Capillary Columns with a Sorbent Based on Functionalized Poly(1-Trimethylsilyl-1-Propyne) for the Elution Analysis of Natural Gas

NASA Astrophysics Data System (ADS)

Yakovleva, E. Yu.; Patrushev, Yu. V.; Pai, Z. P.

2018-05-01

The chromatographic properties of capillary columns prepared using functionalized poly(1- trimethylsilyl-1-propyne) (PTMSP) are evaluated and compared with the performance of a commercial column with divinylbenzene polymer sorbent. The loading capacity of a PTMSP column with dimensions of 30 m × 0.53 mm × 0.8 μm is shown to be about 2.5 times higher than that of a divinylbenzene polymer column with a diameter of 0.32 mm and a film thickness of 10 μm. The increased value of the background current for PTMSP columns at 220°C is explained by the presence of non-polar bulky substituents in the polymer chain. Differences in the order of elution are found for the following pairs of compounds: acetylene-ethylene; ethane-water; butene-1-isobutane; and sulfur dioxide-carbonyl sulfide. On a column with the functionalized PTMC, analysis of a mixture composition close to natural gas is found to be complete within 27 min.

Novel one-pot synthesis of 5-alkenyl-15-alkynylporphyrins and their derivatisation to a butadiyne-linked benzoporphyrin dimer.

PubMed

Yamada, Hiroko; Kushibe, Kayo; Okujuma, Tetsuo; Uno, Hidemitsu; Ono, Noboru

2006-01-28

5-Alkenyl-15-alkynylporphyrins have been obtained unexpectedly by [2 + 2] acid-catalyzed condensation of dipyrrylmethane and TMS propynal in addition to 5,15-dialkynylporphyrin, and the unsymmetrical porphyrin can be converted to a butadiyne-linked dimer by selective desilylation of the alkynyl TMS.

Abundance Profiles for C3 Hydrocarbons in Titan's Atmosphere

NASA Astrophysics Data System (ADS)

Lombardo, Nicholas; Nixon, Conor A.; Achterberg, Richard; Jolly, Antoine; Sung, Keeyoon; Irwin, Patrick; Flasar, F. Michael

2017-10-01

The atmosphere of Titan is of astrobiological importance. Its highly reducing composition and prebiotic chemistry make it analogous to that of the early Earth. Since the Voyager era, several complex hydrocarbons and nitriles have been detected, in some cases making Titan the only known planetary body where these gasses occur naturally. In this work, we report abundance profiles of four major C3 gasses expected to occur in Titan’s atmosphere, derived from Cassini/Composite Infrared Spectrometer (CIRS) data.Using the NEMESIS iterative radiative transfer module, we retrieved vertical abundance profiles for propane (C3H8) and propyne (CHCCH3), both initially detected by the Voyager IRIS instrument. Using newly available line data, we were also able to determine the first vertical abundance profiles for propene (C3H6), initially detected in 2013. We present profiles for several latitudes and times and compare to photochemical model predictions and previous observations. We also discuss our efforts to further the search for allene (CH2CCH2), an isomer of propyne. The abundances we retrieved will help to further our understanding of the chemical pathways that occur in Titan's atmosphere.

High resolution FTIR spectroscopy of the ν7 band of CD3CCH

NASA Astrophysics Data System (ADS)

Pal, Ayan Kumar; Kshirsagar, R. J.

2018-03-01

The high-resolution Fourier transform spectrum of propyne-d3 (CD3CCH) at room temperature has been recorded in the region of the ν7 band (950-1200 cm-1) at an apodized resolution of 0.004 cm-1. About 2400 lines consisting of a total of 25 sub-bands ranging from KΔK = -13 to 12 have been assigned in the ν7 band of CD3CCH. In the fitting analysis, the ν4 = 1 state to which transitions have not been identified in the experimental spectrum included as a "shadow" state. The data have been analyzed taking into account of the strong x-y Coriolis interaction of the ν7 = 1 state with the ν4 = 1 state. l-type interactions between the ± l components of the ν7 = 1 state, and a weak k-type doubling interaction between ν7 = 1 and ν4 = 1 states have been included in the analysis. The vibration-rotation transitions for K ≥ 8 show fairly large amount of deviation and most likely interacted by other nearby states. The transitions upto K = 7 and Jmax = 61 could be fitted with a standard deviation of 0.0007 cm-1.

Absorption Reveals and Hydrogen Addition Explains New Interstellar Aldehydes: Propenal and Propanal

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Jewell, P. R.; Lovas, F. J.; Remijan, A.; Mollendal, H.

2004-01-01

New interstellar molecules propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected largely in absorption toward the star-forming region Sagittarius B2(N) by means of rotational transitions observed with the 100-m Green Bank Telescope (GBT) operating in the range of 18 GHz (lambda approximately 1.7 cm) to 26 GHz (lambda approximately 1.2 cm). The GBT was also used to observe the previously reported interstellar aldehyde propynal (HC2CHO) in Sagittarius B2(N) which is known for large molecules believed to form on interstellar grains. The presence of these three interstellar aldehydes toward Sagittarius B2(N) strongly suggests that simple hydrogen addition on interstellar grains accounts for successively larger molecular species: from propynal to propenal and from propenal to propanal. Energy sources within Sagittarius B2(N) likely permit the hydrogen addition reactions on grain surfaces to proceed. This work demonstrates that successive hydrogen addition is probably an important chemistry route in the formation of a number of complex interstellar molecules. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO).

The interstellar chemistry of H2C3O isomers

PubMed Central

Loison, Jean-Christophe; Agúndez, Marcelino; Marcelino, Núria; Wakelam, Valentine; Hickson, Kevin M.; Cernicharo, José; Gerin, Maryvonne; Roueff, Evelyne; Guélin, Michel

2016-01-01

We present the detection of two H2C3O isomers, propynal and cyclopropenone, toward various starless cores and molecular clouds, together with upper limits for the third isomer propadienone. We review the processes controlling the abundances of H2C3O isomers in interstellar media showing that the reactions involved are gas-phase ones. We show that the abundances of these species are controlled by kinetic rather than thermodynamic effects. PMID:27013768

Development and Binding Mode Assessment of N-[4-[2-propyn-1-yl[(6S)-4,6,7,8-tetrahydro-2-(hydroxymethyl)-4-oxo-3H-cyclopenta[g]quinazolin-6-yl]amino]benzoyl]-L-γ-glutamyl-D-glutamic acid (BGC 945), a Novel Thymidylate Synthase Inhibitor that Targets Tumor Cells

PubMed Central

Tochowicz, Anna; Dalziel, Sean; Eidam, Oliv; O’Connell, Joseph D.; Griner, Sarah; Finer-Moore, Janet S.; Stroud, Robert M.

2013-01-01

N-[4-[2-propyn-1-yl[(6S)-4,6,7,8-tetrahydro-2-(hydroxymethyl)-4-oxo-3H-cyclopenta[g]quinazolin-6-yl]amino]benzoyl]-L-γ-glutamyl-D-glutamic acid 1 (BGC 945, now known as ONX 0801), is a small molecule thymidylate synthase (TS) inhibitor discovered at the Institute of Cancer Research in London. It is licensed by Onyx Pharmaceuticals and is in Phase 1 clinical studies. It is a novel antifolate drug resembling TS inhibitors plevitrexed and raltitrexed that combines enzymatic inhibition of thymidylate synthase with α-folate receptor-mediated targeting of tumor cells. Thus, it has potential for efficacy with lower toxicity due to selective intracellular accumulation through α-folate receptor (α-FR) transport. The α-FR, a cell-surface receptor glycoprotein, which is over expressed mainly in ovarian and lung cancer tumors, has an affinity for 1 similar to that for its natural ligand, folic acid. This study describes a novel synthesis of 1, an X-ray crystal structure of its complex with Escherichia coli TS and 2’-deoxyuridine-5’-monophosphate, and a model for a similar complex with human TS. PMID:23710599

Loading properties of porous layered capillary columns with sorbents of different natures

NASA Astrophysics Data System (ADS)

Patrushev, Y. V.; Nikolaeva, O. A.; Sidelnikov, V. N.

2017-04-01

Loading properties are studied for the commercial porous layered capillary columns GASPRO, Rt-Q-BOND, and for columns with porous layers based on the divinylbenzene-vinylimidazole copolymer (DVB-VIm), poly(trimethylsilyl)propyn (PTMSP) and ordered silica of the MCM-41 type. It is shown that the loading capacity of a column based on MCM-41 is 5-10 times higher than in the other considered columns. The loading properties of porous layered columns and columns for gas-liquid chromatography are compared.

Coherent Synchrotron Radiation for Rotational Spectroscopy: Application to the Rotational Spectrum of Propynal in the 200-750 GHz Range

NASA Astrophysics Data System (ADS)

Barros, J.; Roy, P.; Appadoo, D.; Naughton, D. Mc; Robertson, E.; Manceron, L.

2013-06-01

In storage rings, short electron bunches can produce an intense THz radiation called Coherent Synchrotron Radiation (CSR). The flux of this emission between 250 and 750 GHz (in the mW range, up the 10000 times the regular synchrotron emission) is very advantageous for broad band absorption spectroscopy, using interferometric techniques. This source is, however, inherently difficult to stabilize, and intensity fluctuations lead to artifacts on the FT-based measurements, which strongly limit the use of CSR in particular for high-resolution measurements. At SOLEIL however, by screening different currents and bunch lengths, we defined stable CSR conditions for which the signal-to-noise ratio (S/N) allows for measurements at high resolution. Moreover, we developed an artifact correction system, based on a simultaneous detection of the input and the output signals of the interferometer, which allows to further improve the S/N. For this purpose, the optics and electronics of two bolometers were matched. The stable CSR combined with this ingenious technique allowed us to record for the first time high-resolution FT spectra in the sub-THz range, with a S/N of 100 in a few hours. This enables many applications such as broadband rotational spectra in the THz range, studies of molecules with low frequency torsional modes, absolute intensities determinations, or studies of unstable species. Results obtained on Propynal illustrate these possibilities and enabled to improve significantly the ground state spectroscopic constants.

C3 Hydrocarbon Abundance in Titan's Atmosphere with Cassini Infrared Spectra

NASA Astrophysics Data System (ADS)

Lombardo, Nicholas; Nixon, Conor; Achterberg, Richard; Jolly, Antoine; Sung, Keeyoon; Irwin, Patrick; Flasar, F. M.

2018-01-01

Titan, the largest moon of the Saturn system, has an astrobiologically important atmosphere. The anoxic nature and high N2 abundance make it a strong analog to the early Earth. The secondary species, CH4, is easily photodissociated, and reactions between its dissociated products give rise to highly complex hydrocarbons and nitriles. The Voyager flyby and 14 year Cassini campaign allowed for the intense study of several of these molecules, enabling scientists to increase our understanding of the chemical pathways present above Titan. In this work, we report abundance profiles of four major C3 gasses expected to occur in Titan’s atmosphere, derived from Cassini/Composite Infrared Spectrometer (CIRS) data, allowing us to fill the gaps in the photochemical zoo that is Titan’s atmosphere.Using the NEMESIS iterative radiative transfer module, we retrieved vertical abundance profiles for propane (C3H8) and propyne (CHCCH3) both initially detected by the Voyager IRIS instrument. Using newly available line data, we were also able to determine the first vertical abundance profiles for propene (C3H6), initially detected in 2013. We present profiles for several latitudes and times and compare to photochemical model predictions and previous observations. We also discuss our ongoing search for allene (CH2CCH2), an isomer of propyne, which has yet to be definitively detected. The abundances we determined will help to further our understanding of the chemical pathways that occur in Titan's atmosphere.

Colloquium on High Resolution Molecular Spectroscopy (16th) Held in Universite de Bourgogne, Dijon, France on 6-10 September 1999

DTIC Science & Technology

1999-09-28

part of the talk will be devoted to the high resolution ab- sorption spectroscopy of the vi = 2-6 acetylenic overtone bands of propyned (CH 3-C=C-H...period CATGAS (Calibration Apparatus for Trace GAs Spectra), a transportable laboratory set-up for ab- sorption spectroscopy, was connected to the...the NIR around 1.95- 2.04 nm and 2.26- 2.39 nm, where accurate line parameters of ozone ab- sorption are available by high-resolution Fourier transform

Reduction of unsaturated compounds under interstellar conditions: chemoselective reduction of C≡C and C=C bonds over C=O functional group

NASA Astrophysics Data System (ADS)

Jonusas, Mindaugas; Guillemin, Jean-Claude; Krim, Lahouari

2017-07-01

The knowledge of the H-addition reactions on unsaturated organic molecules bearing a triple or a double carbon-carbon bond such as propargyl or allyl alcohols and a CO functional group such as propynal, propenal or propanal may play an important role in the understanding of the chemical complexity of the interstellar medium. Why different aldehydes like methanal, ethanal, propynal and propanal are present in dense molecular clouds while the only alcohol detected in those cold regions is methanol? In addition, ethanol has only been detected in hot molecular cores. Are those saturated and unsaturated aldehyde and alcohol species chemically linked in molecular clouds through solid phase H-addition surface reactions or are they formed through different chemical routes? To answer such questions, we have investigated a hydrogenation study of saturated and unsaturated aldehydes and alcohols at 10 K. We prove through this experimental study that while pure unsaturated alcohol ices bombarded by H atoms lead to the formation of the corresponding fully or partially saturated alcohols, surface H-addition reactions on unsaturated aldehyde ices exclusively lead to the formation of fully saturated aldehyde. Such results show that in addition to a chemoselective reduction of C≡C and C=C bonds over the C=O group, there is no link between aldehydes and their corresponding alcohols in reactions involving H atoms in dense molecular clouds. Consequently, this could be one of the reasons why some aldehydes such as propanal are abundant in dense molecular clouds in contrast to the non-detection of alcohol species larger than methanol.

