jet by using the IR-VUV (vacuum-ultraviolet) ionization technique. VUV emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser emission served as a source of predissociation or excitation before ionization. The variations of intensity of protonated methanol cluster ions (CH(3)OH)(n)H(+) and CH(3)OH(+) and (CH(3)OH)(2)(+) were monitored as the IR laser light was tuned across the range 2650-3750 cm(-1). Careful processing of these action spectra based on photoionization efficiencies and the production and loss of each cluster due to photodissociation yielded IR spectra of the size-selected clusters. Spectra of methanol clusters in the OH region have been extensively investigated; our results are consistent with previous reports, except that the band near 3675 cm(-1) is identified as being associated with the proton acceptor of (CH(3)OH)(2). Spectra in the CH region are new. In the region 2800-3050 cm(-1), bands near 2845, 2956, and 3007 cm(-1) for CH(3)OH split into 2823, 2849, 2934, 2955, 2984, and 3006 cm(-1) for (CH(3)OH)(2) that correspond to proton donor and proton acceptor, indicating that the methanol dimer has a preferred open-chain structure. In contrast, for (CH(3)OH)(3), the splitting diminishes and the bands near 2837, 2954, and 2987 cm(-1) become narrower, indicating a preferred cyclic structure. Anharmonic vibrational wavenumbers predicted for the methanol open-chain dimer and the cyclic trimer with the B3LYP∕VPT2∕ANO1 level of theory are consistent with experimental results. For the tetramer and pentamer, the spectral pattern similar to that of the trimer but with greater widths was observed, indicating that the most stable structures are also cyclic.

Abundant Methanol Ice toward a Massive Young Stellar Object in the Central Molecular Zone

NASA Astrophysics Data System (ADS)

An, Deokkeun; Sellgren, Kris; Boogert, A. C. Adwin; Ramírez, Solange V.; Pyo, Tae-Soo

2017-07-01

Previous radio observations revealed widespread gas-phase methanol (CH3OH) in the Central Molecular Zone (CMZ) at the Galactic center (GC), but its origin remains unclear. Here, we report the discovery of CH3OH ice toward a star in the CMZ, based on a Subaru 3.4-4.0 μm spectrum, aided by NASA/IRTF L\\prime imaging and 2-4 μm spectra. The star lies ˜8000 au away in projection from a massive young stellar object (MYSO). Its observed high CH3OH ice abundance (17 % +/- 3 % relative to H2O ice) suggests that the 3.535 μm CH3OH ice absorption likely arises in the MYSO’s extended envelope. However, it is also possible that CH3OH ice forms with a higher abundance in dense clouds within the CMZ, compared to within the disk. Either way, our result implies that gas-phase CH3OH in the CMZ can be largely produced by desorption from icy grains. The high solid CH3OH abundance confirms the prominent 15.4 μm shoulder absorption observed toward GC MYSOs arises from CO2 ice mixed with CH3OH. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

The Formation of Secondary Organic Aerosol from the Isoprene + OH Reaction in the Absence of NOx

EPA Science Inventory

The reaction of isoprene (C₅H₈) with hydroxyl radicals has been studied in the absence of nitrogen oxides (NO_x) to determine physical and chemical characteristics of the secondary organic aerosol formed. Experiments were conducted using a smog ch...

Photoabsorption and photodissociation of molecules important in the interstellar medium

NASA Technical Reports Server (NTRS)

Lee, L. C.

1985-01-01

The photoabsorption and photodissociation cross sections of several interstellar molecules and radicals in the 105 to 210 nm region were measured. The research results accomplished are briefly described. Photoabsorption cross sections of OD and CN, and photoabsorption and photodissociation of HCl, and photoabsorption and photodissociation cross sections of CH3OH are discussed.

New thermochemical parameter for describing solvent effects on IR stretching vibration frequencies. Communication 2. Assessment of cooperativity effects.

PubMed

Solomonov, Boris N; Varfolomeev, Mikhail A; Novikov, Vladimir B; Klimovitskii, Alexander E

2006-05-15

Solvent effects on O-H stretching vibration frequency of methanol in hydrogen bond complexes with different bases, CH3OH...B, have been investigated by FTIR spectroscopy. Using chloroform as a solvent results in strengthening of CH3OH...B hydrogen bonding due to cooperativity between CH3OH...B and Cl3CH...CH3OH bonds. A method is proposed for quantifying the hydrogen bond cooperativity effect. The determined cooperativity factors take into account all specific interactions of the solute in proton-donor solvents. In addition, a method of estimation of cooperativity factors Ab and AOX in system (CH3OH)2...B is proposed. It is demonstrated that in such systems, the cooperativity factor of the OH...B bond decreases and that of the OH...O bond increases with increasing the acceptor strength of the base B. The obtained results are in a good agreement with the data obtained previously from matrix-isolation FTIR spectroscopy.

High pressure Raman spectroscopy of H2O-CH3OH mixtures.

PubMed

Hsieh, Wen-Pin; Chien, Yu-Hsiang

2015-02-23

Complex intra-molecular interactions and the hydrogen-bonding network in H2O-volatile mixtures play critical roles in many dynamics processes in physical chemistry, biology, and Earth and planetary sciences. We used high pressure Raman spectroscopy to study the pressure evolution of vibrational frequencies and bonding behavior in H2O-CH3OH mixtures. We found that the presence of low CH3OH content in H2O increases the transition pressure where water crystallizes to ice VI, but does not significantly change the pressure where ice VI transforms to ice VII. Furthermore, the stiffening rates of C-H stretching frequencies dω/dP in CH3OH significantly decrease upon the crystallization of water, and the softening rates of the O-H stretching frequencies of ice VII are suppressed over a narrow pressure range, after which the frequencies of these modes shift with pressure in ways similar to pure CH3OH and ice VII, respectively. Such complex pressure evolution of Raman frequencies along with pronounced variations in Raman intensities of CH3OH within the sample, and the hysteresis of the water-ice VI phase transition suggest pressure-induced segregation of low content CH3OH from ice VII. These findings indicate the significant influence of volatiles on the crystallization of sub-surface ocean and thermal evolution within large icy planets and satellites.

Mass spectrometric study of the negative and positive secondary ions emitted from ethanol microdroplets by MeV-energy heavy ion impact

NASA Astrophysics Data System (ADS)

Kitajima, Kensei; Majima, Takuya; Nishio, Tatsuya; Oonishi, Yoshiki; Mizutani, Shiori; Kohno, Jun-ya; Saito, Manabu; Tsuchida, Hidetsugu

2018-06-01

We have investigated the negative and positive secondary ions emitted from ethanol droplets by 4.0-MeV C3+ impact to reveal the characteristic features of the reaction processes induced by fast heavy ions at the liquid ethanol surface. Analysis of the secondary ions was performed by time-of-flight mass spectrometry for microdroplet targets in a high vacuum environment. Fragment ions, deprotonated cluster ions, and trace amounts of the reaction product ions are observed in the negative secondary ions. The main fragment anions are C2HmO- (m = 1, 3, and 5) and C2H- generated by loss of hydrogen and oxygen atoms. The reaction product anions include deprotonated glycols, larger alcohols, and their dehydrated and dehydrogenated forms generated by secondary reactions between fragments and radicals. Furthermore, C3Hm- (m = 0-2) and C4Hm- (m = 0 and 1) are observed, which could be produced through a plasma state generated in the heavy ion track. Deprotonated ethanol cluster ions, [(EtOH)n - H]-, are observed up to about n = 25. [(EtOH)n - H]- have smaller kinetic energies than the protonated cluster ions (EtOH)nH+. This probably represents the effect of the positive Coulomb potential transiently formed in the ion track. We also discuss the size distributions and structures of the water- and CH2OH-radical-attached ethanol cluster ions.

Decomposition of L-valine under nonthermal dielectric barrier discharge plasma.

PubMed

Li, Yingying; Kojtari, Arben; Friedman, Gary; Brooks, Ari D; Fridman, Alex; Ji, Hai-Feng

2014-02-13

L-Valine solutions in water and phosphate buffer were treated with nonthermal plasma generated by using a dielectric barrier discharge (DBD) device and the products generated after plasma treatments were characterized by (1)H NMR and GC-MS. Our results demonstrate that L-valine is decomposed to acetone, formic acid, acetic acid, threo-methylaspartic acid, erythro-methlyaspartic acid, and pyruvic acid after direct exposure to DBD plasma. The concentrations of these compounds are time-dependent with plasma treatment. The mechanisms of L-valine under the DBD plasma are also proposed in this study. Acetone, pyruvic acid, and organic radicals (•)CHO, CH3COCH2OO(•) (acetonylperoxy), and CH3COC(OH)2OO(•) (1,1-dihydroxypropan-2-one peroxy) may be the determining chemicals in DNA damage.

Experimental binding energies for the metal complexes [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+) for n in the range 4-20.

PubMed

Bruzzi, E; Stace, A J

2014-10-09

A supersonic source of clusters has been used to prepare neutral complexes of methanol in association with an alkaline earth metal atom. From these complexes the following metal-containing dications have been generated through electron ionization: [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+), and for n in the range 4-20, kinetic energy release measurements following the evaporation of a single molecule have been undertaken using a high resolution mass spectrometer. Using finite heat bath theory, these data have been transformed into binding energies for individual methanol molecules attached to each of the three cluster systems. In the larger complexes (n > 6) the results exhibit a consistent trend, whereby the experimental binding energy data for all three metal ions are similar, suggesting that the magnitude of the charge rather than charge density influences the strength of the interaction. From a comparison with data recorded previously for (CH3OH)nH(+) it is found that the 2+ charge on a metal ion has an effect on the binding energy of molecules in complexes containing up to 20 solvent molecules. The results recorded for [Ca(CH3OH)n](2+) show evidence of a very marked transition between n = 6 and 7, which is thought to coincide with the completion of a primary solvation shell and the onset of molecules starting to occupy a second and most probably a third shell.

Relaxation pathways of photoexcited iodide-methanol clusters: a computational investigation.

PubMed

Mak, Chun C; Peslherbe, Gilles H

2014-06-26

Upon photoexcitation of iodide-methanol clusters, I(-)(CH3OH)n, to a charge-transfer-to-solvent (CTTS) excited state, extensive relaxation was found to occur, accompanied by a convoluted modulation of the stability of the excited electron, which ultimately decreases substantially. In order to develop a molecular-level understanding of the relaxation processes of CTTS excited I(-)(CH3OH)n, high-level quantum chemical calculations are first used to investigate the ground, excited, and ionized states of I(-)(CH3OH)n (n = 2). Because of the relatively small size of I(-)(CH3OH)2, it was possible to characterize the contributions of solvent-solvent interactions to the stability of the CTTS excited cluster relative to dissociation into methanol, iodine, and a free electron, which exhibits a substantial dependence on the cluster geometric configuration. Ab initio molecular dynamics simulations of CTTS excited I(-)(CH3OH)3 are then performed to shed some light onto the nature of the relaxation pathways involved in the modulation of the stability of the excited electron in larger clusters. Simulation results suggest that separation of I and (CH3OH)3(-) accompanied by solvent reorganization in the latter can initially stabilize the excited electron, while gradual cluster fragmentation to I, (CH3OH)2(-), and CH3OH ultimately destabilizes it. This work shows, for the first time, that the inability of small CTTS excited I(-)(CH3OH)n to retain a solvated electron may be attributed to the limited hydrogen-bonding capacity of CH3OH, which increases the propensity for fragmentation to smaller clusters with lower excess-electron binding energies, and highlights the critical role of intricate molecular interactions in the electron solvation process.

Effect of energetic electrons on combustion of premixed burner flame

NASA Astrophysics Data System (ADS)

Sasaki, Koichi

2011-10-01

In many studies of plasma-assisted combustion, authors superpose discharges onto flames to control combustion reactions. This work is motivated by more fundamental point of view. The standpoint of this work is that flames themselves are already plasmas. We irradiated microwave power onto premixed burner flame with the intention of heating electrons in it. The microwave power was limited below the threshold for a discharge. We obtained the enhancement of burning velocity by the irradiation of the microwave power, which was understood by the shortening of the flame length. At the same time, we observed the increases in the optical emission intensities of OH and CH radicals. Despite the increases in the optical emission intensities, the optical emission spectra of OH and CH were not affected by the microwave irradiation, indicating that the enhancement of the burning velocity was not attributed to the increase in the gas temperature. On the other hand, we observed significant increase in the optical emission intensity of the second positive system of molecular nitrogen, which is a clear evidence for electron heating in the premixed burner flame. Therefore, it is considered that the enhancement of the burning velocity is obtained by nonequilibrium combustion chemistry which is driven by energetic electrons. By irradiating pulsed microwave power, we examined the time constants for the increases and decreases in the optical emission intensities of N2, OH, CH, and continuum radiation.

Methanol decomposition reactions over a boron-doped graphene supported Ru-Pt catalyst.

PubMed

Damte, Jemal Yimer; Lyu, Shang-Lin; Leggesse, Ermias Girma; Jiang, Jyh Chiang

2018-04-04

The decomposition of methanol is currently attracting research attention due to the potential widespread applications of its end products. In this work, density functional theory (DFT) calculations have been performed to investigate the adsorption and decomposition of methanol on a Ru-Pt/boron doped graphene surface. We find that the most favorable reaction pathway is methanol (CH3OH) decomposition through O-H bond breaking to form methoxide (CH3O) as the initial step, followed by further dehydrogenation steps which generate formaldehyde (CH2O), formyl (CHO), and carbon monoxide (CO). The calculations illustrate that CH3OH and CO groups prefer to adsorb at the Ru-top sites, while CH2OH, CH3O, CH2O, CHO, and H2 groups favor the Ru-Pt bridge sites, indicating the preference of Ru atoms to adsorb the active intermediates or species having lone-pair electrons. Based on the results, it is found that the energy barrier for CH3OH decomposition through the initial O-H bond breaking is less than its desorption energy of 0.95 eV, showing that CH3OH prefers to undergo decomposition to CH3O rather than direct desorption. The study provides in-depth theoretical insights into the potentially enhanced catalytic activity of Ru-Pt/boron doped graphene surfaces for methanol decomposition reactions, thereby contributing to the understanding and designing of an efficient catalyst under optimum conditions.

Methyl-perfluoroheptene-ethers (CH3OC7F13): measured OH radical reaction rate coefficients for several isomers and enantiomers and their atmospheric lifetimes and global warming potentials.

PubMed

Jubb, Aaron M; Gierczak, Tomasz; Baasandorj, Munkhbayar; Waterland, Robert L; Burkholder, James B

2014-05-06

Mixtures of methyl-perfluoroheptene-ethers (CH3OC7F13, MPHEs) are currently in use as replacements for perfluorinated alkanes (PFCs) and poly-ether heat transfer fluids, which are persistent greenhouse gases with lifetimes >1000 years. At present, the atmospheric processing and environmental impact from the use of MPHEs is unknown. In this work, rate coefficients at 296 K for the gas-phase reaction of the OH radical with six key isomers (including stereoisomers and enantiomers) of MPHEs used commercially were measured using a relative rate method. Rate coefficients for the six MPHE isomers ranged from ∼ 0.1 to 2.9 × 10(-12) cm(3) molecule(-1) s(-1) with a strong stereoisomer and -OCH3 group position dependence; the (E)-stereoisomers with the -OCH3 group in an α- position relative to the double bond had the greatest reactivity. Rate coefficients measured for the d3-MPHE isomer analogues showed decreased reactivity consistent with a minor contribution of H atom abstraction from the -OCH3 group to the overall reactivity. Estimated atmospheric lifetimes for the MPHE isomers range from days to months. Atmospheric lifetimes, radiative efficiencies, and global warming potentials for these short-lived MPHE isomers were estimated based on the measured OH rate coefficients along with measured and theoretically calculated MPHE infrared absorption spectra. Our results highlight the importance of quantifying the atmospheric impact of individual components in an isomeric mixture.

Reaction mechanism investigation of furfural conversion to 2-methylfuran on Cu(1 1 1) surface

NASA Astrophysics Data System (ADS)

Ren, Guoqing; Wang, Guiru; Mei, Hua; Xu, Yan; Huang, Ling

2018-07-01

Furfural is a key biomass-derived chemical to produce important biofuels, such as 2-methylfuran. The furfural conversion over Cu(1 1 1)/ZnO catalyst has been investigated by the catalytic evaluation experiments. In order to elucidate the reaction temperature-oriented selectivity, density functional theory calculations were used to study the furfural conversion over Cu(1 1 1) surface. Furfural alcohol forms via F-CHO + 2H → F-CH2O + H → F-CH2OH, and 2-methylfuran forms via dehydration of furfuryl alcohol (F-CH2OH + 2H → F-CH2 + OH + 2H → F-CH3 + OH + H → F-CH3 + H2O). Furthermore, the reaction rates at different temperature (403, 453 and 503 K) have been calculated. As a result, high temperature plays a significant role in enhancing the reaction rate and prompting the reaction selectivity towards 2-methylfuran.

Thermochemical data and additivity group values for ten species of o-xylene low-temperature oxidation mechanism.

PubMed

Canneaux, Sébastien; Vandeputte, Romain; Hammaecher, Catherine; Louis, Florent; Ribaucour, Marc

2012-01-12

o-Xylene could be a good candidate to represent the family of aromatic hydrocarbons in a surrogate fuel. This study uses computational chemistry to calculate standard enthalpies of formation at 298 K, Δ(f)H°(298 K), standard entropies at 298 K, S°(298 K), and standard heat capacities C(p)°(T) over the temperature range 300 K to 1500 K for ten target species present in the low-temperature oxidation mechanism of o-xylene: o-xylene (1), 2-methylbenzyl radical (2), 2-methylbenzylperoxy radical (3), 2-methylbenzyl hydroperoxide (4), 2-(hydroperoxymethyl)benzyl radical (5), 2-(hydroperoxymethyl)benzaldehyde (6), 1-ethyl-2-methylbenzene (7), 2,3-dimethylphenol (8), 2-hydroxybenzaldehyde (9), and 3-hydroxybenzaldehyde (10). Δ(f)H°(298 K) values are weighted averages across the values calculated using five isodesmic reactions and five composite calculation methods: CBS-QB3, G3B3, G3MP2, G3, and G4. The uncertainty in Δ(f)H°(298 K) is also evaluated. S°(298 K) and C(p)°(T) values are calculated at B3LYP/6-311G(d,p) level of theory from molecular properties and statistical thermodynamics through evaluation of translational, rotational, vibrational, and electronic partition functions. S°(298 K) and C(p)°(300 K) values are evaluated using the rigid-rotor-harmonic-oscillator model. C(p)°(T) values at T ≥ 400 K are calculated by treating separately internal rotation contributions and translational, external rotational, vibrational, and electronic contributions. The thermochemical properties of six target species are used to develop six new additivity groups taking into account the interaction between two substituents in ortho (ORT/CH2OOH/ME, ORT/ET/ME, ORT/CHO/OH, ORT/CHO/CH2OOH) or meta (MET/CHO/OH) positions, and the interaction between three substituents (ME/ME/OH123) located one beside the other (positions numbered 1, 2, 3) for two- or three-substituted benzenic species. Two other additivity groups are also developed using the thermochemical properties of benzenic species taken from the literature: the C/CB/H2/OO and the CB/CO groups. These groups extend the capacities of the group additivity method to deal with substituted benzenic species.

Hydroxyl radical generation in electro-Fenton process with a gas-diffusion electrode: Linkages with electro-chemical generation of hydrogen peroxide and iron redox cycle.

PubMed

Yatagai, Tomonori; Ohkawa, Yoshiko; Kubo, Daichi; Kawase, Yoshinori

2017-01-02

The hydroxyl radical generation in an electro-Fenton process with a gas-diffusion electrode which is strongly linked with electro-chemical generation of hydrogen peroxide and iron redox cycle was studied. The OH radical generation subsequent to electro-chemical generations of H 2 O 2 was examined under the constant potential in the range of Fe 2+ dosage from 0 to 1.0 mM. The amount of generated OH radical initially increased and gradually decreased after the maximum was reached. The initial rate of OH radical generation increased for the Fe 2+ dosage <0.25 mM and at higher Fe 2+ dosages remained constant. At higher Fe 2+ dosages the precipitation of Fe might inhibit the enhancement of OH radical generation. The experiments for decolorization and total organic carbon (TOC) removal of azo-dye Orange II by the electro-Fenton process were conducted and the quick decolorization and slow TOC removal of Orange II were found. To quantify the linkages of OH radical generation with dynamic behaviors of electro-chemically generated H 2 O 2 and iron redox cycle and to investigate effects of OH radical generation on the decolorization and TOC removal of Orange II, novel reaction kinetic models were developed. The proposed models could satisfactory clarify the linkages of OH radical generation with electro-chemically generated H 2 O 2 and iron redox cycle and simulate the decolorization and TOC removal of Orange II by the electro-Fenton process.

Analgesic and anticonvulsant effects of extracts from the leaves of Kalanchoe crenata (Andrews) Haworth (Crassulaceae).

PubMed

Nguelefack, T B; Nana, P; Atsamo, A D; Dimo, T; Watcho, P; Dongmo, A B; Tapondjou, L A; Njamen, D; Wansi, S L; Kamanyi, A

2006-06-15

Kalanchoe crenata Andr. (Crassulaceae) is a fleshy herbaceous plant used in the African traditional medicine as remedies against otitis, headache, inflammations, convulsions and general debility. In the present work, the analgesic effects of methylene chloride/methanol (1:1) (CH(2)Cl(2)/CH(3)OH) extract and its hexane, methylene chloride (CH(2)Cl(2)), ethyl acetate, n-butanol fractions and aqueous residue have been evaluated using acetic acid, formalin and pressure test. The anticonvulsant effects of the CH(2)Cl(2)/CH(3)OH extract were also investigated on seizures induced by pentylenetetrazol (PTZ 70 mg/kg), strychnine sulphate (STN 2.5 mg/kg) and thiosemicarbazide (TSC 50 mg/kg). CH(2)Cl(2)/CH(3)OH extract and its fractions, administered orally at the doses of 150 and 300 mg/kg, exhibited protective effect of at least 30% on the pain induced by acetic acid. The CH(2)Cl(2) fraction at 300 mg/kg showed a maximal effect of 78.49%. The CH(2)Cl(2)/CH(3)OH extract and its CH(2)Cl(2) fraction at the doses of 150 and 300 mg/kg significantly reduced the first phase of pain induced by formalin while the second phase was completely inhibited. The CH(2)Cl(2) fraction produced more than 45% reduction in the sensitivity to pain induced by pressure. The CH(2)Cl(2)/CH(3)OH extract of Kalanchoe crenata significantly increased the latency period in seizures induced by PTZ and significantly reduced the duration of seizures induced by the three convulsant agents. The extract protected 20% of animals against death in seizures induced by TSC and STN. These results suggest a peripheral and central analgesic activities as well as an anticonvulsant effect of the leaves of Kalanchoe crenata.

40 CFR 600.113-08 - Fuel economy calculations for FTP, HFET, US06, SC03 and cold temperature FTP tests.

Code of Federal Regulations, 2011 CFR

2011-07-01

... paragraph (g) of this section. CH3OH = Grams/mile CH3OH (methanol) as obtained in paragraph (d) of this..., additionally for methanol-fueled automobiles, methanol (CH3OH) and formaldehyde (HCHO); and additionally for... for HC, CO and CO2; and, additionally for methanol-fueled automobiles, CH3OH and HCHO; and...

Formation, Structure and Properties of Boron Nitride Fibers from Polymer Precursors

DTIC Science & Technology

1992-02-25

conversion, have been demonstrated in this study. Poly(ethylene oxide) (PEO), poly(N-vinyl-2-pyrrolidinone) ( PVP ), and poly(methyl methacrylate) (PMMA) were...vinylpyrrolidinone ( PVP , Mw = 360,000). A 100 ml reaction flask with teflon boiling chips and a 100 ml receiving flask were used on a high boiling distilling...CH 3 OBO) 3 : B(OH)3 Predicted 2 Experiment Experiment, 1 wt% PVP 2:1 47.8 mole% CH 3 OH 39.6 mole% CH 3OH 35.2 mole% CH3 OH 3:1 47.8 - 35.5 4:1 47.8

Theoretical studies on the unimolecular decomposition of ethylene glycol.

PubMed

Ye, Lili; Zhao, Long; Zhang, Lidong; Qi, Fei

2012-01-12

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T).

CH(X2∏, a4∑-) ... OH2 and CH2(X˜3B1, ã1A1) ... OH2 interactions. A first principles investigation

NASA Astrophysics Data System (ADS)

Tzeli, Demeter; Mavridis, Aristides

We have investigated the interaction of the methylidene, CH(X2∏, a4∑-) and methylene, CH2(X˜3B1, ã1A1) with H2O, employing the (P)MPn (n = 2, 4) techniques in conjunction with the sequence of correlation consistent basis sets aug-cc-pVxZ, x = 2, 3, and 4. For the CH ... OH2 system, we have located four minima (m) and three transition states (ts) and for the CH2 ... OH2, five minima and four transition states. All our results have been corrected for zero-point energy (ZPE) and basis set superposition errors (BSSE), while for the most important m_ structures, we report complete basis set (CBS) interaction limits. We also report fully optimized geometries, harmonic frequencies, dipole moments, Mulliken charges, and potential energy curves. The highest CH(X2∏) ... OH2 (m1_2∏) and CH2(ã1A1) ... OH2 (m1_1A1) interactions are the result of electron transfer from the oxygen atom to the empty pπ orbitals of CH(X2∏) and CH2(ã1A1), respectively (ylide-like structures). At the (P)MP4/AQZ//MP2/ATZ level, including ZPE, BSSE, and CBS extrapolation, we obtain ΔE0(BSSE)+CBS = -9.36 kcal/mol at rC ... O = 1.752 Å, and -9.73 kcal/mol at rC ... O = 1.741 Å for the m1_2∏ and m1_1A1, respectively.

Spatial distribution of FIR rotationally excited CH+ and OH emission lines in the Orion Bar PDR⋆

PubMed Central

Parikka, A.; Habart, E.; Bernard-Salas, J.; Goicoechea, J. R.; Abergel, A.; Pilleri, P.; Dartois, E.; Joblin, C.; Gerin, M.; Godard, B.

2016-01-01

Context The methylidyne cation (CH+) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500–1000 K) in photodissociation regions with high incident FUV radiation field. The excitation may also originate in dense gas (> 105 cm−3) followed by nonreactive collisions with H2, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH+ and OH correlate with the excited CO, a tracer of dense and warm gas, and formation pumping contributes to CH+ excitation. Aims Our goal is to examine the spatial distribution of the rotationally excited CH+ and OH emission lines in the Orion Bar in order to establish their physical origin and main formation and excitation mechanisms. Methods We present spatially sampled maps of the CH+ J=3-2 transition at 119.8 µm and the OH Λ-doublet at 84 µm in the Orion Bar over an area of 110″×110″ with Herschel (PACS). We compare the spatial distribution of these molecules with those of their chemical precursors, C+, O and H2, and tracers of warm and dense gas (high-J CO). We assess the spatial variation of CH+ J=2-1 velocity-resolved line profile at 1669 GHz with Herschel HIFI spectrometer observations. Results The OH and especially CH+ lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH+ and OH morphologies indicate that CH+ formation and excitation are strongly related to the observed vibrationally excited H2. This, together with the observed broad CH+ line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 µm emission coincides with a bright young object, proplyd 244-440, which shows that OH can be an excellent tracer of UV-irradiated dense gas. Conclusions The spatial distribution of CH+ and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH+ J=3-2 excitation processes. The excitation of the OH Λ-doublet at 84 µm is mainly sensitive to the temperature and density. PMID:28260804

Hydrogen-bonding behavior of various conformations of the HNO3…(CH3OH)2 ternary system.

PubMed

Özsoy, Hasan; Uras-Aytemiz, Nevin; Balcı, F Mine

2017-12-21

Nine minima were found on the intermolecular potential energy surface for the ternary system HNO 3 (CH 3 OH) 2 at the MP2/aug-cc-pVDZ level of theory. The cooperative effect, which is a measure of the hydrogen-bonding strength, was probed in these nine conformations of HNO 3 …(CH 3 OH) 2 . The results are discussed here in terms of structures, energetics, infrared vibrational frequencies, and topological parameters. The cooperative effect was observed to be an important contributor to the total interaction energies of the cyclic conformers of HNO 3 …(CH 3 OH) 2 , meaning that it cannot be neglected in simulations in which the pair-additive potential is applied. Graphical abstract The H-bonding behavior of various conformations of the HNO 3 (CH 3 OH) 2 trimer was investigated.

Kinetics and Mechanism of the Reaction of Hydoxyl Radicals with Acetonitrile under Atmospheric Conditions

NASA Technical Reports Server (NTRS)

Hynes, A. J.; Wine, P. H.

1997-01-01

The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH3CN (1) and its isotopic variants, OH + CD3CN (2), OD + CH3CN (3), and OD + CD3CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N2, N2/O2, and He buffer gases. In the absence of O2 all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-first rate constants which were proportional to substrate concentration. Data obtained in N2 over the range 50-700 Torr at 298 K are consistent with k(sub 1), showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures in k(sub 1)(T) = (1.1(sup +0.5)/(sub -0.3)) x 10(exp -12) exp[(-1130 +/- 90)/T] cu cm /(molecule s). The kinetics of reaction 2 are found to be pressure dependent with k(sub 2) (298 K) increasing from (1.21 +/- 0.12) x 10(exp -14) to (2.16 +/- 0.11) x 10(exp -14) cm(exp 3)/ (molecule s) over the pressure range 50-700 Torr of N2 at 298 K. Data at pressures greater than 600 Torr give k(sub 2)(T) = (9.4((sup +13.4)(sub -5.0))) x 10(exp -13) exp[(-1180 +/- 250)/T] cu cm/(molecule s). The rates of reactions 3 and 4 are found to be independent of pressure over the range 50-700 Torr of N2 with 298 K rate coefficient given by k(sub 3) =(3.18 +/- 0.40) x 10(exp -14) cu cm/(molecule s) and k(sub 4) = (2.25 +/-0.28) x 10(exp -14) cu cm/(molecule s). In the presence of O2 each reaction shows complex (non-pseudo-first-order) kinetic behavior and/or an apparent decrease in the observed rate constant with increasing [O2], indicating the presence of significant OH or OD regeneration. Observation of regeneration of OH in (2) and OD in (3) is indicative of a reaction channel which proceeds via addition followed by reaction of the adduct, or one of its decomposition products, with O2. The observed OH and OD decay profiles have been modeled by using a simple mechanistic scheme to extract kinetic information about the adduct reations with O2 and branching ratios for OH regeneration. A plausible mechanism for OH regeneration in (2) involves OH addition to the nitrogen atom followed by O2 addition to the cyano carbon atom, isomeriazation and decomposition to D2CO + DOCN + OH. Our results suggest that the OH + CH3CN reaction occurs via a complex mechanism involving both bimolecular and termolecular pathways, analogous to the mechanisms for the the important atmospheric reactions of OH with CO and HNO3.

Isomorphous rare-earth tris[bis(2,6-diisopropylphenyl) phosphate] complexes and their catalytic properties in 1,3-diene polymerization and in the inhibited oxidation of polydimethylsiloxane.

PubMed

Minyaev, Mikhail E; Tavtorkin, Alexander N; Korchagina, Sof'ya A; Bondarenko, Galina N; Churakov, Andrei V; Nifant'ev, Ilya E

2018-05-01

Crystals of mononuclear tris[bis(2,6-diisopropylphenyl) phosphato-κO]pentakis(methanol-κO)lanthanide methanol monosolvates of lanthanum, [La(C 24 H 34 O 4 P) 3 (CH 3 OH) 5 ]·CH 3 OH, (1), cerium, [Ce(C 24 H 34 O 4 P) 3 (CH 3 OH) 5 ]·CH 3 OH, (2), and neodymium, [Nd(C 24 H 34 O 4 P) 3 (CH 3 OH) 5 ]·CH 3 OH, (3), have been obtained by reactions between LnCl 3 (H 2 O) n (n = 6 or 7) and lithium bis(2,6-diisopropylphenyl) phosphate in a 1:3 molar ratio in methanol media. Compounds (1)-(3) crystallize in the monoclinic P2 1 /c space group and have isomorphous crystal structures. All three bis(2,6-diisopropylphenyl) phosphate ligands display a κO-monodentate coordination mode. The coordination number of the metal atom is 8. Each [Ln{O 2 P(O-2,6- i Pr 2 C 6 H 3 ) 2 } 3 (CH 3 OH) 5 ] molecular unit exhibits four intramolecular O-H...O hydrogen bonds, forming six-membered rings. The unit forms two intermolecular O-H...O hydrogen bonds with one noncoordinating methanol molecule. All six hydroxy H atoms are involved in hydrogen bonding within the [Ln{O 2 P(O-2,6- i Pr 2 C 6 H 3 ) 2 } 3 (CH 3 OH) 5 ]·CH 3 OH unit. This, along with the high steric hindrance induced by the three bulky diaryl phosphate ligands, prevents the formation of a hydrogen-bond network. Complexes (1)-(3) exhibit disorder of two of the isopropyl groups of the phosphate ligands. The cerium compound (2) demonstrates an essential catalytic inhibition in the thermal decomposition of polydimethylsiloxane in air at 573 K. Catalytic systems based on the neodymium complex tris[bis(2,6-diisopropylphenyl) phosphato-κO]neodymium, (3'), which was obtained as a dry powder of (3) upon removal of methanol, display a high catalytic activity in isoprene and butadiene polymerization.

Chemical modelling of glycolaldehyde and ethylene glycol in star-forming regions

NASA Astrophysics Data System (ADS)

Coutens, A.; Viti, S.; Rawlings, J. M. C.; Beltrán, M. T.; Holdship, J.; Jiménez-Serra, I.; Quénard, D.; Rivilla, V. M.

2018-04-01

Glycolaldehyde (HOCH2CHO) and ethylene glycol ((CH2OH)2) are two complex organic molecules detected in the hot cores and hot corinos of several star-forming regions. The ethylene glycol/glycolaldehyde abundance ratio seems to show an increase with the source luminosity. In the literature, several surface-chemistry formation mechanisms have been proposed for these two species. With the UCLCHEM chemical code, we explored the different scenarios and compared the predictions for a range of sources of different luminosities with the observations. None of the scenarios reproduce perfectly the trend. A better agreement is, however, found for a formation through recombination of two HCO radicals followed by successive hydrogenations. The reaction between HCO and CH2OH could also contribute to the formation of glycolaldehyde in addition to the hydrogenation pathway. The predictions are improved when a trend of decreasing H2 density within the core region with T≥100 K as a function of luminosity is included in the model. Destruction reactions of complex organic molecules in the gas phase would also need to be investigated, since they can affect the abundance ratios once the species have desorbed in the warm inner regions of the star-forming regions.

Properties of Multiphase Polyurethane Systems.

DTIC Science & Technology

1981-08-01

based on 4,4’-diphenylmethane dilsocyanate (MDI), N -methyl diethanolamine ( MDEA ), and polytetramethylene oxide (PTMO) and were synthesized with four...several levels of ammonium sulfonation (Scheme II) MDI/ MDEA /PTMO Series H04CH2 CH2CH2CH20- H + 0 = C = N -- -CH 2-O- N = C = 0 PTMO MDI 70 C HO OH...catalyst I II11 1 " 0 = C = N "---CH 2 - - N -C-O’-CH 2 CH C2H2 0-4C-’-( >-CH2DMA 1 CH3 70C I * HO - CM2 - CH2 - N - CH2 - CH2 - OH--- MDEA 0 H H 0 CH3H ... H2

Radiation-Induced Chemical Reactions in Hydrogel of Hydroxypropyl Cellulose (HPC): A Pulse Radiolysis Study.

PubMed

Yamashita, Shinichi; Ma, Jun; Marignier, Jean-Louis; Hiroki, Akihiro; Taguchi, Mitsumasa; Mostafavi, Mehran; Katsumura, Yosuke

2016-12-01

We performed studies on pulse radiolysis of highly transparent and shape-stable hydrogels of hydroxypropyl cellulose (HPC) that were prepared using a radiation-crosslinking technique. Several fundamental aspects of radiation-induced chemical reactions in the hydrogels were investigated. With radiation doses less than 1 kGy, degradation of the HPC matrix was not observed. The rate constants of the HPC composing the matrix, with two water decomposition radicals [hydroxyl radical ( • OH) and hydrated electron ([Formula: see text])] in the gels, were determined to be 4.5 × 10 9 and 1.8 × 10 7 M -1 s -1 , respectively. Direct ionization of HPC in the matrix slightly increased the initial yield of [Formula: see text], but the additionally produced amount of [Formula: see text] disappeared immediately within 200 ps, indicating fast recombination of [Formula: see text] with hole radicals on HPC or on surrounding hydration water molecules. Reactions of [Formula: see text] with nitrous oxide (N 2 O) and nitromethane (CH 3 NO 2 ) were also examined. Decay of [Formula: see text] due to scavenging by N 2 O and CH 3 NO 2 were both slower in hydrogels than in aqueous solutions, showing slower diffusions of the reactants in the gel matrix. The degree of decrease in the decay rate was more effective for N 2 O than for CH 3 NO 2 , revealing lower solubility of N 2 O in gel than in water. It is known that in viscous solvents, such as ethylene glycol, CH 3 NO 2 exhibits a transient effect, which is a fast reaction over the contact distance of reactants and occurs without diffusions of reactants. However, such an effect was not observed in the hydrogel used in the current study. In addition, the initial yield of [Formula: see text], which is affected by the amount of the scavenged precursor of [Formula: see text], in hydrogel containing N 2 O was slightly higher than that in water containing N 2 O, and the same tendency was found for CH 3 NO 2 .

Infrared Absorption Spectroscopy and Chemical Kinetics of Free Radicals, Final Technical Report

DOE R&D Accomplishments Database

Curl, Robert F.; Glass, Graham P.

2004-11-01

This research was directed at the detection, monitoring, and study of the chemical kinetic behavior by infrared absorption spectroscopy of small free radical species thought to be important intermediates in combustion. Work on the reaction of OH with acetaldehyde has been completed and published and work on the reaction of O({sup 1}D) with CH{sub 4} has been completed and submitted for publication. In the course of our investigation of branching ratios of the reactions of O({sup 1}D) with acetaldehyde and methane, we discovered that hot atom chemistry effects are not negligible at the gas pressures (13 Torr) initially used. Branching ratios of the reaction of O({sup 1}D) with CH{sub 4} have been measured at a tenfold higher He flow and fivefold higher pressure.

The Effect of the Interannual Variability of the OH Sink on the Interannual Variability of the Atmospheric Methane Mixing Ratio and Carbon Stable Isotope Composition

NASA Astrophysics Data System (ADS)

Guillermo Nuñez Ramirez, Tonatiuh; Houweling, Sander; Marshall, Julia; Williams, Jason; Brailsford, Gordon; Schneising, Oliver; Heimann, Martin

2013-04-01

The atmospheric hydroxyl radical concentration (OH) varies due to changes in the incoming UV radiation, in the abundance of atmospheric species involved in the production, recycling and destruction of OH molecules and due to climate variability. Variability in carbon monoxide emissions from biomass burning induced by El Niño Southern Oscillation are particularly important. Although the OH sink accounts for the oxidation of approximately 90% of atmospheric CH4, the effect of the variability in the distribution and strength of the OH sink on the interannual variability of atmospheric methane (CH4) mixing ratio and stable carbon isotope composition (δ13C-CH4) has often been ignored. To show this effect we simulated the atmospheric signals of CH4 in a three-dimensional atmospheric transport model (TM3). ERA Interim reanalysis data provided the atmospheric transport and temperature variability from 1990 to 2010. We performed simulations using time dependent OH concentration estimations from an atmospheric chemistry transport model and an atmospheric chemistry climate model. The models assumed a different set of reactions and algorithms which caused a very different strength and distribution of the OH concentration. Methane emissions were based on published bottom-up estimates including inventories, upscaled estimations and modeled fluxes. The simulations also included modeled concentrations of atomic chlorine (Cl) and excited oxygen atoms (O(1D)). The isotopic signal of the sources and the fractionation factors of the sinks were based on literature values, however the isotopic signal from wetlands and enteric fermentation processes followed a linear relationship with a map of C4 plant fraction. The same set of CH4emissions and stratospheric reactants was used in all simulations. Two simulations were done per OH field: one in which the CH4 sources were allowed to vary interannually, and a second where the sources were climatological. The simulated mixing ratios and isotopic compositions at global reference stations were used to construct more robust indicators such as global and zonal means and interhemispheric differences. We also compared the model CH4 mixing ratio to satellite observations, for the period 2003 to 2004 with SCIAMACHY and from 2009 to 2010 with GOSAT. The interannual variability of the different OH fields imprinted an interannual variation of the atmospheric CH4 mixing ratio with a magnitude of ±10 ppb, which is comparable to the effect of all sources combined. Meanwhile its effect on the interannual variability of δ13C-CH4 was minor (< 10%). The interannual variability of the mixing ratio interhemispheric difference is dominated by the sources because the OH sink is concentrated in the tropics, thus its interannual variability affects both hemispheres. Meanwhile, although the OH plays an important role in the establishment of an interhemispheric gradient of δ13C-CH4, the interannual variation of this gradient is negligibly affected by the choice of OH field. Overall the study showed that the variability of the OH sink plays a significant role in the interannual variability of the atmospheric methane mixing ratio, and must be considered to improve our understanding of the recent trends in the global methane budget.

Mechanisms for •O2‑ and •OH production on flowerlike BiVO4 photocatalysis based on Electron Spin Resonance

NASA Astrophysics Data System (ADS)

Xu, Xuan; Sun, Yaofang; Fan, Zihong; Zhao, Deqiang; Xiong, Shimin; Zhang, Bingyao; Zhou, Shiyu; Liu, Guotao

2018-03-01

Many studies have focused on the use of BiVO4 as a photocatalyst, but few have investigated the production of free radicals during the photocatalytic process. Following synthesis of flowerlike BiVO4 and characterization by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) Scanning electron microscopy (EDX), UV-Vis and XPS, we successfully prepared BiVO4. Then we used electron spin resonance (ESR) to determine the production and degradation of individual active free radicals, including the superoxide radical (•O2‑) and the hydroxyl radical (•OH). In the first experiment, we used ESR to detect the signals of free radicals (•O2‑ and •OH) under varying oxygen conditions. The results shown that in addition to production by •O2‑, •OH could also be produced by oxidation of h+ to OH‑. In the next experiment, we detected •OH under varying pH to identify the result of the first experiment, and found that signal intensities increased with increasing pH, indicating the mechanism for •OH production. Finally, we conducted a trapping experiment to examine free radical degradation mechanisms. We identified •OH and h+ as the main active free radicals and showed the complete production about •OH. These results improve current knowledge of free radical production mechanisms, which can be used to enhance the photocatalytic performance of BiVO4.

A Computational Investigation of the Oxidative Deboronation of BoroGlycine, H2N–CH2–B(OH)2, Using H2O and H2O2

PubMed Central

Larkin, Joseph D.; Markham, George D.; Milkevitch, Matt; Brooks, Bernard R.; Bock, Charles W.

2014-01-01

We report results from a computational investigation of the oxidative deboronation of BoroGlycine, H2N–CH2–B(OH)2, using H2O and H2O2 as the reactive oxygen species (ROS) to yield aminomethanol, H2N–CH2–OH; these results complement our study on the protodeboronation of BoroGlycine to produce methylamine, H2N–CH3 (Larkin et al. J. Phys. Chem. A, 111, 6489–6500, 2007). Second-order Møller-Plesset (MP2) perturbation theory with Dunning-Woon correlation-consistent (cc) basis sets were used for the calculations with comparisons made to results from Density Functional Theory (DFT) at the PBE1PBE/6-311++G(d,p)(cc-pVDZ) levels. The effects of a bulk aqueous environment were also incorporated into the calculations employing PCM and CPCM methodology. Using H2O as the ROS, the reaction H2O + H2N–CH2–B(OH)2 → H2N–CH2–OH + H–B(OH)2 was calculated to be endothermic, the value of ΔH2980 was +12.0 kcal/mol at the MP2(FC)/cc-pVTZ computational level in vacuo and +13.7 kcal/mol in PCM aqueous media; the corresponding value for the activation barrier, ΔH‡, was +94.3 kcal/mol relative to the separated reactants in vacuo and +89.9 kcal/mol in PCM aqueous media. In contrast, the reaction H2O2 + H2N–CH2–B(OH)2 → H2N–CH2–OH + B(OH)3 was calculated to be highly exothermic with a ΔH2980 value of −100.9 kcal/mol at the MP2(FC)/cc-pVTZ computational level in vacuo and −99.6 kcal/mol in CPCM aqueous media; the highest-energy transition state for the multi-step process associated with this reaction involved the rearrangement of H2N–CH2–B(OH)(OOH) to H2N–CH2–O–B(OH)2 with a ΔH‡ value of +23.2 kcal/mol in vacuo relative to the separated reactants. These computational results for BoroGlycine are in accord with the experimental observations for the deboronation of the FDA approved anti-cancer drug Bortezomib (Velcade™, PS-341) where it was found to be the principle deactivation pathway. (Labutti et al. Chem. Res. Toxicol., 19, 539–546, 2006). PMID:19810757

Facile synthesis of bis(dichalcogenophosphinate)s and a remarkable [Li8(OH)6]2+ polyhedron.

PubMed

Davies, Robert P; Martinelli, M Giovanna; Patel, Laura; White, Andrew J P

2010-05-17

The synthesis and characterization of three lithium complexes of novel bis(dichalcogenophosphinate) ligands are reported: (PhP(S)(2)CH(2)CH(2)P(S)(2)Ph)Li(2)(THF)(4) (2), (PhP(Se)(2)CH(2)CH(2)P(Se)(2)Ph)Li(2)(THF)(4).(PhP(Se)(2)CH(2)CH(2)P(Se)(2)Ph)Li(2)(THF)(6) (3), and [PhP(Te)(2)CH(2)CH(2)P(Te)(2)Ph][Li(8)(OH)(6)(THF)(8)] (4). The synthetic route to these complexes proceeds via the insertion reaction of elemental chalcogens into the phosphorus-lithium bonds of 1,2-dilithio-1,2-di(phenylphosphine)ethylene (1). X-ray analysis of 2 revealed isobidentate coordination of the lithiums by the dithiophosphinate groups. In contrast, the diselenophosphinate groups in 3 coordinate the lithium centers in both isobidentate and monodentate modes, and the ditellurophosphinate groups in 4 form non-coordinate separate ion pairs. The countercation in 4 is shown to be a unique [Li(8)(OH)(6)](2+) rhombic dodecahedral polyhedron, putatively formed from the capping of a hexameric [Li(OH)](6) aggregate with lithium cations on its open faces.

Highly Cooperative Tetrametallic Ruthenium-μ-Oxo-μ-Hydroxo Catalyst for the Alcohol Oxidation Reaction

PubMed Central

Yi, Chae S.; Zeczycki, Tonya N.; Guzei, Ilia A.

2008-01-01

The tetrametallic ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was synthesized in two steps from the monomeric complex (PCy3)(CO)RuHCl (2). The tetrameric complex 1 was found to be a highly effective catalyst for the transfer dehydrogenation of alcohols. Complex 1 showed a different catalytic activity pattern towards primary and secondary benzyl alcohols, as indicated by the Hammett correlation for the oxidation reaction of p-X-C6H4CH2OH (ρ = −0.45) and p-X-C6H4CH(OH)CH3 (ρ = +0.22) (X = OMe, CH3, H, Cl, CF3). Both a sigmoidal curve from the plot of initial rate vs [PhCH(OH)CH3] (K0.5 = 0.34 M; Hill coefficient, n = 4.2±0.1) and the phosphine inhibition kinetics revealed the highly cooperative nature of the complex for the oxidation of secondary alcohols. PMID:18726005

An isomer-specific study of solid nitromethane decomposition pathways - Detection of aci-nitromethane (H2CNO(OH)) and nitrosomethanol (HOCH2NO) intermediates

NASA Astrophysics Data System (ADS)

Maksyutenko, Pavlo; Förstel, Marko; Crandall, Parker; Sun, Bing-Jian; Wu, Mei-Hung; Chang, Agnes H. H.; Kaiser, Ralf I.

2016-08-01

An isomer specific study of energetic electron exposed nitromethane ices was performed via photoionization - reflectron time of flight mass spectrometry (PI-ReTOF-MS) of the subliming products employing tunable vacuum ultraviolet light for ionization. Supported by electronic structure calculations, nitromethane (CH3NO2) was found to isomerize to methyl nitrite (CH3ONO) and also via hydrogen migration to the hitherto elusive aci-nitromethane isomer (H2CNO(OH)). The latter isomerizes to nitrosomethanol (HOCH2NO) through hydroxyl group (OH) migration, and, probably, ring closure to the cyclic 2-hydroxy-oxaziridine isomer (c-H2CON(OH)) as well. The importance of hydrogen migrations was also verified via the nitrosomethane (CH3NO) - formaldehyde oxime isomer (CH2NOH) pair.

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

NASA Astrophysics Data System (ADS)

Buckingham, Grant T.; Porterfield, Jessica P.; Kostko, Oleg; Troy, Tyler P.; Ahmed, Musahid; Robichaud, David J.; Nimlos, Mark R.; Daily, John W.; Ellison, G. Barney

2016-07-01

Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H513CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H513CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckingham, Grant T.; Porterfield, Jessica P.; Kostko, Oleg

2016-07-05

Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 us. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures upmore » to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 13CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 13CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less

Acid-base equilibrium dynamics in methanol and dimethyl sulfoxide probed by two-dimensional infrared spectroscopy.

PubMed

Lee, Chiho; Son, Hyewon; Park, Sungnam

2015-07-21

Two-dimensional infrared (2DIR) spectroscopy, which has been proven to be an excellent experimental method for studying thermally-driven chemical processes, was successfully used to investigate the acid dissociation equilibrium of HN3 in methanol (CH3OH) and dimethyl sulfoxide (DMSO) for the first time. Our 2DIR experimental results indicate that the acid-base equilibrium occurs on picosecond timescales in CH3OH but that it occurs on much longer timescales in DMSO. Our results imply that the different timescales of the acid-base equilibrium originate from different proton transfer mechanisms between the acidic (HN3) and basic (N3(-)) species in CH3OH and DMSO. In CH3OH, the acid-base equilibrium is assisted by the surrounding CH3OH molecules which can directly donate H(+) to N3(-) and accept H(+) from HN3 and the proton migrates through the hydrogen-bonded chain of CH3OH. On the other hand, the acid-base equilibrium in DMSO occurs through the mutual diffusion of HN3 and N3(-) or direct proton transfer. Our 2DIR experimental results corroborate different proton transfer mechanisms in the acid-base equilibrium in protic (CH3OH) and aprotic (DMSO) solvents.

Reaction between peroxynitrite and triphenylphosphonium-substituted arylboronic acid isomers–Identification of diagnostic marker products and biological implications

PubMed Central

Sikora, Adam; Zielonka, Jacek; Adamus, Jan; Debski, Dawid; Dybala-Defratyka, Agnieszka; Michalowski, Bartosz; Joseph, Joy; Hartley, Richard C.; Murphy, Michael P.; Kalyanaraman, Balaraman

2013-01-01

Aromatic boronic acids react rapidly with peroxynitrite (ONOO−) to yield phenols as major products. This reaction was used to monitor ONOO− formation in cellular systems. Previously, we proposed that the reaction between ONOO− and arylboronates (PhB(OH)2) yields a phenolic product (major pathway) and a radical pair PhB(OH)2O•−…•NO2 (minor pathway). [Sikora A. et al., Chem Res Toxicol 24, 687-97, 2011]. In this study, we investigated the influence of a bulky triphenylphosphonium (TPP) group on the reaction between ONOO− and mitochondria-targeted arylboronate isomers (o-, m-, and p-MitoPhB(OH)2). Results from the electron paramagnetic resonance (EPR) spin-trapping experiments unequivocally showed the presence of a phenyl radical intermediate from meta and para isomers, and not from the ortho isomer. The yield of o-MitoPhNO2 formed from the reaction between o-MitoPhB(OH)2 and ONOO− was not diminished by phenyl radical scavengers, suggesting a rapid fragmentation of the o-MitoPhB(OH)2O•− radical anion with subsequent reaction of the resulting phenyl radical with •NO2 in the solvent cage. The DFT quantum mechanical calculations showed that the energy barrier for the dissociation of o-MitoPhB(OH)2O•− radical anion is significantly lower than that of m-MitoPhB(OH)2O•− and p-MitoPhB(OH)2O•− radical anions. The nitrated product, o-MitoPhNO2, is not formed by nitrogen dioxide radical generated by myeloperoxidase in the presence of nitrite anion and hydrogen peroxide, indicating that this specific nitrated product may be used as a diagnostic marker product for ONOO−. Incubation of o-MitoPhB(OH)2 with RAW 264.7 macrophages activated to produce ONOO− yielded the corresponding phenol o-MitoPhOH as well as the diagnostic nitrated product, o-MitoPhNO2. We conclude that the ortho isomer probe reported here is most suitable for specific detection of ONOO− in biological systems. PMID:23611338

A radical pathway in catecholase activity with nickel(II) complexes of phenol based "end-off" compartmental ligands.

PubMed

Ghosh, Totan; Adhikary, Jaydeep; Chakraborty, Prateeti; Sukul, Pradip K; Jana, Mahendra Sekhar; Mondal, Tapan Kumar; Zangrando, Ennio; Das, Debasis

2014-01-14

Seven dinuclear and one dinuclear based dicyanamide bridged polymeric Ni(II) complexes of phenol based compartmental ligands (HL(1)-HL(4)) have been synthesized with the aim to investigate their catecholase-like activity and to evaluate the most probable mechanistic pathway involved in this process. The complexes have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analyses namely [Ni2(L(2))(SCN)3(H2O)(CH3OH)] (), [Ni2(L(4))(SCN)3(CH3OH)2] (), [Ni2(L(2))(SCN)2(AcO)(H2O)] (), [Ni2(L(4))(SCN)(AcO)2] (), [Ni2(L(2))(N3)3(H2O)2] (), [Ni2(L(4))(N3)3(H2O)2] (), [Ni2(L(1))(AcO)2(N(CN)2)]n () and [Ni2(L(3))(AcO)2(N(CN)2)] (), [SCN = isothiocyanate, AcO = acetate, N3 = azide, and N(CN)2 = dicyanamide anion; L(1-4) = 2,6-bis(R2-iminomethyl)-4-R1-phenolato, where R1 = methyl and tert-butyl, R2 = N,N-dimethyl ethylene for L(1-2) and R1 = methyl and tert-butyl, R2 = 2-(N-ethyl) pyridine for L(3-4)]. A UV-vis spectrophotometric study using 3,5-di-tert butylcatechol (3,5-DTBC) reveals that all the complexes are highly active in catalyzing the aerobic oxidation of (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in methanol medium with the formation of hydrogen peroxide. An EPR study confirms the generation of radicals during the catalysis. Cyclic voltammetric studies of the complexes in the presence and absence of 3,5-DTBC have been performed. Reduction of Ni(II) to Ni(I) and that of the imine bond of the ligand system have been detected at ∼-1.0 V and ∼-1.5 V, respectively. Coulometric separation of the species at -1.5 V followed by the EPR study at 77 K confirms the species as an organic radical and thus most probably reduced imine species. Spectroelectrochemical analysis at -1.5 V clearly indicates the oxidation of 3,5-DTBC and thus suggests that the radical pathway is supposed to be responsible for the catecholase-like activity exhibited by the nickel complexes. The ligand centred radical generation has further been verified by density functional theory calculation.

Photoassist-phosphorylated TiO2 as a catalyst for direct formation of 5-(hydroxymethyl)furfural from glucose.

PubMed

Hattori, Masashi; Kamata, Keigo; Hara, Michikazu

2017-02-01

Photo-assisted phosphorylation of an anatase TiO 2 catalyst was examined to improve its catalytic performance for the direct production of 5-(hydroxymethyl)furfural (HMF), a versatile chemical platform, from glucose. In phosphorylation based on simple esterification between phosphoric acid and surface OH groups on anatase TiO 2 with water-tolerant Lewis acid sites, the density of phosphates immobilized on TiO 2 is limited to 2 phosphates nm -2 , which limits selective HMF production. Phosphorylation of the TiO 2 surface under fluorescent light irradiation increases the surface phosphate density to 50%, which is higher than the conventional limit, thus preventing the adsorption of hydrophilic glucose molecules on TiO 2 and resulting in a more selective HMF production over photoassist-phosphorylated TiO 2 .

Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization.

PubMed

Lin, Ching Yeh; Coote, Michelle L; Gennaro, Armando; Matyjaszewski, Krzysztof

2008-09-24

High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R-X; R = CH 2CN, CH(CH 3)CN, C(CH 3) 2CN, CH 2COOC 2H 5, CH(CH 3)COOCH 3, C(CH 3) 2COOCH 3, C(CH 3) 2COOC 2H 5, CH 2Ph, CH(CH 3)Ph, CH(CH 3)Cl, CH(CH 3)OCOCH 3, CH(Ph)COOCH 3, SO 2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R (*), are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R-X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ATRP should occur via concerted dissociative electron transfer rather than a two-step process with radical anion intermediates. Both the homolytic and heterolytic reactions are favored by electron-withdrawing substituents and/or those that stabilize the product alkyl radical, which explains why monomers such as acrylonitrile and styrene require less active ATRP catalysts than vinyl chloride and vinyl acetate. The rate constant of the hypothetical OSET reaction between bromoacetonitrile and Cu (I)/TPMA complex was estimated using Marcus theory for the electron-transfer processes. The estimated rate constant k OSET = approximately 10 (-11) M (-1) s (-1) is significantly smaller than the experimentally measured activation rate constant ( k ISET = approximately 82 M (-1) s (-1) at 25 degrees C in acetonitrile) for the concerted atom transfer mechanism (inner-sphere electron transfer, ISET), implying that the ISET mechanism is preferred. For monomers bearing electron-withdrawing groups, the one-electron reduction of the propagating alkyl radical to the carbanion is thermodynamically and kinetically favored over the one-electron reduction of the corresponding alkyl halide unless the monomer bears strong radical-stabilizing groups. Thus, for monomers such as acrylates, catalysts favoring ISET over OSET are required in order to avoid chain-breaking side reactions.

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

NASA Astrophysics Data System (ADS)

Lew, Michelle M.; Dusanter, Sebastien; Stevens, Philip S.

2018-01-01

One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2-to-HO2 conversion for the Indiana University laser-induced fluorescence-fluorescence assay by gas expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds (VOCs) with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene-derived RO2 radicals and 20 % of alkane-derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign (MCMA-2006), where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.

The dissociation of vibrationally excited CH3OSO radicals and their photolytic precursor, methoxysulfinyl chloride.

PubMed

Alligood, Bridget W; Womack, Caroline C; Straus, Daniel B; Blase, Frances R; Butler, Laurie J

2011-05-21

The dissociation dynamics of methoxysulfinyl radicals generated from the photodissociation of CH(3)OS(O)Cl at 248 nm is investigated using both a crossed laser-molecular beam scattering apparatus and a velocity map imaging apparatus. There is evidence of only a single photodissociation channel of the precursor: S-Cl fission to produce Cl atoms and CH(3)OSO radicals. Some of the vibrationally excited CH(3)OSO radicals undergo subsequent dissociation to CH(3) + SO(2). The velocities of the detected CH(3) and SO(2) products show that the dissociation occurs via a transition state having a substantial barrier beyond the endoergicity; appropriately, the distribution of velocities imparted to these momentum-matched products is fit by a broad recoil kinetic energy distribution extending out to 24 kcal/mol in translational energy. Using 200 eV electron bombardment detection, we also detect the CH(3)OSO radicals that have too little internal energy to dissociate. These radicals are observed both at the parent CH(3)OSO(+) ion as well as at the CH(3)(+) and SO(2)(+) daughter ions; they are distinguished by virtue of the velocity imparted in the original photolytic step. The detected velocities of the stable radicals are roughly consistent with the calculated barriers (both at the CCSD(T) and G3B3 levels of theory) for the dissociation of CH(3)OSO to CH(3) + SO(2) when we account for the partitioning of internal energy between rotation and vibration as the CH(3)OSOCl precursor dissociates. © 2011 American Institute of Physics.

Electrochemical Oxidation of Alkylnitro Compounds PP-1345

DTIC Science & Technology

2004-08-17

to the solution, to deprotonate the methyl group. Figure 22 shows the voltammetric response recorded in a CH3OH /0.2 M Bu4NBF4 solution containing...Voltammogram of Glassy Carbon (GC) Electrode 50 mM TNT/ CH3OH /0.2 M Bu4NBF4/55 mM NaOH 15 The standard redox potential for this reaction was... reaction ). Addition of 100 mM TNT to the basic solution ( CH3OH /0.2 M Bu4NBF4/ 55 mM NaOH) resulted in the appearance of a new oxidation wave with a

Tentative detection of ethylene glycol toward W51/e2 and G34.3+0.2 ⋆⋆⋆

NASA Astrophysics Data System (ADS)

Lykke, J. M.; Favre, C.; Bergin, E. A.; Jørgensen, J. K.

2015-10-01

Context. With only a few low- and high-mass star-formation regions studied in detail so far, it is unclear what role the enviroment plays in complex molecule formation. In this light, a comparison of relative abundances of related species between sources might be useful for explaining any observed differences. Aims: We seek to measure the relative abundance between three important complex organic molecules, ethylene glycol ((CH2OH)2), glycolaldehyde (CH2OHCHO) and methyl formate (HCOOCH3), toward high-mass protostars and thereby provide additional constraints on their formation pathways. Methods: We use IRAM 30 m single-dish observations of the three species toward two high-mass star-forming regions - W51/e2 and G34.3+0.2 - and report a tentative detection of (CH2OH)2 toward both sources. Results: Assuming that (CH2OH)2, CH2OHCHO, and HCOOCH3 spatially coexist, relative abundance ratios, HCOOCH3/(CH2OH)2, of 31 and 35 are derived for G34.3+0.2 and W51/e2, respectively. CH2OHCHO is not detected, but the data provide lower limits to the HCOOCH3/CH2OHCHO abundance ratios of ≥193 for G34.3+0.2 and ≥550 for W51/e2. A comparison of these results to measurements from various sources in the literature indicates that the source luminosities may be correlated with the HCOOCH3/(CH2OH)2 and HCOOCH3/CH2OHCHO ratios. This apparent correlation may be a consequence of the relative time scales each source spend at different temperature ranges in their evolution. Furthermore, we obtain lower limits to the ratio of (CH2OH)2/CH2OHCHO for G34.3+0.2 (≥6) and W51/e2 (≥16). This result confirms that a high (CH2OH)2/CH2OHCHO abundance ratio is not a specific property of comets, as previously speculated. Based on observations carried out with the IRAM 30 m telescope.The reduced spectra (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/582/A64Appendices are available in electronic form at http://www.aanda.org

Influence of meteorology and interrelationship with greenhouse gases (CO2 and CH4) at a sub-urban site of India

NASA Astrophysics Data System (ADS)

Sreenivas, G.; Mahesh, P.; Subin, J.; Kanchana, A. L.; Rao, P. V. N.; Dadhwal, V. K.

2015-12-01

Atmospheric greenhouse gases (GHGs) such as carbon dioxide (CO2) and methane (CH4) are important climate forcing agents due to their significant impact on the climate system. The present study brings out first continuous measurements of atmospheric GHG's using high precision Los Gatos Research's-greenhouse gas analyser (LGR-GGA) over Shadnagar, a suburban site of Central India during the period 2014. The annual mean of CO2 and CH4 over the study region is found to be 394 ± 2.92 and 1.92 ± 0.07 ppm (mean, μ ± 1 SD, σ) respectively. CO2 and CH4 showed a significant seasonal variation during the study period with maximum (minimum) CO2 observed during Pre-monsoon (Monsoon), while CH4 recorded maximum during post-monsoon and minimum in monsoon. A consistent diurnal mixing ratio of these gases is observed with high (low) during night (afternoon) hours throughout the study period. Influences of prevailing meteorology (air temperature, wind speed, wind direction and relative humidity) on GHG's have also been investigated. CO2 and CH4 showed a strong positive correlation during winter, pre-monsoon, monsoon and post-monsoon with R equal to 0.80, 0.80, 0.61 and 0.72 respectively. It implies the seasonal variations in source-sink mechanisms of CO2 and CH4. Present study also confirms implicitly the presence OH radicals as a major sink of CH4 over the study region.

Evaluation of the equivalence ratio of the reacting mixture using intensity ratio of chemiluminescence in laminar partially premixed CH{sub 4}-air flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Yong Ki; Jeon, Chung Hwan; Chang, Young June

An experimental study was performed to investigate the effects of partially premixing, varying the equivalence ratios from 0.79 to 9.52, on OH*, CH* and C{sub 2}* in laminar partially premixed flames. The signals from the electronically excited states of OH*, CH* and C{sub 2}* were detected through interference filters using a photo multiplier tube, which were processed to the intensity ratios (C{sub 2}*/CH*, C{sub 2}*/OH* and CH*/OH*) to determine a correlation with the local equivalence ratios. Furthermore, the consistency between the results of the tomographic reconstruction; Abel inversion technique, image with CCD (Couple Charged Detector) camera and the local radicalmore » intensity with PMT was investigated. The results demonstrated that (1) the flames at F=<1.36 exhibited classical double flame structure, at F>=4.76, the flames exhibited non-premixed-like flame structure and the intermediate flames at 1.36

Visible-light-driven photocatalytic activation of peroxymonosulfate by Cu2(OH)PO4 for effective decontamination.

PubMed

Liu, Guoshuai; Zhou, Yanan; Teng, Jie; Zhang, Jinna; You, Shijie

2018-06-01

The advanced oxidation process (AOP) based on SO 4 - radicals draws an increasing interest in water and wastewater treatment. Producing SO 4 - radicals from the activation of peroxymonosulfate (PMS) by transition metal ions or oxides may be problematic due to high operational cost and potential secondary pollution caused by metal leaching. To address this challenge, the present study reports the efficient production of SO 4 - radicals through visible-light-driven photocatalytic activation (VL-PCA) of PMS by using Cu 2 (OH)PO 4 single crystal for enhanced degradation of a typical recalcitrant organic pollutant, i.e., 2,4-dichlorophenol (2,4-DCP). It took only 7 min to achieve almost 100% removal of 2,4-DCP in the Cu 2 (OH)PO 4 /PMS system under visible-light irradiation and pH-neutral condition. The 2,4-DCP degradation was positively correlated to the amount of Cu 2 (OH)PO 4 and PMS. Both OH and SO 4 - radicals were responsible for enhanced degradation performance, indicated by radical scavenger experiments and electron spin resonance (ESR) measurements. The Cu 2 (OH)PO 4 single crystal exhibited good cyclic stability and negligible metal leaching. According to density functional theory (DFT) calculations, the visible-light-driven transformation of two copper states between trigonal bipyramidal sites and octahedral sites in the crystal structure of Cu 2 (OH)PO 4 facilitates the generation of OH and SO 4 - radicals from the activation of PMS and cleavage of O-O bonds. This study provides the proof-in-concept demonstration of activation of PMS driven by visible light, making the SO 4 - radicals-based AOPs much easier, more economical and more sustainable in engineering applications for water and wastewater treatment. Copyright © 2018 Elsevier Ltd. All rights reserved.

The catalytic effects of H2CO3, CH3COOH, HCOOH and H2O on the addition reaction of CH2OO + H2O → CH2(OH)OOH

NASA Astrophysics Data System (ADS)

Zhang, Tianlei; Lan, Xinguang; Wang, Rui; Roy, Soumendra; Qiao, Zhangyu; Lu, Yousong; Wang, Zhuqing

2018-07-01

The addition reaction of CH2OO + H2O → CH2(OH)OOH without and with X (X = H2CO3, CH3COOH and HCOOH) and H2O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH2OO + H2O → CH2(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH2OO...H2O is favourable one. Water-assisted CH2OO + H2O → CH2(OH)OOH can occur by H2O moiety of (H2O)2 or the whole (H2O)2 forming cyclic structure with CH2OO, where the latter form is more favourable. Because the concentration of H2CO3 is unknown, the influence of CH3COOH, HCOOH and H2O were calculated within 0-30 km altitude of the Earth's atmosphere. The results calculated within 0-5 km altitude show that H2O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%-77.26% and 0.04%-1.76%. Within 5-30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%-98.28%. However, compared with the reaction of CH2OO + HCOOH, the rate of CH2OO...H2O + HCOOH is much slower.

Thermal conductivity of H2O-CH3OH mixtures at high pressures: Implications for the dynamics of icy super-Earths outer shells

NASA Astrophysics Data System (ADS)

Hsieh, Wen-Pin; Deschamps, Frédéric

2015-10-01

Thermal conductivity of H2O-volatile mixtures at extreme pressure-temperature conditions is a key factor to determine the heat flux and profile of the interior temperature in icy bodies. We use time domain thermoreflectance and stimulated Brillouin scattering combined with diamond anvil cells to study the thermal conductivity and sound velocity of water (H2O)-methanol (CH3OH) mixtures to pressures as high as 12 GPa. Compared to pure H2O, the presence of 5-20 wt % CH3OH significantly reduces the thermal conductivity and sound velocity when the mixture becomes ice VI-CH3OH and ice VII-CH3OH phases at high pressures, indicating that the heat transfer is hindered within the icy body. We then apply these results to model the heat transfer through the icy mantles of super-Earths, assuming that these mantles are animated by thermal convection. Our calculations indicate that the decrease of thermal conductivity due to the presence of 10 wt % CH3OH induces a twofold decrease of the power transported by convection.

Resonance stabilization effects on ketone autoxidation: Isomer-specific cyclic ether and ketohydroperoxide formation in the low-temperature (400–625 K) oxidation of diethyl ketone

DOE PAGES

Scheer, Adam M.; Eskola, Arkke J.; Osborn, David L.; ...

2016-10-11

Here, the pulsed photolytic chlorine-initiated oxidation of diethyl ketone [DEK; (CH 3CH 2) 2C=O], 2,2,4,4- d 4-DEK [ d 4-DEK; (CH 3CD 2) 2C=O], and 1,1,1,5,5,5-d 6-DEK [ d 6-DEK; (CD 3CH 2) 2C=O] is studied at 8 torr and 1–2 atm and from 400–625 K. Cl atoms produced by laser photolysis react with diethyl ketone to form either primary (3-pentan-on-1-yl, R P) or secondary (3-pentan-on-2-yl, R S) radicals, which in turn react with O 2. Multiplexed time-of-flight mass spectrometry, coupled to either a hydrogen discharge lamp or tunable synchrotron photoionizing radiation, is used to detect products as a functionmore » of mass, time, and photon energy. At 8 torr, the nature of the chain propagating cyclic ether + OH channel changes as a function of temperature. At 450 K, the production of OH is mainly in conjunction with formation of 2,4-dimethyloxetan-3-one, resulting from reaction of the resonance-stabilized secondary R S with O 2. In contrast, at 550 K and 8 torr, 2-methyl-tetrahydrofuran-3-one, originating from oxidation of the primary radical (RP), is observed as the dominant cyclic ether product. Formation of both of these cyclic ether production channels proceeds via a resonance-stabilized hydroperoxy alkyl (QOOH) intermediate. Little or no ketohydroperoxide (KHP) is observed under the low-pressure conditions. At higher O 2 concentrations and higher pressures (1–2 atm), a strong KHP signal appears as the temperature is increased above 450 K. Definitive isomeric identification from measurements on the deuterated DEK isotopologues indicates the favored pathway produces a γ-KHP via resonance-stabilized alkyl, QOOH, and HOOPOOH radicals. Time-resolved measurements reveal the KHP formation becomes faster and signal more intense upon increasing temperature from 450 to 575 K before intensity drops significantly at 625 K. The KHP time profile also shows a peak followed by a gradual depletion for the extent of experiment. Several tertiary products exhibit a slow accumulation in coincidence with the observed KHP decay. These products can be associated with decomposition of KHP by β-scission pathways or via isomerization of a γ-KHP into a cyclic peroxide intermediate (Korcek mechanism). The oxidation of d 4-DEK, where kinetic isotope effects disfavor γ-KHP formation, shows greatly reduced KHP formation and associated signatures from KHP decomposition products.« less

Global atmospheric concentrations and source strength of ethane

NASA Technical Reports Server (NTRS)

Blake, D. R.; Rowland, F. S.