Radical-molecule reaction C3H+H2O: a mechanistic study.

PubMed

Dong, Hao; Ding, Yi-Hong; Sun, Chia-Chung

2005-02-08

Despite the importance of the C(3)H radical in both combustion and interstellar space, the reactions of C(3)H toward stable molecules have never been studied. In this paper, we report our detailed mechanistic study on the radical-molecule reaction C(3)H+H(2)O at the Becke's three parameter Lee-Yang-Parr-B3LYP6-311G(d,p) and coupled cluster with single, double, and triple excitations-CCSD(T)6-311G(2d,p) (single-point) levels. It is shown that the C(3)H+H(2)O reaction initially favors formation of the carbene-insertion intermediates HCCCHOH (1a,1b) rather than the direct H- or OH-abstraction process. Subsequently, the isomers (1a,1b) can undergo a direct H- extrusion to form the well-known product propynal HCCCHO (P(5)). Highly competitively, (1a,1b) can take the successive 1,4- and 1,2-H-shift interconversion to isomer H(2)CCCHO(2a,2b) and then to isomer H(2)CCHCO(3a,3b), which can finally take a direct C-C bond cleavage to give product C(2)H(3) and CO (P(1)). The other products are kinetically much less feasible. With the overall entrance barrier 10.6 kcal/mol, the title reaction can be important in postburning processes. Particularly, our calculations suggest that the title reaction may play a role in the formation of the intriguing interstellar molecule, propynal HCCCHO. The calculated results will also be useful for the analogous C(3)H reactions such as with ammonia and alkanes.

Laser studies of the photodissociation dynamics of cometary radicals

NASA Technical Reports Server (NTRS)

Jackson, William M.

1991-01-01

In the past year, it was shown that in the 193 nm photolysis of C2H, the C2 radical is produced in a variety of electronic, vibrational, and rotational states. The relative population of the vibrational and rotational states of C2(A 1 Pi u), C2(B 1 Sigma g +), and C2(A 3 Pi u) were determined in a static gas cell and in a pulsed molecular beam. It seems as though the original angular momentum of the C2H molecule appears as part of the angular momentum of the C2 radical. A attempt is being made to discover the mathematical relationship that governs this mapping. New information about the bond dissociation energy of the C2 radical was produces. C2(b 3 Sigma g -) and C2( 1 Delta g) were detected in the photolysis of C2H via time resolved infrared emission spectroscopy. In the former case, vibrational excitation up to v'' = 4 is observed. All of the results suggest that the C2 models in comets need to consider the presence of vibrationally excited C2 radicals in comets. The laser induced fluorescence spectra of the C3 was observed as a product of the 193 nm photolysis of allene and propyne. The populations of the rotational levels are identical in both cases. This result has led us to conclude that an isomerization reaction occurs in the photolysis of propyne which leads to the same C3H2 intermediate that is formed in the photolysis of C3H4. Since the former molecule is one of the most abundant in the interstellar medium it is also likely that its precursor is also present in comets. This would explain why C3 is observed in comets.

Atomic charge transfer-counter polarization effects determine infrared CH intensities of hydrocarbons: a quantum theory of atoms in molecules model.

PubMed

Silva, Arnaldo F; Richter, Wagner E; Meneses, Helen G C; Bruns, Roy E

2014-11-14

Atomic charge transfer-counter polarization effects determine most of the infrared fundamental CH intensities of simple hydrocarbons, methane, ethylene, ethane, propyne, cyclopropane and allene. The quantum theory of atoms in molecules/charge-charge flux-dipole flux model predicted the values of 30 CH intensities ranging from 0 to 123 km mol(-1) with a root mean square (rms) error of only 4.2 km mol(-1) without including a specific equilibrium atomic charge term. Sums of the contributions from terms involving charge flux and/or dipole flux averaged 20.3 km mol(-1), about ten times larger than the average charge contribution of 2.0 km mol(-1). The only notable exceptions are the CH stretching and bending intensities of acetylene and two of the propyne vibrations for hydrogens bound to sp hybridized carbon atoms. Calculations were carried out at four quantum levels, MP2/6-311++G(3d,3p), MP2/cc-pVTZ, QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ. The results calculated at the QCISD level are the most accurate among the four with root mean square errors of 4.7 and 5.0 km mol(-1) for the 6-311++G(3d,3p) and cc-pVTZ basis sets. These values are close to the estimated aggregate experimental error of the hydrocarbon intensities, 4.0 km mol(-1). The atomic charge transfer-counter polarization effect is much larger than the charge effect for the results of all four quantum levels. Charge transfer-counter polarization effects are expected to also be important in vibrations of more polar molecules for which equilibrium charge contributions can be large.

Recent observations of interstellar molecules - Detection of CCO and a limit on H2C3O

NASA Technical Reports Server (NTRS)

Brown, R. D.; Cragg, D. M.; Godfrey, P. D.; Irvine, W. M.; Mcgonagle, D.; Ohishi, M.

1992-01-01

In order to test gas-phase reaction schemes for the production of small oxides of carbon in cold, dense interstellar clouds, we have searched for the radical CCO and for propadienone (H2C3O) in Taurus Molecular Cloud 1, a nearby cloud which exhibits a rich organic chemistry. The radical CCO has been detected with a fractional abundance some two orders of magnitude less than that of CCS, about one order of magnitude less than that of H2CCO, and slightly less than that of C3O. An upper limit has been obtained on the abundance of propadienone which is slightly less than that of its isomer propynal (HC2CHO).

Synthesis of palladium(0) and -(II) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation.

PubMed

Sluijter, Soraya N; Warsink, Stefan; Lutz, Martin; Elsevier, Cornelis J

2013-05-28

A transmetallation route, using silver(I) precursors, to several zero- and di-valent palladium complexes with chelating bis(N-heterocyclic carbene) ligands bearing various N-substituents has been established. The resulting complexes have been characterized by NMR and mass spectroscopy. In addition, the structure of a representative compound, [Pd(0)(bis-(Mes)NHC)(η(2)-ma)] (3a), was confirmed by X-ray crystal structure determination. In contrast to the transfer semihydrogenation, in which only low activity was observed, complex 3a showed activity (TOF = 49 mol(sub) mol(cat)(-1) h(-1)) and selectivity comparable to its monodentate counterparts in the semihydrogenation of 1-phenyl-1-propyne with molecular hydrogen.

Pyrolysis and Matrix-Isolation FTIR of Acetoin

NASA Astrophysics Data System (ADS)

Cole, Sarah; Ellis, Martha; Sowards, John; McCunn, Laura R.

2017-06-01

Acetoin, CH_3C(O)CH(OH)CH_3, is an additive used in foods and cigarettes as well as a common component of biomass pyrolysate during the production of biofuels, yet little is known about its thermal decomposition mechanism. In order to identify thermal decomposition products of acetoin, a gas-phase mixture of approximately 0.3% acetoin in argon was subject to pyrolysis in a resistively heated SiC microtubular reactor at 1100-1500 K. Matrix-isolation FTIR spectroscopy was used to identify pyrolysis products. Many products were observed in analysis of the spectra, including acetylene, propyne, ethylene, and vinyl alcohol. These results provide clues to the overall mechanism of thermal decomposition and are important for predicting emissions from many industrial and residential processes.

Probing Single Pt Atoms in Complex Intermetallic Al13Fe4.

PubMed

Yamada, Tsunetomo; Kojima, Takayuki; Abe, Eiji; Kameoka, Satoshi; Murakami, Yumi; Gille, Peter; Tsai, An Pang

2018-03-21

The atomic structure of a 0.2 atom % Pt-doped complex metallic alloy, monoclinic Al 13 Fe 4 , was investigated using a single crystal prepared by the Czochralski method. High-angle annular dark-field scanning transmission electron microscopy showed that the Pt atoms were dispersed as single atoms and substituted at Fe sites in Al 13 Fe 4 . Single-crystal X-ray structural analysis revealed that the Pt atoms preferentially substitute at Fe(1). Unlike those that have been reported, Pt single atoms in the surface layers showed lower activity and selectivity than those of Al 2 Pt and bulk Pt for propyne hydrogenation, indicating that the active state of a given single-atom Pt site is strongly dominated by the bonding to surrounding Al atoms.

Observation of Spontaneous C=C Bond Breaking in the Reaction between Atomic Boron and Ethylene in Solid Neon.

PubMed

Jian, Jiwen; Lin, Hailu; Luo, Mingbiao; Chen, Mohua; Zhou, Mingfei

2016-07-11

A ground-state boron atom inserts into the C=C bond of ethylene to spontaneously form the allene-like compound H2 CBCH2 on annealing in solid neon. This compound can further isomerize to the propyne-like HCBCH3 isomer under UV light excitation. The observation of this unique spontaneous C=C bond insertion reaction is consistent with theoretical predictions that the reaction is thermodynamically exothermic and kinetically facile. This work demonstrates that the stronger C=C bond, rather than the less inert C-H bond, can be broken to form organoboron species from the reaction of a boron atom with ethylene even at cryogenic temperatures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanofiltration properties of PTMSP in binary organic solvents mixtures

NASA Astrophysics Data System (ADS)

Yushkin, A. A.; Kossov, A. A.; Volkov, V. V.

2016-09-01

In this study, the stability and nanofiltration performance of poly[1-(trimethylsilyl)- 1-propyne] (PTMSP) in ethanol solutions of butylaldehyde, 1-decanal, 1-hexene, 1-decene was evaluated. It was found that PTMSP was insoluble in all aldehyde solutions, but it was soluble at olefin concentration of 80% or higher. Nanofiltration experiments demonstrate that binary mixtures of 1-decanal and ethanol viscosity are not the parameter affecting on membrane permeability and rejection of solute as well as swelling degree. In the case of decanol/ethanol solutions both solution viscosity and molar volume demonstrate the best fit of experimental data. It was shown that with the decrease of ethanol content in the feed, the rejection of anionic solute Remazol Brilliant Blue R (MW 626) increases from 94 up to 97%.

Ultrathin Composite Polymeric Membranes for CO2 /N2 Separation with Minimum Thickness and High CO2 Permeance.

PubMed

Benito, Javier; Sánchez-Laínez, Javier; Zornoza, Beatriz; Martín, Santiago; Carta, Mariolino; Malpass-Evans, Richard; Téllez, Carlos; McKeown, Neil B; Coronas, Joaquín; Gascón, Ignacio

2017-10-23

The use of ultrathin films as selective layers in composite membranes offers significant advantages in gas separation for increasing productivity while reducing the membrane size and energy costs. In this contribution, composite membranes have been obtained by the successive deposition of approximately 1 nm thick monolayers of a polymer of intrinsic microporosity (PIM) on top of dense membranes of the ultra-permeable poly[1-(trimethylsilyl)-1-propyne] (PTMSP). The ultrathin PIM films (30 nm in thickness) demonstrate CO 2 permeance up to seven times higher than dense PIM membranes using only 0.04 % of the mass of PIM without a significant decrease in CO 2 /N 2 selectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal decomposition of pyrazole to vinylcarbene + N 2: A first principles/RRKM study

NASA Astrophysics Data System (ADS)

da Silva, Gabriel

2009-05-01

Thermal decomposition of pyrazole, a five-membered nitrogen-containing heterocycle, has been studied using ab initio G3X theory and RRKM rate theory. The decomposition mechanism involves an intramolecular hydrogen shift to 3 H-pyrazole, followed by ring opening to 3-diazo-1-propene and dissociation to vinylcarbene (CH 2CHCH) + N 2. At 1 atm the calculated rate equation k [s -1] = 1.26 × 10 50T-10.699e -41200/T is obtained, which agrees with the results of flash vacuum pyrolysis experiments. The pyrazole decomposition product vinylcarbene is expected to rearrange to propyne, making pyrazole decomposition essentially thermoneutral. It is hypothesized that at high concentrations vinylcarbene could undergo a self-reaction to 1,3- and 1,4-cyclohexadiene.

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

Loomis, Ryan A.; McGuire, Brett A.; Remijan, Anthony J.

Recently, Lattelais et al. have interpreted aggregated observations of molecular isomers to suggest that there exists a ''minimum energy principle'', such that molecular formation will favor more stable molecular isomers for thermodynamic reasons. To test the predictive power of this principle, we have fully characterized the spectra of the three isomers of C{sub 3}H{sub 2}O toward the well-known molecular region Sgr B2(N). Evidence for the detection of the isomers cyclopropenone (c-C{sub 3}H{sub 2}O) and propynal (HCCCHO) is presented, along with evidence for the non-detection of the lowest zero-point energy isomer, propadienone (CH{sub 2}CCO). We interpret these observations as evidence that chemicalmore » formation pathways, which may be under kinetic control, have a more pronounced effect on final isomer abundances than thermodynamic effects such as the minimum energy principle.« less

UV absorption spectrum of allene radical cations in solid argon

NASA Astrophysics Data System (ADS)

Chin, Chih-Hao; Lin, Meng-Yeh; Huang, Tzu-Ping; Wu, Yu-Jong

2018-05-01

Electron bombardment during deposition of an Ar matrix containing a small proportion of allene generated allene cations. Further irradiation of the matrix sample at 385 nm destroyed the allene cations and formed propyne cations in solid Ar. Both cations were identified according to previously reported IR absorption bands. Using a similar technique, we recorded the ultraviolet absorption spectrum of allene cations in solid Ar. The vibrationally resolved progression recorded in the range of 266-237 nm with intervals of about 800 cm-1 was assigned to the A2E ← X2E transition of allene cations, and the broad continuum absorption recorded in the region of 229-214 nm was assigned to their B2A1 ← X2E transition. These assignments were made based on the observed photolytic behavior of the progressions and the vertical excitation energies and oscillator strengths calculated using time-dependent density functional theory.