1986-01-01

A study of the variation in ethane (C2H6) concentration between northern and southern latitudes over three years is presented together with a new estimate of its source strength. Ethane concentrations vary from 0.07 to 2 p.p.b.v. (parts per billion by volume) in air samples collected in remote surface locations in the Pacific (latitude 71 N-47 S) in all four seasons between September 1984 and June 1985. The variations are consistent with southerly transport from sources located chiefly in the Northern Hemisphere, further modified by seasonal variations in the strength of the reaction of C2H6 with OH radicals. These global data can be combined with concurrent data for CH4 and the laboratory reaction rates of each with OH to provide an estimate of three months as the average atmospheric lifetime for C2H6 and 13 + or - 3 Mtons for its annual atmospheric release.

Computed potential energy surfaces for chemical reactions

NASA Technical Reports Server (NTRS)

Heinemann, K.; Walch, Stephen P.

1992-01-01

The work on the NH + NO system which was described in the last progress report was written up and a draft of the manuscript is included in the appendix. The appendix also contains a draft of a manuscript on an Ar + H + H surface. New work which was completed in the last six months includes the following: (1) calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction; (2) calculations for the NH2 + O reaction; (3) calculations for the CH3 + O2 reaction; and (4) calculations for CH3O and the two decomposition channels--CH2OH and H + H2CO. Detailed descriptions of this work will be given in manuscripts; however, brief descriptions of the CH3 + OH and CH3 + O2 projects are given.

Photolysis of CH{sub 3}CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH{sub 3} and HCO radicals and H atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morajkar, Pranay; Schoemaecker, Coralie; Fittschen, Christa, E-mail: christa.fittschen@univ-lille1.fr

2014-06-07

Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH{sub 3}CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO{sub 2} radicals by reaction with O{sub 2}. The CH{sub 3} radical yield has been determined using the same technique following their conversion into CH{sub 3}O{sub 2}. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO{sub 2} profiles, obtained under various O{sub 2} concentrations, to a complex model, while the CH{submore » 3} yield has been determined relative to the CH{sub 3} yield from 248 nm photolysis of CH{sub 3}I. Time resolved HO{sub 2} profiles under very low O{sub 2} concentrations suggest that another unknown HO{sub 2} forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O{sub 2}. HO{sub 2} profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH{sub 3}CHO + hν{sub 248nm} → CH{sub 3}CHO{sup *}, CH{sub 3}CHO{sup *} → CH{sub 3} + HCO ϕ{sub 1a} = 0.125 ± 0.03, CH{sub 3}CHO{sup *} → CH{sub 3} + H + CO ϕ{sub 1e} = 0.205 ± 0.04, CH{sub 3}CHO{sup *}→{sup o{sub 2}}CH{sub 3}CO + HO{sub 2} ϕ{sub 1f} = 0.07 ± 0.01. The CH{sub 3}O{sub 2} quantum yield has been determined in separate experiments as ϕ{sub CH{sub 3}} = 0.33 ± 0.03 and is in excellent agreement with the CH{sub 3} yields derived from the HO{sub 2} measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH{sub 3}CHO. From arithmetic considerations taking into account the HO{sub 2} and CH{sub 3} measurements we deduce a remaining quantum yield for the molecular pathway: CH{sub 3}CHO{sup *} → CH{sub 4} + CO ϕ{sub 1b} = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH{sub 3}CHO{sup *} → CH{sub 3}CO + H ϕ{sub 1c} = 0.« less

Study of Wastewater Treatment by OH Radicals Using DC and Pulsed Corona Discharge over Water

NASA Astrophysics Data System (ADS)

Tochikubo, Fumiyoshi; Furuta, Yasutomo; Uchida, Satoshi; Watanabe, Tsuneo

2006-04-01

Water treatment by OH radicals is studied using dc and pulsed corona discharge over water at atmospheric pressure and reduced pressure. In particular, we pay attention to the influence of discharge configuration on the efficiency of wastewater treatment. Experiment is carried out in N2 to clarify the contribution of OH radicals. Needle-cylinder electrodes are designed expecting the efficient generation of OH radicals close to the water surface. N,N-dimethyl- p-nitrosoaniline (RNO) solution is used as a persistent test pollutant. The results strongly suggest that OH radical production close to the water surface is a key factor for efficient wastewater treatment. The use of pulsed discharge at reduced pressure is effective in improving RNO reduction efficiency because of the rapid diffusion of OH radicals to the water surface.

Computational Chemical Kinetics for the Reaction of Criegee Intermediate CH2OO with HNO3 and Its Catalytic Conversion to OH and HCO.

PubMed

Raghunath, P; Lee, Yuan-Pern; Lin, M C

2017-05-25

The kinetics and mechanisms for the reaction of the Criegee intermediate CH 2 OO with HNO 3 and the unimolecular decomposition of its reaction product CH 2 (O)NO 3 are important in atmospheric chemistry. The potential-energy profile of the reactions predicted with the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ method shows that the initial association yields a prereaction complex that isomerizes by H migration to yield excited intermediate nitrooxymethyl hydroperoxide NO 3 CH 2 OOH* with internal energy ∼44 kcal mol -1 . A fragmentation of this excited intermediate produces CH 2 (O)NO 3 + OH with its transition state located 5.0 kcal mol -1 below that of the reactants. Further decomposition of CH 2 (O)NO 3 produces HCO + HNO 3 , forming a catalytic cycle for destruction of CH 2 OO by HNO 3 . The rate coefficients and product-branching ratios were calculated in the temperature range 250-700 K at pressure 20-760 Torr (N 2 ) using the variational-transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate coefficient for reaction CH 2 OO + HNO 3 at 295 K, 5.1 × 10 -10 cm 3 molecule -1 s -1 , agrees satisfactorily with the experimental value, (5.4 ± 1.0) × 10 -10 cm 3 molecule -1 s -1 . The predicted branching ratios at 295 K are 0.21 for the formation of NO 3 CH 2 OOH and 0.79 for CH 2 (O)NO 3 + OH at a pressure of 40 Torr (N 2 ), and 0.79 for the formation of NO 3 CH 2 OOH and 0.21 for CH 2 (O)NO 3 + OH at 760 Torr (N 2 ). This new catalytic conversion of CH 2 OO to HCO + OH by HNO 3 might have significant impact on atmospheric chemistry.

Effects of CH3OH Addition on Plasma Electrolytic Oxidation of AZ31 Magnesium Alloys

NASA Astrophysics Data System (ADS)

He, Yongyi; Chen, Li; Yan, Zongcheng; Zhang, Yalei

2015-09-01

Plasma electrolytic oxidation (PEO) films on AZ31 magnesium alloys were prepared in alkaline silicate electrolytes (base electrolyte) with the addition of different volume concentrations of CH3OH, which was used to adjust the thickness of the vapor sheath. The compositions, morphologies, and thicknesses of ceramic layers formed with different CH3OH concentrations were determined via X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). Corrosion behavior of the oxide films was evaluated in 3.5 wt.% NaCl solution using potentiodynamic polarization tests. PEO coatings mainly comprised Mg, MgO, and Mg2SiO4. The addition of CH3OH in base electrolytes affected the thickness, pores diameter, and Mg2SiO4 content in the films. The films formed in the electrolyte containing 12% CH3OH exhibited the highest thickness. The coatings formed in the electrolyte containing different concentrations of CH3OH exhibited similar corrosion resistance. The energy consumption of PEO markedly decreased upon the addition of CH3OH to the electrolytes. The result is helpful for energy saving in the PEO process. supported by National Natural Science Foundation of China (No. 21376088), the Project of Production, Education and Research, Guangdong Province and Ministry of Education (Nos. 2012B09100063, 2012A090300015), and Guangzhou Science and Technology Plan Projects of China (No. 2014Y2-00042)

Interaction of turbulent premixed flames with combustion products: Role of stoichiometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coriton, Bruno Rene Leon; Frank, Jonathan H.; Gomez, Alessandro

Stabilization methods of turbulent flames often involve mixing of reactants with hot products of combustion. The stabilizing effect of combustion product enthalpy has been long recognized, but the role played by the chemical composition of the product gases is typically overlooked. We employ a counterflow system to pinpoint the effects of the combustion product stoichiometry on the structure of turbulent premixed flames under conditions of both stable burning and local extinction. To that end, a turbulent jet of lean-to-rich, CH 4/O 2/N 2-premixed reactants at a turbulent Reynolds number of 1050 was opposed to a stream of hot products ofmore » combustion that were generated in a preburner. While the combustion product stream temperature was kept constant, its stoichiometry was varied independently from that of the reactant stream, leading to reactant-to-product stratification of relevance to practical combustion systems. The detailed structure of the turbulent flame front was analyzed in two series of experiments using laser-induced fluorescence (LIF): joint CH 2O LIF and OH LIF measurements and joint CO LIF and OH LIF measurements. Results revealed that a decrease in local CH 2O+OH and CO+OH reaction rates coincide with the depletion of OH radicals in the vicinity of the combustion product stream. These critical combustion reaction rates were more readily quenched in the presence of products of combustion from a stoichiometric flame, whereas they were favored by lean combustion products. As a result, stoichiometric combustion products contributed to a greater occurrence of local extinction. Furthermore, they limited the capacity of premixed reactants to ignite and of the turbulent premixed flames to stabilize. In contrast, lean and rich combustion products facilitated flame ignition and stability and reduced the rate of local extinction. The influence of the combustion product stream on the turbulent flame front was limited to a zone of approximately two millimeters from the gas mixing layer interface (GMLI) of the product stream. As a result, flame fronts that were separated from the GMLI by larger distances were unaffected by the product stream stoichiometry.« less

Interaction of turbulent premixed flames with combustion products: Role of stoichiometry

DOE PAGES

Coriton, Bruno Rene Leon; Frank, Jonathan H.; Gomez, Alessandro

2016-05-30

Stabilization methods of turbulent flames often involve mixing of reactants with hot products of combustion. The stabilizing effect of combustion product enthalpy has been long recognized, but the role played by the chemical composition of the product gases is typically overlooked. We employ a counterflow system to pinpoint the effects of the combustion product stoichiometry on the structure of turbulent premixed flames under conditions of both stable burning and local extinction. To that end, a turbulent jet of lean-to-rich, CH 4/O 2/N 2-premixed reactants at a turbulent Reynolds number of 1050 was opposed to a stream of hot products ofmore » combustion that were generated in a preburner. While the combustion product stream temperature was kept constant, its stoichiometry was varied independently from that of the reactant stream, leading to reactant-to-product stratification of relevance to practical combustion systems. The detailed structure of the turbulent flame front was analyzed in two series of experiments using laser-induced fluorescence (LIF): joint CH 2O LIF and OH LIF measurements and joint CO LIF and OH LIF measurements. Results revealed that a decrease in local CH 2O+OH and CO+OH reaction rates coincide with the depletion of OH radicals in the vicinity of the combustion product stream. These critical combustion reaction rates were more readily quenched in the presence of products of combustion from a stoichiometric flame, whereas they were favored by lean combustion products. As a result, stoichiometric combustion products contributed to a greater occurrence of local extinction. Furthermore, they limited the capacity of premixed reactants to ignite and of the turbulent premixed flames to stabilize. In contrast, lean and rich combustion products facilitated flame ignition and stability and reduced the rate of local extinction. The influence of the combustion product stream on the turbulent flame front was limited to a zone of approximately two millimeters from the gas mixing layer interface (GMLI) of the product stream. As a result, flame fronts that were separated from the GMLI by larger distances were unaffected by the product stream stoichiometry.« less

Mechanism for degradation of Nafion in PEM fuel cells from quantum mechanics calculations.

PubMed

Yu, Ted H; Sha, Yao; Liu, Wei-Guang; Merinov, Boris V; Shirvanian, Pezhman; Goddard, William A

2011-12-14

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism. © 2011 American Chemical Society

The complexity of Orion: an ALMA view. II. gGg'-ethylene glycol and acetic acid

NASA Astrophysics Data System (ADS)

Favre, C.; Pagani, L.; Goldsmith, P. F.; Bergin, E. A.; Carvajal, M.; Kleiner, I.; Melnick, G.; Snell, R.

2017-07-01

We report the first detection and high angular resolution (1.8″× 1.1″) imaging of acetic acid (CH3COOH) and gGg'-ethylene glycol (gGg'(CH2OH)2) toward the Orion Kleinmann-Low (Orion-KL) nebula. The observations were carried out at 1.3 mm with ALMA during Cycle 2. A notable result is that the spatial distribution of the acetic acid and ethylene glycol emission differs from that of the other O-bearing molecules within Orion-KL. While the typical emission of O-bearing species harbors a morphology associated with a V-shape linking the hot core region to the compact ridge (with an extension toward the BN object), the emission of acetic acid and ethylene glycol mainly peaks at about 2'' southwest from the hot core region (near sources I and n). We find that the measured CH3COOH:aGg'(CH2OH)2 and CH3COOH:gGg'(CH2OH)2 ratios differ from those measured toward the low-mass protostar IRAS 16293-2422 by more than one order of magnitude. Our best hypothesis to explain these findings is that CH3COOH, aGg'(CH2OH)2, and gGg'(CH2OH)2 are formed on the icy surface of grains and are then released into the gas-phase via co-desorption with water, by way of a bullet of matter ejected during the explosive event that occurred in the heart of the nebula about 500-700 yr ago.

Impact of Formaldehyde Addition on Auto-Ignition in Internal-Combustion Engines

NASA Astrophysics Data System (ADS)

Kuwahara, Kazunari; Ando, Hiromitsu; Furutani, Masahiro; Ohta, Yasuhiko

By employing a direct-injection diesel engine equipped with a common-rail type of injection system, by adding formaldehyde (CH2O) to the intake air, and by changing the fuel-injection timing, the compression ratio and the intake-air temperature, a mechanism for CH2O as a fuel additive to affect auto-ignition was discussed. Unlike an HCCI type of engine, the diesel engine can expose an air-fuel mixture only to a limited range of the in-cylinder temperature before the ignition, and can separate low- and high-temperature parts of the mechanism. When low-temperature oxidation starts at a temperature above 900K, there are cases that the CH2O advances the ignition timing. Below 900K, to the contrary, it always retards the timing. It is because, above 900K, a part of the CH2O changes into CO together with H2O2 as an ignition promoter. Below 900K, on the other hand, the CH2O itself acts as an OH radical scavenger against cool-flame reaction, from the beginning of low-temperature oxidation. Then, the engine was modified for its extraordinary function as a gasoline-knocking generator, in order that an effect of CH2O on knocking could be discussed. The CH2O retards the onset of auto-ignition of an end gas. Judging from a large degree of the retardation, the ignition is probably triggered below 900K.

Reactivity of OH and CH3OH Between 22 and 64 K: Modelling the Gas Phase Production of CH3O in Barnard 1B

PubMed Central

Antiñolo, M.; Agúndez, M.; Jiménez, E.; Ballesteros, B.; Canosa, A.; Dib, G. El; Albaladejo, J.; Cernicharo, J.

2016-01-01

In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CH3OH, which has been recently found to be accelerated at low temperatures yielding CH3O as main product. This finding opened the question of whether the CH3O observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CH3OH and OH. Several chemical models including this reaction and grain-surface processes have been developed to explain the observed abundance of CH3O with little success. Here we report for the first time rate coefficients for the gas-phase reaction of OH and CH3OH down to a temperature of 22 K, very close to those in cold interstellar clouds. Two independent experimental set-ups based on the supersonic gas expansion technique coupled to the pulsed laser photolysis-laser induced fluorescence technique were used to determine rate coefficients in the temperature range 22-64 K. The temperature dependence obtained in this work can be expressed as k(22-64 K) = (3.6 ± 0.1) × 10−12(T/300 K)−(1.0±0.2) cm3 molecule−1 s−1. Implementing this expression in a chemical model of a cold dense cloud results in CH3O/CH3OH abundance ratios similar or slightly lower than the value of ∼ 3 × 10−3 observed in Barnard 1b. This finding confirms that the gas-phase reaction between OH and CH3OH is an important contributor to the formation of interstellar CH3O. The role of grain-surface processes in the formation of CH3O, although it cannot be fully neglected, remains controversial. PMID:27279655

Reactivity of OH and CH3OH Between 22 and 64 K: Modelling the Gas Phase Production of CH3O in Barnard 1B.

PubMed

Antiñolo, M; Agúndez, M; Jiménez, E; Ballesteros, B; Canosa, A; Dib, G El; Albaladejo, J; Cernicharo, J

2016-05-20

In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CH 3 OH, which has been recently found to be accelerated at low temperatures yielding CH 3 O as main product. This finding opened the question of whether the CH 3 O observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CH 3 OH and OH. Several chemical models including this reaction and grain-surface processes have been developed to explain the observed abundance of CH 3 O with little success. Here we report for the first time rate coefficients for the gas-phase reaction of OH and CH 3 OH down to a temperature of 22 K, very close to those in cold interstellar clouds. Two independent experimental set-ups based on the supersonic gas expansion technique coupled to the pulsed laser photolysis-laser induced fluorescence technique were used to determine rate coefficients in the temperature range 22-64 K. The temperature dependence obtained in this work can be expressed as k (22-64 K) = (3.6 ± 0.1) × 10 -12 ( T/ 300 K) -(1.0±0.2) cm 3 molecule -1 s -1 . Implementing this expression in a chemical model of a cold dense cloud results in CH 3 O/CH 3 OH abundance ratios similar or slightly lower than the value of ∼ 3 × 10 -3 observed in Barnard 1b. This finding confirms that the gas-phase reaction between OH and CH 3 OH is an important contributor to the formation of interstellar CH 3 O. The role of grain-surface processes in the formation of CH 3 O, although it cannot be fully neglected, remains controversial.

Ab initio studies on the solvation, electronic structures and intracluster reactions in M(+)L(n), with M(+)=magnesium and calcium singly-charged ions, L=water, methanol, ammonia, and n=1-6, and the elimination of a hydrogen atom in H atom in hydrated sodium clusters

NASA Astrophysics Data System (ADS)

Chan, Ka Wai

The solvation and electronic structures of M+Ln, with M+ = Mg+ and Cat, L = H2O, CH 3OH and NH3, n=1-6 were investigated by ab initio calculations using G03 package and density functional theory based ab initio molecular dynamics (AIMD) simulations with projector augmented-wave (PAW) method and a planewave basis set using Vienna Ab initio Simulation Package (VASP). Furthermore, ab initio studies on the intracluster reactions of Mg+ and Ca+ ions with different solvent molecules, H2O, CH3OH and NH3, were also done using G03 package. Finally, the elimination of a H atom in Na(H2O)n was studied. Such studies on the interactions and reactivity in gas clusters can provide insights into their analogies existing in condense phase. Interactions of Mg+ and Ca+ ions in different solvent molecules, H2O, CH3OH and NH3, were calculated with B3LYP and MP2 methods with basis sets 6-31+g** and 6-311+g**. A systematic comparison on the structures and reactivities of these clusters should provide a better understanding on the interplay of the ion-solvent, solvent-solvent, and electron-solvent interactions. It can provide a better understanding on the structures and bonding of complexes having analogies to those existing in condense phase. For Mg+(CH3OH)n and Ca+(CH 3OH)n, both H-elimination from OH/CH bond and CH3-elimination were investigated. H-elimination from O---H bond becomes more accessible for large cluster due to the diffusion of electron density to O---H bond. Studies on the H-elimination in Mg+(NH3)n and H-elimination from C---H bond in Mg+(CH3OH) n show that the reaction barriers flatten above 20 kcal/mol as n reaches 4 and above. These calculation results prove that the source of loss of H atom in ground state Mg+(CH3OH)n should be through the O---H bond rather than through the C---H bond. Compared to Mg+(CH3OH)n, the reaction barriers for H-elimination in Mg+(NH3)n is much larger, which is in consistent with the experimental observation of little H-elimination for Mg+(NH3)n unless it's photo-excited. The examination of neutral Na(H2O)n clusters, n=4~15 for H-elimination was carried out. The reaction profile for H-elimination was obtained by energy minimization at constrained O---H distance which was successively increased. There was a general trend of decreasing reaction barrier, as the cluster size grows. In contrast to Mg+(H 2O)n, the expected switch-off of H-elimination as in Mg +(H2O)n cannot be observed.

Investigations of a Combustor Using a 9-Point Swirl-Venturi Fuel Injector: Recent Experimental Results

NASA Technical Reports Server (NTRS)

Hicks, Yolanda R.; Heath, Christopher M.; Anderson, Robert C.; Tacina, Kathleen M.

2012-01-01

This paper explores recent results obtained during testing in an optically-accessible, JP8-fueled, flame tube combustor using baseline Lean Direct Injection (LDI) research hardware. The baseline LDI geometry has nine fuel/air mixers arranged in a 3 x 3 array. Results from this nine-element array include images of fuel and OH speciation via Planar Laser-Induced Fluorescence (PLIF), which describe fuel spray pattern and reaction zones. Preliminary combustion temperatures derived from Stokes/Anti-Stokes Spontaneous Raman Spectroscopy are also presented. Other results using chemiluminescence from major combustion radicals such as CH* and C2* serve to identify the primary reaction zone, while OH PLIF shows the extent of reaction further downstream. Air and fuel velocities and fuel drop size results are also reported.

Detection of OH stretching mode of CH3OH chemisorbed on Ni3+ and Ni4+ by infrared photodissociation spectroscopy.

PubMed

Hirabayashi, Shinichi; Okawa, Ryuji; Ichihashi, Masahiko; Kondow, Tamotsu; Kawazoe, Yoshiyuki

2007-08-09

Structures of nickel cluster ions adsorbed with methanol, Ni3+ (CH3OH)m (m = 1-3) and Ni4+ (CH3OH)m (m = 1-4) were investigated by using infrared photodissociation (IR-PD) spectroscopy based on a tandem-type mass spectrometer, where they were produced by passing Ni3,4+ through methanol vapor under a multiple collision condition. The IR-PD spectra were measured in the wavenumber region between 3100 and 3900 cm-1. In each IR-PD spectrum, a single peak was observed at a wavenumber lower by approximately 40 cm-1 than that of the OH stretching vibration of a free methanol molecule and was assigned to the OH stretching vibrations of the methanol molecules in Ni3,4+ (CH3OH)m. The photodissociation was analyzed by assuming that Ni3,4+ (CH3OH)m dissociate unimolecularly after the photon energy absorbed by them is statistically distributed among the accessible modes of Ni3,4+ (CH3OH)m. In comparison with the calculations performed by the density functional theory, it is concluded that (1) the oxygen atom of each methanol molecule is bound to one of the nickel atoms in Ni3,4+ (defined as molecular chemisorption), (2) the methanol molecules in Ni3,4+ (CH3OH)m do not form any hydrogen bonds, and (3) the cross section for demethanation [CH4 detachment from Nin+ (CH3OH)] is related to the electron density distribution inside the methanol molecule.

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

DOE PAGES

Buckingham, Grant T.; Porterfield, Jessica P.; Kostko, Oleg; ...

2016-07-05

Cycloheptatrienyl (tropyl) radical, C 7H 7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. In this study, the pyrolysis products resulting from C 7H 7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C 7H 7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals domore » not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C 7H 7) radicals but rather only benzyl (C 6H 5CH 2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C 6H 5CH 2, C 6H 5CD 2, C 6D 5CH 2, and C 6H 5 13CH 2. Finally, analysis of the temperature dependence for the pyrolysis of the isotopic species (C 6H 5CD 2, C 6D 5CH 2, and C 6H 5 13CH 2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckingham, Grant T.; National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden Colorado 80401; Porterfield, Jessica P.

2016-07-07

Cycloheptatrienyl (tropyl) radical, C{sub 7}H{sub 7}, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C{sub 7}H{sub 7} were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C{sub 7}H{sub 7} are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize tomore » benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C{sub 7}H{sub 7}) radicals but rather only benzyl (C{sub 6}H{sub 5}CH{sub 2}). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C{sub 6}H{sub 5}CH{sub 2}, C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less

Influence of Meteorology and interrelationship with greenhouse gases (CO2 and CH4) at a suburban site of India

NASA Astrophysics Data System (ADS)

Sreenivas, Gaddamidi; Mahesh, Pathakoti; Subin, Jose; Lakshmi Kanchana, Asuri; Venkata Narasimha Rao, Pamaraju; Dadhwal, Vinay Kumar

2016-03-01

Atmospheric greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), are important climate forcing agents due to their significant impacts on the climate system. The present study brings out first continuous measurements of atmospheric GHGs using high-precision LGR-GGA over Shadnagar, a suburban site of Central India during the year 2014. The annual mean CO2 and CH4 over the study region are found to be 394 ± 2.92 and 1.92 ± 0.07 ppm (μ ± 1σ) respectively. CO2 and CH4 show a significant seasonal variation during the study period with maximum (minimum) CO2 observed during pre-monsoon (monsoon), while CH4 recorded the maximum during post-monsoon and minimum during monsoon. Irrespective of the seasons, consistent diurnal variations of these gases are observed. Influences of prevailing meteorology (air temperature, wind speed, wind direction, and relative humidity) on GHGs have also been investigated. CO2 and CH4 show a strong positive correlation during winter, pre-monsoon, monsoon, and post-monsoon with correlation coefficients (Rs) equal to 0.80, 0.80, 0.61, and 0.72 respectively, indicating a common anthropogenic source for these gases. Analysis of this study reveals the major sources for CO2 are soil respiration and anthropogenic emissions while vegetation acts as a main sink, whereas the major source and sink for CH4 are vegetation and presence of hydroxyl (OH) radicals.

Measurements of free radicals in a megacity during the Clean Air for London Project

NASA Astrophysics Data System (ADS)

Heard, Dwayne; Whalley, Lisa; Stone, Daniel; Clancy, Noel; Lee, James; Kleffman, Jorg; Laufs, Sebastian; Bandy, Brian

2013-04-01

Free radicals control the photo-oxidative chemistry of the atmosphere, being responsible for the transformation of primary emissions into secondary pollutants such as NO2, O3, multifunctional species and particulates. Here we present measurements of OH, HO2 and RO2 radicals and OH reactivity recorded at North Kensington, Central London, during two Intensive Operational Periods (IOPs) of the Clear Air for London (Clearflo) project in the summer and winter of 2012. OH and HO2 were measured using laser-induced fluorescence (LIF) spectroscopy at low pressure (the FAGE technique), and RO2 was measured using the recently developed ROXLIF technique, which utilises an external flow-reactor interfaced to FAGE, and which is able to discriminate between HO2 and organic peroxy radicals. Through control of reagent gases we are further able to provide a separate measurement of those RO2 species which are known to give an interference for HO2 measurements (namely alkene, aromatic and large-chain alkane derived RO2). OH reactivity was measured using laser-flash photolysis combined with FAGE. Low concentrations of radicals were observed during the winter IOP, with mixing ratios of [OH] ~ 0.04 pptv, [HO2] ~ 0.4 pptv, and [RO2] ~ 1.6 pptv at noon, all displaying a negative correlation with NO. The photolysis of O3 and subsequent reaction of O(1D) with H2O vapour was only a minor contribution to radical production in winter, with photolysis of HONO a major radical source. The summer IOP coincided with the London Olympic Games, with a number of pollution events, with ozone peaking at 100 ppbv (exceeding EU air quality directives) and elevated radical concentrations (peak [OH] ~ 0.14 pptv, [HO2] ~ 4 pptv, [RO2] ~ 6.4 pptv) being observed. The net rate of ozone production was calculated from radical observations and agreed well with measured ozone production, suggesting that advection/dilution by continental air-masses was not playing a significant role in determining ozone concentrations in London at that time. The ability to partially speciate RO2 enabled the contribution towards ozone production from different types of parent VOCs to be assessed. Steady-state analyses, using OH reactivity measurements to constrain the rate of loss of OH, gave reasonable agreement for [OH] but an additional HO2 sink was required to match [HO2]. The photolysis of HONO and carbonyl species and the decomposition of PAN were the dominant sources of radicals in London in summer.

40 CFR 86.127-12 - Test procedures; overview.

Code of Federal Regulations, 2012 CFR

2012-07-01

...: (1) Gaseous exhaust THC, NMHC, NMOG, CO, NOX, CO2, N2O, CH4, CH3OH, C2H5OH, C2H4O, and HCHO. (2... exhaust emission test is designed to determine gaseous THC, NMHC, NMOG, CO, CO2, CH4, NOX, N2O, and... THC using a heated sample line and analyzer; the other gaseous emissions (CH4, CO, CO2, N2O, and NOX...

40 CFR 86.127-12 - Test procedures; overview.

Code of Federal Regulations, 2013 CFR

2013-07-01

...: (1) Gaseous exhaust THC, NMHC, NMOG, CO, NOX, CO2, N2O, CH4, CH3OH, C2H5OH, C2H4O, and HCHO. (2... exhaust emission test is designed to determine gaseous THC, NMHC, NMOG, CO, CO2, CH4, NOX, N2O, and... THC using a heated sample line and analyzer; the other gaseous emissions (CH4, CO, CO2, N2O, and NOX...

40 CFR 86.127-12 - Test procedures; overview.

Code of Federal Regulations, 2014 CFR

2014-07-01

...: (1) Gaseous exhaust THC, NMHC, NMOG, CO, NOX, CO2, N2O, CH4, CH3OH, C2H5OH, C2H4O, and HCHO. (2... exhaust emission test is designed to determine gaseous THC, NMHC, NMOG, CO, CO2, CH4, NOX, N2O, and... THC using a heated sample line and analyzer; the other gaseous emissions (CH4, CO, CO2, N2O, and NOX...

Cooperative triple-proton/hydrogen atom relay in 7-azaindole(CH3OH)2 in the gas phase: remarkable change in the reaction mechanism from vibrational-mode specific to statistical fashion with increasing internal energy.

PubMed

Sakota, Kenji; Inoue, Naomi; Komoto, Yusuke; Sekiya, Hiroshi

2007-05-31

The 7-azaindole-methanol 1:2 cluster [7AI(CH(3)OH)2] undergoes excited-state triple-proton/hydrogen atom transfer (ESTPT/HT) along the hydrogen-bonded network in the gas phase. The measurements of the resonance-enhanced multiphoton ionization (REMPI) spectra of 7AI(CH(3)OH)2-d(n) (n = 0-3), where subscript n indicates the number of deuterium, and the fluorescence excitation spectrum of 7AI(CH(3)OH)2-d(0) allowed us to investigate the ESTPT/HT dynamics. By comparing the intensity ratios of the vibronic bands between 7AI(CH(3)OH)2-d(0) and 7AI(CH(3)OH)2-d(3) in REMPI spectra, we obtained the lower limit of an acceleration factor (f(a)(low)) of 7AI(CH(3)OH)2-d(0), which is the ratio of the reaction rate for the excitation of a vibronic state to that of the zero-point state in S(1). The f(a)(low) values are 2.7 +/- 0.83 and 4.0 +/- 1.2 for an in-phase intermolecular stretching vibration (sigma(1)) and its overtone (2sigma(1)) observed at 181 cm(-1) and 359 cm(-1) in the excitation spectrum, respectively, while that of the vibration (nu(2)/sigma(1) or nu(3)/sigma(1)) at 228 cm(-1) is 1.1 +/- 0.83. Thus, vibrational-mode-specific ESTPT/HT occurs in the low-energy region (600 cm(-1)). The excitation of an intramolecular ring mode (nu(intra)) of 7AI at 744 cm(-1) substantially enhances the reaction rate (f(a)(low) = 4.4 +/- 0.98), but the increase of f(a)(low) is not prominent for the excitation of v(intra) + sigma(1) at 926 cm(-1) (f(a)(low) = 5.0 +/- 1.6), although the sigma(1) mode is excited. These results suggest that the ESTPT/HT reaction in 7AI(CH(3)OH)2-d(0) directly proceeds from the photoexcited states with the internal energy less than approximately 600 cm(-1), but it occurs from the isoenergetically vibrational-energy redistributed states when the internal energy is large. This shows a remarkable feature of ESTPT/HT in 7AI(CH(3)OH)2; the nature of the reaction mechanism changes from vibrational-mode specific to statistical fashion with increasing the internal energy. The hydrogen-bonded network in 7AI(CH(3)OH)2-d(0) is represented by a directed graph. This shows that ESTPT/HT is one of the simplest examples of cooperative phenomena.

[Analysis of streamer properties and emission spectroscopy of 2-D OH distribution of pulsed corona discharge].

PubMed

Zhao, Lei; Gao, Xiang; Luo, Zhong-Yang; Xuan, Jian-Yong; Jiang, Jian-Ping; Cen, Ke-Fa

2011-11-01

Streamer plays a key role in the process of OH radical generation. The propagation of primary and secondary streamers of positive wire-plate pulsed corona discharge was observed using a short gate ICCD in air environment. The influence of the applied voltage on the properties was investigated. It was shown that the primary streamer propagation velocity, electric coverage and length of secondary streamer increased significantly with increasing the applied voltage. Then 2-D OH distribution was investigated by the emission spectrum. With the analysis of the OH emission spectra, the distribution of OH radicals showed a trend of decreasing from the wire electrode to its circumambience. Compared with the streamer propagation trace, the authors found that OH radical distribution and streamer are in the same area. Both OH radical concentration and the intensity of streamer decreased when far away from the wire electrode.

Stereospecific Formation of Interstrand Carbinolamine DNA Crosslinks by Crotonaldehyde- and Acetaldehyde-Derived α-CH3-γ-OH-1,N2-Propano-2’-deoxyguanosine Adducts in the 5′-CpG-3′ Sequence

PubMed Central

Cho, Young-Jin; Wang, Hao; Kozekov, Ivan D.; Kurtz, Andrew J.; Jacob, Jaison; Voehler, Markus; Smith, Jarrod; Harris, Thomas M.; Lloyd, R. Stephen; Rizzo, Carmelo J.; Stone, Michael P.

2008-01-01

The crotonaldehyde- and acetaldehyde-derived R- and S-α-CH3-γ-OH-1,N2-propanodeoxyguanosine adducts were monitored in single-stranded and duplex oligodeoxynucleotides using NMR spectroscopy. In both instances the cis and trans diastereomers of the α-CH3 and γ-OH groups underwent slow exchange, with the trans diastereomers being favored. In single-stranded oligodeoxynucleotides, the aldehyde intermediates were not detected spectroscopically, but their presence was revealed through the formation of N-terminal conjugates with the tetrapeptide KWKK. When annealed into 5′-d(GCTAGCXAGTCC)-3′•5′-d(GGACTCYCTAGC)-3′ containing the 5′-CpG-3′ sequence context (X=R- or S-α-CH3-γ-13C-OH-PdG; Y=15N2-dG), at pH 7, partial opening of the R- or S-α-CH3-γ-13C-OH-PdG adducts to the corresponding N2-(3-oxo-1-methyl-propyl)-dG aldehydes was observed at temperatures below the Tm of the duplexes. These aldehydes equilibrated with their geminal diol hydrates; higher temperatures favored the aldehydes. When annealed opposite to T, the S-α-CH3-γ-13C-OH-PdG adduct was stable. At 37 °C, an interstrand DNA crosslink was observed spectroscopically only for the R-α-CH3-γ-OH-PdG adduct. Molecular modeling predicted that the interstrand crosslink formed by the R-α-CH3-γ-OH-PdG adduct introduced less disruption into the duplex structure than did the crosslink arising from the S-α-CH3-γ-OH-PdG adduct, due to differing orientations of the R- and S-CH3 groups. Modeling also predicted that the α-methyl group of the aldehyde arising from the R-α-CH3-γ-OH-PdG adduct oriented in the 3′ direction in the minor groove, facilitating crosslinking. In contrast, the α-methyl group of the aldehyde arising from the S-α-CH3-γ-OH-PdG adduct oriented in the 5′ direction within the minor groove potentially hindering crosslinking. NMR revealed that for the R-α-CH3-γ-OH-PdG adduct, the carbinolamine form of the crosslink was favored in duplex DNA, in situ, with the imine or Schiff base form of the crosslink remaining below the level of spectroscopic detection. Molecular modeling predicted that the carbinolamine linkage maintained Watson-Crick hydrogen bonding at both of the tandem C•G base pairs. Dehydration of the carbinolamine crosslink to an imine, or cyclization of the latter to form a pyrimidopurinone crosslink, required disruption of Watson-Crick hydrogen bonding at one or both of the crosslinked base pairs. PMID:16485895

The Tropospheric Lifetimes of Halocarbons and Their Reactions with OH Radicals: an Assessment Based on the Concentration of CO-14

NASA Technical Reports Server (NTRS)

Derwent, Richard G.; Volz-Thomas, Andreas

1990-01-01

Chemical reaction with hydroxyl radicals formed in the troposphere from ozone photolysis in the presence of methane, carbon monoxide and nitrogen oxides provides an important removal mechanism for halocarbons containing C-H and C = C double bonds. The isotropic distribution in atmospheric carbon monoxide was used to quantify the tropospheric hydroxyl radical distribution. Here, this methodology is reevaluated in the light of recent chemical kinetic data evaluations and new understandings gained in the life cycles of methane and carbon monoxide. None of these changes has forced a significant revision in the CO-14 approach. However, it is somewhat more clearly apparent how important basic chemical kinetic data are to the accurate establishment of the tropospheric hydroxyl radical distribution.