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

NONE

In order to develop the conditions for preparing polymers with different molecular masses, the authors continued their investigation of TMSP (1-(trimethylsilyl)-1-propyne) polymerization catalyzed by TaCl{sub 5} and TaCl{sub 5}/BuLi at various ratios of VTMS (regulator of molecular mass of the polymer) : catalyst. They also studied the effect of the structure of silahydrocarbon on the process of TMSP polymerization. To this end, they carried out polymerization of TMSP in the presence of additives of vinylphenyldimethylsilane and vinylallyldimethylsilane. The conditions of experiments and the results obtained are shown. The method for controlling the molecular mass of PTMSP makes it possible tomore » prepare PTMSP suitable for manufacture of both flat membranes and hollow fibers. The paper also describes the experimental study of PTMSP gas permeability, gas sorption in PTMSP, and a computer program for the prediction of all gas permeability parameters of polymers.« less

Chromatographic properties PLOT multicapillary columns.

PubMed

Nikolaeva, O A; Patrushev, Y V; Sidelnikov, V N

2017-03-10

Multicapillary columns (MCCs) for gas chromatography make it possible to perform high-speed analysis of the mixtures of gaseous and volatile substances at a relatively large amount of the loaded sample. The study was performed using PLOT MCCs for gas-solid chromatography (GSC) with different stationary phases (SP) based on alumina, silica and poly-(1-trimethylsilyl-1-propyne) (PTMSP) polymer as well as porous polymers divinylbenzene-styrene (DVB-St), divinylbenzene-vinylimidazole (DVB-VIm) and divinylbenzene-ethylene glycol dimethacrylate (DVB-EGD). These MCCs have the efficiency of 4000-10000 theoretical plates per meter (TP/m) and at a column length of 25-30cm can separate within 10-20s multicomponent mixtures of substances belonging to different classes of chemical compounds. The sample amount not overloading the column is 0.03-1μg and depends on the features of a porous layer. Examples of separations on some of the studied columns are considered. Copyright © 2017 Elsevier B.V. All rights reserved.

Organic Microporous Nanofillers with Unique Alcohol Affinity for Superior Ethanol Recovery toward Sustainable Biofuels.

PubMed

Cheng, Xi Quan; Konstas, Kristina; Doherty, Cara M; Wood, Colin D; Mulet, Xavier; Xie, Zongli; Ng, Derrick; Hill, Matthew R; Lau, Cher Hon; Shao, Lu

2017-05-09

To minimize energy consumption and carbon footprints, pervaporation membranes are fast becoming the preferred technology for alcohol recovery. However, this approach is confined to small-scale operations, as the flux of standard rubbery polymer membranes remain insufficient to process large solvent volumes, whereas membrane separations that use glassy polymer membranes are prone to physical aging. This study concerns how the alcohol affinity and intrinsic porosity of networked, organic, microporous polymers can simultaneously reduce physical aging and drastically enhance both flux and selectivity of a super glassy polymer, poly-[1-(trimethylsilyl)propyne] (PTMSP). Slight loss in alcohol transportation channels in PTMSP is compensated by the alcohol affinity of the microporous polymers. Even after continuous exposure to aqueous solutions of alcohols, PTMSP pervaporation membranes loaded with the microporous polymers outperform the state-of-the-art and commercial pervaporation membranes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Butanol production from lignocellulose by simultaneous fermentation, saccharification, and pervaporation or vacuum evaporation.

PubMed

Díaz, Víctor Hugo Grisales; Tost, Gerard Olivar

2016-10-01

Techno-economic study of acetone, butanol and ethanol (ABE) fermentation from lignocellulose was performed. Simultaneous saccharification, fermentation and vacuum evaporation (SFS-V) or pervaporation (SFS-P) were proposed. A kinetic model of metabolic pathways for ABE fermentation with the effect of phenolics and furans in the growth was proposed based on published laboratory results. The processes were optimized in Matlab®. The end ABE purification was carried out by heat-integrated distillation. The objective function of the minimization was the total annualized cost (TAC). Fuel consumption of SFS-P using poly[1-(trimethylsilyl)-1-propyne] membrane was between 13.8 and 19.6% lower than SFS-V. Recovery of furans and phenolics for the hybrid reactors was difficult for its high boiling point. TAC of SFS-P was increased 1.9 times with supplementation of phenolics and furans to 3g/l each one for its high toxicity. Therefore, an additional detoxification method or an efficient pretreatment process will be necessary. Copyright © 2016 Elsevier Ltd. All rights reserved.

Interfacial and transport properties of nanoconstrained inorganic and organic materials

NASA Astrophysics Data System (ADS)

Kocherlakota, Lakshmi Suhasini

Nanoscale constraints impact the material properties of both organic and inorganic systems. The systems specifically studied here are (i) nanoconstrained polymeric systems, poly(l-trimethylsilyl-1-propyne) (PTMSP) and poly(ethylene oxide) (PEO) relevant to gas separation membranes (ii) Zwitterionic polymers poly(sulfobetaine methacrylate)(pSBMA), poly(carboxybetaine acrylamide) (pCBAA), and poly(oligo(ethylene glycol) methyl methacrylate) (PEGMA) brushes critical for reducing bio-fouling (iii) Surface properties of N-layer graphene sheets. Interfacial constraints in ultrathin poly(l-trimethylsilyl-1-propyne) (PTMSP) membranes yielded gas permeabilities and CO2/helium selectivities that exceed bulk PTMSP membrane transport properties by up to three-fold for membranes of submicrometer thickness. Indicative of a free volume increase, a molecular energetic mobility analysis (involving intrinsic friction analysis) revealed enhanced methyl side group mobilities in thin PTMSP membranes with maximum permeation, compared to bulk films. Aging studies conducted over the timescales relevant to the conducted experiments signify that the free volume states in the thin film membranes are highly unstable in the presence of sorbing gases such as CO2. To maintain this high free volume configuration of polymer while improving the temporal stability an "inverse" architecture to conventional polymer nanocomposites was investigated, in which the polymer phase of PTMSP and PEO were interfacially and dimensionally constrained in nanoporous anodic aluminum oxide (AAO) membranes. While with this architecture the benefits of nanocomposite and ultrathin film membranes of PTMSP could be reproduced and improved upon, also the temporal stability could be enhanced substantially. The PEO-AAO nanocomposite membranes also revealed improved gas selectivity properties of CO2 over helium. In the thermal transition studies of zwitterionic pSBMA brushes a reversible critical transition temperature of 60 °C in 27 nm films was evidenced, indicating changes in molecular conformations with respect to the temperature. pCBAA and pEGMA brushes displayed no thermal transitions, suggesting that the molecular conformations of these systems were insensitive to temperature in the investigated regime. The surface energy of a dimensionally constrained inorganic system, graphene is studied via local Hamaker constant determination from a single graphene layer to bulk graphite. Intrinsic friction scattering analysis of dipolar fluctuations of the Van der Waals interactions between an atomic force microscopy tip and graphene layers revealed a four-fold reduction in the surface energy from bulk HOPG to graphene. A numerical analysis based on electron energy loss spectroscopy confirms quantitatively the results.

Positron induced scattering cross sections for hydrocarbons relevant to plasma

NASA Astrophysics Data System (ADS)

Singh, Suvam; Antony, Bobby

2018-05-01

This article explores positron scattering cross sections by simple hydrocarbons such as ethane, ethene, ethyne, propane, and propyne. Chemical erosion processes occurring on the surface due to plasma-wall interactions are an abundant source of hydrocarbon molecules which contaminate the hydrogenic plasma. These hydrocarbons play an important role in the edge plasma region of Tokamak and ITER. In addition to this, they are also one of the major components in the planetary atmospheres and astrophysical mediums. The present work focuses on calculation of different positron impact interactions with simple hydrocarbons in terms of the total cross section (Qtot), elastic cross section (Qel), direct ionization cross section (Qion), positronium formation cross section (Qps), and total ionization cross section (Qtion). Knowing that the positron-plasma study is one of the trending fields, the calculated data have diverse plasma and astrophysical modeling applications. A comprehensive study of Qtot has been provided where the inelastic cross sections have been reported for the first time. Comparisons are made with those available from the literature, and a good agreement is obtained with the measurements.

Palladium-catalyzed Reppe carbonylation.

PubMed

Kiss, G

2001-11-01

PdX2L2/L/HA (A = weakly coordinating anion, L = phosphine) complexes are active catalysts in the hydroesterification of alkenes, alkynes, and conjugated dienes. Shell, the only major corporate player in the field, recently developed two very active catalyst systems tailored to the hydroesterification of either alkenes or alkynes. The hydroesterification of propyne with their Pd(OAc)2/PN/HA (PN = (2-pyridyl)diphenylphosphine, HA = strong acid with weakly coordinating anion, like methanesulfonic acid) catalyst has been declared commercially ready. However, despite the significant progress in the activity of Pd-hydroesterification catalysts, further improvements are warranted. Thus, for example, activity maintenance still seems to be an issue. Homogeneous Pd catalysts are prone to a number of deactivation reactions. Activity and stability promoters are often corrosive and add to the complexity of the system, making it less attractive. Nonetheless, the versatility of the process and its tolerance toward the functional groups of substrates should appeal especially to the makers of specialty products. Although hydroesterification yields esters from alkenes, alkynes, and dienes in fewer steps than hydroformylation does, the latter has some advantages at the current state of the art. (1) Hydroformylation catalysts, particularly some recently published phosphine-modified Rh systems, can achieve very high regioselectivity for the linear product that hydroesterification catalysts cannot match yet. By analogy with hydroformylation, bulkier ligands ought to be tested in hydroesterification to increase normal-ester selectivity. (2) Hydroformylation is proven, commercial. Hydroesterification can only replace it if it can provide significant economic incentives. Similar or just marginally better performance could not justify the cost of development of a new technology. (3) Hydroesterification requires pure CO while hydroformylation uses syngas, a mixture of CO and H2. The latter is typically more available and less expensive (for industrial applications CO is most often separated from syngas). (4) The acid component of the hydroesterification catalyst makes the process corrosive. It would be desirable to develop new hydroesterification catalysts that do not require acid stabilizer/activity booster. Clearly, any new hydroesterification technology will directly compete with the hydroformylation route. This is especially true for olefin feeds, since both processes add one CO to the olefin, yielding oxygenates that can be converted into identical products. For some niche applications, like the production of MMA from propyne, hydroesterification seems to have an advantage as compared to hydroformylation due to the high activity and selectivity of the Pd(OAc)2/(2-pyridyl)diphenylphosphine catalyst. Since hydroesterification is an emerging technology, it is reasonable to assume that the potential for improvement is greater than in the mature hydroformylation. It is therefore possible that hydroesterification will become competitive in the future; thus, continued effort in the field is warranted.

Development of vinylic and acetylenic functionalized structures based on high permeable glassy polymers as membrane materials for gas mixtures separation

NASA Astrophysics Data System (ADS)

Roizard, D.; Kiryukhina, Y.; Masalev, A.; Khotimskiy, V.; Teplyakov, V.; Barth, D.

2013-03-01

There are several challenging separation problems in industries which can be solved with the help of membrane technologies. It is the case for instance of the purification of gas energy carriers (i.e. H2, CH4) from CO2 as well as the CO2 recovery from flue gas. Glassy polymers containing trimethylsilyl residues like poly(1-trimethylsilyl-1-propyne) [PTMSP] and polyvinyltrimethylsilane [PVTMS] are known to exhibit good membrane properties for gas separation. This paper reports two ways of improving their performances based on the controlled introduction of selective groups - alkyl imidazomium salts (C4I) and polyethyleneglycol (M-PEG)- able to enhance CO2 selectivity. CO2 Isotherm sorption data and permeability measurements have shown that the membrane performances could be significantly improved when C4I and M-PEG were introduced as residues covalently bounded to the main polymer chain. Moreover the introduced bromine reactive centres could also be used to induce chemical crosslinking giving rise to more resistant and stable membranes to organic vapours. With the C4I groups, the CO2 sorption could be enhanced by a factor 4.4.

Improved method for mutagenicity testing of gaseous compounds by using a gas sampling bag.

PubMed

Araki, A; Noguchi, T; Kato, F; Matsushima, T

1994-05-01

A simple and safety gas exposure method was developed using a gas sampling bag as an exposure vessel and a preparation vessel of diluted gas. The gas exposure conditions such as amount of S9 in the plate, volume of gas for the plate, amount of top agar, exposure period and exposure temperature were examined by mutagenicity testing of 1,3-butadiene using the gas sampling bag. Mutagenicity tests of 14 compounds and 1,3-butadiene on S. typhimurium TA98, TA100, TA1535 and TA1537, and E. coli WP2 uvrA were also examined by the developed gas exposure method. 1,3-Butadiene, propyne (methyl acetylene), monochlorodifluoromethane, ethylchloride, diborane and silane were mutagenic. 1-Butene, 2-butene, 2-methylpropene, methyl vinyl ether, trichlorofluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, 1,1-difluoroethane and phosphine were not mutagenic on S. typhimurium TA98, TA100, TA1535 and TA1537, and E. coli WP2 uvrA with or without metabolic activation. These results were compatible with a previous report, and this developed method has the advantage that it can be tested easily and safely for combustible and self-combustible substances such as 1,3-butadiene and silane.

Internal energy of HCl upon photolysis of 2-chloropropene at 193 nm investigated with time-resolved Fourier-transform spectroscopy and quasiclassical trajectories

NASA Astrophysics Data System (ADS)

Chang, Chih-Min; Huang, Yu-Hsuan; Liu, Suet-Yi; Lee, Yuan-Pern; Pombar-Pérez, Marta; Martínez-Núñez, Emilio; Vázquez, Saulo A.

2008-12-01

Following photodissociation of 2-chloropropene (H2CCClCH3) at 193 nm, vibration-rotationally resolved emission spectra of HCl (υ ≤6) in the spectral region of 1900-2900 cm-1 were recorded with a step-scan time-resolved Fourier-transform spectrometer. All vibrational levels show a small low-J component corresponding to ˜400 K and a major high-J component corresponding to 7100-18 700 K with average rotational energy of 39±311 kJ mol-1. The vibrational population of HCl is inverted at υ =2, and the average vibrational energy is 86±5 kJ mol-1. Two possible channels of molecular elimination producing HCl+propyne or HCl+allene cannot be distinguished positively based on the observed internal energy distribution of HCl. The observed rotational distributions fit qualitatively with the distributions of both channels obtained with quasiclassical trajectories (QCTs), but the QCT calculations predict negligible populations for states at small J. The observed vibrational distribution agrees satisfactorily with the total QCT distribution obtained as a weighted sum of contributions from both four-center elimination channels. Internal energy distributions of HCl from 2-chloropropene and vinyl chloride are compared.

Mechanism-based inactivation of benzo(a)pyrene hydroxylase by aryl acetylenes and aryl olefins

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

Gan, L.S.; Lu, J.Y.L.; Alworth, W.L.

A series of aryl acetylenes and aryl olefins have been examined as substrates and inhibitors of cytochrome P-450 dependent monooxgenases in liver microsomes from 5,6-benzoflavone or phenobarbital pretreated rats. 1-Ethynylpyrene, 3-ethynylperylene, 2-ethynylfluorene, methyl 1-pyrenyl acetylene, cis- and trans-1-(2-bromovinyl)pyrene, and 1-allylpyrene serve as mechanism-based irreversible inactivators (suicide inhibitors) of benzo(a)pyrene hydroxylase, while 1-vinylpyrene and phenyl 1-pyrenyl acetylene do not cause a detectable suicide inhibition of benzo(a)pyrene hydroxylase. The mechanism-based loss of benzo(a)pyrene hydroxylase caused by the aryl acetylenes is not accompanied by a corresponding loss of the P-450 content of the microsomes (suicide destruction). The suicide inhibition by these aryl acetylenesmore » therefore does not involve covalent binding to the heme moiety of the monooxygenase. Nevertheless, in the presence of NADPH, /sup 3/H-labeled 1-ethynylpyrene becomes covalently attached to the cytochrome P-450 protein; the measured stoichiometry of binding is one 1-ethynylpyrene per P-450 heme unit. The authors conclude that the inhibition of benzo(a)pyrene hydroxylase produced by 1-ethynylpyrene may be related to the mechanism of suicide inhibition of P-450 activity by chloramphenicol rather than the mechanism of suicide destruction of P-450 previously described for acetylene and propyne.« less

a KA-BAND Chirped-Pulse Fourier Transform Microwave Spectrometer.

NASA Astrophysics Data System (ADS)

Zaleski, Daniel P.; Neill, Justin L.; Muckle, Matthew T.; Pate, Brooks H.; Carroll, P. Brandon; Weaver, Susanna L. Widicus

2010-06-01

The design and performance of a new chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer operating from 25-40 GHz will be discussed. A 10.5-3 GHz linear frequency sweep, generated by a 24 GS/s arbitrary waveform generator, is upconverted by a 23.00 GHz phase-locked oscillator, then fed into an active doubler to create a 25-40 GHz chirped pulse. After amplification with a 60-80 W pulsed traveling wave tube amplifier, the pulse is broadcast across a molecular beam chamber where it interacts with a molecular sample. The molecular FID signal is downconverted with the 23 GHz oscillator so that it can be digitized on a 50 GS/s oscilloscope with 16 GHz hardware bandwidth. The sensitivity and phase stability of this spectrometer is comparable to that of the previously reported 6.5-18.5 CP-FTMW spectrometer. On propyne (μ=0.78 D), a single-shot signal to noise ratio of approximately 200:1 is observed on the J=2-1 rotational transition at 34183 MHz when the full bandwidth is swept; optimal excitation is observed for this transition with a 250 MHz bandwidth sweep. The emission has a T_2 lifetime of 4 μs. Early results from this spectrometer, particularly in the study of species of astrochemical interest, will be presented. G.G. Brown et al., Rev. Sci. Instrum. 79 (2008) 053103.

Dissociative Ionization and Thermal Decomposition of Cyclopentanone

PubMed Central

Pastoors, Johan I. M.; Bodi, Andras; Hemberger, Patrick

2017-01-01

Abstract Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2H4, and C2H5, leading to daughter ions at m/z 56 and 55. Exploring the C5H8O. + potential energy surface reveals hydrogen tunneling to play an important role in low‐energy decarbonylation and probably also in the ethene‐loss processes, yielding 1‐butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl‐radical loss and a second ethene‐loss channel, respectively. A statistical Rice–Ramsperger–Kassel–Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed‐shell pyrolysis products, namely 1,3‐butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass‐selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies. PMID:28692134

Photodissociation dynamics of gaseous CpCo(CO)2 and ligand exchange reactions of CpCoH2 with C3H4, C3H6, and NH3.

PubMed

Oana, Melania; Nakatsuka, Yumiko; Albert, Daniel R; Davis, H Floyd

2012-05-31

The photodissociation dynamics of CpCo(CO)(2) was studied in a molecular beam using photofragment translational energy spectroscopy with 157 nm photoionization detection of the metallic products. At 532 and 355 nm excitation, the dominant one-photon channel involved loss of a single CO ligand producing CpCoCO. The product angular distributions were isotropic, and a large fraction of excess energy appeared as product vibrational excitation. Production of CpCO + 2CO resulted from two-photon absorption processes. The two-photon dissociation of mixtures containing CpCo(CO)(2) and H(2) at the orifice of a pulsed nozzle was used to produce a novel 16-electron unsaturated species, CpCoH(2). Transition metal ligand exchange reactions, CpCoH(2) + L → CpCoL + H(2) (L = propyne, propene, or ammonia), were studied under single-collision conditions for the first time. In all cases, ligand exchange occurred via 18-electron association complexes with lifetimes comparable to their rotational periods. Although ligand exchange reactions were not detected from CpCoH(2) collisions with methane or propane (L = CH(4) or C(3)H(8)), a molecular beam containing CpCoCH(4) was produced by photolysis of mixtures containing CpCo(CO)(2) and CH(4).

Detailed and reduced chemical-kinetic descriptions for hydrocarbon combustion

NASA Astrophysics Data System (ADS)

Petrova, Maria V.

Numerical and theoretical studies of autoignition processes of fuels such as propane are in need of realistic simplified chemical-kinetic descriptions that retain the essential features of the detailed descriptions. These descriptions should be computationally feasible and cost-effective. Such descriptions are useful for investigating ignition processes that occur, for example, in homogeneous-charge compression-ignition engines, for studying the structures and dynamics of detonations and in fields such as multi-dimensional Computational Fluid Dynamics (CFD). Reduced chemistry has previously been developed successfully for a number of other hydrocarbon fuels, however, propane has not been considered in this manner. This work focuses on the fuels of propane, as well propene, allene and propyne, for several reasons. The ignition properties of propane resemble those of other higher hydrocarbons but are different from those of the lower hydrocarbons (e.g. ethylene and acetylene). Propane, therefore, may be the smallest hydrocarbon that is representative of higher hydrocarbons in ignition and detonation processes. Since the overall activation energy and ignition times for propane are similar to those of other higher hydrocarbons, including liquid fuels that are suitable for many applications, propane has been used as a model fuel for several numerical and experimental studies. The reason for studying elementary chemistry of propene and C3H4 (allene or propyne) is that during the combustion process, propane breaks down to propene and C3H4 before proceeding to products. Similarly, propene combustion includes C3H4 chemistry. In studying propane combustion, it is therefore necessary to understand the underlying combustion chemistry of propene as well as C3H 4. The first part of this thesis focuses on obtaining and testing a detailed chemical-kinetic description for autoignition of propane, propene and C 3H4, by comparing predictions obtained with this detailed mechanism against numerous experimental data available from shock-tube studies and flame-speed measurements. To keep the detailed mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K and equivalence ratios less than about 3. Based on this detailed chemistry description, short (or skeletal) mechanisms are then obtained for each of the three fuels by eliminating reactions that are unimportant for the autoignition process under conditions presented above. This was achieved by utilizing tools such as sensitivity and reaction pathway analyses. Two distinct methodologies were then used in order to obtain a reduced mechanism for autoignition from the short mechanisms. A Systematic Reduction approach is first taken that involves introducing steady-state approximations to as many species as analytically possible. To avoid resorting to numerical methods, the analysis for obtaining ignition times for heptane, presented by Peters and co-workers is followed in order to obtain a rough estimate for an expression of propane ignition time. The results from this expression are then compared to the ignition times obtained computationally with the detailed mechanism. The second method is an Empirical Approach in which chemistry is not derived formally, but rather postulated empirically on the basis of experimental, computational and theoretical observations. As a result, generalized reduced mechanisms are proposed for autoignition of propane, propene and C3H 4. Expressions for ignition times obtained via this empirical approach are compared to the computational results obtained from the detailed mechanism.

Mixed Matrix Membranes for O2/N2 Separation: The Influence of Temperature

PubMed Central

Fernández-Barquín, Ana; Casado-Coterillo, Clara; Valencia, Susana; Irabien, Angel

2016-01-01

In this work, mixed matrix membranes (MMMs) composed of small-pore zeolites with various topologies (CHA (Si/Al = 5), LTA (Si/Al = 1 and 5), and Rho (Si/Al = 5)) as dispersed phase, and the hugely permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) as continuous phase, have been synthesized via solution casting, in order to obtain membranes that could be attractive for oxygen-enriched air production. The O2/N2 gas separation performance of the MMMs has been analyzed in terms of permeability, diffusivity, and solubility in the temperature range of 298–333 K. The higher the temperature of the oxygen-enriched stream, the lower the energy required for the combustion process. The effect of temperature on the gas permeability, diffusivity, and solubility of these MMMs is described in terms of the Arrhenius and Van’t Hoff relationships with acceptable accuracy. Moreover, the O2/N2 permselectivity of the MMMs increases with temperature, the O2/N2 selectivities being considerably higher than those of the pure PTMSP. In consequence, most of the MMMs prepared in this work exceeded the Robeson’s upper bound for the O2/N2 gas pair in the temperature range under study, with not much decrease in the O2 permeabilities, reaching O2/N2 selectivities of up to 8.43 and O2 permeabilities up to 4,800 Barrer at 333 K. PMID:27196937

On the Relative Stability of Cumulenone and Aldehyde Isomers: when we HEAT345(Q) Things UP

NASA Astrophysics Data System (ADS)

Lee, Kelvin; McCarthy, Michael C.; Stanton, John F.

2017-06-01

Isomers of H_2C_{2n+1}O are examples of complex organic molecules that are either known or proposed to exist in the interstellar medium. For the smallest of these chains (H_2C_3O) only two of three isomers are observed in space: propynal (HC(O)CCH) and cyclopropenone (c-C_3H_2O), while evidence for the remaining isomer propadienone (H_2C_3O) is currently lacking. Potentially, this behaviour may be rationalised by a thermodynamic argument: several studies have provided quantum chemical calculations in an effort to determine the relative thermodynamic stability between these three isomers. An early study by Radom, at the SCF/6-31G** level ranked HC(O)CCH as the thermodynamic minimum, followed by H_2C_3O, and c-C_3H_2O. The most recent determination by Karton and Talbi, using W2-F12 theory, places H_2C_3O as the lowest energy isomer; 2.5 kJ mol^{-1} lower than the HC(O)CCH form. In an attempt to resolve this long-standing ambiguity, we were motivated to provide high level calculations based on the HEAT protocol. In this talk, we will discuss the relative stability of H_2C_3O and H_2C_5O isomers, along with their sulfur analogues, as revealed by HEAT345(Q) theory.

Low-Temperature Synchrotron Photoionization Study of 2-Methyl-3-buten-2-ol (MBO) Oxidation Initiated by O(3P) Atoms in the 298-650 K Range.