A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states

NASA Astrophysics Data System (ADS)

Nguyen, Trong-Nghia; Putikam, Raghunath; Lin, M. C.

2015-03-01

We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH2OO and anti/syn-CH3C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH2OO and anti-CH3C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH3C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C-H bonds. For syn-CH3C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH3 group by the terminal O atom producing CH2C(H)O-OH. At 298 K, the intramolecular insertion process in CH2OO was found to be 600 times faster than the commonly assumed ring-closing reaction.

Activation of C-O and C-C bonds and formation of novel HAlOH-ether complexes: an EPR study of the reaction of ground-state Al atoms with methylethyl ether and diethyl ether.

PubMed

Brunet, François D; Feola, Julie C; Joly, Helen A

2012-03-15

Reaction mixtures, containing Al atoms and methylethyl ether (MEE) or diethyl ether (DEE) in an adamantane matrix, were prepared with the aid of a metal-atom reactor known as a rotating cryostat. The EPR spectra of the resulting products were recorded from 77-260 K, at 10 K intervals. Al atoms were found to insert into methyl-O, ethyl-O, and C-C bonds to form CH(3)AlOCH(2)CH(3), CH(3)OAlCH(2)CH(3), and CH(3)OCH(2)AlCH(3), respectively, in the case of MEE while DEE produced CH(3)CH(2)AlOCH(2)CH(3) and CH(3)AlCH(2)OCH(2)CH(3), respectively. From the intensity of the transition lines attributed to the Al atom C-O insertion products of MEE, insertion into the methyl-O bond is preferred. The Al hyperfine interaction (hfi) extracted from the EPR spectra of the C-O insertion products was greater than that of the C-C insertion products, that is, 5.4% greater for the DEE system and 7% greater for the MEE system. The increase in Al hfi is thought to arise from the increased electron-withdrawing ability of the substituents bonded to Al. Besides HAlOH, resulting from the reaction of Al atoms with adventitious water, novel mixed HAlOH:MEE and HAlOH:DEE complexes were identified with the aid of isotopic studies involving H(2)(17)O and D(2)O. The Al and H hfi of HAlOH were found to decrease upon complex formation. These findings are consistent with the nuclear hfi calculated using a density functional theory (DFT) method with close agreement between theory and experiment occurring at the B3LYP level using a 6-311+G(2df,p) basis set.

Ultrafast photochemistry of methyl hydroperoxide on ice particles

PubMed Central

Kamboures, M. A.; Nizkorodov, S. A.; Gerber, R. B.

2009-01-01

Simulations show that photodissociation of methyl hydroperoxide, CH3OOH, on water clusters produces a surprisingly wide range of products on a subpicosecond time scale, pointing to the possibility of complex photodegradation pathways for organic peroxides on aerosols and water droplets. Dynamics are computed at several excitation energies at 50 K using a semiempirical PM3 potential surface. CH3OOH is found to prefer the exterior of the cluster, with the CH3O group sticking out and the OH group immersed within the cluster. At atmospherically relevant photodissociation wavelengths the OH and CH3O photofragments remain at the surface of the cluster or embedded within it. However, none of the 25 completed trajectories carried out at the atmospherically relevant photodissociation energies led to recombination of OH and CH3O to form CH3OOH. Within the limited statistics of the available trajectories the predicted yield for the recombination is zero. Instead, various reactions involving the initial fragments and water promptly form a wide range of stable molecular products such as CH2O, H2O, H2, CO, CH3OH, and H2O2. PMID:19846778

G331.512–0.103: An Interstellar Laboratory for Molecular Synthesis. I. The Ortho-to-para Ratios for CH3OH and CH3CN

NASA Astrophysics Data System (ADS)

Mendoza, Edgar; Bronfman, Leonardo; Duronea, Nicolas U.; Lépine, Jacques R. D.; Finger, Ricardo; Merello, Manuel; Hervías-Caimapo, Carlos; Gama, Diana R. G.; Reyes, Nicolas; Åke-Nyman, Lars

2018-02-01

Spectral line surveys reveal rich molecular reservoirs in G331.512–0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyze the physical conditions of the source by means of CH3OH and CH3CN. The observations were performed with the APEX Telescope. Six different system configurations were defined to cover most of the band within (292–356) GHz as a consequence, we detected a forest of lines toward the central core. A total of 70 lines of A/E–CH3OH and A/E–CH3CN were analyzed, including torsionally excited transitions of CH3OH ({ν }t=1). In a search for all the isotopologues, we identified transitions of 13CH3OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each A and E symmetry of CH3OH and CH3CN; the derived column densities indicate an A/E equilibrated ratio for both tracers. The results reveal that CH3CN and CH3OH trace a hot and cold component with {T}k∼ 141 K and {T}k∼ 74 K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact (≲ 5\\buildrel{\\prime\\prime}\\over{.} 5) with gas density n(H2) = (0.7–1)×107 cm‑3. The CH3OH/CH3CN abundance ratio and the evidences for prebiotic and complex organic molecules suggest a rich and active chemistry toward G331.512–0.103.

Molecular structure, supramolecular association and anion sensing by chlorodiorganotin(IV) methylferrocenyldithiocarbamates

NASA Astrophysics Data System (ADS)

Yadav, Reena; Awasthi, Mahendra Kumar; Singh, Amita; Kociok-Köhn, Gabriele; Trivedi, Manoj; Prasad, Rajendra; Shahid, Mohammad; Kumar, Abhinav

2017-10-01

Three new chlorodiorganotin(IV) methylferrocenyl dithiocarbamate complexes viz. [(FcCH2)(CH2CH2OH)NCS2SnMe2(Cl)] (1), [(FcCH2)(CH2CH2OH)NCS2SnnBu2(Cl)] (2) and [(FcCH2)(CH2CH2OH)NCS2SnPh2(Cl)] (3) have been synthesized and characterized by elemental analysis, IR, UV-Vis, 1H, 13C and 119Sn NMR spectroscopy and X-ray crystallography. The crystal structure of 1 indicates that the coordination geometries around the tin(IV) center is intermediate between ideal trigonal-bipyramidal and square pyramidal coordination polyhedra bonded through two sulfur atoms of the dithiocarbamate ligand in an isobidentate mode, two CH3 groups and one chlorine atom. Since, in 2 and 3 only alkyl and aryl fragments have been changed we infer that both 2 and 3 would also have the same behaviors in the solution state as observed in 1. Ionic interactions abilities of 1-3 are examined in acetonitrile through UV-vis absorption spectroscopy which offers reasonably good selectivity and sensitivity towards the detection of the acetate ion. Compounds 1-3 exhibit a bathochromic shift with the acetate ion with a moderate association constant.

Dosimetry determines the initial OH radical concentration in fast photochemical oxidation of proteins (FPOP).

PubMed

Niu, Ben; Zhang, Hao; Giblin, Daryl; Rempel, Don L; Gross, Michael L

2015-05-01

Fast photochemical oxidation of proteins (FPOP) employs laser photolysis of hydrogen peroxide to give OH radicals that label amino acid side-chains of proteins on the microsecond time scale. A method for quantitation of hydroxyl radicals after laser photolysis is of importance to FPOP because it establishes a means to adjust the yield of •OH, offers the opportunity of tunable modifications, and provides a basis for kinetic measurements. The initial concentration of OH radicals has yet to be measured experimentally. We report here an approach using isotope dilution gas chromatography/mass spectrometry (GC/MS) to determine quantitatively the initial •OH concentration (we found ~0.95 mM from 15 mM H2O2) from laser photolysis and to investigate the quenching efficiencies for various •OH scavengers.

Comprehensive characterization and understanding of micro-fuel cells operating at high methanol concentrations.

PubMed

Gago, Aldo S; Esquivel, Juan-Pablo; Sabaté, Neus; Santander, Joaquín; Alonso-Vante, Nicolas

2015-01-01

We report on the analysis of the performance of each electrode of an air-breathing passive micro-direct methanol fuel cell (µDMFC) during polarization, stabilization and discharge, with CH3OH (2-20 M). A reference electrode with a microcapillary was used for separately measuring the anode the cathode potential. Information about the open circuit potential (OCP), the voltage and the mass transport related phenomena are available. Using 2 M CH3OH, the anode showed mass transport problems. With 4 and 6 M CH3OH both electrodes experience this situation, whereas with 10 and 20 M CH3OH the issue is attributed to the cathode. The stabilization and fuel consumption time depends mainly on the cathode performance, which is very sensitive to fuel crossover. The exposure to 20 M CH3OH produced a loss in performance of more than 75% of the highest power density (16.3 mW·cm(-2)).

Cooperatively enhanced ionic hydrogen bonds in Cl-(CH3OH)(1-3)Ar clusters.

PubMed

Beck, Jordan P; Lisy, James M

2010-09-23

Infrared predissociation (IRPD) spectra of Cl−(CH3OH)1-3Ar and Cl-(CH3OD)1-3Ar were obtained in the OH and CH stretching regions. The use of methanol-d1 was necessary to distinguish between CH stretches and hydrogen-bonded OH features. The spectra of Cl-(CH3OH)2-3Ar show intense features at frequencies lower than the CH stretches, indicating structures with very strong hydrogen bonds. These strong hydrogen bonds arise from structures in which a Cl-···methanol ionic hydrogen bond is cooperatively enhanced by the presence of a second shell and, in the case of Cl-(CH3OH)3Ar, a third shell methanol. The strongest hydrogen bond is observed in the Cl-(CH3OH)3Ar spectrum at 2733 cm-1, shifted a remarkable -948 cm-1 from the neutral, gas-phase methanol value. Harmonic, ab initio frequency calculations are not adequate in describing these strong hydrogen bonds. Therefore, we describe a simple computational approach to better approximate the hydrogen bond frequencies. Overall, the results of this study indicate that high-energy isomers are very efficiently trapped using our experimental method of introducing Cl- into neutral, cold methanol-argon clusters.

Laser Ionization Studies of Hydrocarbon Flames.

NASA Astrophysics Data System (ADS)

Bernstein, Jeffrey Scott

Resonance-enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF) are applied as laser based flame diagnostics for studies of hydrocarbon combustion chemistry. rm CH_4/O_2, C _2H_4/O_2, and rm C_2H_6/O_2 low pressure ( ~20 Torr), stoichiometric burner stabilized flat flames are studied. Density profiles of intermediate flame species, existing at ppm concentrations, are mapped out as a function of distance from the burner head. Profiles resulting from REMPI and LIF detection are obtained for HCO, CH_3, H, O, OH, CH, and CO flame radicals. The above flame systems are computer modeled against currently accepted combustion mechanisms using the Chemkin and Premix flame codes developed at Sandia National Laboratories. The modeled profile densities show good agreement with the experimental results of the CH_4/O_2 flame system, thus confirming the current C1 kinetic flame mechanism. Discrepancies between experimental and modeled results are found with the C2 flames. These discrepancies are partially amended by modifying the rate constant of the rm C_2H_3+rm O_2 to H_2CO + HCO reaction. The modeled results computed with the modified rate constant strongly suggest that the kinetics of several or possibly many reactions in the C2 mechanism need refinement.

Detection of Hydroxyl and Perhydroxyl Radical Generation from Bleaching Agents with Nuclear Magnetic Resonance Spectroscopy.

PubMed

Sharma, Himanshu; Sharma, Divya S

Children/adolescent's orodental structures are different in anatomy and physiology from that of adults, therefore require special attention for bleaching with oxidative materials. Hydroxyl radical (OH . ) generation from bleaching agents has been considered directly related to both its clinical efficacy and hazardous effect on orodental structures. Nonetheless bleaching agents, indirectly releasing hydrogen peroxide (H 2 O 2 ), are considered safer yet clinically efficient. Apart from OH . , perhydroxyl radicals (HO 2 . ) too, were detected in bleaching chemistry but not yet in dentistry. Therefore, the study aims to detect the OH . and HO 2 . from bleaching agents with their relative integral value (RIV) using 31 P nuclear magnetic resonance ( 31 PNMR) spectroscope. Radicals were generated with UV light in 30% H 2 O 2 , 35% carbamide peroxide (CP), sodium perborate tetrahydrate (SPT) and; neutral and alkaline 30% H 2 O 2 . Radicals were spin-trapped with DIPPMPO in NMR tubes for each test agents as a function of time (0, 1, 2, 3min) at their original pH. Peaks were detected for OH . and HO 2 . on NMR spectrograph. RIV were read and compared for individual radicals detected. Only OH . were detected from acidic and neutral bleaching agent (30% acidic and neutral H 2 O 2 , 35%CP); both HO 2 . and OH . from 30% alkaline H 2 O 2 ; while only HO 2 . from more alkaline SPT. RIV for OH . was maximum at 1min irradiation of acidic 30%H 2 O 2 and 35%CP and minimum at 1min irradiation of neutral 30%H 2 O 2 . RIV for HO 2 . was maximum at 0min irradiation of alkaline 30%H 2 O 2 and minimum at 2min irradiation of SPT. The bleaching agents having pH- neutral and acidic were always associated with OH . ; weak alkaline with both OH . and HO 2 . ; and strong alkaline with HO 2 . only. It is recommended to check the pH of the bleaching agents and if found acidic, should be made alkaline to minimize oxidative damage to enamel itself and then to pulp/periodontal tissues. H 2 O 2 : hydrogen peroxide CP: carbamide peroxide SP: sodium perborate SPT: sodium perborate tetrahydrate ROS: reactive oxygen species 31 PNMR: 31 P nuclear magnetic resonance spectroscope RIV: relative integral value OH 2 . : hydroxyl radical HO 2 . : perhydroxyl radical O 2 . : super oxide radical DIPPMPO: 5-(Diisopropoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide DEPMPO: 5-diethoxyphosphoryl-5-methyl-1-pyrroline-n-oxide DMPO: 5,5-dimethyl-1-pyrroline-N-oxide D 2 O: heavy water EDTA: ethylene diamine tetra acetic acid.

Spectroscopic properties of morin in various CH3OH-H2O and CH3CN-H2O mixed solvents.

PubMed

Park, Hyoung-Ryun; Im, Seo-Eun; Seo, Jung-Ja; Kim, Bong-Gon; Yoon, Jin Ah; Bark, Ki-Min

2015-01-01

The specific fluorescence properties of morin (3,2',4',5,7-pentahydroxyflavone) were studied in various CH3OH-H2O and CH3CN-H2O mixed solvents. Although the dihedral angle is large in the S0 state, morin has an almost planar molecular structure in the S1 state owing to the very low rotational energy barrier around the interring bond between B and the A, C ring. The excited state intramolecular proton transfer (ESIPT) at the S1 state cannot occur immediately after excitation, S1 → S0 fluorescence can be observed. Two conformers, Morin A and B have been known. At the CH3OH-H2O, Morin B will be the principal species but at the CH3CN-H2O, Morin A is the principal species. At the CH3OH-H2O, owing to the large Franck-Condon (FC) factor for S2 → S1 internal convernal (IC) and flexible molecular structure, only S1 → S0 fluorescence was exhibited. At the CH3CN-H2O, as the FC factor for S2 → S1 IC is small and molecular structure is rigid, S2 → S0 and S1 → S0 dual fluorescence was observed. This abnormal fluorescence property was further supported by the small pK1 value, effective delocalization of the lone pair electrons of C(2')-OH to the A, C ring, and a theoretical calculation. © 2014 The American Society of Photobiology.

Determination of Combustion Product Radicals in a Hydrocarbon Fueled Rocket Exhaust Plume

NASA Technical Reports Server (NTRS)

Langford, Lester A.; Allgood, Daniel C.; Junell, Justin C.

2007-01-01

The identification of metallic effluent materials in a rocket engine exhaust plume indicates the health of the engine. Since 1989, emission spectroscopy of the plume of the Space Shuttle Main Engine (SSME) has been used for ground testing at NASA's Stennis Space Center (SSC). This technique allows the identification and quantification of alloys from the metallic elements observed in the plume. With the prospect of hydrocarbon-fueled rocket engines, such as Rocket Propellant 1 (RP-1) or methane (CH4) fueled engines being considered for use in future space flight systems, the contributions of intermediate or final combustion products resulting from the hydrocarbon fuels are of great interest. The effect of several diatomic molecular radicals, such as Carbon Dioxide , Carbon Monoxide, Molecular Carbon, Methylene Radical, Cyanide or Cyano Radical, and Nitric Oxide, needs to be identified and the effects of their band systems on the spectral region from 300 nm to 850 nm determined. Hydrocarbon-fueled rocket engines will play a prominent role in future space exploration programs. Although hydrogen fuel provides for higher engine performance, hydrocarbon fuels are denser, safer to handle, and less costly. For hydrocarbon-fueled engines using RP-1 or CH4 , the plume is different from a hydrogen fueled engine due to the presence of several other species, such as CO2, C2, CO, CH, CN, and NO, in the exhaust plume, in addition to the standard H2O and OH. These species occur as intermediate or final combustion products or as a result of mixing of the hot plume with the atmosphere. Exhaust plume emission spectroscopy has emerged as a comprehensive non-intrusive sensing technology which can be applied to a wide variety of engine performance conditions with a high degree of sensitivity and specificity. Stennis Space Center researchers have been in the forefront of advancing experimental techniques and developing theoretical approaches in order to bring this technology to a more mature stage.

Gas-phase tropospheric chemistry of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin.

PubMed

Zhang, Chenxi; Sun, Xiaomin

2014-01-15

Growing attention has been devoted to understanding the formation and destruction of polyfluorinated dibenzo-p-dioxins (PFDDs). High-accuracy molecular orbital calculations have been performed to investigate the tropospheric oxidation reaction of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin (TFDD) initiated by OH radical, NO3 radical and O3. The rate constant of TFDD reaction triggered by the OH radical, NO3 radical and O3 is about 2.30 × 10(-11)cm(3) molecule(-l) s(-l), 3.18 × 10(-13)cm(3) molecule(-l) s(-l), and 3.30 × 10(-19)cm(3) molecule(-l) s(-l), respectively. OH radical is the major gas phase tropospheric sink for TFDD. Once TFDD-OH intermediates are produced in the initial reactions, they can react with tropospheric O2 subsequently to generate peroxy radical isomers. The TFDD-OH-O2 can further react with tropospheric NO via isomerization or combination, resulting that the dioxin ring will be ruptured completely. This study can serve as a template for tropospheric degradation of the gaseous PFDDs, which is beneficial for assessing their tropospheric behaviors. © 2013 Elsevier B.V. All rights reserved.

Microheterogeneity in CH3OH/CD3OH mixture

NASA Astrophysics Data System (ADS)

Wrzeszcz, Władysław; Mazurek, Sylwester; Szostak, Roman; Tomza, Paweł; Czarnecki, Mirosław A.

2018-01-01

Recently, we demonstrated the presence of microheterogeneity in binary mixtures of unlike alcohols. [RSC Adv. 2016, 6, 37195-37202] The aim of this work was examination if this phenomenon occurs also in the mixture of very similar alcohols like CH3OH and CD3OH. Theoretical calculations suggest that the isotopic substitution in methyl group influences properties of the OH group. Hence, one can expect that this effect may lead to partial separation of CH3OH and CD3OH at a molecular level and it contributes to deviation from the ideal mixture. This work evidences that CH3OH/CD3OH mixture also deviates from the ideal one, but the extent of this deviation is much smaller as compared with the mixtures of other alcohols. It is of particular note that this deviation results mainly from the difference between the CH3 and CD3 groups, while the contribution from the OH groups is small. The structure of CH3OH/CD3OH mixture at a molecular level is similar to the structure of binary mixtures of other alcohols. The mixture is composed of the homoclusters of both alcohols and the mixed clusters. The homoclusters existing in the mixture are similar to those present in bulk alcohols. The highest population of the heteroclusters and the largest deviation from the ideal mixture were observed at equimolar mixture. Both the experimental and theoretical results reveal that in CH3OH/CD3OH mixture dominate the cyclic tetramers and larger clusters, while the population of the linear clusters is negligible. Though the extent and strength of hydrogen bonding in both alcohols are the same, the position and intensity of the 2ν(OH) band for CH3OH and CD3OH are different. We propose possible explanation of this observation.

Microheterogeneity in CH3OH/CD3OH mixture.

PubMed

Wrzeszcz, Władysław; Mazurek, Sylwester; Szostak, Roman; Tomza, Paweł; Czarnecki, Mirosław A

2018-01-05

Recently, we demonstrated the presence of microheterogeneity in binary mixtures of unlike alcohols. [RSC Adv. 2016, 6, 37195-37202] The aim of this work was examination if this phenomenon occurs also in the mixture of very similar alcohols like CH 3 OH and CD 3 OH. Theoretical calculations suggest that the isotopic substitution in methyl group influences properties of the OH group. Hence, one can expect that this effect may lead to partial separation of CH 3 OH and CD 3 OH at a molecular level and it contributes to deviation from the ideal mixture. This work evidences that CH 3 OH/CD 3 OH mixture also deviates from the ideal one, but the extent of this deviation is much smaller as compared with the mixtures of other alcohols. It is of particular note that this deviation results mainly from the difference between the CH 3 and CD 3 groups, while the contribution from the OH groups is small. The structure of CH 3 OH/CD 3 OH mixture at a molecular level is similar to the structure of binary mixtures of other alcohols. The mixture is composed of the homoclusters of both alcohols and the mixed clusters. The homoclusters existing in the mixture are similar to those present in bulk alcohols. The highest population of the heteroclusters and the largest deviation from the ideal mixture were observed at equimolar mixture. Both the experimental and theoretical results reveal that in CH 3 OH/CD 3 OH mixture dominate the cyclic tetramers and larger clusters, while the population of the linear clusters is negligible. Though the extent and strength of hydrogen bonding in both alcohols are the same, the position and intensity of the 2ν(OH) band for CH 3 OH and CD 3 OH are different. We propose possible explanation of this observation. Copyright © 2017 Elsevier B.V. All rights reserved.

Gas-phase products and secondary organic aerosol formation from the ozonolysis and photooxidation of myrcene

NASA Astrophysics Data System (ADS)

Böge, Olaf; Mutzel, Anke; Iinuma, Yoshiteru; Yli-Pirilä, Pasi; Kahnt, Ariane; Joutsensaari, Jorma; Herrmann, Hartmut

2013-11-01

In this study, the ozone and OH-radical reactions of myrcene were investigated in an aerosol chamber (at 292-295 K and 50% relative humidity) to examine the gas-phase oxidation products and secondary organic aerosol (SOA) formation. The ozone reaction studies were performed in the presence and absence of CO, which serves as an OH radical scavenger. In the photooxidation experiments OH radicals were generated by photolysis of methyl nitrite. The ozonolysis of myrcene in the presence of CO resulted in a substantial yield of 4-vinyl-4-pentenal (55.3%), measured as m/z 111 plus m/z 93 using proton transfer reaction-mass spectrometry (PTR-MS) and confirmed unambiguously as C7H10O by denuder measurements and HPLC/ESI-TOFMS analysis of its 2,4-dinitrophenylhydrazine (DNPH) derivative. Additionally, the formation of two different organic dicarbonyls with m/z 113 and a molecular formula of C6H8O2 were observed (2.1%). The yields of these dicarbonyls were higher in the ozonolysis experiments without an OH scavenger (5.4%) and even higher (13.8%) in the myrcene OH radical reaction. The formation of hydroxyacetone as a direct product of the myrcene reaction with ozone with a molar yield of 17.6% was also observed. The particle size distribution and volume concentrations were monitored and facilitated the calculation of SOA yields, which ranged from 0 to 0.01 (ozonolysis in the presence of CO) to 0.39 (myrcene OH radical reaction). Terpenylic acid was found in the SOA samples collected from the ozonolysis of myrcene in the absence of an OH scavenger and the OH radical-initiated reaction of myrcene but not in samples collected from the ozonolysis in the presence of CO as an OH radical scavenger, suggesting that terpenylic acid formation involves the reaction of myrcene with an OH radical. A reaction mechanism describing the formation of terpenylic acid is proposed.

Quantification of Hydroxyl Radical reactivity in the urban environment using the Comparative Reactivity Method (CRM)

NASA Astrophysics Data System (ADS)

Panchal, Rikesh; Monks, Paul

2015-04-01

Hydroxyl (OH) radicals play an important role in 'cleansing' the atmosphere of many pollutants such as, NOx, CH4 and various VOCs, through oxidation. To measure the reactivity of OH, both the sinks and sources of OH need to be quantified, and currently the overall sinks of OH seem not to be fully constrained. In order to measure the total rate loss of OH in an ambient air sample, all OH reactive species must be considered and their concentrations and reaction rate coefficients with OH known. Using the method pioneered by Sinha and Williams at the Max Plank Institute Mainz, the Comparative Reactivity Method (CRM) which directly quantifies total OH reactivity in ambient air without the need to consider the concentrations of individual species within the sample that can react with OH, has been developed and applied in a urban setting. The CRM measures the concentration of a reactive species that is present only in low concentrations in ambient air, in this case pyrrole, flowing through a reaction vessel and detected using Proton Transfer Reaction - Mass Spectrometry (PTR-MS). The poster will show a newly developed and tested PTR-TOF-MS system for CRM. The correction regime will be detailed to account for the influence of the varying humidity between ambient air and clean air on the pyrrole signal. Further, examination of the sensitivity dependence of the PTR-MS as a function of relative humidity and H3O+(H2O) (m/z=37) cluster ion allows the correction for the humidity variation, between the clean humid air entering the reaction vessel and ambient air will be shown. NO, present within ambient air, is also a potential interference and can cause recycling of OH, resulting in an overestimation of OH reactivity. Tests have been conducted on the effects of varying NO concentrations on OH reactivity and a correction factor determined for application to data when sampling ambient air. Finally, field tests in the urban environment at the University of Leicester will be shown coupled to an examination of trends in OH reactivity and other air quality markers such NOx and black carbon.

Reaction mechanism and kinetics of the degradation of terbacil initiated by OH radical - A theoretical study

NASA Astrophysics Data System (ADS)

Ponnusamy, S.; Sandhiya, L.; Senthilkumar, K.

2018-02-01

The reaction of terbacil with OH radical is studied by using electronic structure calculations. The reaction of terbacil with OH radical is found to proceed by H-atom abstraction, Cl-atom abstraction and OH addition reactions. The initially formed alkyl radical will undergo atmospheric transformation in the presence of molecular oxygen leading to the formation of peroxy radical. The reaction of peroxy radical with other atmospheric oxidants, such as HO2 and NO radicals is studied. The rate constant is calculated for the H-atom abstraction reactions over the temperature range of 200-1000 K. The results obtained from electronic structure calculations and kinetic study show that the H-atom abstraction reaction is more favorable. The calculated lifetime of terbacil is 24 h in normal atmospheric OH concentration. The rate constant calculated for H-atom abstraction reactions is 6 × 10-12, 4.4 × 10-12 and 3.2 × 10-12 cm3molecule-1s-1, respectively which is in agreement with the previous literature value of 1.9 × 10-12 cm3molecule-1s-1.

Electron spin resonance of gamma-irradiated poly/ethylene 2,6-naphthalene dicarboxylate/.

NASA Technical Reports Server (NTRS)

Rogowski, R. S.; Pezdirtz, G. F.

1971-01-01

The two types of radicals trapped in gamma-irradiated PEN 2,6 are identified by ESR as - O - CH - CH2 - O - (radical I) and a radical located on the naphthalene ring (radical II). The concentrations of the radicals in the gross polyer are 10 to 20% of I and 80 to 90% of II. Similar trapped radicals are established in beta-irradiated PET, a structurally related polymer.

A flexible 1,8-naphthyridyl derivative and its Zn(II) complexes: synthesis, structures, spectroscopic properties and recognition of Cd(II).

PubMed

Zhang, Hui-Miao; Fu, Wen-Fu; Gan, Xin; Xu, Yan-Qing; Wang, Jun; Xu, Quan-Qing; Chi, Shao-Ming

2008-12-21

A flexible ligand bis(7-methyl-1,8-naphthyridine-2-ylamino)methane (), having kappa(4)-chelating and kappa(2)-bridging modes, and its intriguing structural complexes of Zn(II) with mu-OH, kappa(1)-OAc, mu-kappa(1)-OAc and mu-kappa(2)-OAc ligands, [Zn(2)()(2)(OH)](ClO(4))(3) (), [Zn(4)()(2)(OAc)(6)(OH)(2)].CH(2)Cl(2) (.CH(2)Cl(2)) and [Zn(5)()(2)(OAc)(10)](n).4nH(2)O (.4H(2)O) were synthesized and their structures were determined by X-ray crystallography. These compounds exhibited intense blue fluorescent emissions with a lambda(max) in the range of 380-410 nm in CH(2)Cl(2), CH(3)CN and CH(3)OH solutions, and solid-state emissions centered at 416, 463, 490 and 451 nm were observed for the compounds , , and at room temperature, respectively. The investigated fluorescence properties of associated with various metal ions showed that the fluorescence enhancement of with Cd(II) was more sensitive than with other interfering cations.

Universal Strategy for Ultrathin Pt-M (M = Fe, Co, Ni) Nanowires for Efficient Catalytic Hydrogen Generation.

PubMed

Bai, Shuxing; Huang, Bolong; Shao, Qi; Huang, Xiaoqing

2018-06-25

Methanol (CH 3 OH) reformation with water (H 2 O) to in situ release hydrogen (H 2 ) is regarded as a hopeful H 2 production approach for polymer electrolyte membrane fuel cells, while developing highly efficient CH 3 OH reformation catalysts still remains a great challenge. Herein, a series of Pt-based ultrafine nanowires (UNWs) with high surface atom ratio are used as highly active and stable catalysts for CH 3 OH reformation to H 2 . By tuning Pt 3 M (M = Fe, Co, Ni), support and the composition of the Pt x Fe UNWs, the optimized Pt 4 Fe UNWs/Al 2 O 3 exhibits excellent catalytic behaviors with the high H 2 turnover frequency reaching to 2035.8 h -1 , more than 4 times higher than that of Pt UNWs/Al 2 O 3 . The reaction mechanism investigated by diffuse reflectance infrared Fourier transform spectroscopy turns out that the production of H 2 undergoes the CH 3 OH decomposition to *CO and gas-shift reaction of *CO with H 2 O. Combing with the XPS result and the density functional theory calculations, the high CH 3 OH reformation activity of Pt 4 Fe UNWs/Al 2 O 3 is attributable to synergism between Pt and Fe, which facilitates H 2 desorption and intermediate HCOO* and *COO formations via the reaction between *CO and OH - .

ESR study of electron reactions with esters and triglycerides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sevilla, M.D.; Morehouse, K.M.; Swarts, S.

1981-04-02

Reactions which occurred after electron attachment at 77K to a number of small carboxylic acid esters and triglycerides in an aqueous glass are reported. Most ester anions are found to decay on warming to form alkyl radicals by ..beta.. scission: RC(O/sup -/)OR' ..-->.. RCO/sub 2//sup -/ + R'.. The alkyl radical (R'.) produced by annealing is found to abstract hydrogen from the parent ester at an ..cap alpha..-carbon site, R'.+ R''CH/sub 2/CO/sub 2/R' ..-->.. R''CHCO/sub 2/R', or in the case of ethyl formate from the formate hydrogen, CH/sub 3/CH/sub 2/.+ HCO/sub 2/C/sub 2/H/sub 5/ ..-->.. C/sub 2/H/sub 6/ +.CO/sub 2/C/submore » 2/H/sub 5/. Results found for the methyl formate anion suggest hydrogen abstraction by the anion itself may compete with alkyl radical formation. The anion of the triglyceride triacetin is found to undergo an analogous mechanism to the ester anions producing the propane diol diester radical, .CH/sub 2/CH(Ac)CH/sub 2/(Ac), Ac = acetate. This species subsequently abstracts hydrogen from the parent compound to produce the ..cap alpha..-carbon radical, .CH/sub 2/CO/sub 2/R. Results found after annealing the tripropionin radical anion give evidence for abstraction from the ..cap alpha.. carbon in the propionate side groups producing CH/sub 3/CHCO/sub 2/R. Studies of a ..gamma..-irradiated ester (ethyl myristate) and two triglycerides (tripalmitin and tristearin) yield results which suggest that the mechanism of ester anion decay found in aqueous glasses applies to ..gamma..-irradiated neat long-chain esters and triglycerides. Results found in this work are compared to the results of product analysis.« less

Ionizing radiation-induced destruction of benzene and dienes in aqueous media.

PubMed

Al-Sheikhly, Mohamad; Poster, Dianne L; An, Jung-Chul; Neta, Pedatsur; Silverman, Joseph; Huie, Robert E

2006-05-01

Pulse radiolysis with spectrophotometric and conductometric detection was utilized to study the formation and reactions of radicals from benzene and dienes in aqueous solutions. The benzene OH adduct, *C6H6OH, reacts with O2 (k = 3 x 10(8) L mol(-1) s(-1)) in a reversible reaction. The peroxyl radical, HOC6H6O2*, undergoes O2*- elimination, bimolecular decay, and reaction with benzene to initiate a chain reaction, depending on the dose rate, benzene concentration, and pH. The occurrence of the chain reaction is demonstrated in low-dose-rate gamma radiolysis experiments where the consumption of O2 was monitored. 1,4-Cyclohexadiene, 1,4-hexadiene, and 1,4-pentadiene form OH-adducts and undergo H-abstraction by O*- radicals. The OH-adducts react with O2 to form peroxyl radicals. These peroxyl radicals, however, do not undergo unimolecular O2*- elimination but rather decay by second-order processes, which lead to subsequent steps of O2*- elimination.

OH Radical Reactions with Nitroimidazole and Nitrotriazole Derivatives

NASA Astrophysics Data System (ADS)

Gümüş, Selçuk

2012-04-01

The reactions between hydroxyl radical and 5-nitro-1H-imidazole (A), 2-nitro-1H-imidazole (B), and 3-nitro-4H-1,2,4-triazole (C) were theoretically investigated using B3LYP/6-31G(d,p) level of theory. The OH radical additions to double bonds were explored in bulk solvent (water). The data presented show that the barriers to reaction were very low, 3-7 kcal/mol, indicating fast reactions. Thermodynamically, OH addition to position 2 of structure A leads to the most stable radical product. The main geometrical parameters are reported for reactants, transition states, and radical products together with some energetic data of the nitro-imidazolone-type final compounds.

Molecular maser flares in the high-mass star-forming region IRAS18566+0408

NASA Astrophysics Data System (ADS)

Halbe, Daniel M.