PubMed

Fathi, Yasmin; Price, Chelsea; Meloni, Giovanni

2017-04-20

This work studies the oxidation of 2-methyl-3-buten-2-ol initiated by O( 3 P) atoms. The oxidation was investigated at room temperature, 550, and 650 K. Using the synchrotron radiation from the Advanced Light Source (ALS) of the Lawrence Berkley National Laboratory, reaction intermediates and products were studied by multiplexed photoionization mass spectrometry. Mass-to-charge ratios, kinetic time traces, photoionization spectra, and adiabatic ionization energies for each primary reaction species were obtained and used to characterize their identity. Using electronic structure calculations, potential energy surface scans of the different species produced throughout the oxidation were examined and presented in this paper to further validate the primary chemistry occurring. Branching fractions of primary products at all three temperatures were also provided. At room temperature only three primary products formed: ethenol (26.6%), acetaldehyde (4.2%), and acetone (53.4%). At 550 and 650 K the same primary products were observed in addition to propene (5.1%, 11.2%), ethenol (18.1%, 2.8%), acetaldehyde (8.9%, 5.7%), cyclobutene (1.6%, 10.8%), 1-butene (2.0%, 10.9%), trans-2-butene (3.2%, 23.1%), acetone (50.4%, 16.8%), 3-penten-2-one (1.0%, 11.5%), and 3-methyl-2-butenal (0.9%, 2.5%), where the first branching fraction value in parentheses corresponds to the 550 K data. At the highest temperature, a small amount of propyne (1.0%) was also observed.

Hyper-Cross-Linked Additives that Impede Aging and Enhance Permeability in Thin Polyacetylene Films for Organic Solvent Nanofiltration.

PubMed

Cheng, Xi Quan; Konstas, Kristina; Doherty, Cara M; Wood, Colin D; Mulet, Xavier; Xie, Zongli; Ng, Derrick; Hill, Matthew R; Shao, Lu; Lau, Cher Hon

2017-04-26

Membrane materials with high permeability to solvents while rejecting dissolved contaminants are crucial to lowering the energy costs associated with liquid separations. However, the current lack of stable high-permeability materials require innovative engineering solutions to yield high-performance, thin membranes using stable polymers with low permeabilities. Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) is one of the most permeable polymers but is extremely susceptible to physical aging. Despite recent developments in anti-aging polymer membranes, this research breakthrough has yet to be demonstrated on thin PTMSP films supported on porous polymer substrates, a crucial step toward commercializing anti-aging membranes for industrial applications. Here we report the development of scalable, thin film nanocomposite membranes supported on polymer substrates that are resistant to physical aging while having high permeabilities to alcohols. The selective layer is made up of PTMSP and nanoporous polymeric additives. The nanoporous additives provide additional passageways to solvents, enhancing the high permeability of the PTMSP materials further. Through intercalation of polyacetylene chains into the sub-nm pores of organic additives, physical aging in the consequent was significantly hindered in continuous long-term operation. Remarkably we also demonstrate that the additives enhance both membrane permeability and rejection of dissolved contaminants across the membranes, as ethanol permeability at 5.5 × 10 -6 L m m -2 h -1 bar -1 with 93% Rose Bengal (1017.6 g mol -1 ) rejection, drastically outperforming commercial and state-of-the-art membranes. These membranes can replace energy-intensive separation processes such as distillation, lowering operation costs in well-established pharmaceutical production processes.

A dynamic two-dimensional system for measuring volatile organic compound volatilization and movement in soils.

PubMed

Allaire, S E; Yates, S R; Ernst, F F; Gan, J

2002-01-01

There is an important need to develop instrumentation that allows better understanding of atmospheric emission of toxic volatile compounds associated with soil management. For this purpose, chemical movement and distribution in the soil profile should be simultaneously monitored with its volatilization. A two-dimensional rectangular soil column was constructed and a dynamic sequential volatilization flux chamber was attached to the top of the column. The flux chamber was connected through a manifold valve to a gas chromatograph (GC) for real-time concentration measurement. Gas distribution in the soil profile was sampled with gas-tight syringes at selected times and analyzed with a GC. A pressure transducer was connected to a scanivalve to automatically measure the pressure distribution in the gas phase of the soil profile. The system application was demonstrated by packing the column with a sandy loam in a symmetrical bed-furrow system. A 5-h furrow irrigation was started 24 h after the injection of a soil fumigant, propargyl bromide (3-bromo-1-propyne; 3BP). The experience showed the importance of measuring lateral volatilization variability, pressure distribution in the gas phase, chemical distribution between the different phases (liquid, gas, and sorbed), and the effect of irrigation on the volatilization. Gas movement, volatilization, water infiltration, and distribution of degradation product (Br-) were symmetric around the bed within 10%. The system saves labor cost and time. This versatile system can be modified and used to compare management practices, estimate concentration-time indexes for pest control, study chemical movement, degradation, and emissions, and test mathematical models.

A density functional for core-valence correlation energy

NASA Astrophysics Data System (ADS)

Ranasinghe, Duminda S.; Frisch, Michael J.; Petersson, George A.

2015-12-01

A density functional, ɛCV-DFT(ρc, ρv), describing the core-valence correlation energy has been constructed as a linear combination of ɛLY Pcorr(ρc), ɛV WN5corr(ρc, ρv), ɛPBEcorr(ρc, ρv), ɛSlaterex(ρc, ρv), ɛHCTHex(ρc, ρv), ɛHFex(ρc, ρv), and F CV -DFT (" separators=" N i , Z i ) , a function of the nuclear charges. This functional, with 6 adjustable parameters, reproduces (±0.27 kcal/mol rms error) a benchmark set of 194 chemical energy changes including 9 electron affinities, 18 ionization potentials, and 167 total atomization energies covering the first- and second-rows of the periodic table. This is almost twice the rms error (±0.16 kcal/mol) obtained with CCSD(T)/MTsmall calculations, but less than half the rms error (±0.65 kcal/mol) obtained with MP2/GTlargeXP calculations, and somewhat smaller than the rms error (±0.39 kcal/mol) obtained with CCSD/MTsmall calculations. The largest positive and negative errors from ɛCV-DFT(ρc, ρv) were 0.88 and -0.75 kcal/mol with the set of 194 core-valence energy changes ranging from +3.76 kcal/mol for the total atomization energy of propyne to -9.05 kcal/mol for the double ionization of Mg. Evaluation of the ɛCV-DFT(ρc, ρv) functional requires less time than a single SCF iteration, and the accuracy is adequate for any model chemistry based on the CCSD(T) level of theory.

Construction of combustion models for rapeseed methyl ester bio-diesel fuel for internal combustion engine applications.

PubMed

Golovitchev, Valeri I; Yang, Junfeng

2009-01-01

Bio-diesel fuels are non-petroleum-based diesel fuels consisting of long chain alkyl esters produced by the transesterification of vegetable oils, that are intended for use (neat or blended with conventional fuels) in unmodified diesel engines. There have been few reports of studies proposing theoretical models for bio-diesel combustion simulations. In this study, we developed combustion models based on ones developed previously. We compiled the liquid fuel properties, and the existing detailed mechanism of methyl butanoate ester (MB, C(5)H(10)O(2)) oxidation was supplemented by sub-mechanisms for two proposed fuel constituent components, C(7)H(16) and C(7)H(8)O (and then, by mp2d, C(4)H(6)O(2) and propyne, C(3)H(4)) to represent the combustion model for rapeseed methyl ester described by the chemical formula, C(19)H(34)O(2) (or C(19)H(36)O(2)). The main fuel vapor thermal properties were taken as those of methyl palmitate C(19)H(36)O(2) in the NASA polynomial form of the Burcat database. The special global reaction was introduced to "crack" the main fuel into its constituent components. This general reaction included 309 species and 1472 reactions, including soot and NO(x) formation processes. The detailed combustion mechanism was validated using shock-tube ignition-delay data under diesel engine conditions. For constant volume and diesel engine (Volvo D12C) combustion modeling, this mechanism could be reduced to 88 species participating in 363 reactions.

Cometabolic degradation of chlorinated alkenes by alkene monooxygenase in a propylene-grown Xanthobacter strain.

PubMed Central

Ensign, S A; Hyman, M R; Arp, D J

1992-01-01

Propylene-grown Xanthobacter cells (strain Py2) degraded several chlorinated alkenes of environmental concern, including trichloroethylene, 1-chloroethylene (vinyl chloride), cis- and trans-1,2-dichloroethylene, 1,3-dichloropropylene, and 2,3-dichloropropylene. 1,1-Dichloroethylene was not degraded efficiently, while tetrachloroethylene was not degraded. The role of alkene monooxygenase in catalyzing chlorinated alkene degradations was established by demonstrating that glucose-grown cells which lack alkene monooxygenase and propylene-grown cells in which alkene monooxygenase was selectively inactivated by propyne were unable to degrade the compounds. C2 and C3 chlorinated alkanes were not oxidized by alkene monooxygenase, but a number of these compounds were inhibitors of propylene and ethylene oxidation, suggesting that they compete for binding to the enzyme. A number of metabolites enhanced the rate of degradation of chlorinated alkenes, including propylene oxide, propionaldehyde, and glucose. Propylene stimulated chlorinated alkene oxidation slightly when present at a low concentration but became inhibitory at higher concentrations. Toxic effects associated with chlorinated alkene oxidations were determined by measuring the propylene oxidation and propylene oxide-dependent O2 uptake rates of cells previously incubated with chlorinated alkenes. Compounds which were substrates for alkene monooxygenase exhibited various levels of toxicity, with 1,1-dichloroethylene and trichloroethylene being the most potent inactivators of propylene oxidation and 1,3- and 2,3-dichloropropylene being the most potent inactivators of propylene oxide-dependent O2 uptake. No toxic effects were seen when cells were incubated with chlorinated alkenes anaerobically, indicating that the product(s) of chlorinated alkene oxidation mediates toxicity. PMID:1444418

A Near-Threshold Shape Resonance in the Valence-Shell Photoabsorption of Linear Alkynes

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

Jacovella, U.; Holland, D. M. P.; Boyé-Péronne, S.

2015-12-17

The room-temperature photoabsorption spectra of a number of linear alkynes with internal triple bonds (e.g., 2-butyne, 2-pentyne, and 2- and 3-hexyne) show similar resonances just above the lowest ionization threshold of the neutral molecules. These features result in a substantial enhancement of the photoabsorption cross sections relative to the cross sections of alkynes with terminal triple bonds (e.g., propyne, 1-butyne, 1-pentyne,...). Based on earlier work on 2-butyne [Xu et al., J. Chem. Phys. 2012, 136, 154303], these features are assigned to excitation from the neutral highest occupied molecular orbital (HOMO) to a shape resonance with g (l = 4) charactermore » and approximate pi symmetry. This generic behavior results from the similarity of the HOMOs in all internal alkynes, as well as the similarity of the corresponding g pi virtual orbital in the continuum. Theoretical calculations of the absorption spectrum above the ionization threshold for the 2- and 3-alkynes show the presence of a shape resonance when the coupling between the two degenerate or nearly degenerate pi channels is included, with a dominant contribution from l = 4. These calculations thus confirm the qualitative arguments for the importance of the l = 4 continuum near threshold for internal alkynes, which should also apply to other linear internal alkynes and alkynyl radicals. The 1-alkynes do not have such high partial waves present in the shape resonance. The lower l partial waves in these systems are consistent with the broader features observed in the corresponding spectra.« less

ACE-FTS Observation of a Young Biomass Burning Plume: First Reported Measurements of C2H4, C3H6O, H2CO and PAN by Infrared Occultation from Space

NASA Technical Reports Server (NTRS)

Coheur, Pierre-Francois; Herbin, Herve; Clerbaux, Cathy; Hurtmans, Daniel; Wespes, Catherine; Carleer, Michel; Turquety, Solene; Rinsland, Curtis P.; Remedios, John; Hauglustaine, Didier;

Inactivation of Toluene 2-Monooxygenase in Burkholderia cepacia G4 by Alkynes

PubMed Central

Yeager, Chris M.; Bottomley, Peter J.; Arp, Daniel J.; Hyman, Michael R.

1999-01-01

High concentrations of acetylene (10 to 50% [vol/vol] gas phase) were required to inhibit the growth of Burkholderia cepacia G4 on toluene, while 1% (vol/vol) (gas phase) propyne or 1-butyne completely inhibited growth. Low concentrations of longer-chain alkynes (C5 to C10) were also effective inhibitors of toluene-dependent growth, and 2- and 3-alkynes were more potent inhibitors than their 1-alkyne counterparts. Exposure of toluene-grown B. cepacia G4 to alkynes resulted in the irreversible loss of toluene- and o-cresol-dependent O2 uptake activities, while acetate- and 3-methylcatechol-dependent O2 uptake activities were unaffected. Toluene-dependent O2 uptake decreased upon the addition of 1-butyne in a concentration- and time-dependent manner. The loss of activity followed first-order kinetics, with apparent rate constants ranging from 0.25 min−1 to 2.45 min−1. Increasing concentrations of toluene afforded protection from the inhibitory effects of 1-butyne. Furthermore, oxygen, supplied as H2O2, was required for inhibition by 1-butyne. These results suggest that alkynes are specific, mechanism-based inactivators of toluene 2-monooxygenase in B. cepacia G4, although the simplest alkyne, acetylene, was relatively ineffective compared to longer alkynes. Alkene analogs of acetylene and propyne—ethylene and propylene—were not inactivators of toluene 2-monooxygenase activity in B. cepacia G4 but were oxidized to their respective epoxides, with apparent Ks and Vmax values of 39.7 μM and 112.3 nmol min−1 mg of protein−1 for ethylene and 32.3 μM and 89.2 nmol min−1 mg of protein−1 for propylene. PMID:9925593

Surface modification of PTMSP membranes by plasma treatment: Asymmetry of transport in organic solvent nanofiltration.