We report results of a long-termmonitoring study of 6cmformaldehyde (H 2CO), 6.035GHz hydroxyl (OH), and 6.7GHz methanol (CH3OH) masers in the young high-mass protostellar object IRAS18566+0408 (G37.55+0.20). This is the only high-mass star-forming region where correlated variability of three different maser species has been reported. The observations were conducted with the 305m Arecibo Radio Telescope, and together with data from the literature, we present H2CO flux density measurements from 2002 to 2014, CH3OH data from 2006 to 2013, and discuss OH observations obtained between 2008 and 2012. Our extended monitoring observations of the H2CO maser agree with the quasi-periodic flare phenomenon and exponential decrease in quiescent and flare flux densities proposed by Araya and collaborators in 2010. We also confirm the occurrence of 6.035GHz OH flares and a time delay with respect to the H2CO flares. An analysis between the variability behavior of different CH3OH maser components and the H2CO maser suggests that multiple variability mechanisms are responsible for CH3OH flux density changes.

Understanding in situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project (ClearfLo)

NASA Astrophysics Data System (ADS)

Whalley, Lisa K.; Stone, Daniel; Dunmore, Rachel; Hamilton, Jacqueline; Hopkins, James R.; Lee, James D.; Lewis, Alastair C.; Williams, Paul; Kleffmann, Jörg; Laufs, Sebastian; Woodward-Massey, Robert; Heard, Dwayne E.

2018-02-01

Measurements of OH, HO2, RO2i (alkene and aromatic-related RO2) and total RO2 radicals taken during the ClearfLo campaign in central London in the summer of 2012 are presented. A photostationary steady-state calculation of OH which considered measured OH reactivity as the OH sink term and the measured OH sources (of which HO2+ NO reaction and HONO photolysis dominated) compared well with the observed levels of OH. Comparison with calculations from a detailed box model utilising the Master Chemical Mechanism v3.2, however, highlighted a substantial discrepancy between radical observations under lower NOx conditions ([NO] < 1 ppbv), typically experienced during the afternoon hours, and indicated that the model was missing a significant peroxy radical sink; the model overpredicted HO2 by up to a factor of 10 at these times. Known radical termination steps, such as HO2 uptake on aerosols, were not sufficient to reconcile the model-measurement discrepancies alone, suggesting other missing termination processes. This missing sink was most evident when the air reaching the site had previously passed over central London to the east and when elevated temperatures were experienced and, hence, contained higher concentrations of VOCs. Uncertainties in the degradation mechanism at low NOx of complex biogenic and diesel related VOC species, which were particularly elevated and dominated OH reactivity under these easterly flows, may account for some of the model-measurement disagreement. Under higher [NO] (> 3 ppbv) the box model increasingly underpredicted total [RO2]. The modelled and observed HO2 were in agreement, however, under elevated NO concentrations ranging from 7 to 15 ppbv. The model uncertainty under low NO conditions leads to more ozone production predicted using modelled peroxy radical concentrations ( ˜ 3 ppbv h-1) versus ozone production from peroxy radicals measured ( ˜ 1 ppbv h-1). Conversely, ozone production derived from the predicted peroxy radicals is up to an order of magnitude lower than from the observed peroxy radicals as [NO] increases beyond 7 ppbv due to the model underprediction of RO2 under these conditions.

The Reaction of Criegee Intermediate CH 2OO with Water Dimer: Primary Products and Atmospheric Impact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheps, Leonid; Rotavera, Brandon; Eskola, Arkke J.

The rapid reaction of the smallest Criegee intermediate, CH 2OO, with water dimers is the dominant removal mechanism for CH 2OO in the Earth's atmosphere, but its products are not well understood. This reaction was recently suggested as a significant source of the most abundant tropospheric organic acid, formic acid (HCOOH), which is consistently underpredicted by atmospheric models. Furthermore, using time-resolved measurements of reaction kinetics by UV absorption and product analysis by photoionization mass spectrometry, we show that the primary products of this reaction are formaldehyde and hydroxymethyl hydroperoxide (HMHP), with direct HCOOH yields of less than 10%. Incorporating ourmore » results into a global chemistry-transport model further reduces HCOOH levels by 10–90%, relative to previous modeling assumptions, which indicates that the reaction CH 2OO + water dimer by itself cannot resolve the discrepancy between the measured and predicted HCOOH levels.« less

The Reaction of Criegee Intermediate CH 2OO with Water Dimer: Primary Products and Atmospheric Impact

DOE PAGES

Sheps, Leonid; Rotavera, Brandon; Eskola, Arkke J.; ...

2017-08-04

The rapid reaction of the smallest Criegee intermediate, CH 2OO, with water dimers is the dominant removal mechanism for CH 2OO in the Earth's atmosphere, but its products are not well understood. This reaction was recently suggested as a significant source of the most abundant tropospheric organic acid, formic acid (HCOOH), which is consistently underpredicted by atmospheric models. Furthermore, using time-resolved measurements of reaction kinetics by UV absorption and product analysis by photoionization mass spectrometry, we show that the primary products of this reaction are formaldehyde and hydroxymethyl hydroperoxide (HMHP), with direct HCOOH yields of less than 10%. Incorporating ourmore » results into a global chemistry-transport model further reduces HCOOH levels by 10–90%, relative to previous modeling assumptions, which indicates that the reaction CH 2OO + water dimer by itself cannot resolve the discrepancy between the measured and predicted HCOOH levels.« less

ALMA Observations of the IRDC Clump G34.43+00.24 MM3: Complex Organic and Deuterated Molecules

NASA Astrophysics Data System (ADS)

Sakai, Takeshi; Yanagida, Takahiro; Furuya, Kenji; Aikawa, Yuri; Sanhueza, Patricio; Sakai, Nami; Hirota, Tomoya; Jackson, James M.; Yamamoto, Satoshi

2018-04-01

We have observed complex organic molecules (COMs) and deuterated species toward a hot core/corino (HC) associated with the infrared dark cloud clump G34.43+00.24 MM3 with the Atacama Large Millimeter/submillimeter Array. We have detected six normal-COMs (CH3OH, CH3CHO, CH3CH2CN, CH3OCH3, HCOOCH3, and NH2CHO), one deuterated-COM (CH2DCN), and two deuterated fundamental molecules (D2CO and DNC) toward G34.43+00.24 MM3 HC. None of these lines, except for CH3OH, are detected toward the shocked regions in our data, which suggests that COMs do not originate in shocks. The abundance of the COMs relative to CH3OH in G34.43+00.24 MM3 HC is found to be similar to those in high-mass hot cores, rather than those in hot corinos in low-mass star-forming regions. This result suggests that the physical conditions of the warm-up phase of G34.43+00.24 MM3 HC are similar to those of high-mass sources. On the other hand, the D2CO abundance relative to CH3OH in G34.43+00.24 MM3 HC is higher than that of other hot cores, and seems to be comparable to that of hot corinos. The relatively high D2CO/CH3OH ratio of G34.43+00.24 MM3 HC implies a long cold starless phase of G34.43+00.24 MM3 HC.

Measurements of hydroxyl and hydroperoxy radicals during CalNex-LA: Model comparisons and radical budgets

NASA Astrophysics Data System (ADS)

Griffith, S. M.; Hansen, R. F.; Dusanter, S.; Michoud, V.; Gilman, J. B.; Kuster, W. C.; Veres, P. R.; Graus, M.; de Gouw, J. A.; Roberts, J.; Young, C.; Washenfelder, R.; Brown, S. S.; Thalman, R.; Waxman, E.; Volkamer, R.; Tsai, C.; Stutz, J.; Flynn, J. H.; Grossberg, N.; Lefer, B.; Alvarez, S. L.; Rappenglueck, B.; Mielke, L. H.; Osthoff, H. D.; Stevens, P. S.

2016-04-01

Measurements of hydroxyl (OH) and hydroperoxy (HO2*) radical concentrations were made at the Pasadena ground site during the CalNex-LA 2010 campaign using the laser-induced fluorescence-fluorescence assay by gas expansion technique. The measured concentrations of OH and HO2* exhibited a distinct weekend effect, with higher radical concentrations observed on the weekends corresponding to lower levels of nitrogen oxides (NOx). The radical measurements were compared to results from a zero-dimensional model using the Regional Atmospheric Chemical Mechanism-2 constrained by NOx and other measured trace gases. The chemical model overpredicted measured OH concentrations during the weekends by a factor of approximately 1.4 ± 0.3 (1σ), but the agreement was better during the weekdays (ratio of 1.0 ± 0.2). Model predicted HO2* concentrations underpredicted by a factor of 1.3 ± 0.2 on the weekends, while measured weekday concentrations were underpredicted by a factor of 3.0 ± 0.5. However, increasing the modeled OH reactivity to match the measured total OH reactivity improved the overall agreement for both OH and HO2* on all days. A radical budget analysis suggests that photolysis of carbonyls and formaldehyde together accounted for approximately 40% of radical initiation with photolysis of nitrous acid accounting for 30% at the measurement height and ozone photolysis contributing less than 20%. An analysis of the ozone production sensitivity reveals that during the week, ozone production was limited by volatile organic compounds throughout the day during the campaign but NOx limited during the afternoon on the weekends.

Highly Depleted Ethane and Slightly Depleted Methanol in Comet 21P/Giacobini-Zinner: Application of Empirical g-Factors for CH3OH Near 50K

NASA Technical Reports Server (NTRS)

DiSanti, Michael A.; Bonev, Boncho P.; Mumma, Michael J.; Villanueva, Geronimo L.

2010-01-01

We report high resolution (lambda/delta lambda approximately 24,000) observations of Comet 21 P/Giacobini-Zinner (21P) between approximately 2.85 -- 3.54 micrometers, obtained with NIRSPEC at Keck 2 on UT 2005 June 03 (R(sub h) = 1.12 AU, delta = 1.45 AU). These simultaneously sampled multiple emissions from the v7 band of C2H6 and the v2 and v3 bands of CH3OH, together with several hot bands of H2O, permitting a direct measure of parent volatile abundances in 21P. Our spectra reveal highly depleted C2H6 (0.13-0.14 percent relative to H2O) and CH3OH/C2H6 approximately 10, consistent with previously published abundances from observations in the IR [1,2] and millimeter sub-mm (reporting CH3OH/H2O [3]) during its previous apparition in 1998. We observed similarly high CH3OH/C2H6, and also similar rotational temperature to that measured for 21 P, in Comet 8P/Tuttle [4,5]. We used our (higher signal-to-noise) NIRSPEC observations of 8P to produce effective (empirical) CH3OH g-factors for several lines in the v2 band. These will be presented together with interpretation of our results, including constraints on the spin temperature of water. We acknowledge support from the NASA Planetary Atmospheres, Planetary Astronomy, and Astrobiology Programs and from the NSF Astronomy and Astrophysics Research Grants Program.

Investigation of potential interferences in the detection of atmospheric ROx radicals by laser-induced fluorescence under dark conditions

NASA Astrophysics Data System (ADS)

Fuchs, H.; Tan, Z.; Hofzumahaus, A.; Broch, S.; Dorn, H.-P.; Holland, F.; Künstler, C.; Gomm, S.; Rohrer, F.; Schrade, S.; Tillmann, R.; Wahner, A.

2015-11-01

Direct detection of highly reactive, atmospheric hydroxyl radicals (OH) is widely accomplished by laser-induced fluorescence (LIF) instruments. The technique is also suitable for the indirect measurement of HO2 and RO2 peroxy radicals by chemical conversion to OH. It requires sampling of ambient air into a low pressure cell, where OH fluorescence is detected after excitation by 308 nm laser radiation. Although the residence time of air inside the fluorescence cell is typically only on the order of milliseconds, there is potential that additional OH is internally produced, which would artificially increase the measured OH concentration. Here, we present experimental studies investigating potential interferences in the detection of OH and peroxy radicals for the LIF instruments of Forschungszentrum Jülich for nighttime conditions. For laboratory experiments, the inlet of the instrument was overflown by excess synthetic air containing one or more reactants. In order to distinguish between OH produced by reactions upstream of the inlet and artificial signals produced inside the instrument, a chemical titration for OH was applied. Additional experiments were performed in the simulation chamber SAPHIR where simultaneous measurements by an open-path differential optical absorption spectrometer (DOAS) served as reference for OH to quantify potential artifacts in the LIF instrument. Experiments included the investigation of potential interferences related to the nitrate radical (NO3, N2O5), related to the ozonolysis of alkenes (ethene, propene, 1-butene, 2,3-dimethyl-2-butene, α-pinene, limonene, isoprene), and the laser photolysis of acetone. Experiments studying the laser photolysis of acetone yield OH signals in the fluorescence cell, which are equivalent to 0.05 × 106 cm-3 OH for a mixing ratio of 5 ppbv acetone. Under most atmospheric conditions, this interference is negligible. No significant interferences were found for atmospheric concentrations of reactants during ozonolysis experiments. Only for α-pinene, limonene, and isoprene at reactant concentrations which are orders of magnitude higher than in the atmosphere artificial OH could be detected. The value of the interference depends on the turnover rate of the ozonolysis reaction. For example, an apparent OH concentration of approximately 1 × 106 cm-3 is observed, if 5.8 ppbv limonene reacts with 600 ppbv ozone. Experiments with the nitrate radical NO3 reveal a small interference signal in the OH, HO2 and RO2 detection. Dependencies on experimental parameters point to artificial OH formation by surface reactions at the chamber walls or in molecular clusters in the gas expansion. The signal scales with the presence of NO3 giving equivalent radical concentrations of 1.1 × 105 cm-3 OH, 1 × 107 cm-3 HO2, and 1.7 × 107 cm-3 RO2 per 10 pptv NO3.

The chemical composition of comet C/2012 S1 (ISON) between 1.2 au and 0.35 au from the Sun

NASA Astrophysics Data System (ADS)

DiSanti, M.; Bonev, B.; Gibb, E.; Villanueva, G.; Paganini, L.; Mumma, M.; Keane, J.; Meech, K.; Blake, G.; McKay, A.

2014-07-01

Introduction: By virtue of their small size and prolonged storage at large heliocentric distances (R_h), comets remain largely preserved. As a result, their ices encode a record of physical and chemical conditions in the early Solar System [1,2]. The recent apparition of C/2012 S1 (ISON) [3], a dynamically new sun-grazing comet, provided a rare opportunity to both prepare for and subsequently conduct compositional studies to well within 1 au from the Sun. Observations: We obtained high-resolution spectra (Resolving Power approximately 25,000) of Comet ISON on four dates (UT 2013 Oct. 22, 24, 25, and Nov. 7) using NIRSPEC [4] at Keck 2, and on six dates (Nov. 15 through 19, and Nov. 22) using CSHELL [5] at the NASA InfraRed Telescope Facility (IRTF). Our observations provided a measure of volatile production rates and abundance ratios (relative to H_2O) over a wide range of heliocentric distances (R_h = 1.23--0.35 au). NIRSPEC is cross-dispersed and so allows for simultaneous measure of multiple trace species together with H_2O, thereby avoiding most sources of systematic uncertainty, for example those associated with differences in slit losses and with flux calibration among settings. CSHELL has limited spectral coverage per setting, requiring judicious targeting of specific molecular emissions that (when possible) simultaneously encompass lines of H_2O and/or OH prompt emission, which serves as a proxy for water production provided equivalent OH line g-factors are known [6]. Despite this limitation, the IRTF is unique among ground-based IR observatories in its ability to conduct observations during daytime. This permitted obtaining compositional measurements of Comet ISON to a minimum solar elongation angle of 20 degrees. These will be discussed, and comparisons will be made with previously-reported results from observations with NIRSPEC [7] and HST [8]. Results: A suite of molecules (H_2O, CO, H_2CO, CH_3OH, C_2H_6, C_2H_2, CH_4, HCN, and NH_3) and radicals (OH, NH_2) were targeted and detected. Our serial measurements of production rates permitted a search for potential changes in molecular abundances as Comet ISON approached the Sun. The abundances of certain species (CO, C_2H_6, CH_3OH, CH_4) remained relatively constant with R_h, while others (e.g., H_2CO and HCN) increased in abundance with decreasing R_h, for example, as could result from potential compositional heterogeneity in the nucleus and/or release from increasingly heated grains in the coma.

Development of Army High-Energy Fuel for Diesel/Turbine Powered Surface Equipment

DTIC Science & Technology

1979-10-01

approximately CH2(R)CH(RI)CH2 OPO(OH)O(CH2 ) 2 N(OH)(CH 3 ) 3 , where R and R1 are fatty acid groups. The phosphatides are mixtures of diglyceride residues from...In the JP-lO/H2 0 microemulsions, three different emulsifying agents were used, all similar in type, but with varying acid numbers. The agents...designated as EA-8, EA-12, and EA-37, had acid numbers of approximately 14, 18.5, and >20, respectively. All three were visually stable (no settling) for 1

Ionization dynamics of the water trimer: A direct ab initio MD study

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto; Takada, Tomoya

2013-03-01

Ionization dynamics of the cyclic water trimer (H2O)3 have been investigated by means of direct ab initio molecular dynamics (AIMD) method. Two reaction channels, complex formation and OH dissociation, were found following the ionization of (H2O)3. In both channels, first, a proton was rapidly transferred from H2O+ to H2O (time scale is ˜15 fs after the ionization). In complex channel, an ion-radical contact pair (H3O+-OH) solvated by the third water molecule was formed as a long-lived H3O+(OH)H2O complex. In OH dissociation channel, the second proton transfer further takes place from H3O+(OH) to H2O (time scale is 50-100 fs) and the OH radical is separated from the H3O+. At the same time, the OH dissociation takes place when the excess energy is efficiently transferred into the kinetic energy of OH radical. The OH dissociation channel is significantly minor, and almost all product channels were the complex formation. The reaction mechanism was discussed on the basis of theoretical results.

Electron Paramagnetic Resonance Spectroscopic Study on Nonequilibrium Reaction Pathways in the Photolysis of Solid Nitromethane (CH3NO2) and D3-Nitromethane (CD3NO2).

PubMed

Tsegaw, Yetsedaw Andargie; Sander, Wolfram; Kaiser, Ralf I

2016-03-10

Thin films of nitromethane (CH3NO2) along with its isotopically labeled counterpart D3-nitromethane (CD3NO2) were photolyzed at discrete wavelength between 266 nm (4.7 eV) and 121 nm (10.2 eV) to explore the underlying mechanisms involved in the decomposition of model compounds of energetic materials in the condensed phase at 5 K. The chemical modifications of the ices were traced in situ via electron paramagnetic resonance, thus focusing on the detection of (hitherto elusive) reaction intermediates and products with unpaired electrons. These studies revealed the formation of two carbon-centered radicals [methyl (CH3), nitromethyl (CH2NO2)], one oxygen-centered radical [methoxy (CH3O)], two nitrogen-centered radicals [nitrogen monoxide (NO), nitrogen dioxide (NO2)], as well as atomic hydrogen (H). The decomposition products of these channels and the carbon-centered nitromethyl (CH2NO2) radical in particular represent crucial reaction intermediates leading via sequential molecular mass growth processes in the exposed nitromethane samples to complex organic molecules as predicted previously by dynamics calculations. The detection of the nitromethyl (CH2NO2) radical along with atomic hydrogen (H) demonstrated the existence of a high-energy decomposition pathway, which is closed under collisionless conditions in the gas phase.

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

NASA Astrophysics Data System (ADS)

Zhang, Ji-Dong; Zhang, Li-Li

2017-12-01

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO2 radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO2 + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO2 + FOX-7 results in the formation of NO3 radical, which has never been detected experimentally during the decomposition of FOX-7.

Laboratory measurements of H-D substitution rates in solid methanol-dn (n=0-2) at 10 K

NASA Astrophysics Data System (ADS)

Nagaoka, Akihiro; Watanabe, Naoki; Kouchi, Akira

The deuterium fractionation of interstellar methanol is investigated experimentally using the ASURA (Apparatus for SUrface Reactions in Astrophysics) system. Recent observations toward the low-mass protostars IRAS16293 found the very high D/H ratios in formaldehyde and methanol up to 0.2 and 0.4, respectively (Loinard et al. 2000; Parise et al. 2004; Aikawa et al. 2005). To date, several models have been proposed to explain D-fractionation mechanism. Pure gas-phase models are difficult to reproduce the D-fractionation, particularly, for multideuterated species, while the results of some gas-grain models can achieve the observed fractionation levels fairly well (Stantcheva & Herbst 2003). However, the gas-grain models require many assumptions regarding the grain surface reactions. Then, the experiments on the surface reaction have been highly desirable. In this context, we performed the experiments on the formation of deuterated formaldehyde and methanol on cold (10 K) interstellar grain analogues and revealed that a key route for the D-fractionation is not successive addition of H and D to CO as previously considered (e.g., Charnley, Tielens, & Rodgers 1997) but H-D substitution in solid CH3OH on icy grains (Nagaoka, Watanabe, & Kouchi 2005). We report the results of further experiments on the deuteration of CH3OH using a cold (30 K) atomic D beam. The relative rates of H-D substitution reactions; CH3OH → CH2DOH, CH2DOH → CHD2OH, CHD2OH → CD3OH, were measured. Experiments were performed using the ASURA system described previously (Watanabe et al. 2004; Nagaoka, Watanabe, & Kouchi 2005). The experimental procedure is as follows. An aluminum substrate was placed in the centre of an ultra-high vacuum chamber (10-10 Torr) and cooled to 10 K by a helium refrigerator. The solid samples of normal and deuterated methanol (CH3OH, CH2DOH, CHD2OH) were vapor-deposited on the substrate. The D atoms produced by dissociation of D2 molecules by microwave discharge were irradiated to samples. D atoms were cooled to 30 K in the atomic source chamber before irradiation. During the irradiation with D atoms, we measured the variations of chemical composition of the samples, in-situ, with FT-IR. From the attenuation curves of parent molecules upon the irradiation with cold D atoms, we determined the relative rates of H-D substitution reactions (k1, k2, k3) of solid methanol;

Catalyst mixtures

DOEpatents

Masel, Richard I.; Rosen, Brian A.

2017-02-14

Catalysts that include at least one catalytically active element and one helper catalyst can be used to increase the rate or lower the overpotential of chemical reactions. The helper catalyst can simultaneously act as a director molecule, suppressing undesired reactions and thus increasing selectivity toward the desired reaction. These catalysts can be useful for a variety of chemical reactions including, in particular, the electrochemical conversion of CO.sub.2 or formic acid. The catalysts can also suppress H.sub.2 evolution, permitting electrochemical cell operation at potentials below RHE. Chemical processes and devices using the catalysts are also disclosed, including processes to produce CO, OH.sup.-, HCO.sup.-, H.sub.2CO, (HCO.sub.2).sup.-, H.sub.2CO.sub.2, CH.sub.3OH, CH.sub.4, C.sub.2H.sub.4, CH.sub.3CH.sub.2OH, CH.sub.3COO.sup.-, CH.sub.3COOH, C.sub.2H.sub.6, O.sub.2, H.sub.2, (COOH).sub.2, or (COO.sup.-).sub.2, and a specific device, namely, a CO.sub.2 sensor.

Sulfur Dioxide Accelerates the Heterogeneous Oxidation Rate of Organic Aerosol by Hydroxyl Radicals

DOE PAGES

Richards-Henderson, Nicole K.; Goldstein, Allen H.; Wilson, Kevin R.

2016-03-08

There remains considerable uncertainty in how anthropogenic gas phase emissions alter the oxidative aging of organic aerosols in the troposphere. Here we observe a 10-20 fold acceleration in the effective heterogeneous OH oxidation rate of organic aerosol in the presence of SO 2. This acceleration originates from the radical chain reactions propagated by alkoxy radicals, which are formed efficiently inside the particle by the reaction of peroxy radicals with SO 2. As the OH approaches atmospheric concentrations, the radical chain length increases, transforming the aerosol at rates predicted to be up to 10 times the OH-aerosol collision frequency. Model predictions,more » constrained by experiments over orders of magnitude changes in [OH] and [SO 2], suggest that in polluted regions the heterogeneous processing of organic aerosols by OH ([SO 2] ≥ 40 ppb) occur on similar time scales as analogous gas-phase oxidation reactions. These results provide evidence for a previously unidentified mechanism by which organic aerosol oxidation is enhanced by anthropogenic gas phase emissions. (Chemical Equation Presented).« less

DFT study on dry reforming of methane over Ni2Fe overlayer of Ni(1 1 1) surface

NASA Astrophysics Data System (ADS)

Xu, Li-li; Wen, Hong; Jin, Xin; Bing, Qi-ming; Liu, Jing-yao

2018-06-01

We reported the complete catalytic cycle of dry reforming of methane (DRM) on Ni2Fe overlayer of Ni(1 1 1) surface by periodic density functional theory (DFT) calculations. The pathways for dehydrogenation of CH4 and CO2 activation were located. Our results demonstrate that compared with pure Ni(1 1 1) surface, the introduction Fe into Ni increases the energy barrier of CH dissociation to carbon and hydrogen atoms, thereby suppressing coke deposition on the surface, while it promotes the H-induced CO2 activation pathway to form OH radical, and thus not only the surface oxygen but also OH are responsible for the oxidation of CHx (x = 0,1) on the Ni2Fe overlayer. The most favorable pathway of CH/C oxidation is found to be CH∗ + OH∗ → CHOH∗ → CHO∗ + H∗ → CO∗ + 2H∗, with the rate-limiting energy barrier of 1.12 eV. Furthermore, since Fe is oxidized partially to FeO leading to a partial dealloying under DRM conditions, we also studied the surface-carbon removal and the activity for the reforming of methane on the FeO ribbon supported Ni(1 1 1) (FeO/Ni) interface by DFT+U method. The surface C reacts with lattice oxygen of FeO to produce CO via a Mars-van Krevelen (MvK) mechanism, with a very lower energy barrier of 0.16 eV. The present results show that the introduction of Fe into Ni has a positive effect on the activity toward DRM and has an improved coke resistance.

Central role of carbonyl compounds in atmospheric chemistry

NASA Astrophysics Data System (ADS)

Lary, D. J.; Shallcross, D. E.

2000-08-01

With the exception of acetone it is not generally recognized how important atmospheric carbonyls and alkyl radicals are in the lower stratosphere and upper troposphere. Carbonyl compounds are the crucial intermediate species for the autocatalytic production of OH. For example, in the upper troposphere and lower stratosphere it is calculated based on data assimilation analysis of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) data that CH3 production due to the degradation of carbonyls contributes around 40% to the overall production of CH3, a key initiation step for HOx production, with the contribution due to the photolysis of CH3CHO being comparable to that of acetone. So correctly modeling the alkyl radical concentrations is of central importance and has not be given the attention it deserves to date. The reactions of carbonyls with Br and Cl are also major sources of HBr and HCl. In short, carbonyl compounds play a central role in atmospheric chemistry close to the tropopause, and this is directly relevant to issues such as the assessment of the impact of air traffic, and ozone depletion.

Reduction of RuVI≡N to RuIII-NH3 by Cysteine in Aqueous Solution.

PubMed

Wang, Qian; Man, Wai-Lun; Lam, William W Y; Yiu, Shek-Man; Tse, Man-Kit; Lau, Tai-Chu

2018-05-21

The reduction of metal nitride to ammonia is a key step in biological and chemical nitrogen fixation. We report herein the facile reduction of a ruthenium(VI) nitrido complex [(L)Ru VI (N)(OH 2 )] + (1, L = N, N'-bis(salicylidene)- o-cyclohexyldiamine dianion) to [(L)Ru III (NH 3 )(OH 2 )] + by l-cysteine (Cys), an ubiquitous biological reductant, in aqueous solution. At pH 1.0-5.3, the reaction has the following stoichiometry: [(L)Ru VI (N)(OH 2 )] + + 3HSCH 2 CH(NH 3 )CO 2 → [(L)Ru III (NH 3 )(OH 2 )] + + 1.5(SCH 2 CH(NH 3 )CO 2 ) 2 . Kinetic studies show that at pH 1 the reaction consists of two phases, while at pH 5 there are three distinct phases. For all phases the rate law is rate = k 2 [1][Cys]. Studies on the effects of acidity indicate that both HSCH 2 CH(NH 3 + )CO 2 - and - SCH 2 CH(NH 3 + )CO 2 - are kinetically active species. At pH 1, the reaction is proposed to go through [(L)Ru IV (NHSCH 2 CHNH 3 CO 2 H)(OH 2 )] 2+ (2a), [(L)Ru III (NH 2 SCH 2 CHNH 3 CO 2 H)(OH 2 )] 2+ (3), and [(L)Ru IV (NH 2 )(OH 2 )] + (4) intermediates. On the other hand, at pH around 5, the proposed intermediates are [(L)Ru IV (NHSCH 2 CHNH 3 CO 2 )(OH 2 )] + (2b) and [(L)Ru IV (NH 2 )(OH 2 )] + (4). The intermediate ruthenium(IV) sulfilamido species, [(L)Ru IV (NHSCH 2 CHNH 3 CO 2 H)(OH 2 )] 2+ (2a) and the final ruthenium(III) ammine species, [(L)Ru III (NH 3 )(MeOH)] + (5) (where H 2 O was replaced by MeOH) have been isolated and characterized by various spectroscopic methods.

Synthesis, characterization and reactivity of trinuclear Cu(II) complexes derived from disalicylaldehyde malonoyldihydrazone

NASA Astrophysics Data System (ADS)

Koch, Angira; Kumar, Arvind; De, Arjun K.; Phukan, Arnab; Lal, Ram A.

2014-08-01

Three new homotrinuclear copper(II) complexes [Cu3(slmh)(μ-Cl)2(CH3OH)3]ṡ0.5CH3OH (1), [Cu3(slmh)(NO3)2(CH3OH)5]ṡ1.5CH3OH (2) and [Cu3(slmh)(μ-ClO4)2(CH3OH)3]ṡ2CH3OH (3) from disalicylaldehyde malonoyldihydrazone have been synthesized and characterized. The composition of the complexes has been established on the basis of data obtained from analytical and thermoanalytical data. The structure of the complexes has been discussed in the light of molar conductance, electronic, FT-IR and far-IR spectral data, magnetic moment and EPR spectral studies. The molar conductance values for the complexes in DMSO solution indicate that all of them are non-electrolyte. The magnetic moment values for the complexes suggest considerable metal-metal intramolecular interaction between metal ions in the structural unit of the complexes. The EPR spectral features reveal that at RT, the ground state for the complexes is a mixture of the quartet state (S = 3/2) and doublet state (S = ½). At lower temperature, the ground state for the complexes is dx2-y2 with considerable contribution from dz2 orbital. Dihydrazone ligand is present in enol form in all of the complexes. The complexes have distorted square pyramidal stereochemistry. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry. Hydrogen peroxide mediated oxidation of benzyl alcohol catalyzed by complex 1 has been studied.

Investigation of OH Radical Regeneration from Isoprene Oxidation Across Different NOx Regimes in the Atmosphere Simulation Chamber SAPHIR

NASA Astrophysics Data System (ADS)

Novelli, A.; Bohn, B.; Dorn, H. P.; Häseler, R.; Hofzumahaus, A.; Kaminski, M.; Yu, Z.; Li, X.; Tillmann, R.; Wegener, R.; Fuchs, H.; Kiendler-Scharr, A.; Wahner, A.

2017-12-01

The hydroxyl radical (OH) is the dominant daytime oxidant in the troposphere. It starts the degradation of volatile organic compounds (VOC) originating from both anthropogenic and biogenic emissions. Hence, it is a crucial trace species in model simulations as it has a large impact on many reactive trace gases. Many field campaigns performed in isoprene dominated environment in low NOx conditions have shown large discrepancies between the measured and the modelled OH radical concentrations. These results have contributed to the discovery of new regeneration paths for OH radicals from isoprene-OH second generation products with maximum efficiency at low NO. The current chemical models (e.g. MCM 3.3.1) include this novel chemistry allowing for an investigation of the validity of the OH regeneration at different chemical conditions. Over 11 experiments focusing on the OH oxidation of isoprene were performed at the SAPHIR chamber in the Forschungszentrum Jülich. Measurements of VOCs, NOx, O3, HONO were performed together with the measurement of OH radicals (by both LIF-FAGE and DOAS) and OH reactivity. Within the simulation chamber, the NO mixing ratio was varied between 0.05 to 2 ppbv allowing the investigation of both the "new" regeneration path for OH radicals and the well-known NO+HO2 mechanism. A comparison with the MCM 3.3.1 that includes the upgraded LIM1 mechanism showed very good agreement (within 10%) for the OH data at all concentrations of NOx investigated. Comparison with different models, without LIM1 and with updated rates for the OH regeneration, will be presented together with a detailed analysis of the impact of this study on results from previous field campaigns.

Speciated Monitoring of Gas-Phase Organic Peroxy Radicals by Chemical Ionization Mass Spectrometry: Cross-Reactions between CH3O2, CH3(CO)O2, (CH3)3CO2, and c-C6H11O2.

PubMed

Nozière, Barbara; Hanson, David R

2017-11-09

Organic peroxy radicals ("RO 2 ", with R organic) are key intermediates in most oxygen-rich systems, where organic compounds are oxidized (natural environment, flames, combustion engines, living organisms, etc). But, until recently, techniques able to monitor simultaneously and distinguish between RO 2 species ("speciated" detection) have been scarce, which has limited the understanding of complex systems containing these radicals. Mass spectrometry using proton transfer ionization has been shown previously to detect individual gas-phase RO 2 separately. In this work, we illustrate its ability to speciate and monitor several RO 2 simultaneously by investigating reactions involving CH 3 O 2 , CH 3 C(O)O 2 , c-C 6 H 11 O 2 , and (CH 3 ) 3 CO 2 . The detection sensitivity of each of these radicals was estimated by titration with NO to between 50 and 1000 Hz/ppb, with a factor from 3 to 5 of uncertainties, mostly due to the uncertainties in knowing the amounts of added NO. With this, the RO 2 concentration in the reactor was estimated between 1 × 10 10 and 1 × 10 12 molecules cm -3 . When adding a second radical species to the reactor, the kinetics of the cross-reaction could be studied directly from the decay of the first radical. The time-evolution of two and sometimes three different RO 2 was followed simultaneously, as the CH 3 O 2 produced in further reaction steps was also detected in some systems. The rate coefficients obtained are (in molecule -1 cm 3 s -1 ): k CH3O2+CH3C(O)O2 = 1.2 × 10 -11 , k CH3O2+t-butylO2 = 3.0 × 10 -15 , k c-hexylO2+CH3O2 = 1.2 × 10 -13 , k t-butylO2+CH3C(O)O2 = 3.7 × 10 -14 , and k c-hexylO2+t-butylO2 = 1.5 × 10 -15 . In spite of their good comparison with the literature and good reproducibility, large uncertainties (×5/5) are recommended on these results because of those in the detection sensitivities. This work is a first illustration of the potential applications of this technique for the investigation of organic radicals in laboratory and in more complex systems.

Identification of atomic-level mechanisms for gas-phase X- + CH3Y SN2 reactions by combined experiments and simulations.

PubMed

Xie, Jing; Otto, Rico; Mikosch, Jochen; Zhang, Jiaxu; Wester, Roland; Hase, William L

2014-10-21

For the traditional model of gas-phase X(-) + CH3Y SN2 reactions, C3v ion-dipole pre- and postreaction complexes X(-)---CH3Y and XCH3---Y(-), separated by a central barrier, are formed. Statistical intramolecular dynamics are assumed for these complexes, so that their unimolecular rate constants are given by RRKM theory. Both previous simulations and experiments have shown that the dynamics of these complexes are not statistical and of interest is how these nonstatistical dynamics affect the SN2 rate constant. This work also found there was a transition from an indirect, nonstatistical, complex forming mechanism, to a direct mechanism, as either the vibrational and/or relative translational energy of the reactants was increased. The current Account reviews recent collaborative studies involving molecular beam ion-imaging experiments and direct (on-the-fly) dynamics simulations of the SN2 reactions for which Cl(-), F(-), and OH(-) react with CH3I. Also considered are reactions of the microsolvated anions OH(-)(H2O) and OH(-)(H2O)2 with CH3I. These studies have provided a detailed understanding of the atomistic mechanisms for these SN2 reactions. Overall, the atomistic dynamics for the Cl(-) + CH3I SN2 reaction follows those found in previous studies. The reaction is indirect, complex forming at low reactant collision energies, and then there is a transition to direct reaction between 0.2 and 0.4 eV. The direct reaction may occur by rebound mechanism, in which the ClCH3 product rebounds backward from the I(-) product or a stripping mechanism in which Cl(-) strips CH3 from the I atom and scatters in the forward direction. A similar indirect to direct mechanistic transition was observed in previous work for the Cl(-) + CH3Cl and Cl(-) + CH3Br SN2 reactions. At the high collision energy of 1.9 eV, a new indirect mechanism, called the roundabout, was discovered. For the F(-) + CH3I reaction, there is not a transition from indirect to direct reaction as Erel is increased. The indirect mechanism, with prereaction complex formation, is important at all the Erel investigated, contributing up ∼60% of the reaction. The remaining direct reaction occurs by the rebound and stripping mechanisms. Though the potential energy curve for the OH(-) + CH3I reaction is similar to that for F(-) + CH3I, the two reactions have different dynamics. They are akin, in that for both there is not a transition from an indirect to direct reaction. However, for F(-) + CH3I indirect reaction dominates at all Erel, but it is less important for OH(-) + CH3I and becomes negligible as Erel is increased. Stripping is a minor channel for F(-) + CH3I, but accounts for more than 60% of the OH(-) + CH3I reaction at high Erel. Adding one or two H2O molecules to OH(-) alters the reaction dynamics from that for unsolvated OH(-). Adding one H2O molecule enhances indirect reaction at low Erel, and changes the reaction mechanism from primarily stripping to rebound at high Erel. With two H2O molecules the dynamics is indirect and isotropic at all collision energies.

Reactions of hydroxyalkyl radicals with cysteinyl peptides in a nanoESI plume.

PubMed

Stinson, Craig A; Xia, Yu

2014-07-01

In biological systems, carbon-centered small molecule radicals are primarily formed via external radiation or internal radical reactions. These radical species can react with a variety of biomolecules, most notably nucleic acids, the consequence of which has possible links to gene mutation and cancer. Sulfur-containing peptides and proteins are reactive toward a variety of radical species and many of them behave as radical scavengers. In this study, the reactions between alkyl alcohol carbon-centered radicals (e.g., •CH2OH for methanol) and cysteinyl peptides within a nanoelectrospray ionization (nanoESI) plume were explored. The reaction system involved ultraviolet (UV) irradiation of a nanoESI plume using a low pressure mercury lamp consisting of 185 and 254 nm emission bands. The alkyl alcohol was added as solvent into the nanoESI solution and served as the precursor of hydroxyalkyl radicals upon UV irradiation. The hydroxyalkyl radicals subsequently reacted with cysteinyl peptides either containing a disulfide linkage or free thiol, which led to the formation of peptide-S-hydroxyalkyl product. This radical reaction coupled with subsequent MS/MS was shown to have analytical potential by cleaving intrachain disulfide linked peptides prior to CID to enhance sequence information. Tandem mass spectrometry via collision-induced dissociation (CID), stable isotope labeling, and accurate mass measurement were employed to verify the identities of the reaction products.

Reactions of Hydroxyalkyl Radicals with Cysteinyl Peptides in a NanoESI Plume

NASA Astrophysics Data System (ADS)

Stinson, Craig A.; Xia, Yu

2014-07-01

In biological systems, carbon-centered small molecule radicals are primarily formed via external radiation or internal radical reactions. These radical species can react with a variety of biomolecules, most notably nucleic acids, the consequence of which has possible links to gene mutation and cancer. Sulfur-containing peptides and proteins are reactive toward a variety of radical species and many of them behave as radical scavengers. In this study, the reactions between alkyl alcohol carbon-centered radicals (e.g., •CH2OH for methanol) and cysteinyl peptides within a nanoelectrospray ionization (nanoESI) plume were explored. The reaction system involved ultraviolet (UV) irradiation of a nanoESI plume using a low pressure mercury lamp consisting of 185 and 254 nm emission bands. The alkyl alcohol was added as solvent into the nanoESI solution and served as the precursor of hydroxyalkyl radicals upon UV irradiation. The hydroxyalkyl radicals subsequently reacted with cysteinyl peptides either containing a disulfide linkage or free thiol, which led to the formation of peptide- S-hydroxyalkyl product. This radical reaction coupled with subsequent MS/MS was shown to have analytical potential by cleaving intrachain disulfide linked peptides prior to CID to enhance sequence information. Tandem mass spectrometry via collision-induced dissociation (CID), stable isotope labeling, and accurate mass measurement were employed to verify the identities of the reaction products.

Synthesis of hierarchical ZnV2O6 nanosheets with enhanced activity and stability for visible light driven CO2 reduction to solar fuels

NASA Astrophysics Data System (ADS)

Bafaqeer, Abdullah; Tahir, Muhammad; Amin, Nor Aishah Saidina

2018-03-01

Hierarchical nanostructures have lately garnered enormous attention because of their remarkable performances in energy storage and catalysis applications. In this study, novel hierarchical ZnV2O6 nanosheets, formulated by one-step solvothermal method, for enhanced photocatalytic CO2 reduction with H2O to solar fuels has been investigated. The structure and properties of the catalysts were characterized by XRD, FESEM, TEM, BET, UV-vis, Raman and PL spectroscopy. The hierarchical ZnV2O6 nanosheets show excellent performance towards photoreduction of CO2 with H2O to CH3OH, CH3COOH and HCOOH under visible light. The main product yield, CH3OH of 3253.84 μmol g-cat-1 was obtained over ZnV2O6, 3.4 times the amount of CH3OH produced over the ZnO/V2O5 composite (945.28 μmol g-cat-1). In addition, CH3OH selectivity of 39.96% achieved over ZnO/V2O5, increased to 48.78% in ZnV2O6 nanosheets. This significant improvement in photo-activity over ZnV2O6 structure was due to hierarchical structure with enhanced charge separation by V2O5. The obtained ZnV2O6 hierarchical nanosheets exhibited excellent photocatalytic stability for selective CH3OH production.

Radical observations during the Clean air for London project

NASA Astrophysics Data System (ADS)

Whalley, L. K.; Stone, D.; Clancy, N.; Lee, J. D.; Laufs, S.; Kleffmann, J.; Heard, D. E.

2012-12-01

With greater than 50 % of the global population residing in urban conurbations, poor urban air quality has a demonstrable effect on human health. OH and HO2 radicals, (collectively termed HOx) together with RO2 radicals, mediate virtually all of the oxidative chemistry in the atmosphere, being responsible for the transformation of primary emissions into secondary pollutants such as NO2, O3 and particulates. Understanding the chemistry of free-radicals in the atmosphere is essential in improving predictions of the lifetimes of pollutants and spatial scales of their transport within urban areas. Results from earlier field campaigns in urban and polluted regions have demonstrated the significance of HONO photolysis and alkene ozonolysis in the production of HOx radicals. In many cases, however, measurements of HONO have not been made, reducing the ability to evaluate model successes for OH in these environments. Here we present measurements of OH, HO2, RO2 and OH reactivity taken during the wintertime (January - February, 2012) and summertime (July - August, 2012) as part of the Clean air for London (ClearfLo) project in London. RO2 was detected using a newly developed flow-reactor laser-induced fluorescence technique which is able to discriminate between HO2 and organic peroxy radicals [1]. Low concentrations of radicals were observed during the wintertime, midday [OH], [HO2] and [RO2] were ~ 0.04, 0.8 and 1.5 pptv respectively, comparable to observations of radicals at other urban locations in winter [2,3,4], and which displayed a negative correlation with NO concentrations. OH reactivity was high and largely tracked the diurnal profiles of NOx and CO, with the highest reactivity ~100 s-1 observed during the morning rush hour. Analysis of factors controlling OH concentrations during the wintertime suggests that the formation of OH from the photolysis of O3 and subsequent reaction of O(1D) with H2O is a minor contribution both under high and low NOx conditions owing to the low rate of photolysis experienced and instead OH from photolysis of HONO (measured during ClearfLo using the LOPAP technique) [5], ozonolysis of alkenes and the reaction of HO2 with NO dominated the oxidative capacity of this urban location. Summertime observations coincided with the London 2012 Olympics. During this observational period, a number of high pollution events were observed where meteorological conditions favoured sustained, elevated ozone production (peaking at 100 ppbv). Radical concentrations were elevated during these episodes, with [OH], [HO2] and [RO2] peaking at ~ 0.16, 14 and 10 pptv respectively. The influence of HO2 and RO2 radicals on ozone production during these episodes will be presented along with a comparison of factors influencing modelled radical concentrations during the summer and wintertime. [1] Fuchs, H. et al., Review of Scientific Instruments, 79, 084104, 2008 [2] Heard, D.E. et al., Geophysical Research Letters, 13, L18112, 2004 [3] Ren, X. et al., Atmospheric Environment, 40, S252-S263, 2006 [4] Kanaya, Y. et al., Journal of Geophysical Research - Atmospheres, 112, D21312, 2007 [5] Kleffmann, J. et al., Atmospheric Environment, 40, 3640-3652, 2006

The crypto-OH radical in the damage of DNA by bleomycin-Fe2+?

PubMed

Bartkowiak, A; Grzelinska, E; Bartosz, G; Zabłocka, J; Leyko, W

1982-01-01

1. Effects of various OH scavengers, superoxide dismutase and catalase on the formation of malondialdehyde-like products from DNA by bleomycin-Fe2+ were studied. In no case was a protective effect observed. 2. These results can be interpreted on the basis that a crypto-OH radical mediates the damage to DNA by bleomycin-Fe2+.

Transformations of Aromatic Compounds by Nitrosomonas europaea

PubMed Central

Keener, William K.; Arp, Daniel J.

1994-01-01

Benzene and a variety of substituted benzenes inhibited ammonia oxidation by intact cells of Nitrosomonas europaea. In most cases, the inhibition was accompanied by transformation of the aromatic compound to a more oxidized product or products. All products detected were aromatic, and substituents were often oxidized but were not separated from the benzene ring. Most transformations were enhanced by (NH4)2SO4 (12.5 mM) and were prevented by C2H2, a mechanism-based inactivator of ammonia monooxygenase (AMO). AMO catalyzed alkyl substituent hydroxylations, styrene epoxidation, ethylbenzene desaturation to styrene, and aniline oxidation to nitrobenzene (and unidentified products). Alkyl substituents were preferred oxidation sites, but the ring was also oxidized to produce phenolic compounds from benzene, ethylbenzene, halobenzenes, phenol, and nitrobenzene. No carboxylic acids were identified. Ethylbenzene was oxidized via styrene to two products common also to oxidation of styrene; production of styrene is suggestive of an electron transfer mechanism for AMO. Iodobenzene and 1,2-dichlorobenzene were oxidized slowly to halophenols; 1,4-dichlorobenzene was not transformed. No 2-halophenols were detected as products. Several hydroxymethyl (-CH2OH)-substituted aromatics and p-cresol were oxidized by C2H2-treated cells to the corresponding aldehydes, benzaldehyde was reduced to benzyl alcohol, and o-cresol and 2,5-dimethylphenol were not depleted. PMID:16349282

Promotional effects of chemisorbed oxygen and hydroxide in the activation of C-H and O-H bonds over transition metal surfaces

NASA Astrophysics Data System (ADS)

Hibbitts, David; Neurock, Matthew

2016-08-01

Electronegative coadsorbates such as atomic oxygen (O*) and hydroxide (OH*) can act as Brønsted bases when bound to Group 11 as well as particular Group 8-10 metal surfaces and aid in the activation of X-H bonds. First-principle density functional theory calculations were carried out to systematically explore the reactivity of the C-H bonds of methane and surface methyl intermediates as well as the O-H bond of methanol directly and with the assistance of coadsorbed O* and OH* intermediates over Group 11 (Cu, Ag, and Au) and Group 8-10 transition metal (Ru, Rh, Pd, Os, Ir, and Pt) surfaces. C-H as well as O-H bond activation over the metal proceeds via a classic oxidative addition type mechanism involving the insertion of the metal center into the C-H or O-H bond. O* and OH* assist C-H and O-H activation over particular Group 11 and Group 8-10 metal surfaces via a σ-bond metathesis type mechanism involving the oxidative addition of the C-H or O-H bond to the metal along with a reductive deprotonation of the acidic C-H and O-H bond over the M-O* or M-OH* site pair. The O*- and OH*-assisted C-H activation paths are energetically preferred over the direct metal catalyzed C-H scission for all Group 11 metals (Cu, Ag, and Au) with barriers that are 0.4-1.5 eV lower than those for the unassisted routes. The barriers for O*- and OH*-assisted C-H activation of CH4 on the Group 8-10 transition metals, however, are higher than those over the bare transition metal surfaces by as much as 1.4 eV. The C-H activation of adsorbed methyl species show very similar trends to those for CH4 despite the differences in structure between the weakly bound methane and the covalently adsorbed methyl intermediates. The activation of the O-H bond of methanol is significantly promoted by O* as well as OH* intermediates over both the Group 11 metals (Cu, Ag, and Au) as well as on all Group 8-10 metals studied (Ru, Rh, Pd, Os, Ir, and Pt). The O*- and OH*-assisted CH3O-H barriers are 0.6 to 2.0 eV lower than unassisted barriers, with the largest differences occurring on Group 11 metals. The higher degree of O*- and OH*-promotion in activating methanol over that in methane and methyl is due to the stronger interaction between the basic O* and OH* sites and the acidic proton in the O-H bond of methanol versus the non-acidic H in the C-H bond of methane. A detailed analysis of the binding energies and the charges for O* and OH* on different metal surfaces indicates that the marked differences in the properties and reactivity of O* and OH* between the Group 11 and Group 8-10 metals is due to the increased negative charge on the O-atoms (in O* as well as OH*) bound to Group 11 metals. The promotional effects of O* and OH* are consistent with a proton-coupled electron transfer and the cooperative role of the metal-O* or metal-OH* pair in carrying out the oxidative addition and reductive deprotonation of the acidic C-H and O-H bonds. Ultimately, the ability of O* or OH* to act as a Brønsted base depends upon its charge, its binding energy on the metal surface (due to shifts in its position during X-H activation), and the acidity of the H-atom being abstracted.

Insights into the degradation of (CF3)2CHOCH3 and its oxidative product (CF3)2CHOCHO & the formation and catalytic degradation of organic nitrates

NASA Astrophysics Data System (ADS)

Bai, Feng-Yang; Jia, Zi-Man; Pan, Xiu-Mei

2018-06-01

In this work, a systematic investigation of the atmospheric oxidation mechanism of (CF3)2CXOCH3 and their oxidative products (CF3)2CXOCHO (X = H, F) initiated by OH radical or Cl atom is performed by density functional theory. This study reveals that the introduction of NO and O2 promotes the formation of organic nitrates, which are hygroscopic and are inclined to form secondary organic aerosols (SOA) and can affect the air quality. The rate constants of the individual reactions are found to be in agreement with the experimental results. One of the intriguing findings of this work is that the peroxynitrite of (CF3)2CHOCH2OONO formed from the subsequent reactions of (CF3)2CHOCH3 is more favorable to isomerize to organic nitrate (CF3)2CHOCH2ONO2 than to dissociate into alkoxy radical (CF3)2CHOCH2O and NO2 because of the lower energy barrier of isomerization. The second significant observation is that the organic nitrate can be degraded more favorably with the presence of NH3, CH3NH2, and CH3NHCH3 than its naked decomposition reaction (CF3)2CHOCH2ONO2→(CF3)2CHOCHO + HONO. The ammonium salt, a vital part of haze, is harmful to human health and can be formed in the existence of the NH3, CH3NH2, and CH3NHCH3. In addition, the toxic substance of peroxyalkyl nitrate (CF3)2CHOC(O)ONO2 which can reduce the visibility of the atmosphere is produced as the primary subsequent oxidation product of (CF3)2CHOCHO in a NO-rich environment. The main species detected experimentally are confirmed by this study. The computational results are crucial to risk assessment and pollution prevention of the volatile organic compounds (VOCs).

Ab initio Quantum Chemical Studies of Reactions in Astrophysical Ices. Reactions Involving CH3OH, CO2, CO, HNCO in H2CO/NH3/H2O Ices

NASA Technical Reports Server (NTRS)

Woon, David E.

2006-01-01

While reactions between closed shell molecules generally involve prohibitive barriers in the gas phase, prior experimental and theoretical studies have demonstrated that some of these reactions are significantly enhanced when confined within an icy grain mantle and can occur efficiently at temperatures below 100 K with no additional energy processing. The archetypal case is the reaction of formaldehyde (H2CO) and ammonia (NH3) to yield hydroxymethylamine (NH2CH2OH). In the present work we have characterized reactions involving methanol (CH3OH), carbon dioxide (CO2), carbon monoxide (CO), and isocyanic acid (HNCO) in search of other favorable cases. Most of the emphasis is on CH3OH, which was investigated in the two-body reaction with one H2CO and the three-body reaction with two H2CO molecules. The addition of a second H2CO to the product of the reaction between CH3OH and H2CO was also considered as an alternative route to longer polyoxymethylene polymers of the -CH2O- form. The reaction between HNCO and NH3 was studied to determine if it can compete against the barrierless charge transfer process that yields OCN(-) and NH4(+). Finally, the H2CO + NH3 reaction was revisited with additional benchmark calculations that confirm that little or no barrier is present when it occurs in ice.

Simultaneous hydrogenation and UV-photolysis experiments of NO in CO-rich interstellar ice analogues; linking HNCO, OCN-, NH2CHO, and NH2OH

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Chuang, K.-J.; van Dishoeck, E. F.; Ioppolo, S.; Linnartz, H.

2016-08-01

The laboratory work presented here simulates the chemistry on icy dust grains as typical for the `CO freeze-out stage' in dark molecular clouds. It differs from previous studies in that solid-state hydrogenation and vacuum UV photoprocessing are applied simultaneously to co-depositing molecules. In parallel, the reactions at play are described for fully characterized laboratory conditions. The focus is on the formation of molecules containing both carbon and nitrogen atoms, starting with NO in CO-, H2CO-, and CH3OH-rich ices at 13 K. The experiments yield three important conclusions. (1) Without UV processing hydroxylamine (NH2OH) is formed, as reported previously. (2) With UV processing (energetic) NH2 is formed through photodissociation of NH2OH. This radical is key in the formation of species with an N-C bond. (3) The formation of three N-C bearing species, HNCO, OCN-, and NH2CHO, is observed. The experiments put a clear chemical link between these species; OCN- is found to be a direct derivative of HNCO and the latter is shown to have the same precursor as formamide (NH2CHO). Moreover, the addition of VUV competing channels decreases the amount of NO molecules converted into NH2OH by at least one order of magnitude. Consequently, this decrease in NH2OH formation yield directly influences the amount of NO molecules that can be converted into HNCO, OCN-, and NH2CHO.

Hydroxyl radicals from secondary organic aerosol decomposition in water

NASA Astrophysics Data System (ADS)

Tong, Haijie; Arangio, Andrea M.; Lakey, Pascale S. J.; Berkemeier, Thomas; Liu, Fobang; Kampf, Christopher J.; Brune, William H.; Pöschl, Ulrich; Shiraiwa, Manabu

2016-02-01

We found that ambient and laboratory-generated secondary organic aerosols (SOA) form substantial amounts of OH radicals upon interaction with liquid water, which can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA formed by ozonolysis of terpenes (α-pinene, β-pinene, limonene) is ˜ 0.1 % upon extraction with pure water and increases to ˜ 1.5 % in the presence of Fe2+ ions due to Fenton-like reactions. Upon extraction of SOA samples from OH photooxidation of isoprene, we also detected OH yields of around ˜ 0.1 %, which increases upon addition of Fe2+. Our findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decomposition can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols.

Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region

DOE PAGES

Franke, Peter R.; Tabor, Daniel P.; Moradi, Christopher P.; ...

2016-12-13

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite [CH 3(CH 2) 3ONO] and i-butyl nitrite [(CH 3) 2CHCH 2ONO], respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the CH stretching region. Several previously unreported bands are observed between 2800 and 3150 cm –1. The CH stretching modes observed above 3000 cm –1 are in excellent agreement with CCSD(T) anharmonic frequencies computed using second-order vibrational perturbation theory. However, between 2800 and 3000 cm –1, the spectra of n- andmore » i-propyl radicals become congested and difficult to assign due to the presence of multiple anharmonic resonance polyads. To model the spectrally congested region, Fermi and Darling-Dennison resonances are treated explicitly using “dressed” Hamiltonians and CCSD(T) quartic force fields in the normal mode representation, and the agreement with experiment is less than satisfactory. Computations employing local mode effective Hamiltonians reveal the origin of the spectral congestion to be strong coupling between the high frequency CH stretching modes and the lower frequency CH n bending/scissoring motions. The most significant coupling is between stretches and bends localized on the same CH 2/CH 3 group. As a result, spectral simulations using the local mode approach are in excellent agreement with experiment.« less

Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franke, Peter R.; Tabor, Daniel P.; Moradi, Christopher P.

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite [CH 3(CH 2) 3ONO] and i-butyl nitrite [(CH 3) 2CHCH 2ONO], respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the CH stretching region. Several previously unreported bands are observed between 2800 and 3150 cm –1. The CH stretching modes observed above 3000 cm –1 are in excellent agreement with CCSD(T) anharmonic frequencies computed using second-order vibrational perturbation theory. However, between 2800 and 3000 cm –1, the spectra of n- andmore » i-propyl radicals become congested and difficult to assign due to the presence of multiple anharmonic resonance polyads. To model the spectrally congested region, Fermi and Darling-Dennison resonances are treated explicitly using “dressed” Hamiltonians and CCSD(T) quartic force fields in the normal mode representation, and the agreement with experiment is less than satisfactory. Computations employing local mode effective Hamiltonians reveal the origin of the spectral congestion to be strong coupling between the high frequency CH stretching modes and the lower frequency CH n bending/scissoring motions. The most significant coupling is between stretches and bends localized on the same CH 2/CH 3 group. As a result, spectral simulations using the local mode approach are in excellent agreement with experiment.« less

Synergistic disinfection and removal of biofilms by a sequential two-step treatment with ozone followed by hydrogen peroxide.

PubMed

Tachikawa, Mariko; Yamanaka, Kenzo

2014-11-01

Synergistic disinfection and removal of biofilms by ozone (O3) water in combination with hydrogen peroxide (H2O2) solution was studied by determining disinfection rates and observing changes of the biofilm structure in situ by confocal laser scanning microscopy (CLSM) using an established biofilm of Pseudomonas fluorescence. The sequential treatment with O3, 1.0-1.7 mg/L, followed by H2O2, 0.8-1.1%, showed synergistic disinfection effects, while the reversed treatment, first H2O2 followed by O3, showed only an additive effect. The decrease of synergistic disinfection effect by addition of methanol (CH3OH), a scavenger of hydroxyl radical (OH), into the H2O2 solution suggested generation of hydroxyl radicals on or in the biofilm by the sequential treatment with O3 followed by H2O2. The primary treatment with O3 increased disinfection rates of H2O2 in the secondary treatment, and the increase of O3 concentration enhanced the rates. The cold temperature of O3 water (14 °C and 8 °C) increased the synergistic effect, suggesting the increase of O3 adsorption and hydroxyl radical generation in the biofilm. CLSM observation showed that the sequential treatment, first with O3 followed by H2O2, loosened the cell connections and thinned the extracellular polysaccharides (EPS) in the biofilm. The hydroxyl radical generation in the biofilm may affect the EPS and biofilm structure and may induce effective disinfection with H2O2. This sequential treatment method may suggest a new practical procedure for disinfection and removal of biofilms by inorganic oxidants such as O3 and H2O2. Copyright © 2014 Elsevier Ltd. All rights reserved.

Laboratory kinetic studies of OH and CO2 relevant to upper atmospheric radiation balance

NASA Technical Reports Server (NTRS)

Nelson, David D.; Zahniser, Mark S.; Kolb, Charles E.

1994-01-01

During the first year of this program, we have made considerable progress toward the measurement of the dipole moments of vibrationally excited OH radicals. Our primary accomplishments have been 1) the modification of the original slit jet spectrometer for the study of radical species and 2) the observation of infrared chemiluminescence from the vibrationally excited OH radicals formed in the H + ozone reaction in the supersonic jet. We are optimistic that we will soon observe OH* laser induced fluorescence in the jet. Modulation of this fluorescence with microwave radiation in an applied electric field will be the final step required for the precise determination of the vibrational dependence of the OH dipole moment.

Photodissociation of nitromethane cluster anions.

PubMed

Goebbert, Daniel J; Khuseynov, Dmitry; Sanov, Andrei

2010-08-28

Three types of anionic fragments are observed in the photodissociation of nitromethane cluster anions, (CH(3)NO(2))(n)(-), n=1-6, at 355 nm: NO(2)(-)(CH(3)NO(2))(k), (CH(3)NO(2))(k)(-), and OH(-) (k

Combining Ambient Measurements of OH Radicals and OH Reactivity in a Tropical Rainforest during the OP-3 Project: Resolving the Magnitude of the Missing OH Sources and Sinks

NASA Astrophysics Data System (ADS)

Whalley, L. K.; Edwards, P.; Furneaux, K. L.; Goddard, A.; George, I. J.; Evans, M. J.; Heard, D. E.; Team Op-3

2010-12-01

The self cleansing capacity of the troposphere and the lifetime of key greenhouse gases are controlled to a large extent by the OH radical. In environments where biogenic VOC emissions are high and NOx concentrations are low, for example in tropical rainforests, the current understanding of tropospheric chemistry suggests that OH radical concentrations should be suppressed. OH measurements made in such regions, however, have highlighted higher than expected OH radical concentrations that cannot be replicated by chemical models constrained with the currently known OH formation pathways [1]. Here we report OH and OH reactivity measurements made during the OP-3 project that took place in the Borneo rainforest in 2008. Concentrations of OH displayed a clear diurnal cycle, peaking at solar noon, with significant concentrations observed: up to 8.7×106 molecule cm-3 (60 min average). Although j(O1D) levels and humidity were high, low O3 concentrations limited the rate of primary OH production from ozone photolysis. OH reactivity measurements were made using a sliding injector flow-tube reactor technique, with OH detection by LIF. Mean OH reactivities of 15.5 s-1 were observed with daily maximum OH reactivity of 24.7 ± 11.1 s-1 shortly after local solar noon, coinciding with peak isoprene concentrations. Minimum values of 7.2 ± 2.2 s-1 were observed just before sun rise. Using the measured OH and OH reactivity in a constrained box model containing detailed MCM chemistry we are able to fully resolve the magnitude of the missing OH source. We find that significant OH sources must be present - in addition to primary production - in order to maintain the elevated levels of OH levels recorded. Inclusion of an additional OH source formed as a recycled product of isoprene oxidation [2] improves the modelled OH agreement but reduces the modelled to measured HO2 agreement. To replicate both OH and HO2, a process that recycles HO2 to OH is required; equivalent to the OH recycling effect of 0.74 ppbv of NO. The model is unable to account for all of the OH reactivity; to simulate the OH reactivity a range of unmeasured sinks must be invoked. In general we believe that the simultaneous measurement of OH reactivity and OH concentration enables the separation of OH sources and sinks, allowing a more comprehensive test of our understanding of the radical chemistry occurring in this chemically complex environment. [1] J. Lelieveld, T. M. Butler, J. N. Crowley et al.: Nature, 2008, 452, p.737 - 740 [2] J. Peeters, T. L. Nguyen & L. Vereecken, PCCP, 2009, 11, p.5935 - 5939

A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Trong-Nghia; Department of Physical Chemistry, Hanoi University of Science and Technology, Hanoi; Putikam, Raghunath

2015-03-28

We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH{sub 2}OO and anti/syn-CH{sub 3}C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH{sub 2}OO and anti-CH{sub 3}C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH{sub 3}C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C–H bonds. For syn-CH{sub 3}C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH{sub 3} groupmore » by the terminal O atom producing CH{sub 2}C(H)O–OH. At 298 K, the intramolecular insertion process in CH{sub 2}OO was found to be 600 times faster than the commonly assumed ring-closing reaction.« less

Atmospheric lifetimes, infrared spectra and degradation products of a series of hydrofluoroethers

NASA Astrophysics Data System (ADS)

Cavalli, F.; Glasius, M.; Hjorth, J.; Rindone, B.; Jensen, N. R.

The rate constants of the reactions between the OH radical and a series of hydrofluoroethers (HFE) have been measured. The reaction of OH with CHF 2OCF 2OCHF 2 (1), CHF 2OCF 2CF 2OCHF 2 (2), CHF 2OCF 2CF 2OCF 2OCHF 2 (3) and CH 3OC 4F 9 (4) were investigated at 295±3 K and 740±5 Torr total pressure. The following values of the rate constants were determined for the reaction with the OH radical: k1=(2.4±0.7)×10 -15 cm 3 molecule -1 s -1, k2=(4.7±1.6)×10 -15 cm 3 molecule -1 s -1, k3=(4.6±1.6)×10 -15 cm 3 molecule -1 s -1 and k4=(7.2±1.6)×10 -15 cm 3 molecule -1 s -1. (All values are given with 2 σ uncertainties). Infrared spectra were obtained for all four HFEs in the range from 600 to 4000 cm -1 (3 to 17 μm), with the following IBI-values (integrated band intensities): IBI 1= (5.19±0.23)×10 -16 cm molecule -1 for the 978-1584 cm -1 band, IBI 2=(6.04±0.13)×10 -16 cm molecule -1 for the 930-1501 cm -1 band, IBI 3=(8.49±0.34)×10 -16 cm molecule -1 from the 963-1587 cm -1 band and IBI 4=(4.23±0.14)×10 -16 cm molecule -1 for the 845-1428 cm -1 band. Carbonyl fluoride, CF 2O, was the only fluorine-containing degradation product that was found from the Cl atom-initiated reactions of both CHF 2OCF 2OCF 2CF 2OCHF 2 and CH 3OC 4F 9, with measured product yields of 60-97% and 20-40% (based on carbon atoms), respectively. Due to the high uptake parameter of CF 2O to liquid water, its lifetime in the atmosphere is very short (with an upper limit between 15 and 30 d). It is rapidly incorporated into raindrops/aerosols, where it eventually degrades to HF and CO 2. The GWP of CF 2O is therefore negligible compared to those of CFC-11 and CFC-12.

Methane-methanol cycle for the thermochemical production of hydrogen

DOEpatents

Dreyfuss, Robert M.; Hickman, Robert G.

1976-01-01

A thermochemical reaction cycle for the generation of hydrogen from water comprising the following sequence of reactions wherein M represents a metal: CH.sub.4 + H.sub.2 O .fwdarw. CO + 3H.sub.2 (1) co + 2h.sub.2 .fwdarw. ch.sub.3 oh (2) ch.sub.3 oh + so.sub.2 + mo .fwdarw. mso.sub.4 + ch.sub.4 (3) mso.sub.4 .fwdarw. mo + so.sub.2 + 1/2o.sub.2 (4) the net reaction is the decomposition of water into hydrogen and oxygen.

Catalytic Activity of Nanosized CuO-ZnO Supported on Titanium Chips in Hydrogenation of Carbon Dioxide to Methyl Alcohol.

PubMed

Ahn, Ho-Geun; Lee, Hwan-Gyu; Chung, Min-Chul; Park, Kwon-Pil; Kim, Ki-Joong; Kang, Byeong-Mo; Jeong, Woon-Jo; Jung, Sang-Chul; Lee, Do-Jin

2016-02-01

In this study, titanium chips (TC) generated from industrial facilities was utilized as TiO2 support for hydrogenation of carbon dioxide (CO2) to methyl alcohol (CH3OH) over Cu-based catalysts. Nano-sized CuO and ZnO catalysts were deposited on TiO2 support using a co-precipitation (CP) method (CuO-ZnO/TiO2), where the thermal treatment of TC and the particle size of TiC2 are optimized on CO2 conversion under different reaction temperature and contact time. Direct hydrogenation of CO2 to CH3OH over CuO-ZnO/TiO2 catalysts was achieved and the maximum selectivity (22%) and yield (18.2%) of CH3OH were obtained in the range of reaction temperature 210-240 degrees C under the 30 bar. The selectivity was readily increased by increasing the flow rate, which does not affect much to the CO2 conversion and CH3OH yield.

Environmentally persistent free radicals (EPFRs)-2. Are free hydroxyl radicals generated in aqueous solutions?

PubMed

Khachatryan, Lavrent; Dellinger, Barry

2011-11-01

A chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed to measure the production of hydroxyl radical (·OH) in aqueous suspensions of 5% Cu(II)O/silica (3.9% Cu) particles containing environmentally persistent free radicals (EPFRs) of 2-monochlorophenol (2-MCP). The results indicate: (1) a significant differences in accumulated DMPO-OH adducts between EPFR containing particles and non-EPFR control samples, (2) a strong correlation between the concentration of DMPO-OH adducts and EPFRs per gram of particles, and (3) a slow, constant growth of DMPO-OH concentration over a period of days in solution containing 50 μg/mL EPFRs particles + DMPO (150 mM) + reagent balanced by 200 μL phosphate buffered (pH = 7.4) saline. However, failure to form secondary radicals using standard scavengers, such as ethanol, dimethylsulfoxide, sodium formate, and sodium azide, suggests free hydroxyl radicals may not have been generated in solution. This suggests surface-bound, rather than free, hydroxyl radicals were generated by a surface catalyzed-redox cycle involving both the EPFRs and Cu(II)O. Toxicological studies clearly indicate these bound free radicals promote various types of cardiovascular and pulmonary disease normally attributed to unbound free radicals; however, the exact chemical mechanism deserves further study in light of the implication of formation of bound, rather than free, hydroxyl radicals.

A three-dimensional model of the atmospheric chemistry of E and Z-CF3CH=CHCl (HCFO-1233(zd) (E/Z))

NASA Astrophysics Data System (ADS)

Sulbaek Andersen, Mads P.; Schmidt, Johan A.; Volkova, Aleksandra; Wuebbles, Donald J.

2018-04-01

Using a 3-dimensional global atmospheric chemistry and transport model we investigated the atmospheric degradation of HCFO-1233zd(E), E-CF3CH=CHCl, a commercially important, new hydrofluorocarbon replacement compound. Atmospheric degradation of E-CF3CH=CHCl is initiated by reaction with OH radicals, which leads to several chemical oxidation products. Dissemination of these oxidation products to the environment is of concern due to the possible formation of trifluoroacetic acid (TFA) as a degradation product. The model indicates that the average global yield of TFA from atmospheric processing of E-CF3CH=CHCl is approximately 2%. The annually averaged atmospheric lifetime of E-CF3CH=CHCl was found to be approximately 36 days (12 days for Z-CF3CH=CHCl). As E-CF3CH=CHCl is short lived, by far the majority of its Cl atoms will be released and deposited in the lower atmosphere, and the impact on stratospheric ozone is insignificant. An Ozone Depletion Potential of 0.00030 was determined. The Photochemical Ozone Creation Potential was evaluated and a value of 3.6 determined. Finally, we derive a Global Warming Potential for E-CF3CH=CHCl for a 100 year time horizon of <5. For comparison, data for the stereoismeric analogue, Z-CF3CH=CHCl, was also obtained from the model.