PubMed

Volkov, A V; Tsarkov, S E; Gilman, A B; Khotimsky, V S; Roldughin, V I; Volkov, V V

2015-08-01

For the first time, the effect of asymmetry of the membrane transport was studied for organic solvents and solutes upon their nanofiltration through the plasma-modified membranes based on poly(1-trimethylsilyl-1-propyne) (PTMSP). Plasma treatment is shown to provide a marked hydrophilization of the hydrophobic PTMSP surface (the contact angle of water decreases from 88 down to 20°) and leads to the development of a negative charge of -5.2 nC/cm(2). The XPS measurements prove the formation of the oxygen-containing groups (Si-O and C-O) due to the surface modification. The AFM images show that the small-scale surface roughness of the plasma-treated PTMSP sample is reduced but the large-scale surface heterogeneities become more pronounced. The modified membranes retain their hydrophilic surface properties even after the nanofiltration tests and 30-day storage under ambient conditions. The results of the filtration tests show that when the membrane is oriented so that its modified layer contacts the feed solution, the membrane permeability for linear alcohols (methanol-propanol) and acetone decreases nearly two times. When the modified membrane surface faces the permeate, the membrane is seen to regain its transport characteristics: the flux becomes equal to that of the unmodified PTMSP. The well-pronounced effect of the transport asymmetry is observed for the solution of the neutral dye Solvent Blue 35 in methanol, ethanol, and acetone. For example, the initial membrane shows the negative retention for the Solvent Blue 35 dye (-16%) upon its filtration from the ethanol solution whereas, for the modified PTMSP membrane, the retention increases up to 17%. Various effects contributing to the asymmetry of the membrane transport characteristics are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

VizieR Online Data Catalog: Gas-phase detection of c-C3H3

NASA Astrophysics Data System (ADS)

Zhao, D.; Doney, K. D.; Linnartz, H.

2017-03-01

The experimental setup has been described in detail by Zhao et al. (2013CPL...565..132Z, 2014JMoSp.296....1Z). In brief, the c-C3H3+ cations are generated by discharging a propyne (C3H4):He ~ 1:200 gas mixture in a multi-layer slit discharge nozzle (Motylewski & Linnartz 1999RScI...70.1305M) in combination with a pulsed valve (General Valve, Series 9,2 mm orifice). The gas mixture is expanded with a backing pressure of ~7 bar through a 300umx3cm slit into a vacuum chamber. A pulsed negative high voltage (-600 V/300 mA) with a ~600 us duration is found to be optimum for c-C3H3+ production, is applied to the expanding gas mixture, and is set to coincide with the expanding gas pulse (~800 us). Continuous-wave cavity ring-down spectroscopy (cw-CRDS) is used to record spectra in direct absorption. The axis of the optical cavity is aligned parallel to and ~2 mm downstream of the slit nozzle throat. A single-mode cw optical parametric oscillator (Aculight), operating at ~3.15 um with a bandwidth <5x10-5cm-1, is employed as tunable IR light source. A hardware-based (boxcar integrator) multi-trigger and timing scheme recently reported by Zhao et al. (2013CPL...565..132Z) is used to apply cw-CRDS to the pulsed plasma. In the present experiment, typical ring-down time values are ~8-10 us, corresponding to a detection sensitivity, i.e., noise equivalent absorption, of up to ~2x10-7 per centimeter for the 3 cm long plasma jet. (1 data file).

Descent without Modification? The Thermal Chemistry of H2O2 on Europa and Other Icy Worlds.

PubMed

Loeffler, Mark J; Hudson, Reggie L

2015-06-01

The strong oxidant H2O2 is known to exist in solid form on Europa and is suspected to exist on several other Solar System worlds at temperatures below 200 K. However, little is known of the thermal chemistry that H2O2 might induce under these conditions. Here, we report new laboratory results on the reactivity of solid H2O2 with eight different compounds in H2O-rich ices. Using infrared spectroscopy, we monitored compositional changes in ice mixtures during warming. The compounds CH4 (methane), C3H4 (propyne), CH3OH (methanol), and CH3CN (acetonitrile) were unaltered by the presence of H2O2 in ices, showing that exposure to either solid H2O2 or frozen H2O+H2O2 at cryogenic temperatures will not oxidize these organics, much less convert them to CO2. This contrasts strongly with the much greater reactivity of organics with H2O2 at higher temperatures, and particularly in the liquid and gas phases. Of the four inorganic compounds studied, CO, H2S, NH3, and SO2, only the last two reacted in ices containing H2O2, NH3 making NH4+ and SO2 making SO(4)2- by H+ and e- transfer, respectively. An important astrobiological conclusion is that formation of surface H2O2 on Europa and that molecule's downward movement with H2O-ice do not necessarily mean that all organics encountered in icy subsurface regions will be destroyed by H2O2 oxidation.

Descent Without Modification? The Thermal Chemistry of H2O2 on Europa and Other Icy Worlds

NASA Technical Reports Server (NTRS)

Loeffler, Mark Josiah; Hudson, Reggie Lester

2015-01-01

The strong oxidant H2O2 is known to exist in solid form on Europa and is suspected to exist on several other Solar System worlds at temperatures below 200 K. However, little is known of the thermal chemistry that H2O2 might induce under these conditions. Here, we report new laboratory results on the reactivity of solid H2O2 with eight different compounds in H2O-rich ices. Using infrared spectroscopy, we monitored compositional changes in ice mixtures during warming. The compounds CH4 (methane), C3H4 (propyne), CH3OH (methanol), and CH3CN (acetonitrile) were unaltered by the presence of H2O2 in ices, showing that exposure to either solid H2O2 or frozen H2O+H2O2 at cryogenic temperatures will not oxidize these organics, much less convert them to CO2. This contrasts strongly with the much greater reactivity of organics with H2O2 at higher temperatures, and particularly in the liquid and gas phases. Of the four inorganic compounds studied, CO, H2S, NH3, and SO2, only the last two reacted in ices containing H2O2, NH3 making NHþ 4 and SO2 making SO2 4 by H+ and e - transfer, respectively. An important astrobiological conclusion is that formation of surface H2O2 on Europa and that molecule's downward movement with H2O-ice do not necessarily mean that all organics encountered in icy subsurface regions will be destroyed by H2O2 oxidation.

The vanadium nitrogenase of Azotobacter chroococcum. Reduction of acetylene and ethylene to ethane.

PubMed Central

Dilworth, M J; Eady, R R; Eldridge, M E

1988-01-01

1. The vanadium (V-) nitrogenase of Azobacter chroococcum transfers up to 7.4% of the electrons used in acetylene (C2H2) reduction for the formation of ethane (C2H6). The apparent Km for C2H2 (6 kPa) is the same for either ethylene (C2H4) or ethane (C2H6) formation and much higher than the reported Km values for C2H2 reduction to C2H4 by molybdenum (Mo-) nitrogenases. Reduction of C2H2 in 2H2O yields predominantly [cis-2H2]ethylene. 2. The ratio of electron flux yielding C2H6 to that yielding C2H4 (the C2H6/C2H4 ratio) is increased by raising the ratio of Fe protein to VFe protein and by increasing the assay temperature up to at least 40 degrees C. pH values above 7.5 decrease the C2H6/C2H4 ratio. 3. C2H4 and C2H6 formation from C2H2 by V-nitrogenase are not inhibited by H2. CO inhibits both processes much less strongly than it inhibits C2H4 formation from C2H2 with Mo-nitrogenase. 4. Although V-nitrogenase also catalyses the slow CO-sensitive reduction of C2H4 to C2H6, free C2H4 is not an intermediate in C2H6 formation from C2H2. 5. Propyne (CH3C identical to CH) is not reduced by the V-nitrogenase. 6. Some implications of these results for the mechanism of C2H6 formation by the V-nitrogenase are discussed. PMID:3162672

Termolecular ion-molecule reactions in Titan's atmosphere. IV. A search made at up to 1 micron in pure hydrocarbons

NASA Technical Reports Server (NTRS)

Anicich, Vincent G.; Wilson, Paul; McEwan, Murray J.

2003-01-01

The results of a study of ion-molecule reactions occurring in pure methane, acetylene, ethylene, ethane, propyne, propene, propane, and diacetylene at pressures up to 40 microns of pressure are reported. A variety of experimental methods are used: The standard double resonance in an ICR, for determination of the precursor ions and the modulated double resonance ejection in an ICR, for the determination of the daughter ions. The FA-SIFT technique was used for validation and examination of termolecular reactions with rate coefficients that are less than 10(-26) cm(6) s(-1). An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and to search for any missing reactions and reaction channels that may have been omitted from earlier investigations. A specific objective of this work was to extend the study to the highest pressures possible to find out if there were any important termolecular reaction channels occurring. A new approach was used here. In the pure hydrocarbon gases the mass spectra were followed as a function of the pressure changes of the gas. An initial guess was first made using the current literature as a source of the reaction kinetics that were expected. A model of the ion abundances was produced from the solution of the partial differential equations in terms of reaction rate coefficients and initial abundances. The experimental data was fitted to the model for all of the pressures by a least squares minimization to the reaction rate coefficients and initial abundances. The reaction rate coefficients obtained from the model were then compared to the literature values. Several new channels and reactions were discovered when the modeled fits were compared to the actual data. This is all explained in the text and the implications of these results are discussed for the Titan atmosphere.

Chemistry of the High-mass Protostellar Molecular Clump IRAS 16562–3959

NASA Astrophysics Data System (ADS)

Guzmán, Andrés E.; Guzmán, Viviana V.; Garay, Guido; Bronfman, Leonardo; Hechenleitner, Federico

2018-06-01

We present molecular line observations of the high-mass molecular clump IRAS 16562‑3959 taken at 3 mm using the Atacama Large Millimeter/submillimeter Array at 1.″7 angular resolution (0.014 pc spatial resolution). This clump hosts the actively accreting high-mass young stellar object (HMYSO) G345.4938+01.4677, which is associated with a hypercompact H II region. We identify and analyze emission lines from 22 molecular species (encompassing 34 isomers) and classify them into two groups, depending on their spatial distribution within the clump. One of these groups gathers shock tracers (e.g., SiO, SO, HNCO) and species formed in dust grains like methanol (CH3OH), ethenone or ketene (H2CCO), and acetaldehyde (CH3CHO). The second group collects species closely resembling the dust continuum emission morphology and are formed mainly in the gas phase, like hydrocarbons (CCH, c-C3H2, CH3CCH), cyanopolyynes (HC3N and HC5N), and cyanides (HCN and CH3C3N). Emission from complex organic molecules (COMs) like CH3OH, propanenitrile (CH3CH2CN), and methoxymethane (CH3OCH3) arise from gas in the vicinity of a hot molecular core (T ≳ 100 K) associated with the HMYSO. Other COMs such as propyne (CH3CCH), acrylonitrile (CH2CHCN), and acetaldehyde seem to better trace warm (T ≲ 80 K) dense gas. In addition, deuterated ammonia (NH2D) is detected mostly in the outskirts of IRAS 16562‑3959 and associated with near-infrared dark globules, probably gaseous remnants of the clump’s prestellar phase. The spatial distribution of molecules in IRAS 16562‑3959 supports the view that in protostellar clumps, chemical tracers associated with different evolutionary stages—starless to hot cores/H II regions—exist coevally.

Effects of biomass burning on summertime nonmethane hydrocarbon concentrations in the Canadian wetlands

NASA Technical Reports Server (NTRS)

Blake, D. R.; Smith, T. W., Jr.; Chen, T.-Y.; Whipple, W. J.; Rowland, F. S.

1994-01-01

Approximately 900 whole air samples were collected and assayed for selected C2-C10 hydrocarbons and seven halocarbons during the 5-week Arctic Boundary Layer Expedition (ABLE) 3B conducted in eastern Canadian wetland areas. In more than half of the 46 vertical profiles flown, enhanced nonmethane hydrocarbon (NMHC) concentrations attributable to plumes from Canadian forest fires were observed. Urban plumes, also enhanced in many NMHCs, were separately identified by their high correlation with elevated levels of perchloroethene. Emission factors relative to ethane were determined for 21 hydrocarbons released from Canadian biomass burning. Using these data for ethane, ethyne, propane, n-butane, and carbon monoxide enhancements from the literature, global emissions of these four NMHCs were estimated. Because of its very short atmospheric lifetime and its below detection limit background mixing ratio, 1,3-butadiene is an excellent indicator of recent combustion. No statistically significant emissions of nitrous oxide, isoprene, or CFC 12 were observed in the biomass-burning plumes encountered during ABLE 3B. The presence of the short-lived biogenically emitted isoprene at altitudes as high as 3000 m implies that mixing within the planetary boundary layer (PBL) was rapid. Although background levels of the longer-lived NMHCs in this Canadian region increase during the fire season, isoprene still dominated local hydroxyl radical photochemistry within the PBL except in the immediate vicinity of active fires. The average biomass-burning emission ratios for hydrocarbons from an active fire sampled within minutes of combustion were, relative to ethane, ethene, 2.45; ethyne 0.57; propane, 0.25; propene, 0.73; propyne, 0.06; n-butane, 0.09; i-butane, 0.01; 1-butene, 0.14; cis-2-butene, 0.02; trans-2-butene, 0.03; i-butylene, 0.07; 1,3-butadiene, 0.12; n-pentane, 0.05; i-pentane, 0.03; 1-pentene, 0.06; n-hexane, 0.05; 1-hexene, 0.07; benzene, 0.37; toluene, 0.16.

Conformers, infrared spectrum and UV-induced photochemistry of matrix-isolated furfuryl alcohol.

PubMed

Araujo-Andrade, C; Gómez-Zavaglia, A; Reva, I D; Fausto, R

2012-03-08

The infrared spectra of furfuryl alcohol (2-furanmethanol, FFA) were investigated for FFA monomers isolated in low-temperature argon matrices. The structural interpretation of the obtained experimental spectra was assisted by analysis of the molecule's conformational landscape. According to the DFT(B3LYP)/6-311++G(d,p) calculations, five different minimum energy structures were found on the potential energy surface of the molecule. They can be defined by the orientation of the OCCO and CCOH dihedral angles: GG', GG, TG, TT, GT (G = +gauche, G' = -gauche, T = trans) and have a symmetry equivalent configuration: GG' = G'G, GG = G'G', TG = TG', GT = G'T. When zero-point energies are taken into account, only three (GG', GG, and TT) out of the five unique minima correspond to stable structures. The most stable conformer GG' (OCCO, 72.7°; CCOH, -59.3°), which in gas phase at room temperature accounts for ∼65% of the total population, was the only form isolated in the argon matrices at 14 K. The other two relevant forms convert into conformer GG' during matrix deposition. The low temperature glassy and crystalline states of FFA were also obtained and their infrared spectra assigned, suggesting the sole existence of the GG' conformer also in these phases. The photochemical behavior of FFA induced in situ, by tunable UV-laser, was also studied. The longest wavelength resulting in photochemical changes in the structure of the irradiated sample was found to be λ = 229 nm. Such UV irradiation of the matrix-isolated FFA led to production of formaldehyde and different isomeric C(4)H(4)O species. Cycloprop-2-ene-1-carbaldehyde and buta-2,3-dienal (two conformers) are the main initial C(4)H(4)O photoproducts formed upon short-time excitation at λ = 229 nm. But-3-ynal (two conformers) was the principal photoproduct resulting from prolonged excitation at λ= 229 nm, being consumed upon irradiation at shorter wavelengths (λ < 227.5 nm). Vinyl ketene is produced from FFA in the trans conformation and undergoes isomerization to the cis form upon irradiation at λ < 227.5 nm. Cyclopropene, propyne, allene, and CO were also identified in the irradiated matrices (in particular at the later stages of irradiation), suggesting that the photoproduced aldehydes partially decarbonylate during the performed photochemical experiments.

The CO-H2 van der Waals complex and complex organic molecules in cold molecular clouds: A TMC-1C survey

NASA Astrophysics Data System (ADS)

Potapov, A.; Sánchez-Monge, Á.; Schilke, P.; Graf, U. U.; Möller, Th.; Schlemmer, S.

2016-10-01

Context. Almost 200 different species have been detected in the interstellar medium (ISM) during the last decades, revealing not only simple species but complex molecules with more than six atoms. Other exotic compounds, like the weakly-bound dimer (H2)2, have also been detected in astronomical sources like Jupiter. Aims: We aim to detect, for the first time, the CO-H2 van der Waals complex in the ISM, which could be a sensitive indicator for low temperatures if detected. Methods: We used the IRAM 30 m telescope, located in Pico Veleta (Spain), to search for the CO-H2 complex in a cold, dense core in TMC-1C (with a temperature of ~10 K). All the brightest CO-H2 transitions in the 3 mm (80-110 GHz) band were observed with a spectral resolution of 0.5-0.7 km s-1, reaching a rms noise level of ~2 mK. The simultaneous observation of a broad frequency band, 16 GHz, allowed us to conduct a serendipitous spectral line survey. Results: We did not detected any lines belonging to the CO-H2 complex. We set up a new, more stringent upper limit for its abundance to be [CO-H2]/[CO] ~ 5 × 10-6, while we expect the abundance of the complex to be in the range ~10-8-10-3. The spectral line survey has allowed us to detect 75 lines associated with 41 different species (including isotopologues). We detect a number of complex organic species, for example methyl cyanide (CH3CN), methanol (CH3OH), propyne (CH3CCH), and ketene (CH2CO), associated with cold gas (excitation temperatures ~7 K), confirming the presence of these complex species not only in warm objects but also in cold regimes. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Reduced spectra (FITS 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/594/A117

Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: high acetaldehyde, ketene, isoprene and isocyanic acid in wintertime air of the Kathmandu Valley

NASA Astrophysics Data System (ADS)

Sarkar, C.; Sinha, V.; Kumar, V.; Rupakheti, M.; Panday, A. K.; Mahata, K.; Rupakheti, D.; Kathayat, B.; Lawrence, M. G.

2015-12-01

During SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in the winter of 2012-2013, a comprehensive study was carried out to characterize the chemical composition of ambient Kathmandu air for speciated VOCs by deploying a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), the first time to be deployed in South Asia. Due to its high mass resolution (m/Δm > 4200) and temporal resolution (1 minute), 71 ion peaks were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the Valley. Of the 71, 38 species were found to have campaign average concentrations > 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers. Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m/z=69.070) and furan (m/z=69.033). Comparison with several sites elsewhere in the world showed mixing ratios of acetaldehyde (~ 9 ppb), acetonitrile (~1 ppb) and isoprene (~ 1 ppb) to be among the highest measured anywhere in the world. Two "new" ambient compounds namely, methanamide (m/z = 46.029) and acetamide (m/z=60.051) which can photochemically produce isocyanic acid in the atmosphere, are reported in this study alongwith nitromethane (a tracer for diesel exhaust) and ketene (a very reactive compound). Two distinct periods were identified during the campaign based on high daytime biogenic emissions of isoprene even in winter and biomass fired brick kiln emissions of acetonitrile, benzene and isocyanic acid. Biomass burning and biomass fired brick kiln emissions were found to be the dominant source for compounds such as propyne, propene, benzene and propanenitrile which correlated strongly with biomass burning tracer acetonitrile (r2 > 0.7). The calculated total VOC OH reactivity was dominated by acetaldehyde (20.1%), ketene (ethenone) (17.1%), isoprene (16.8 %) and propene (15.6%), while oxygenated VOCs and isoprene collectively contributed to more than 70% of the total ozone production potential. The first ambient measurements from any site in South Asia of compounds with significant health effects such as isocyanic acid, formamide, acetamide, naphthalene and nitromethane are reported in this study.

Pressure-dependent rate constants for PAH growth: formation of indene and its conversion to naphthalene

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

Mebel, Alexander M.; Georgievskii, Yuri; Jasper, Ahren W.

2016-01-01

Unraveling the mechanisms for growth of polycyclic aromatic hydrocarbons (PAHs) requires accurate temperature- and pressure-dependent rate coefficients for a great variety of feasible pathways. Even the pathways for the formation of the simplest PAHs, indene and naphthalene, are fairly complex. These pathways provide important prototypes for modeling larger PAH growth. In this work we employ the ab initio RRKM theory-based master equation approach to predict the rate constants involved in the formation of indene and its conversion to naphthalene. The reactions eventually leading to indene involve C9Hx (x = 8–11) potential energy surfaces (PESs) and include C6H5 + C3H4 (allenemore » and propyne), C6H6 + C3H3, benzyl + C2H2, C6H5 + C3H6, C6H6 + C3H5 and C6H5 + C3H5. These predictions allow us to make a number of valuable observations on the role of various mechanisms. For instance, we demonstrate that reactions which can significantly contribute to the formation of indene include phenyl + allene and H-assisted isomerization to indene of its major product, 3-phenylpropyne, benzyl + acetylene, and the reactions of the phenyl radical with propene and the allyl radical, both proceeding via the 3-phenylpropene intermediate. 3-Phenylpropene can be activated to a 1-phenylallyl radical, which in turn rapidly decomposes to indene. Next, indene can be converted to benzofulvene or naphthalene under typical combustion conditions, via its activation by H atom abstraction and methyl substitution on the five-membered ring followed by isomerization and decomposition of the resulting 1-methylindenyl radical, C10H9 → C10H8 + H. Alternatively, the same region of the C10H9 PES can be accessed through the reaction of benzyl with propargyl, C7H7 + C3H3 → C10H10 → C10H9 + H, which therefore can also contribute to the formation of benzofulvene or naphthalene. Benzofulvene easily transforms to naphthalene by H-assisted isomerization. An analysis of the effect of pressure on the reaction outcome and relative product yields is given, and modified Arrhenius fits of the rate constants are reported for the majority of the considered reactions. Ultimately, the implementation of such expressions in detailed kinetic models will help quantify the role of these reactions for PAH growth in various environments.« less

Titan's atmospheric chemistry: Photolysis of gas mixtures containing hydrogen cyanide and carbon monoxide at 185 and 254 nm

NASA Astrophysics Data System (ADS)

Tran, Buu N.; Force, Michael; Briggs, Robert G.; Ferris, James P.; Persans, Peter; Chera, John J.

2008-01-01

The formation of organic compounds in the atmosphere of Titan is an ongoing process of the generation of complex organics from the simplest hydrocarbon, methane. Solar radiation and magnetosphere electrons are the main energy sources that drive the reactions in Titan's atmosphere. Since energy from solar radiation is 200 times greater than that from magnetosphere electrons, we have investigated the products formed by the action of UV radiation (185 and 254 nm) on a mixture of gases containing nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene, the basic gas mixture (BGM) that simulates aspects of Titan's atmosphere using a flow reactor [Tran, B.N., Ferris, J.P., Chera, J.J., 2003a. Icarus 162, 114-124; Tran, B.N., Joseph, J.C., Force, M., Briggs, R.G., Vuitton, V., Ferris, J.P., 2005. Icarus 177, 106-115]. The present research extends these studies by the addition of carbon monoxide and hydrogen cyanide to the BGM. Quantum yields for the loss of reactants and the formation of volatile products were determined and compared with those measured in the absence of the hydrogen cyanide and carbon monoxide. The GCMS analyses of the volatile photolysis products from the BGM, with added hydrogen cyanide, had a composition similar to that of the BGM while the photolysis products of the BGM with added carbon monoxide contained many oxygenated compounds. The infrared spectrum of the corresponding solid product revealed the absorption band of a ketone group, which was probably formed from the reaction of carbon monoxide with the free radicals generated by photolysis of acetylene and ethylene. Of particular interest was the observation that the addition of HCN to the gas mixture only resulted in a very small change in the C/N ratio and in the intensity of the C tbnd N frequency at 2210 cm -1 in the infrared spectrum suggesting that little HCN is incorporated into the haze analog. The C/N ratio of the haze analogs was found to be in the 10-12 range. The UV spectra of the solid products formed when HCN or CO added to the BGM is similar to the UV absorption formed from the BGM alone. This result is consistent with absence of additional UV chromophores to the solid product when these mixtures are photolyzed. The following photoproducts, which were not starting materials in our photochemical studies, have been observed on Titan: acetonitrile, benzene, diacetylene, ethane, propene, propane, and propyne.

Crossed beam studies of elementary reactions of N and C atoms and CN radicals of importance in combustion.

PubMed

Casavecchia, P; Balucani, N; Cartechini, L; Capozza, G; Bergeat, A; Volpi, G G

2001-01-01

The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in combustion have been investigated by using the crossed molecular beam scattering method with mass spectrometric detection. The novel capability of producing intense, continuous beams of the radical reagents by a radio-frequency discharge beam source was exploited. From angular and velocity distribution measurements obtained in the laboratory frame, primary reaction products have been identified and their angular and translational energy distributions in the center-of-mass system, as well as branching ratios, have been derived. The dominant N/H exchange channel has been examined in the reaction N(2D) + CH4, which is found to lead to H + CH2NH (methylenimine) and H + CH3N (methylnitrene); no H2 elimination is observed. In the reaction N(2D) + H2O the N/H exchange channel has been found to occur via two competing pathways leading to HNO + H and HON + H, while formation of NO + H2 is negligible. Formation of H + H2CCCH (propargyl) is the dominant pathway, at low collision energy (Ec), of the C(3P) + C2H4 reaction, while at high Ec formation of the less stable C3H3 isomers (cyclopropenyl and/or propyn-1-yl) also occurs; the H2 elimination channel is negligible. The H elimination channel has also been found to be the dominant pathway in the C(3P,1D) + CH3CCH reaction leading to C4H3 isomers and, again, no H2 elimination has been observed to occur. In contrast, both H and H2 elimination, leading in comparable ratio to C3H + H and C3(X1 sigma g+) + H2(X1 sigma g+), respectively, have been observed in the reaction C(3P) + C2H2(X1 sigma g+). The occurrence of the spin-forbidden molecular pathway in this reaction, never detected before, has been rationalized by invoking the occurrence of intersystem crossing between triplet and singlet manifolds of the C3H2 potential energy surfaces. The reaction CN(X2 sigma +) + C2H2 has been found to lead to internally excited HCCCN (cyanoacetylene) + H. For all the reactions the dynamics have been discussed in the light of recent theoretical calculations on the relevant potential energy surfaces. Previous, lower resolution studies on C and CN reactions carried out using pulsed beams are noted. Finally, throughout the paper the relevance of these results to combustion chemistry is considered.