Kinetic study of the reaction of chlorine atoms with hydroxyacetone in gas-phase

NASA Astrophysics Data System (ADS)

Stoeffler, Clara; Joly, Lilian; Durry, Georges; Cousin, Julien; Dumelié, Nicolas; Bruyant, Aurélien; Roth, Estelle; Chakir, Abdelkhaleq

2013-12-01

In this letter the kinetics of the reaction of hydroxyacetone CH3C(O)CH2OH with Cl atoms is investigated using the relative rate technique. Experiments are carried out in a 65 L multipass photoreactor in the temperature range of 281-350 K. A mid-infrared spectrometer based on a quantum cascade laser in external cavity emitting at 9.5 μm is used to analyze the reactants. The determined rate coefficient for the investigated reaction is (1.7 ± 0.3) × 10-11exp(381.5 ± 57.3/T). The results are presented and discussed in terms of precision and compared with those obtained previously. The impact of Cl atoms on the atmospheric life time of hydroxyacetone is also discussed. Developing analytical techniques to quantify this compound in the atmosphere. Several methods of measurement have been used including the technique of proton transfer mass spectrometry (PTR-MS) [2] and derivatization with a chemical agent such as dinitrophenylhydrazine (DNPH) [3,4] followed by GC/MS or HPLC analyses. The HA amount in the troposphere was found to be in the order of a few hundred parts per trillion by volume [4], Performing laboratory experiments in order to study the HA reactivity with atmospheric oxidants. The first study on the kinetic of the reaction between OH radicals and HA was made by Dagault et al. [5] whose work was performed at room temperature by flash photolysis-resonance fluorescence. The determined rate constant implies a lifetime of a few days for HA relative to oxidation by OH radicals. Orlando et al. performed mechanistic and kinetics studies of the reaction of HA with OH radicals and Cl atoms at room temperature using a relative method [6]. Products detection was performed using FTIR spectroscopy. Moreover, these authors studied the photolysis of HA to determine its quantum yield and UV absorption spectrum. These studies showed that HA is principally removed from the atmosphere by reaction with OH radicals. Kinetic studies of the reaction of OH radicals with HA as a function of temperature (233-298 K) were performed by Dillon et al. [7]. An experimental (laser photolysis/FIL) and theoretical approach (quantum calculation) were realized. This study showed that the oxidation of HA by OH-radicals has a negative temperature coefficient which is explained by an intermediate complex formation. Another study as a function of temperature was conducted by Butkovskaya et al. using the technique of a turbulent flow reactor coupled with a mass spectrometer chemical ionization [8]. This work was purely mechanistic and it shows that the mechanism of this reaction changes with temperature: a temperature increase favors the production yields of methanoic and ethanoic acids and reduces the formation yield of methylglyoxal [8]. Our work is motivated by the fact that the kinetic studies of the reaction of HA with chlorine radicals are rare in comparison with the kinetic studies of the reaction of HA with OH radicals. So far, only one such kinetic study is reported in the literature. It has been carried out by Orlando et al. at 294 K [6]. To the best of our knowledge, this reaction has not yet been studied as a function of temperature. Therefore, to enrich kinetic data concerning this compound, the study of HA with Cl atoms reaction as a function of temperature has been undertaken. Experiments are carried out using the relative technique in a simulation chamber coupled with an infrared Fourier transform (FTIR) spectrometer and a quantum cascade laser in external cavity (ECQCL) at 1 bar with the temperature ranging 277-350 K. Using both FTIR and ECQCL techniques allows comparing the measurements sensitivity and improving the kinetic precision determination. The FTIR spectroscopy is widely used to perform kinetic measurements whereas the ECQCL spectrometer is quite original in kinetic studies. Laser spectrometry indeed presents advantages such as high sensitivity, high resolution, and fast acquisition time compared to the FTIR spectrometer. The ECQCL principle is based on a quantum cascade laser coupled with an external cavity that includes a diffraction grating as a wavelength-selective element. The diffraction grating is rotated via a motor at a step of 0.001 cm-1 (30 MHz). As the grating position is adjusted, the wavelength-dependent feedback into the gain media is tuned. This concept of frequency selective feedback allows the laser to achieve narrow linewidth and high tunability (˜100 cm-1) [9]. Spectroscopy by ECQCL offers the possibility to record a part of the molecular rovibrational spectrum and new opportunities for kinetic studies. Results with the ECQCL spectrometry and the FTIR techniques will be presented and compared together as well as with the literature data.

Understanding in-situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project

NASA Astrophysics Data System (ADS)

Whalley, Lisa; Stone, Daniel; Sharp, Thomas; Garraway, Shani; Bannan, Thomas; Percival, Carl; Hopkins, James; Holmes, Rachel; Hamilton, Jacqui; Lee, James; Laufs, Sebastian; Kleffmann, Jörg; Heard, Dwayne

2014-05-01

With greater than 50 % of the global population residing in urban conurbations, poor urban air quality has a demonstrable effect on human health. OH and HO2 radicals, (collectively termed HOx) together with RO2 radicals, mediate virtually all of the oxidative chemistry in the atmosphere, being responsible for the transformation of primary emissions into secondary pollutants such as NO2, O3 and particulates. Here we present measurements of OH, HO2, partially speciated RO2 (distinguishing smaller alkane related RO2 from larger alkane/alkene/aromatic related RO2), ClNO2 and OH reactivity measurements taken during the ClearfLo campaign in central London in the summer of 2012. Comparison with calculations from a detailed box model utilising the Master Chemical Mechanism v3.2 tested our ability to reproduce radical levels, and enabled detailed radical budgets to be determined, highlighting for example the important role of the photolysis of nitrous acid (HONO) and carbonyl species as radical sources. Speciation of RO2 enabled the break-down of ozone production from different classes of VOCs to be calculated directly and compared with model calculations. Summertime observations of radicals have helped to identify that increases in photolytic sources of radicals on warm, sunny days can significantly increase local ozone concentrations leading to exceedances of EU air quality recommendations of 60 ppbV. The photolytic breakdown of ClNO2 to Cl atoms can more than double radical concentrations in the early morning; although the integrated increase in radical concentrations over a 24 hr period in model runs when ClNO2 photolysis is included is more modest. On average we calculate just under a 1 ppb increase in ozone due to the presence of ClNO2 in London air. OH reactivity was found to be greatest during morning and evening rush hours. Good agreement between the modelled OH reactivity and observations could be achieved when reactivity associated with model generated photo-oxidation products was considered in addition to the measured primary OH reactants. Carbonyl species such as formaldehyde, acetaldehyde and acetone have been identified as the VOC class dominating organic OH reactivity. As such, together with the direct radical source contribution by photolysis, these species dominate local ozone production in London. Modelling studies comparing the observed carbonyl concentrations with model predictions suggest that over 50% of the total concentration may be directly emitted and, hence, London's in-situ chemistry may be considered to contribute significantly to the ozone levels observed.

Tropospheric OH and HO2 radicals: field measurements and model comparisons.

PubMed

Stone, Daniel; Whalley, Lisa K; Heard, Dwayne E

2012-10-07

The hydroxyl radical, OH, initiates the removal of the majority of trace gases in the atmosphere, and together with the closely coupled species, the hydroperoxy radical, HO(2), is intimately involved in the oxidation chemistry of the atmosphere. This critical review discusses field measurements of local concentrations of OH and HO(2) radicals in the troposphere, and in particular the comparisons that have been made with numerical model calculations containing a detailed chemical mechanism. The level of agreement between field measurements of OH and HO(2) concentrations and model calculations for a given location provides an indication of the degree of understanding of the underlying oxidation chemistry. We review the measurement-model comparisons for a range of different environments sampled from the ground and from aircraft, including the marine boundary layer, continental low-NO(x) regions influenced by biogenic emissions, the polluted urban boundary layer, and polar regions. Although good agreement is found for some environments, there are significant discrepancies which remain unexplained, a notable example being unpolluted, forested regions. OH and HO(2) radicals are difficult species to measure in the troposphere, and we also review changes in detection methodology, quality assurance procedures such as instrument intercomparisons, and potential interferences.

Rotationally-resolved excitation spectroscopy of the alkoxy and alkylthio radicals in a supersonic jet

NASA Technical Reports Server (NTRS)

Misra, Prabhakar; Zhu, Xinming; Bryant, Hosie L.; Kamal, Mohammed M.

1993-01-01

Rotationally-resolved laser excitation spectra have been obtained for the alkoxy radicals (CH3O, C2H5O, i-C3H7O) and the alkylthio radicals (CH3S, C2H5S, i-C3H7S) in a supersonic jet expansion. Low resolution (0.2/cm) excitation spectra have helped identify several vibronic bands belonging to the A-X electronic system for these jet-cooled free radicals. High resolution (0.07/cm) laser-induced fluorescence excitation spectra have aided the unraveling of the associated rotational structure and in certain cases (CH3O and CH3S, for example) enabled explicit rotational (J,K) assignments of the transitions.

The effect of ethanol gas impurity on the discharge mode and discharge products of argon plasma jet at atmospheric pressure

NASA Astrophysics Data System (ADS)

Xia, Wenjie; Liu, Dingxin; Xu, Han; Wang, Xiaohua; Liu, Zhijie; Rong, Mingzhe; Kong, Michael G.

2018-05-01

Argon is a widely used working gas of plasmas, which is much cheaper than helium but on the other hand much more difficult to generate diffuse discharge at atmospheric pressure. In order to meet the application requirements, plenty of researches have been reported to facilitate the diffuse discharge happening for argon plasmas, and in this paper an approach of using ethanol gas (EtOH) impurity is investigated. The discharge characteristics of Ar + EtOH plasma jet are studied as a function of the applied voltage and the concentration of EtOH, from which the concentration of EtOH between ∼200 and ∼3300 parts per million (ppm) is determined necessary for the generation of diffuse discharge. Compared with the helium plasma jet in literature, it is deduced that the diffuse discharge is probably caused by the Penning ionization happening between the metastable argon and EtOH. The discharge products of Ar + EtOH (672 ppm) plasma jet are measured and the corresponding chemistry pathways are analyzed. About 20% of EtOH is decomposed via complex chemical reactions to form more than a dozen of neutral species, such as CH3CHO, CH3COOH, CO, H2O, and C n H2n+2 (n ≥ 3), and various kinds of ionic species, including C+, CH+, ArH+, {{{{O}}}2}-, CH3CH2O‑, etc.

Oxidation of carbon monoxide, hydrogen peroxide and water at a boron doped diamond electrode: the competition for hydroxyl radicals.

PubMed

Kisacik, Izzet; Stefanova, Ana; Ernst, Siegfried; Baltruschat, Helmut

2013-04-07

Boron doped diamond (BDD) electrodes have an extremely high over-voltage for oxygen evolution from water, which favours its use in oxidation processes of other compounds at high potentials. We used a rotating ring disc (RRDE) assembly and differential electrochemical mass spectrometry (DEMS) in order to monitor the consumption or the production of species in the course of the electrode processes. By intercepting the intermediate of the electrochemical water oxidation with chemical reactions we demonstrate clearly, albeit indirectly, that in the water oxidation process at BDD above 2.5 V the first step is the formation of ˙OH radicals. The electro-oxidation of CO to CO2 at BDD electrodes proceeds only via a first attack by ˙OH radicals followed by a further electron transfer to the electrode. At potentials below the onset of oxygen evolution from water, H2O2 is oxidised by a direct electron transfer to the BDD electrode, while at higher potentials, two different reactions paths compete for the ˙OH radicals formed in the first electron transfer from water: one, where these ˙OH radicals react with each other followed by further electron transfers leading to O2 on the one hand and one, where ˙OH radicals react with other species like H2O2 or CO with subsequent electron transfers on the other hand.

Zn x Cd1-x S tunable band structure-directing photocatalytic activity and selectivity of visible-light reduction of CO2 into liquid solar fuels

NASA Astrophysics Data System (ADS)

Tang, Lanqin; Kuai, Libang; Li, Yichang; Li, Haijin; Zhou, Yong; Zou, Zhigang

2018-02-01

A series of Zn x Cd1-x S monodispersed nanospheres were successfully synthesized with tunable band structures. As-prepared Zn x Cd1-x S solid solutions show much enhanced photocatalytic efficiency for CO2 photoreduction in aqueous solutions under visible light irradiation, relative to pure CdS analog. Methanol (CH3OH) and acetaldehyde (CH3CHO) are the major products of CO2 photoreduction for the solid solutions with x = 0, 0.2, and 0.5. Interestingly, Zn0.8Cd0.2S photocatalyst with a wide band gap can also additionally generate ethanol (CH3CH2OH) besides CH3OH and CH3CHO. The balance between the band structure-directing redox capacity and light absorption should be considered to influence both product yield and selectivity of CO2 photoreduction. The possible photoreduction mechanism was tentatively proposed.

Selective oxidation of methanol and ethanol on supported ruthenium oxide clusters at low temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Haichao; Iglesia, Enrique

RuO2 domains supported on SnO2, ZrO2, TiO2, Al2O3, and SiO2 catalyze the oxidative conversion of methanol to formaldehyde, methylformate, and dimethoxymethane with unprecedented rates and high combined selectivity (>99 percent) and yield at low temperatures (300-400 K). Supports influence turnover rates and the ability of RuO2 domains to undergo redox cycles required for oxidation turnovers. Oxidative dehydrogenation turnover rates and rates of stoichiometric reduction of RuO2 in H2 increased in parallel when RuO2 domains were dispersed on more reducible supports. These support effects, the kinetic effects of CH3OH and O2 on reaction rates, and the observed kinetic isotope effects withmore » CH3OD and CD3OD reactants are consistent with a sequence of elementary steps involving kinetically relevant H-abstraction from adsorbed methoxide species using lattice oxygen atoms and with methoxide formation in quasi-equilibrated CH3OH dissociation on nearly stoichiometric RuO2 surfaces. Anaerobic transient experiments confirmed that CH3OH oxidation to HCHO requires lattice oxygen atoms and that selectivities are not influenced by the presence of O2. Residence time effects on selectivity indicate that secondary HCHO-CH3OH acetalization reactions lead to hemiacetal or methoxymethanol intermediates that convert to dimethoxymethane in reactions with CH3OH on support acid sites or dehydrogenate to form methylformate on RuO2 and support redox sites. These conclusions are consistent with the tendency of Al2O3 and SiO2 supports to favor dimethoxymethane formation, while SnO2, ZrO2, and TiO2 preferentially form methylformate. These support effects on secondary reactions were confirmed by measured CH3OH oxidation rates and selectivities on physical mixtures of supported RuO2 catalysts and pure supports. Ethanol also reacts on supported RuO2 domains to form predominately acetaldehyde and diethoxyethane at 300-400 K. The bifunctional nature of these reaction pathways and the remarkable ability of RuO2-based catalysts to oxidize CH3OH to HCHO at unprecedented low temperatures introduce significant opportunities for new routes to complex oxygenates, including some containing C-C bonds, using methanol or ethanol as intermediates derived from natural gas or biomass.« less

Long-Term Monitoring of Molecular Masers in IRAS 18566+0408

NASA Astrophysics Data System (ADS)

Halbe, Daniel Michael; Araya, Esteban; Hofner, Peter; Linz, Hendrik; Olmi, Luca; Kurtz, Stan

2016-01-01

We report results of a long-term monitoring study of 6 cm formaldehyde (H2CO),6.035 GHz hydroxyl (OH), and 6.7 GHz methanol (CH3OH) masers in the young high-mass protostellar object IRAS 18566+0408 (G37.55+0.20). This is the only high-mass star forming region where correlated variability of three different maser species has been reported. The observations were conducted with the 305m Arecibo Radio Telescope and the Very Large Array. Together with data from the literature, we present H2CO flux density measurements from 2002 to 2014, CH3OH data from 2006 to 2015, and OH observations from 2008 to 2015. Our extended monitoring observations of the H2CO maser agree with quasi-periodic variability and exponential flux density decrease during the quiescent and flare states as proposed by Araya and collaborators in 2010. We also confirm the occurrence of 6.035 GHz OH flares and a time delay with respect to the H2CO flares (first reported by Al-Marzouk and collaborators in 2012). An analysis of the variability behavior of different CH3OH velocity components and the H2CO maser suggests that multiple variability mechanisms may be responsible for the CH3OH flux density changes.

Theoretical perspectives on the mechanism and kinetics of the OH radical-initiated gas-phase oxidation of PCB126 in the atmosphere.

PubMed

Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Wang, Wenxing

2015-06-01

Polychlorinated biphenyls (PCBs) primarily exist in the gas phase in air and may undergo atmospheric oxidation degradations, particularly the oxidation reaction initiated by OH radicals. In this work, the mechanism of the OH radical-initiated atmospheric oxidation of the most toxic PCB congener 3,3',4,4',5-pentachlorobiphenyl (PCB126) was investigated by using quantum chemistry methods. The rate constants of the crucial elementary reactions were estimated by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The oxidation products of the reaction of PCB126 with OH radicals include 3,3',4,4',5-pentachlorobiphenyl-ols, chlorophenols, 2,3,4,7,8-pentachlorodibenzofuran, 2,3,4,6,7-pentachlorodibenzofuran, dialdehydes, 3,3',4,4',5-pentachloro-5'-nitro-biphenyl, and 4,5-dichloro-2-nitrophenol. Particularly, the formation of polychlorinated dibenzofurans (PCDFs) from the atmospheric oxidation of PCBs is revealed for the first time. The overall rate constant of the OH addition reaction is 2.52×10(-13)cm(3)molecule(-1)s(-1) at 298K and 1atm. The atmospheric lifetime of PCB126 determined by OH radicals is about 47.08days which indicates that PCB126 can be transported long distances from local to global scales. Copyright © 2015 Elsevier B.V. All rights reserved.

Reaction Mechanisms and Structural and Physicochemical Properties of Caffeic Acid Grafted Chitosan Synthesized in Ascorbic Acid and Hydroxyl Peroxide Redox System.

PubMed

Liu, Jun; Pu, Huimin; Chen, Chong; Liu, Yunpeng; Bai, Ruyu; Kan, Juan; Jin, Changhai

2018-01-10

The ascorbic acid (AA) and hydroxyl peroxide (H 2 O 2 ) redox pair induced free radical grafting reaction is a promising approach to conjugate phenolic groups with chitosan (CS). In order to reveal the exact mechanisms of the AA/H 2 O 2 redox pair induced grafting reaction, free radicals generated in the AA/H 2 O 2 redox system were compared with hydroxyl radical ( • OH) produced in the Fe 2+ /H 2 O 2 redox system. Moreover, the structural and physicochemical properties of caffeic acid grafted CS (CA-g-CS) synthesized in these two redox systems were compared. Results showed that only ascorbate radical (Asc •- ) was produced in the AA/H 2 O 2 system. The reaction between Asc •- and CS produced novel carbon-centered radicals, whereas no new free radicals were detected when • OH reacted with CS. Thin layer chromatography, UV-vis, Fourier transform infrared, and nuclear magnetic resonance spectroscopic analyses all confirmed that CA was successfully grafted onto CS through Asc •- . However, CA could be hardly grafted onto CS via • OH. CA-g-CS synthesized through Asc •- exhibited lower thermal stability and crystallinity than the reaction product obtained through • OH. For the first time, our results demonstrated that the synthesis of CA-g-CS in the AA/H 2 O 2 redox system was mediated by Asc •- rather than • OH.

Radiolysis study of genistein in methanolic solution

NASA Astrophysics Data System (ADS)

Jung, Hee Jin; Park, Hae Ran; Jung, Uhee; Jo, Sung Kee

2009-06-01

The aim of the present work was to identify products obtained from genistein by ionizing radiation and to enhance the antioxidant properties of genistein through radiation-induced transformation. Genistein dissolved in methanol was irradiated γ-rays at a dose of 100 kGy. NMR and (HR) EI-MS spectroscopy were used to identify radiolysis products (GM1 and GM2). We proposed that rad CH 2OH may be implicated in the formation GM1 and GM2 during radiolysis of genistein in methanol. The genistein in methanol solution showed higher DPPH radical scavenging activity after γ-irradiation. Then, the antioxidant activities of radiolysis products were evaluated and compared to those of genistein.

Hydrogen-assisted versus hydroxyl-assisted CO dissociation over Co-doped Cu(111): A DFT study

NASA Astrophysics Data System (ADS)

Zha, Hao; Dong, Xiuqin; Yu, Yingzhe; Zhang, Minhua

2018-03-01

First principle based density functional theory (DFT) was used to calculate the step-by-step hydrogenation and dissociation reaction network of carbon monoxide (CO) over Co-doped Cu(111) surface as a model for understanding the lateral interaction of surface hydroxyl species (OH) on these reactions. We discussed the Csbnd O bond length and the adsorption energy changes of reaction intermediates under different adsorption circumstances for purpose of making out the effect of surface hydroxyl on the reaction selectivity. Reaction intermediates co-adsorbed with H atom and hydroxyl could undergo H-assisted or OH-assisted routes. The calculations show that the OH-assisted route prefers with the formation of COH, CHOH and CH2OH while general H-assisted route prefers with the formation of HCO, CH2O and CH3O. Considering the rather low activation barrier of COH, CHOH and CH2OH to form CHX, the existence of hydroxyl on the surface is in favor of boosting the CHX and suppressing the methanol.

Radiation exposure - how do CT scans for appendicitis compare between a free standing children's hospital and non-dedicated pediatric facilities?

PubMed

Sharp, Nicole E; Raghavan, Maneesha U; Svetanoff, Wendy J; Thomas, Priscilla T; Sharp, Susan W; Brown, James C; Rivard, Douglas C; St Peter, Shawn D; Holcomb, George W

2014-06-01

We compare the amount of radiation children receive from CT scans performed at non-dedicated pediatric facilities (OH) versus those at a dedicated children's hospital (CH). Using a retrospective chart review, all children undergoing CT scanning for appendicitis at an OH were compared to children undergoing CT imaging for appendicitis at a CH between January 2011 and November 2012. One hundred sixty-three children underwent CT scans at 42 different OH. Body mass index was similar between the two groups (21.00±6.49kg/m(2), 19.58±5.18kg/m(2), P=0.07). Dose length product (DLP) was 620±540.3 at OH and 253.78±211.08 at CH (P < 0.001). OH CT scans accurately diagnosed appendicitis in 81%, while CT scans at CH were accurate in 95% (P=0.026). CTDIvol was recorded in 65 patients with subset analysis showing CTDIvol of 16.98±15.58 and 4.89±2.64, a DLP of 586.25±521.59 and 143.54±41.19, and size-specific dose estimate (SSDE) of 26.71±23.1 and 3.81±2.02 at OH and CH, respectively (P<0.001). Using SSDE as a marker for radiation exposure, children received 86% less radiation and had improved diagnostic accuracy when CT scans are performed at a CH. Copyright © 2014 Elsevier Inc. All rights reserved.

Decontamination of 2-Chloroethyl Ethyl Sulfide by Pulsed Corona Plasma

NASA Astrophysics Data System (ADS)

Li, Zhanguo; Hu, Zhen; Cao, Peng; Zhao, Hongjie

2014-11-01

Decontamination of 2-chloroethyl ethyl sulfide (2-CEES, CH3CH2SCH2CH2Cl) by pulsed corona plasma was investigated. The results show that 212.6 mg/m3 of 2-CEES, with the gas flow rate of 2 m3/h, can be decontaminated to 0.09 mg/m3. According to the variation of the inlet and outlet concentration of 2-CEES vapor with retention time, it is found that the reaction of 2-CEES in a pulsed corona plasma system follows the first order reaction, with the reaction rate constant of 0.463 s-1. The decontamination mechanism is discussed based on an analysis of the dissociation energy of chemical bonds and decontamination products. The C-S bond adjacent to the Cl atom will be destroyed firstly to form CH3CH2S· and ·CH2CH2Cl radicals. CH3CH2S· can be decomposed to ·C2H5 and ·S. ·S can be oxidized to SO2, while ·C2H5 can be finally oxidized to CO2 and H2O. The C-Cl bond in the ·CH2CH2Cl radical can be destroyed to form ·CH2CH2. and ·Cl, which can be mineralized to CO2, H2O and HCl. The H atom in the ·CH2CH2Cl radical can also be substituted by ·Cl to form CHCl2-CHCl2.

Ionizing Collisions of Electrons with Radical Species OH, H2 O2 and HO2; Theoretical Calculations

NASA Astrophysics Data System (ADS)

Joshipura, K. N.; Pandya, S. H.; Vaishnav, B. G.; Patel, U. R.

2016-05-01

In this paper we present our calculated total ionization cross sections (TICS) of electron impact on radical targets OH, H2 O2 and HO2 at energies from threshold to 2000 eV. Reactive species such as these pose difficulties in measurements of electron scattering cross sections. No measured data have been reported in this regard except an isolated TICS measurement on OH radical, and hence the present work on the title radicals hold significance. These radical species are present in an environment in which water molecules undergo dissociation (neutral or ionic) in interactions with photons or electrons. The embedding environments could be quite diverse, ranging from our atmosphere to membranes of living cells. Ionization of OH, H2 O2 or HO2 can give rise to further chemistry in the relevant bulk medium. Therefore, it is appropriate and meaningful to examine electron impact ionization of these radicals in comparison with that of water molecules, for which accurate da are available. For the OH target single-centre scattering calculations are performed by starting with a 4-term complex potential, that describes simultaneous elastic plus inelastic scattering. TICS are obtained from the total inelastic cross sections in the complex scattering potential - ionization contribution formalism , a well established method. For H2 O2 and HO2 targets, we employ the additivity rule with overlap or screening corrections. Detailed results will be presented in the Conference.

ESR, spectroscopic, and quantum-chemical studies on the electronic structures of complexes formed by Cu(I) with radicals (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritsan, N.P.; Usov, O.M.; Shokhirev, N.V.

1986-07-01

The optical and ESR spectra have been examined for complexes of Cu(I) with various radicals, which contain various numbers of Cl/sup -/ ions in the central-atom coordination sphere. The spin-Hamiltonian parameters have been determined for all these radical complexes, and the observed ESR spectra have been compared with those calculated with allowance for second-order effects. The observed values for the isotropic and anisotropic components of the HFI constant from the central ion have been used to estimate the contributions from the 4s and 3d/sup 2//sub z/ orbitals of the copper ion to the unpaired-electron MO. Quantum-chemical calculations have been performedmore » by the INDO method on the electronic structures and geometries of complexes formed by CH/sub 2/OH with Cu(I) for various Cl/sup -/ contents in the coordination sphere. The radical is coordinated by the ..pi.. orbital on the carbon atom, and the stabilities of the radical complexes decrease as the number of Cl/sup -/ ions in the coordination sphere increases. A geometry close to planar for the CuCl/sub 4//sup 3 -/ fragment in a complex containing four Cl/sup -/ ions.« less

Synthesis and Evaluation of Strychnos Alkaloids as MDR Reversal Agents for Cancer Cell Eradication

DTIC Science & Technology

2014-01-01

followed by magnesium in MeOH to afford 11 in 75% yield (one-pot). Alkylation with (Z)-2-iodobutenyl bromide23 and acyla- tion with bromoacetyl chloride...eluting with MeOH/CH2Cl2 (0.4:9.6? 1:9). The material was washed with a solution of 25% aq NaOH (10 mL), which afforded 24 mg (71%) of Table 2...with MeOH/CH2Cl2 (0.4:9.6? 1:9). The material was washed with a solution of 25% aq NaOH (10 mL), which afforded 90 mg (86%) of 2 as yellow liquid

Redox Potential and C-H Bond Cleaving Properties of a Nonheme FeIV=O Complex in Aqueous Solution

PubMed Central

Wang, Dong; Zhang, Mo; Bühlmann, Philippe; Que, Lawrence

2010-01-01

High-valent iron-oxo intermediates have been identified as the key oxidants in the catalytic cycles of many nonheme enzymes. Among the large number of synthetic FeIV=O complexes characterized to date, [FeIV(O)(N4Py)]2+ (1) exhibits the unique combination of thermodynamic stability, allowing its structural characterization by X-ray crystallography, and oxidative reactivity sufficient to cleave C-H bonds as strong as those in cyclohexane (DC-H = 99.3 kcal mol-1). However, its redox properties are not yet well understood. In this work, the effect of protons on the redox properties of 1 has been investigated electrochemically in nonaqueous and aqueous solutions. While the cyclic voltammetry of 1 in CH3CN is complicated by coupling of several chemical and redox processes, the FeIV/III couple is reversible in aqueous solution with E1/2 = +0.41 V vs. SCE at pH 4 and involves the transfer of one electron and one proton to give the FeIII-OH species. This is in fact the first example of reversible electrochemistry to be observed for this family of nonheme oxoiron(IV) complexes. C-H bond oxidations by 1 have been studied in H2O and found to have reactions rates that depend on the C-H bond strength but not on the solvent. Furthermore, our electrochemical results have allowed a DO-H value of 78(2) kcal mol-1 to be calculated for the FeIII-OH unit derived from 1. Interestingly, although this DO-H value is 6-11 kcal mol-1 lower than those corresponding to oxidants such as [FeIV(O)(TMP)] (TMP = tetramesitylporphinate), [RuIV(O)(bpy)2(py)]2+ (bpy = bipyridine, py = pyridine) and the tert-butylperoxyl radical, the oxidation of dihydroanthracene by 1 occurs at a rate comparable to those for these other oxidants. This comparison suggests that the nonheme N4Py ligand environment confers a kinetic advantage over the others that enhances the C-H bond cleavage ability of 1. PMID:20476758

Investigation of potential interferences in the detection of atmospheric ROx radicals by laser-induced fluorescence under dark conditions

NASA Astrophysics Data System (ADS)

Fuchs, Hendrik; Tan, Zhaofeng; Hofzumahaus, Andreas; Broch, Sebastian; Dorn, Hans-Peter; Holland, Frank; Künstler, Christopher; Gomm, Sebastian; Rohrer, Franz; Schrade, Stephanie; Tillmann, Ralf; Wahner, Andreas

2016-04-01

Direct detection of highly reactive, atmospheric hydroxyl radicals (OH) is widely accomplished by laser-induced fluorescence (LIF) instruments. The technique is also suitable for the indirect measurement of HO2 and RO2 peroxy radicals by chemical conversion to OH. It requires sampling of ambient air into a low-pressure cell, where OH fluorescence is detected after excitation by 308 nm laser radiation. Although the residence time of air inside the fluorescence cell is typically only on the order of milliseconds, there is potential that additional OH is internally produced, which would artificially increase the measured OH concentration. Here, we present experimental studies investigating potential interferences in the detection of OH and peroxy radicals for the LIF instruments of Forschungszentrum Jülich for nighttime conditions. For laboratory experiments, the inlet of the instrument was over flowed by excess synthetic air containing one or more reactants. In order to distinguish between OH produced by reactions upstream of the inlet and artificial signals produced inside the instrument, a chemical titration for OH was applied. Additional experiments were performed in the simulation chamber SAPHIR where simultaneous measurements by an open-path differential optical absorption spectrometer (DOAS) served as reference for OH to quantify potential artifacts in the LIF instrument. Experiments included the investigation of potential interferences related to the nitrate radical (NO3, N2O5), related to the ozonolysis of alkenes (ethene, propene, 1-butene, 2,3-dimethyl-2-butene, α-pinene, limonene, isoprene), and the laser photolysis of acetone. Experiments studying the laser photolysis of acetone yield OH signals in the fluorescence cell, which are equivalent to 0.05 × 106 cm-3 OH for a mixing ratio of 5 ppbv acetone. Under most atmospheric conditions, this interference is negligible. No significant interferences were found for atmospheric concentrations of reactants during ozonolysis experiments. Only for propene, α-pinene, limonene, and isoprene at reactant concentrations, which are orders of magnitude higher than in the atmosphere, could artificial OH be detected. The value of the interference depends on the turnover rate of the ozonolysis reaction. For example, an apparent OH concentration of approximately 1 × 106 cm-3 is observed when 5.8 ppbv limonene reacts with 600 ppbv ozone. Experiments with the nitrate radical NO3 reveal a small interference signal in the OH, HO2, and RO2 detection. Dependencies on experimental parameters point to artificial OH formation by surface reactions at the chamber walls or in molecular clusters in the gas expansion. The signal scales with the presence of NO3 giving equivalent radical concentrations of 1.1 × 105 cm-3 OH, 1 × 107 cm-3 HO2, and 1.7 × 107 cm-3 RO2 per 10 pptv NO3.

Effect of the superposition of a dielectric barrier discharge onto a premixed gas burner flame

NASA Astrophysics Data System (ADS)

Zaima, Kazunori; Takada, Noriharu; Sasaki, Koichi

2011-10-01

We are investigating combustion control with the help of nonequilibrium plasma. In this work, we examined the effect of dielectric barrier discharge (DBD) on a premixed burner flame with CH4/O2/Ar gas mixture. The premixed burner flame was covered with a quartz tube. A copper electrode was attached on the outside of the quartz tube, and it was connected to a high-voltage power supply. DBD inside the quartz tube was obtained between the copper electrode and the grounded nozzle of the burner which was placed at the bottom of the quartz tube. We clearly observed that the flame length was shortened by superposing DBD onto the bottom part of the flame. The shortened flame length indicates the enhancement of the burning velocity. We measured the optical emission spectra from the bottom region of the flame. As a result, we observed clear line emissions from Ar, which were never observed from the flame without DBD. We evaluated the rotational temperatures of OH and CH radicals by spectral fitting. As a result, the rotational temperature of CH was not changed, and the rotational temperature of OH was decreased by the superposition of DBD. According to these results, it is considered that the enhancement of the burning velocity is not caused by gas heating. New reaction pathways are suggested.

OH and O radicals production in atmospheric pressure air/Ar/H2O gliding arc discharge plasma jet

NASA Astrophysics Data System (ADS)

N, C. ROY; M, R. TALUKDER; A, N. CHOWDHURY

2017-12-01

Atmospheric pressure air/Ar/H2O gliding arc discharge plasma is produced by a pulsed dc power supply. An optical emission spectroscopic (OES) diagnostic technique is used for the characterization of plasmas and for identifications of {{OH}} and {{O}} radicals along with other species in the plasmas. The OES diagnostic technique reveals the excitation T x ≈ 5550-9000 K, rotational T r ≈ 1350-2700 K and gas T g ≈ 850-1600 K temperatures, and electron density {n}{{e}}≈ ({1.1-1.9})× {10}14 {{{cm}}}-3 under different experimental conditions. The production and destruction of {{OH}} and {{O}} radicals are investigated as functions of applied voltage and air flow rate. Relative intensities of {{OH}} and {{O}} radicals indicate that their production rates are increased with increasing {{Ar}} content in the gas mixture and applied voltage. {n}{{e}} reveals that the higher densities of {{OH}} and {{O}} radicals are produced in the discharge due to more effective electron impact dissociation of {{{H}}}2{{O}} and {{{O}}}2 molecules caused by higher kinetic energies as gained by electrons from the enhanced electric field as well as by enhanced {n}{{e}}. The productions of {{OH}} and {{O}} are decreasing with increasing air flow rate due to removal of Joule heat from the discharge region but enhanced air flow rate significantly modifies discharge maintenance properties. Besides, {T}{{g}} significantly reduces with the enhanced air flow rate. This investigation reveals that {{Ar}} plays a significant role in the production of {{OH}} and {{O}} radicals.

Interstellar Ice Chemistry: From Water to Complex Organics

NASA Astrophysics Data System (ADS)

Oberg, Karin I.; Fayolle, E.; Linnartz, H.; van Dishoeck, E.; Fillion, J.; Bertin, M.

2013-06-01

Molecular cloud cores, protostellar envelopes and protoplanetary disk midplanes are all characterized by freeze-out of atoms and molecules (other than H and H2) onto interstellar dust grains. On the grain surface, atom addition reactions, especially hydrogenation, are efficient and H2O forms readily from O, CH3OH from CO etc. The result is an icy mantle typically dominated by H2O, but also rich in CO2, CO, NH3, CH3OH and CH4. These ices are further processed through interactions with radiation, electrons and energetic particles. Because of the efficiency of the freeze-out process, and the complex chemistry that succeeds it, these icy grain mantles constitute a major reservoir of volatiles during star formation and are also the source of much of the chemical evolution observed in star forming regions. Laboratory experiments allow us to explore how molecules and radicals desorb, dissociate, diffuse and react in ices when exposed to different sources of energy. Changes in ice composition and structure is constrained using infrared spectroscopy and mass spectrometry. By comparing ice desorption, segregation, and chemistry efficiencies under different experimental conditions, we can characterize the basic ice processes, e.g. diffusion of different species, that underpin the observable changes in ice composition and structure. This information can then be used to predict the interstellar ice chemical evolution. I will review some of the key laboratory discoveries on ice chemistry during the past few years and how they have been used to predict and interpret astronomical observations of ice bands and gas-phase molecules associated with ice evaporation. These include measurements of thermal diffusion in and evaporation from ice mixtures, non-thermal diffusion efficiencies (including the recent results on frequency resolved UV photodesorption), and the expected temperature dependencies of the complex ice chemistry regulated by radical formation and diffusion. Based on these examples I will argue that the combination of laboratory experiments and observations is crucial to formulate and to test hypotheses on key processes that regulate the interstellar ice chemistry.

[Determination of prostaglandin F2alpha release in the rat spinal cord upon hydroxyl free radical damage by high performance liquid chromatography].

PubMed

Li, L

1997-05-01

As prostaglandin F2alpha is present in biological materials, and plays an important physiological role at trace level in the living body, then, highly sensitive determination of PGs is required. Various fluorescence derivatization reagents have been proposed for the determination of PGs. The 3-bromomethyl-6,7-methylenedioxyl-1-methyl-2(1H)-quinoxalinone was found to be a highly sensitive fluorescence derivatization reagent for PGF2alpha in HPLC with a detectable limit of 10-15 fmol for PGF2alpha. In this work we optimized its reaction conditions. Thus the PGF2alpha was extracted from the microdialysates with ethyl acetate at pH 3.0-3.5 following which the extracts were evaporated to dryness. The residue was derivatized by adding acetonitrile, KHCO3, Br-DMEQ and 18-crown-6-ether at 50 degrees C for 30min in the dark. The corresponding fluorescent derivatives produced were separated on a C8 column (Phase-Sep Ltd.), 5microm, 4.6mm x 150mm. Stepwise elution with different ratios of A and B was carried out. 30:10:60 of CHsCN:CH3OH:H2O constituted A solution and 35:30:35 made B solution. The A/B (97/3) was first run for 25 min and A/B (50/50) for the next 15min. Then the column was equilibrated with A/B (97/3) for 20min before the next sample injected. Fluorescence detector was used at lambdaEX 370nm and lambdaEM 455nm, and flow-rate of 2.0mL/min. Because the most evidence for a role of free radicals in tissue damage is indirect, we attempt to determine whether OH causes release of arachidonic acid products in vivo. We did this by (1) generating OH radical in vivo in rat spinal cord by administering H2O2 and FeCl2/EDTA through two parallel microdialysis fibers so they mixed in the cord, and (2) analyzing PGF2alpha in microdialysates in response to OH generation by HPLC. We utilized dialysis fibers of < or = 220microm external diameter including their coating except for a 2mm dialysis zone which was coated with a thin layer of silicon rubber. When the animal was clamped, two microdialysis fibers glued together were inserted through the cord until the dialysis zone just placed in the gray matters of the cord. The time course of changes in levels of PGF2alpha during OH generation by Fe/H2O2 is given. Typical chromatogram of the dialysate collected from one animal is illustrated. Prostaglandin F2alpha dramatically increased in response to hydroxyl radical generation from undetectable (basal level) to about 333 +/- 166nmol/L (SD, n = 5) in 90min, Prostaglandin F2alpha was undetectable when either H2O2 or FeCl2/EDTA was administered alone in control experiments, demonstrating that its formation was caused by generated hydroxyl radical.

The interstellar C-H stretching band near 3.4 microns - Constraints on the composition of organic material in the diffuse interstellar medium

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Allamandola, L. J.; Tielens, A. G. G. M.; Pendleton, Y.; Sellgren, K.

1991-01-01

The composition and history of dust in the diffuse ISM was studied using 3600-2700/cm absorption spectra of objects which have widely varying amounts of visual extinctions along different lines of sight. The 3300/cm and 2950/cm features are attributed to O-H and C-H stretching vibrations, respectively. The O-H feature in OH 32.8-0.3 is suggestive of circumstellar water ice and is probably not due to material in the diffuse ISM. The features in the 3100-2700/cm region are attributed either to C-H vibrations or to M stars. The spectra of the latter show a series of narrow features in this region that are identified with photospheric OH. Objects in which these bands are seen include OH 01-477, T629-5, and the Galactic center source IRS 7. The C-H stretch feature of diffuse ISM dust has subpeaks which fall within 5/cm of C-H stretching vibrations in the -CH2- and -CH3 groups of saturated aliphatic hydrocarbons.

Temperature- and Pressure-Dependent Kinetics Studies of Atomic Chlorine Reactions with Some Fluorinated Olefins and Ethers

NASA Astrophysics Data System (ADS)

Nicovich, J. M.; Wine, P. H.; Mazumder, S.; Hatzis, G. P.; Jiang, M.

2016-12-01

Laser flash photolysis of Cl2CO/N2/CO2/X mixtures (X = CF3CH=CH2, E-CF3CH=CHCl, E-CF3CH=CHF, (CF3)2CHOCH3, and CF3CF2CH2OCH3), has been coupled with time-resolved detection of Cl atoms by atomic resonance fluorescence spectroscopy to study the kinetics of Cl + X reactions as a function of temperature (T) and pressure (P). The Cl + X reactions were chosen for study because (1) the compounds X are potentially useful substitutes for ozone depleting substances in practical applications, (2) literature results demonstrate that Cl + X reactions are 60-120 times faster than the corresponding OH + X reactions at ambient T and P, suggesting that reaction with Cl is a significant atmospheric loss process for the compounds X, and (3) to our knowledge, Cl + X kinetics have not previously been studied as functions of T and P. For the Cl + olefin reactions, falloff curves are measured over the approximate T ranges 220-300 K. At elevated temperatures, equilibrium constants are determined for Cl + olefin association/dissociation, thus allowing C-Cl bond strengths in the product haloalkyl radicals to be evaluated. Arrhenius expressions are determined for the (P-independent) Cl + ether reactions over the approximate range of T 200-500K. The Cl + CF3CF2CH2OCH3 reaction is quite fast and its rate coefficient is nearly independent of T. The Cl + (CF3)2CHOCH3 reaction is somewhat slower and has a non-Arrhenius T dependence.

The effect of fuel inlet turbulence intensity on H2/CH4 flame structure of MILD combustion using the LES method

NASA Astrophysics Data System (ADS)

Afarin, Yashar; Tabejamaat, Sadegh

2013-06-01

Large eddy simulations (LES) are employed to investigate the effect of the inlet turbulence intensity on the H2/CH4 flame structure in a hot and diluted co-flow stream which emulates the (Moderate or Intense Low-oxygen Dilution) MILD combustion regime. In this regard, three fuel inlet turbulence intensity profiles with the values of 4%, 7% and 10% are superimposed on the annular mixing layer. The effects of these changes on the flame structure under the MILD condition are studied for two oxygen concentrations of 3% and 9% (by mass) in the oxidiser stream and three hot co-flow temperatures 1300, 1500 and 1750 K. The turbulence-chemistry interaction of the numerically unresolved scales is modelled using the (Partially Stirred Reactor) PaSR method, where the full mechanism of GRI-2.11 represents the chemical reactions. The influences of the turbulence intensity on the flame structure under the MILD condition are studied by using the profile of temperature, CO and OH mass fractions in both physical and mixture fraction spaces at two downstream locations. Also, the effects of this parameter are investigated by contours of OH, HCO and CH2O radicals in an area near the nozzle exit zone. Results show that increasing the fuel inlet turbulence intensity has a profound effect on the flame structure particularly at low oxygen mass fraction. This increment weakens the combustion zone and results in a decrease in the peak values of the flame temperature and OH and CO mass fractions. Furthermore, increasing the inlet turbulence intensity decreases the flame thickness, and increases the MILD flame instability and diffusion of un-burnt fuel through the flame front. These effects are reduced by increasing the hot co-flow temperature which reinforces the reaction zone.

The Chemical Composition of Comet C/2012 S1 (ISON) between 1.2 and 0.35 AU of the Sun

NASA Astrophysics Data System (ADS)

DiSanti, Michael A.; Bonev, Boncho P.; Gibb, Erika L.; Villanueva, Geronimo L.; Paganini, Lucas; Mumma, Michael J.; Keane, Jacqueline V.; Meech, Karen J.; Blake, Geoff A.; McKay, Adam J.

2014-11-01

The apparition of dynamically new, sun-grazing C/2012 S1 (ISON) [1] generated considerable ground- and space-based interest, and provided the rare opportunity to conduct compositional studies to heliocentric distances (Rh) well within 1 AU. We report gas production rates and molecular abundances from high-resolution (λ/Δλ ~ 25,000) spectra on four dates (UT 2013 Oct 22, 24, 25, and Nov 7) using NIRSPEC [2] at Keck 2, and on six dates (Nov 15 through 19, and Nov 22) using CSHELL [3] at the NASA-IRTF. This permitted measuring volatile abundances over a wide range in Rh.NIRSPEC is cross-dispersed and so allows simultaneous measure of trace species together with H2O, thereby avoiding most sources of systematic uncertainty, for example those associated with differences in slit losses and flux calibration among echelle orders. CSHELL has limited spectral coverage per setting, however the IRTF is unique among ground-based IR observatories in allowing daytime observations. This permitted compositional measurements of ISON to a minimum solar elongation angle of 20 degrees.A suite of molecules (H2O, CO, H2CO, CH3OH, C2H6, C2H2, CH4, HCN, NH3) and radicals (OH, NH2) were targeted and detected. Our serial measurements allowed a search for potential changes in molecular abundances relative to H2O. Those of some species (CO, C2H6, CH3OH, CH4) remained relatively constant with Rh, while others (e.g., H2CO, HCN) increased in abundance with decreasing Rh, for example as could result from potential compositional heterogeneity in the nucleus and/or release from increasingly heated grains in the coma. Results from our serial measurements of ISON will be presented and discussed.References: [1] Nevski V. and Novichonok A. (2012) CBET 3238. [2] McLean, I. S., et al. (1998) Proc. SPIE 3354, 566-578. [3] Tokunaga A, et al. (1990) Proc. SPIE, 1235, 131-143. This work is supported through the NASA Planetary Astronomy, Planetary Atmospheres, and Astrobiology Programs, and the National Science Foundation. We gratefully acknowledge the NASA-HQ Planetary Science Division for promoting the Comet ISON observing campaign, and Keck and IRTF for allotting dedicated observing time for ISON.

Ambient measurements of OH and HO2 radicals and the OH reactivity in and above the Borneo Rainforest

NASA Astrophysics Data System (ADS)

Heard, D. E.; Whalley, L. K.; Furneaux, K. L.; Edwards, P.; Commane, R.; Goddard, A.; Ingham, T.; Evans, M.

2008-12-01

Ground-based measurements of OH, HO2 and the OH reactivity have been made as part of the OP3 project that took place at the Bukit Atur Global Atmospheric Watch station in the Danum Valley forest conservation area in Sabah, Borneo in 2008. The project consisted of two intensive measurement periods in April and July. Aircraft measurements of OH and HO2 above the ground site were also performed and preliminary data will be presented. The OH and HO2 radicals exhibit a distinct diurnal profile, broadly following the j(O1D) profile that was measured simultaneously (daytime [OH] ~ 2 - 5 x 106 molecule cm-3, [HO2] ~ 1 - 1.5 x 108 molecule cm-3). NO, which peaked in the early morning hours ([NO] ~ 100 pptV) and isoprene, which peaked in the afternoon ([isoprene] ~ 2 - 5 ppbV) were found to influence the OH profile. Both OH and HO2 persisted into the night and were detectable even after j(O1D) had fallen to zero (nighttime [OH] ~ 2.5 x 105 molecule cm-3, [HO2] ~ 2 x 107 molecule cm-3), suggesting night-time radical sources. The OH reactivity tracked the isoprene concentration, exhibiting maximum reactivity just after midday when isoprene levels peaked. Zero dimensional models, using a variety of mechanisms, have been used to predict the [OH], [HO2] and the OH reactivity that were observed. The models, constrained with measured OH sources and sinks, are used to test the hypothesis that OH is recycled from isoprene oxidation in this low NOx environment

Mechanism of the reaction, CH4+O(1D2)→CH3+OH, studied by ultrafast and state-resolved photolysis/probe spectroscopy of the CH4ṡO3 van der Waals complex

NASA Astrophysics Data System (ADS)

Miller, C. Cameron; van Zee, Roger D.; Stephenson, John C.

2001-01-01

The mechanism of the reaction CH4+O(1D2)→CH3+OH was investigated by ultrafast, time-resolved and state-resolved experiments. In the ultrafast experiments, short ultraviolet pulses photolyzed ozone in the CH4ṡO3 van der Waals complex to produce O(1D2). The ensuing reaction with CH4 was monitored by measuring the appearance rate of OH(v=0,1;J,Ω,Λ) by laser-induced fluorescence, through the OH A←X transition, using short probe pulses. These spectrally broad pulses, centered between 307 and 316 nm, probe many different OH rovibrational states simultaneously. At each probe wavelength, both a fast and a slow rise time were evident in the fluorescence signal, and the ratio of the fast-to-slow signal varied with probe wavelength. The distribution of OH(v,J,Ω,Λ) states, Pobs(v,J,Ω,Λ), was determined by laser-induced fluorescence using a high-resolution, tunable dye laser. The Pobs(v,J,Ω,Λ) data and the time-resolved data were analyzed under the assumption that different formation times represent different reaction mechanisms and that each mechanism produces a characteristic rovibrational distribution. The state-resolved and the time-resolved data can be fit independently using a two-mechanism model: Pobs(v,J,Ω,Λ) can be decomposed into two components, and the appearance of OH can be fit by two exponential rise times. However, these independent analyses are not mutually consistent. The time-resolved and state-resolved data can be consistently fit using a three-mechanism model. The OH appearance signals, at all probe wavelengths, were fit with times τfast≈0.2 ps, τinter≈0.5 ps and τslow≈5.4 ps. The slowest of these three is the rate for dissociation of a vibrationally excited methanol intermediate (CH3OH*) predicted by statistical theory after complete intramolecular energy redistribution following insertion of O(1D2) into CH4. The Pobs(v,J,Ω,Λ) was decomposed into three components, each with a linear surprisal, under the assumption that the mechanism producing OH at a statistical rate would be characterized by a statistical prior. Dissociation of a CH4O* intermediate before complete energy randomization was identified as producing OH at the intermediate rate and was associated with a population distribution with more rovibrational energy than the slow mechanism. The third mechanism produces OH promptly with a cold rovibrational distribution, indicative of a collinear abstraction mechanism. After these identifications were made, it was possible to predict the fraction of signal associated with each mechanism at different probe wavelengths in the ultrafast experiment, and the predictions proved consistent with measured appearance signals. This model also reconciles data from a variety of previous experiments. While this model is the simplest that is consistent with the data, it is not definitive for several reasons. First, the appearance signals measured in these experiments probe simultaneously many OH(v,J,Ω,Λ) states, which would tend to obfuscate differences in the appearance rate of specific rovibrational states. Second, only about half of the OH(v,J,Ω,Λ) states populated by this reaction could be probed by laser-induced fluorescence through the OH A←X band with our apparatus. Third, the cluster environment might influence the dynamics compared to the free bimolecular reaction.

High-temperature oxidation chemistry of n-butanol--experiments in low-pressure premixed flames and detailed kinetic modeling.

PubMed

Hansen, N; Harper, M R; Green, W H

2011-12-07

An automated reaction mechanism generator is used to develop a predictive, comprehensive reaction mechanism for the high-temperature oxidation chemistry of n-butanol. This new kinetic model is an advancement of an earlier model, which had been extensively tested against earlier experimental data (Harper et al., Combust. Flame, 2011, 158, 16-41). In this study, the model's predictive capabilities are improved by targeting isomer-resolved quantitative mole fraction profiles of flame species in low-pressure flames. To this end, a total of three burner-stabilized premixed flames are isomer-selectively analyzed by flame-sampling molecular-beam time-of-flight mass spectrometry using photoionization by tunable vacuum-ultraviolet synchrotron radiation. For most species, the newly developed chemical kinetic model is capable of accurately reproducing the experimental trends in these flames. The results clearly indicate that n-butanol is mainly consumed by H-atom abstraction with H, O, and OH, forming predominantly the α-C(4)H(9)O radical (CH(3)CH(2)CH(2)˙CHOH). Fission of C-C bonds in n-butanol is only predicted to be significant in a similar, but hotter flame studied by Oßwald et al. (Combust. Flame, 2011, 158, 2-15). The water-elimination reaction to 1-butene is found to be of no importance under the premixed conditions studied here. The initially formed isomeric C(4)H(9)O radicals are predicted to further oxidize by reacting with H and O(2) or to decompose to smaller fragments via β-scission. Enols are detected experimentally, with their importance being overpredicted by the model.

Laboratory detection of a new interstellar free radical CH2CN(2B1)

NASA Technical Reports Server (NTRS)

Saito, Shuji; Yamamoto, Satoshi; Irvine, W. M.; Ziurys, L. M.; Suzuki, Hiroko

1988-01-01

An asymmetric-top free radical CH2CN with a 2B1 ground state was detected by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11-10 to 14-13 a-type rotational transitions in the frequency region of 220-260 GHz. Hyperfine resolved components for the N = 4-3 and 5-4 transitions were resolved in the 80 and 100 GHz regions, respectively. Molecular constants were determined and U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1 were assigned to the N = 5-4, 4-3, 2-1, and 1-0 transitions with K(-1) = 0 of the CH2CN radical.

Atmospheric reactivity of hydroxyl radicals with guaiacol (2-methoxyphenol), a biomass burning emitted compound: Secondary organic aerosol formation and gas-phase oxidation products

NASA Astrophysics Data System (ADS)

Lauraguais, Amélie; Coeur-Tourneur, Cécile; Cassez, Andy; Deboudt, Karine; Fourmentin, Marc; Choël, Marie

2014-04-01

Methoxyphenols are low molecular weight semi-volatile polar aromatic compounds produced from the pyrolysis of wood lignin. The reaction of guaiacol (2-methoxyphenol) with hydroxyl radicals has been studied in the LPCA simulation chamber at (294 ± 2) K, atmospheric pressure, low relative humidity (RH < 1%) and under high-NOx conditions using CH3ONO as OH source. The aerosol production was monitored using a SMPS (Scanning Mobility Particle Sizer); the SOA yields were in the range from 0.003 to 0.87 and the organic aerosol formation can be expressed by a one-product gas/particle partitioning absorption model. Transmission (TEM) and Scanning (SEM) Electron Microscopy observations were performed to characterize the physical state of SOA produced from the OH reaction with guaiacol; they display both liquid and solid particles (in an amorphous state). GC-FID (Gas Chromatography - Flame Ionization Detection) and GC-MS (Gas Chromatography - Mass Spectrometry) analysis show the formation of nitroguaiacol isomers as main oxidation products in the gas- and aerosol-phases. In the gas-phase, the formation yields were (10 ± 2) % for 4-nitroguaiacol (1-hydroxy-2-methoxy-4-nitrobenzene; 4-NG) and (6 ± 2) % for 3- or 6-nitroguaiacol (1-hydroxy-2-methoxy-3-nitrobenzene or 1-hydroxy-2-methoxy-6-nitrobenzene; 3/6-NG; the standards are not commercially available so both isomers cannot be distinguished) whereas in SOA their yield were much lower (≤0.1%). To our knowledge, this work represents the first identification of nitroguaiacols as gaseous oxidation products of the OH reaction with guaiacol. As the reactivity of nitroguaiacols with atmospheric oxidants is probably low, we suggest using them as biomass burning emission gas tracers. The atmospheric implications of the guaiacol + OH reaction are also discussed.

OH, HO2, and HO2* Radical Chemistry During PROPHET-AMOS 2016: Measurements and Model Comparison

NASA Astrophysics Data System (ADS)

Bottorff, B.; Lew, M.; Rickly, P.; Stevens, P. S.

2017-12-01

The hydroxyl (OH) and peroxy radicals, both the hydroperoxy radical (HO2) and organic peroxy radicals (RO2), play an important role in atmospheric chemistry. In addition to controlling lifetimes of many trace gases important to issues of global climate change, reactions of these radicals can also lead to the production of ozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicals in remote forest environments have shown serious discrepancies with modeled concentrations. These results bring into question our understanding of the atmospheric chemistry of isoprene and other biogenic VOCs under low NOX conditions. In the summer of 2016, OH, HO2 and HO2* (HO2 + αRO2) radicals were measured using the Indiana University Laser-Induced Fluorescence Fluorescence Assay by Gas Expansion (LIF-FAGE) technique as part of the Program for Research on Oxidants: PHtochemistry, Emissions, and Transport- Atmospheric Measurements of Oxidants in Summer (PROPHET-AMOS). This campaign took place in a forested area in northern Michigan characterized by high mixing ratios of isoprene and low mixing ratios of NOX. Ambient measurements from this campaign will be compared to previous measurements at this site and to modeled predictions using both the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism. Potential interferences associated with the OH measurements will also be examined.

Nanosized CuO and ZnO catalyst supported on titanium chip for conversion of carbon dioxide to methyl alcohol.

PubMed

Seo, Hyeong-Seok; Park, Chul-Min; Kim, Ki-Joong; Jeong, Woon-Jo; Chung, Min-Chul; Jung, Sang-Chul; Kim, Sang-Chai; Ahn, Ho-Geun

2013-08-01

In order to reutilize spent metallic titanium chips (TC) as catalyst support or photocatalytic materials, the surface of the TC was modified by thermal treatment under air atmosphere. TC-supported nanosized CuO and ZnO catalysts were prepared by impregnation (IMP) and co-precipitation (CP) method, respectively. The catalytic activity for CO2 hydrogenation to CH3OH was investigated using a flow-typed reactor under various reaction pressures. The crystals of CuO and ZnO was well formed on TC. CO2 conversion, CH3OH selectivity, and CH3OH yield were obtained as a function of time on stream over CuO-ZnO/TC catalysts. Conversion of CO2 to CH3OH over CuO-ZnO/TC catalyst by CP method and CuO/ZnO/TC catalyst by IMP method were ca. 16% and ca. 12%, respectively. Conversion of CO2 over CuO-ZnO/TC catalyst by CP method was increased with increasing reaction temperature in the range of 15-30 atm. Maximum selectivity and yield to CH3OH over CuO-ZnO/TC at 250 degrees C were ca. 90% at 20 atm and ca. 18.2% at 30 atm, respectively.

Generation of hydroxyl radical in isolated pea root cell wall, and the role of cell wall-bound peroxidase, Mn-SOD and phenolics in their production.

PubMed

Kukavica, Biljana; Mojovic, Milos; Vuccinic, Zeljko; Maksimovic, Vuk; Takahama, Umeo; Jovanovic, Sonja Veljovic

2009-02-01

The hydroxyl radical produced in the apoplast has been demonstrated to facilitate cell wall loosening during cell elongation. Cell wall-bound peroxidases (PODs) have been implicated in hydroxyl radical formation. For this mechanism, the apoplast or cell walls should contain the electron donors for (i) H(2)O(2) formation from dioxygen; and (ii) the POD-catalyzed reduction of H(2)O(2) to the hydroxyl radical. The aim of the work was to identify the electron donors in these reactions. In this report, hydroxyl radical (.OH) generation in the cell wall isolated from pea roots was detected in the absence of any exogenous reductants, suggesting that the plant cell wall possesses the capacity to generate .OH in situ. Distinct POD and Mn-superoxide dismutase (Mn-SOD) isoforms different from other cellular isoforms were shown by native gel electropho-resis to be preferably bound to the cell walls. Electron paramagnetic resonance (EPR) spectroscopy of cell wall isolates containing the spin-trapping reagent, 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO), was used for detection of and differentiation between .OH and the superoxide radical (O(2)(-).). The data obtained using POD inhibitors confirmed that tightly bound cell wall PODs are involved in DEPMPO/OH adduct formation. A decrease in DEPMPO/OH adduct formation in the presence of H(2)O(2) scavengers demonstrated that this hydroxyl radical was derived from H(2)O(2). During the generation of .OH, the concentration of quinhydrone structures (as detected by EPR spectroscopy) increased, suggesting that the H(2)O(2) required for the formation of .OH in isolated cell walls is produced during the reduction of O(2) by hydroxycinnamic acids. Cell wall isolates in which the proteins have been denaturated (including the endogenous POD and SOD) did not produce .OH. Addition of exogenous H(2)O(2) again induced the production of .OH, and these were shown to originate from the Fenton reaction with tightly bound metal ions. However, the appearance of the DEPMPO/OOH adduct could also be observed, due to the production of O(2)(-). when endogenous SOD has been inactivated. Also, O(2)(-). was converted to .OH in an in vitro horseradish peroxidase (HRP)/H(2)O(2) system to which exogenous SOD has been added. Taken together with the discovery of the cell wall-bound Mn-SOD isoform, these results support the role of such a cell wall-bound SOD in the formation of .OH jointly with the cell wall-bound POD. According to the above findings, it seems that the hydroxycinnamic acids from the cell wall, acting as reductants, contribute to the formation of H(2)O(2) in the presence of O(2) in an autocatalytic manner, and that POD and Mn-SOD coupled together generate .OH from such H(2)O(2).

Ion energy distributions and the density of CH3 radicals in a low pressure inductively coupled CH4/H2 plasma used for nanocrystalline diamond deposition

NASA Astrophysics Data System (ADS)

Okada, Katsuyuki; Komatsu, Shojiro; Matsumoto, Seiichiro

2003-11-01

Ion energy distributions (IEDs) and the density of CH3 radicals (n) in a 13.56 MHz radio frequency (rf) low pressure inductively coupled CH4/H2 plasma used for nanocrystalline diamond deposition have been investigated with a quadrupole mass spectrometer. The energy distributions of positive ions were measured in a CH4/H2 plasma with 50 mTorr of the gas pressure at 500 W of the plasma input power, and were compared with those of an Ar plasma. We have found that the IEDs of Ar+, CH4+, and C2H5+ have a nearly monoenergetic peak, and a hump due to a small degree of capacitive coupling. The plasma potentials obtained from the peaks are consistent with the previously reported values measured with a Langmuir probe. On the other hand, the IEDs of H+, H2+, and H3+ have a clear asymmetric double peak due to the modulation of rf driven glow discharge. The n monotonously increases with increasing pressure. The n indicates that CH3 radicals are main precursors for the growth of nanocrystalline diamond. The estimated sticking coefficient of the CH3 radical is comparable with the reported value.

Homogeneous reduction of CO2 by photogenerated pyridinyl radicals.

PubMed

Riboni, Francesca; Selli, Elena; Hoffmann, M R; Colussi, A J

2015-05-14

We report that 1-hydropyridinyl radicals (1-PyH(•)) photogenerated in solution react with dissolved CO2 en route to its 2e(-) reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H2O mixtures saturated with 1 atm of CO2 yields a suite of products, among which we identified Na(HCOO)2(-) (m/z(-) = 113), C5H6NCOO(-) (m/z(-) = 124), and C5H10O2NCOO(-) (m/z(-) = 160) species by electrospray ionization mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO2 neutrals via collisionally induced dissociation. We infer that 1-PyH(•) [from (1) (3)Py* + 2-PrOH → 1-PyH(•) + (•)PrOH] adds to CO2, in competition with radical-radical reactions, leading to intermediates that are in turn reduced by (•)PrOH into the observed species. The formation of carboxylates in this system, which is shown to require CO2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e(-) reduction of CO2 by 2-PrOH initiated by Py*. We evaluate a rate constant (2) k2(1-PyH(•) + CO2 → (•)Py-1-COOH) ≈ O (10) M(-1) s(-1) and an activation energy E2 ≥ 9 kcal mol(-1) that are compatible with thermochemical estimates for this reaction.

Site-Specific Imaging of Elemental Steps in Dehydration of Diols on TiO 2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acharya, Danda P.; Yoon, Yeohoon; Li, Zhenjun

2013-11-26

The conversion of diols on partially reduced TiO 2(110) at low coverage was studied using variable-temperature scanning tunneling microscopy, temperature programmed desorption and density functional theory calculations. We find, that below ~230 K, ethane-1,2-diol and propane-1,3-diol molecules adsorb predominantly on five-fold coordinated Ti5c atoms. The dynamic equilibrium between molecularly bound and dissociated species resulting from O-H bond scission and reformation is observed. As the diols start to diffuse on the Ti5c rows above ~230 K, they dissociate irreversibly upon encountering bridging oxygen (O b) vacancy (VO’s) defects. Two dissociation pathways, one via O-H and the other via C-O bond scissionmore » leading to identical surface intermediates, hydroxyalkoxy, O b-(CH 2)n-OH (n = 2, 3) and bridging hydroxyl, HO b, are seen. For O-H bond scission, the O b-(CH 2)n-OH is found on the position of the original VO, while for C-O scission it is found on the adjacent Ob site. Theoretical calculations suggest that the observed mixture of C-O/O-H bond breaking processes are a result of the steric factors enforced upon the diols by the second OH group that is bound to a Ti5c site. At room temperature, rich dissociation/reformation dynamics of the second, Ti5c-bound O-H leads to the formation of dioxo, Ob-(CH 2)n-OTi, species. Above ~400 K, both O b-(CH 2)n-OH and Ob-(CH 2)n-OTi species convert into a new intermediate, that is centered on Ob row. Combined experimental and theoretical evidence shows that this intermediate is most likely a new dioxo, O b-(CH 2) 2-Ob, species. Further annealing leads to sequential C-Ob bond cleavage and alkene desorption above ~ 500 K. Simulations find that the sequential C-O bond breaking process follows a homolytic diradical pathway with the first C-O bond breaking event accompanied by a non-adiabatic electron transfer within the TiO 2(110) substrate.« less

Electronic quenching of OH A 2Σ + radicals in collisions with molecular hydrogen

NASA Astrophysics Data System (ADS)

Pollack, Ilana B.; Lei, Yuxiu; Stephenson, Thomas A.; Lester, Marsha I.

2006-04-01

Collisional quenching of electronically excited OH A 2Σ + radicals by molecular hydrogen introduces nonradiative pathways that rapidly remove OH population from the excited state, and result in a significantly decreased fluorescence lifetime. One of these pathways is shown to lead to ground state OH X 2Π products with ˜1 eV of internal excitation in both highly excited rotational levels of v = 1 and the lowest rotational levels of v = 2. This highly nonstatistical OH X 2Π product distribution reflects the passage of the HO-H 2 system through the conical intersection regions that couple the ground and excited state surfaces.

Microsolvation effects on the reactivity of oxy-nucleophiles: the case of gas-phase SN2 reactions of YO-(CH3OH) n=1,2 towards CH3Cl.

PubMed

Yun-Yun, Liu; Fang-Zhou, Qiu; Jun, Zhu; Yi, Ren; Kai-Chung, Lau

2017-06-01

The modified G4(MP2) method was applied to explore microsolvation effects on the reactivity of four solvated normal oxy-nucleophiles YO - (CH 3 OH) n=1,2 (Y = CH 3 , C 2 H 5 , FC 2 H 4 , ClC 2 H 4 ), and five α-oxy-nucleophiles YO - (CH 3 OH) n=1,2 (Y = HO, CH 3 O, F, Cl, Br), in gas-phase S N 2 reactions towards the substrate CH 3 Cl. Based on a Brønsted-type plot, our calculations reveal that the overall activation barriers of five microsolvated α-oxy-nucleophiles are obviously smaller than the prediction from the correlation line constructed by four normal microsolvated ones to different degrees, and clearly demonstrate the existence of an α-effect in the presence of one or two methanol molecule(s). Moreover, it was found that the α-effect of the mono-methanol microsolvated α-nucleophile is stronger than that of the monohydrated α-nucleophile. However, the α-effect of YO - (CH 3 OH) 2 becomes weaker for Y = HO and CH 3 O, whereas it becomes stronger for Y = F, Cl, Br than that of YO - (H 2 O) 2 , which can be explained by analyses of the activation strain model in the two cases. It was also found that the rationale about the low ionization energy of α-nucleophile inducing the α-effect was not widely significant. Graphical abstract Variation of alpha-effect in the gas-phase S N 2 reaction with the microsolvation.

Cold and intense OH radical beam sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ploenes, Ludger; Meerakker, Sebastiaan Y. T. van de; Haas, Dominik

2016-05-15

We present the design and performance of two supersonic radical beam sources: a conventional pinhole-discharge source and a dielectric barrier discharge (DBD) source, both based on the Nijmegen pulsed valve. Both designs have been characterized by discharging water molecules seeded in the rare gases Ar, Kr, or Xe. The resulting OH radicals have been detected by laser-induced fluorescence. The measured OH densities are (3.0 ± 0.6) × 10{sup 11} cm{sup -3} and (1.0 ± 0.5) × 10{sup 11} cm{sup -3} for the pinhole-discharge and DBD sources, respectively. The beam profiles for both radical sources show a relative longitudinal velocity spreadmore » of about 10%. The absolute rotational ground state population of the OH beam generated from the pinhole-discharge source has been determined to be more than 98%. The DBD source even produces a rotationally colder OH beam with a population of the ground state exceeding 99%. For the DBD source, addition of O{sub 2} molecules to the gas mixture increases the OH beam density by a factor of about 2.5, improves the DBD valve stability, and allows to tune the mean velocity of the radical beam.« less

EPR, ENDOR, and DFT study of free radicals in L-lysine·HCl·2H2O single crystals X-irradiated at 298 K.

PubMed

Zhou, Yiying; Nelson, William H

2011-10-27

With K-band EPR (Electron Paramagnetic Resonance), ENDOR (Electron-Nuclear DOuble Resonance), and EIE (ENDOR-induced EPR) techniques, three free radicals (RI-RIII) in L-lysine hydrochloride dihydrate single crystals X-irradiated at 298 K were detected at 298 K, and six radicals (R1, R1', R2-R5) were detected if the temperature was lowered to 66 K from 298 K. R1 and RI dominated the central portion of the EPR at 66 and 298 K, respectively, and were identified as main chain deamination radicals, (-)OOCĊH(CH(2))(4)(NH(3))(+). R1' was identified as a main chain deamination radical with the different configuration from R1 at 66 K, and it probably formed during cooling the temperature from 298 to 66 K. The configurations of R1, R1', and RI were analyzed with their coupling tensors. R2 and R3 each contain one α- and four β-proton couplings and have very similar EIEs at three crystallographic axes. The two-layer ONIOM calculations (at B3LYP/6-31G(d,p):PM3) support that R2 and R3 are from different radicals: dehydrogenation at C4, (-)OOCCH(NH(3))(+)CH(2)ĊH(CH(2))(2)(NH(3))(+), and dehydrogenation at C5, (-)OOCCH(NH(3))(+)(CH(2))(2)ĊHCH(2)(NH(3))(+), respectively. The comparisons of the coupling tensors indicated that R2 (66 K) is the same radical as RII (298 K), and R3 is the same as RIII. Thus, RII and RIII also are the radicals of C4 and C5 dehydrogenation. R4 and R5 are minority radicals and were observed only when temperature was lowered to 66 K. R4 and R5 were only tentatively assigned as the side chain deamination radical, (-)OOCCH (NH(3))(+)(CH(2))(3)ĊH(2), and the radical dehydrogenation at C3, (-)OOCCH(NH(3))(+)ĊH(CH(2))(3)(NH(3))(+), respectively, although the evidence was indirect. From simulation of the EPR (B//a, 66 K), the concentrations of R1, R1', and R2-R5 were estimated as: R1, 50%; R1', 11%; R2, 14%; R3, 16%; R4, 6%; R5, 3%.

EPR study of gamma-irradiated N-methyl-L-alanine, DL-2-methyl glutamic acid hemihydrate and Di-leucine hydrochloride in solid state

NASA Astrophysics Data System (ADS)

Sütçü, Kerem; Osmanoğlu, Y. Emre

2017-12-01

In this study, it was aimed to investigate ɣ-irradiated powders of N-methyl-L-alanine (NMLA), DL-2-methyl glutamic acid hemihydrate (DL2MGAH), and Di-leucine hydrochloride (DLHCl) at room temperature by electron paramagnetic resonance spectroscopy. After the γ-irradiation the samples indicated the existence of the CH3ĊNHCH3COOH, HOOCCH3NH2CĊHCH2COOH·1/2H2O and (CH3)2ĊCH2CH NHCOOHCOCH (NH2HCl) CH2CH (CH3)2 radicals, respectively. The spectral parameters of the radicals were determined. The results were compared with the earlier studies and discussed accordingly.