Formation of C3 and C2 in Cometary Comae

NASA Astrophysics Data System (ADS)

Hölscher, Alexander

2015-03-01

Comets are remnants from the Solar System formation. They reside at large distances from the Sun and are believed to store deep freeze imprints of the chemical and physical conditions at the time the Solar System formed. The main ice component of a comet is H2O followed by CO and CO2 with additional small amounts of molecules with varying complexity. Comets also contain large amounts of dust. If a comet approaches the Sun the ices begin to sublimate giving rise to the cometary coma. The molecules producing the coma can be observed in the infrared, the radio wavelength range and at optical wavelengths. To constrain the formation of the Solar System, models require knowledge of the composition for a statistically significant number of comets. This favors optical observations of e.g. C3 (tricarbon) and C2 (dicarbon) since these species allow observations even of relatively faint comets and do not require space missions (infrared observations). However, one has to link these observed photodissociation product species (daughter species) to the molecules that originally sublimated from the comet nucleus surface, i.e. the so-called parent molecules, as e.g. C2H2 (acetylene) for C2. However, for C3 no parent molecules have been identified so far. This thesis investigates the formation of C3 and C2 radicals in cometary comae due to photodissociation of observed and in the literature proposed hydrocarbon parent molecules. For this purpose a one-dimensional multi-fluid coma chemistry model has been improved and applied. This work added new photo reactions to the model, updated the hydrocarbon photo rate coefficients and quantified their uncertainty. A sensitivity analysis has been carried out to determine the reactions whose uncertainty most affect the model output uncertainty. Special attention should be paid to these so-called key reactions in future laboratory experiments and quantum chemical computations to reduce the model output uncertainty more effectively. This will allow to better constrain which parent molecules are responsible for the observational C3 and C2 column densities. Based on observations of the four sample comets C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), 9P (Tempel 1) and C/1995 O1 (Hale-Bopp), this work investigates which combination of the following proposed parent molecules C4H2 (diacetylene), CH2C2H2 (allene), CH3C2H (propyne), C2H4 (ethene) and observed parent molecules C2H2 and HC3N (cyanoacetylene) can best reproduce the observational C3 and C2 column densities in cometary comae, taking into account the uncertainties in photodissociation rate coefficients. It was found that the investigated photodissociation rate coefficients have large uncertainties and also a significant effect on the C3 and C2 model column densities. The responsible key reactions were determined with the sensitivity analysis. The important result of this thesis is that one can reasonably well reproduce the observations of comets with the improved model at rh = 1.00 AU (NEAT) and rh = 3.78 AU (Hale-Bopp), within the photodissociation uncertainties using realistic parent molecule production rate ratios and by various combinations of the investigated parent molecules. To confirm the agreement (NEAT, Hale-Bopp) and to clearify remaining discrepancies (LINEAR, Tempel 1) between model and observations requires additional observations of parent and daughter molecules in the coma of comets as well as in situ measurements of cometary ices (Rosetta).zeige weniger

Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C2-C10 volatile organic compounds (VOCs), CO2, CH4, CO, NO, NO2, NOy, O3 and SO2

NASA Astrophysics Data System (ADS)

Simpson, I. J.; Blake, N. J.; Barletta, B.; Diskin, G. S.; Fuelberg, H. E.; Gorham, K.; Huey, L. G.; Meinardi, S.; Rowland, F. S.; Vay, S. A.; Weinheimer, A. J.; Yang, M.; Blake, D. R.

2010-08-01

Oil sands comprise 30% of the world's oil reserves and the crude oil reserves in Canada's oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen contained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is increasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta's oil sands mining sites. We present high-precision gas chromatography measurements of 76 speciated C2-C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenates, halocarbons, and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measurements of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8. Methane, CO, CO2, NO, NO2, NOy, SO2 and 53 VOCs (e.g., halocarbons, sulphur species, NMHCs) showed clear statistical enhancements (up to 1.1-397×) over the oil sands compared to local background values and, with the exception of CO, were higher over the oil sands than at any other time during the flight. Twenty halocarbons (e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or were minimally enhanced (< 10%) over the oil sands. Ozone levels remained low because of titration by NO, and three VOCs (propyne, furan, MTBE) remained below their 3 pptv detection limit throughout the flight. Based on their mutual correlations, the compounds emitted by the oil sands industry fell into two groups: (1) evaporative emissions from the oil sands and its products and/or from the diluent used to lower the viscosity of the extracted bitumen (i.e., C4-C9 alkanes, C5-C6 cycloalkanes, C6-C8 aromatics), together with CO; and (2) emissions associated with the mining effort (i.e., CO2, CO, CH4, NO, NO2, NOy, SO2, C2-C4 alkanes, C2-C4 alkenes, C9 aromatics, short-lived solvents such as C2Cl4 and C2HCl3, and longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second group, SO2 and NO were remarkably enhanced over the oil sands, with maximum enhancements of 38.7 and 5.0 ppbv, or 383 and 319× the local background, respectively. The SO2 enhancements are comparable to maximum values measured in heavily polluted megacities such as Mexico City and are attributed to coke combustion. By contrast, relatively poor correlations between CH4 ethane and propane suggest low natural gas leakage despite its heavy use at the surface mining sites. In addition to the emission of many trace gases, the natural drawdown of OCS by vegetation was absent above the surface mining operations, presumably because of the widespread land disturbance. Unexpectedly, the mixing ratios of α- and β-pinene were much higher over the oil sands (up to 217 and 610 pptv, respectively) than over vegetation in the background boundary layer (20±7 and 84±24 pptv, respectively), and the pinenes correlated well with several industrial tracers that were elevated in the oil sands plumes. Because so few independent measurements from the oil sands mining industry exist, this study provides an important initial characterization of trace gas emissions from oil sands surface mining operations.

Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: high acetaldehyde, isoprene and isocyanic acid in wintertime air of the Kathmandu Valley

NASA Astrophysics Data System (ADS)

Sarkar, C.; Sinha, V.; Kumar, V.; Rupakheti, M.; Panday, A.; Mahata, K. S.; Rupakheti, D.; Kathayat, B.; Lawrence, M. G.

2015-09-01

The Kathmandu Valley in Nepal suffers from severe wintertime air pollution. Volatile organic compounds (VOCs) are key constituents of air pollution, though their specific role in the Valley is poorly understood due to insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in Nepal in the winter of 2012-2013, a comprehensive study was carried out to characterize the chemical composition of ambient Kathmandu air, including the determination of speciated VOCs by deploying a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS)-the first such deployment in South Asia. 71 ion peaks (for which measured ambient concentrations exceeded the 2 σ detection limit) were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the Valley. Of the 71 species, 37 were found to have campaign average concentrations greater than 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers as a result of the high mass resolution (m/Δm > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The highest average VOC mixing ratios during the measurement period were (in rank order): acetaldehyde (8.8 ppb), methanol (7.4 ppb), acetone (4.2 ppb), benzene (2.7 ppb), toluene (1.5 ppb), isoprene (1.1 ppb), acetonitrile (1.1 ppb), C8-aromatics (~ 1 ppb), furan (~ 0.5 ppb), and C9-aromatics (0.4 ppb). Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m/z = 69.070) and furan (m/z = 69.033). Comparison with wintertime measurements from several locations elsewhere in the world showed mixing ratios of acetaldehyde (~ 9 ppb), acetonitrile (~ 1 ppb) and isoprene (~ 1 ppb) to be among the highest reported till date. Two "new" ambient compounds namely, formamide (m/z = 46.029) and acetamide (m/z = 60.051), which can photochemically produce isocyanic acid in the atmosphere, are reported in this study along with nitromethane (a tracer for diesel exhaust) which has only recently been detected in ambient studies. Two distinct periods were selected during the campaign for detailed analysis: the first was associated with high wintertime emissions of biogenic isoprene, and the second with elevated levels of ambient acetonitrile, benzene and isocyanic acid from biomass burning activities. Emissions from biomass burning and biomass co-fired brick kilns were found to be the dominant sources for compounds such as propyne, propene, benzene and propanenitrile which correlated strongly with acetonitrile (r2 > 0.7), a chemical tracer for biomass burning. The calculated total VOC OH reactivity was dominated by acetaldehyde (24.0 %), isoprene (20.2 %) and propene (18.7 %), while oxygenated VOCs and isoprene collectively contributed to more than 68 % of the total ozone production potential. Based on known SOA yields and measured ambient concentrations in the Kathmandu Valley, the relative SOA production potential of VOCs were: benzene > naphthalene > toluene > xylenes > monoterpenes > trimethyl-benzenes > styrene > isoprene. The first ambient measurements from any site in South Asia of compounds with significant health effects such as isocyanic acid, formamide, acetamide, naphthalene and nitromethane have been reported in this study. Our results suggest that mitigation of intense wintertime biomass burning activities, in particular point sources such biomass co-fired brick kilns, would be important to reduce the emission and formation of toxic VOCs (such as benzene and isocyanic acid) in the Kathmandu Valley and improve its air quality.

Overview of VOC emissions and chemistry from PTR-TOF-MS measurements during the SusKat-ABC campaign: high acetaldehyde, isoprene and isocyanic acid in wintertime air of the Kathmandu Valley

NASA Astrophysics Data System (ADS)

Sarkar, Chinmoy; Sinha, Vinayak; Kumar, Vinod; Rupakheti, Maheswar; Panday, Arnico; Mahata, Khadak S.; Rupakheti, Dipesh; Kathayat, Bhogendra; Lawrence, Mark G.

2016-03-01

The Kathmandu Valley in Nepal suffers from severe wintertime air pollution. Volatile organic compounds (VOCs) are key constituents of air pollution, though their specific role in the valley is poorly understood due to insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in Nepal in the winter of 2012-2013, a comprehensive study was carried out to characterise the chemical composition of ambient Kathmandu air, including the determination of speciated VOCs, by deploying a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) - the first such deployment in South Asia. In the study, 71 ion peaks (for which measured ambient concentrations exceeded the 2σ detection limit) were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the valley. Of the 71 species, 37 were found to have campaign average concentrations greater than 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers as a result of the high mass resolution (m / Δm > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The concentration ranking in the average VOC mixing ratios during our wintertime deployment was acetaldehyde (8.8 ppb) > methanol (7.4 ppb) > acetone + propanal (4.2 ppb) > benzene (2.7 ppb) > toluene (1.5 ppb) > isoprene (1.1 ppb) > acetonitrile (1.1 ppb) > C8-aromatics ( ˜ 1 ppb) > furan ( ˜ 0.5 ppb) > C9-aromatics (0.4 ppb). Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m / z = 69.070) and furan (m / z = 69.033). Comparison with wintertime measurements from several locations elsewhere in the world showed mixing ratios of acetaldehyde ( ˜ 9 ppb), acetonitrile ( ˜ 1 ppb) and isoprene ( ˜ 1 ppb) to be among the highest reported to date. Two "new" ambient compounds, namely formamide (m / z = 46.029) and acetamide (m / z = 60.051), which can photochemically produce isocyanic acid in the atmosphere, are reported in this study along with nitromethane (a tracer for diesel exhaust), which has only recently been detected in ambient studies. Two distinct periods were selected during the campaign for detailed analysis: the first was associated with high wintertime emissions of biogenic isoprene and the second with elevated levels of ambient acetonitrile, benzene and isocyanic acid from biomass burning activities. Emissions from biomass burning and biomass co-fired brick kilns were found to be the dominant sources for compounds such as propyne, propene, benzene and propanenitrile, which correlated strongly with acetonitrile (r2 > 0.7), a chemical tracer for biomass burning. The calculated total VOC OH reactivity was dominated by acetaldehyde (24.0 %), isoprene (20.2 %) and propene (18.7 %), while oxygenated VOCs and isoprene collectively contributed to more than 68 % of the total ozone production potential. Based on known secondary organic aerosol (SOA) yields and measured ambient concentrations in the Kathmandu Valley, the relative SOA production potential of VOCs were benzene > naphthalene > toluene > xylenes > monoterpenes > trimethylbenzenes > styrene > isoprene. The first ambient measurements from any site in South Asia of compounds with significant health effects such as isocyanic acid, formamide, acetamide, naphthalene and nitromethane have been reported in this study. Our results suggest that mitigation of intense wintertime biomass burning activities, in particular point sources such biomass co-fired brick kilns, would be important to reduce the emission and formation of toxic VOCs (such as benzene and isocyanic acid) in the Kathmandu Valley.

Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C2-C10 volatile organic compounds (VOCs), CO2, CH4, CO, NO, NO2, NOy, O3 and SO2

NASA Astrophysics Data System (ADS)

Simpson, I. J.; Blake, N. J.; Barletta, B.; Diskin, G. S.; Fuelberg, H. E.; Gorham, K.; Huey, L. G.; Meinardi, S.; Rowland, F. S.; Vay, S. A.; Weinheimer, A. J.; Yang, M.; Blake, D. R.

2010-12-01

Oil sands comprise 30% of the world's oil reserves and the crude oil reserves in Canada's oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen contained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is increasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta's oil sands mining sites. We present high-precision gas chromatography measurements of 76 speciated C2-C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenated hydrocarbons, halocarbons and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measurements of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8. Carbon dioxide, CH4, CO, NO, NO2, NOy, SO2 and 53 VOCs (e.g., non-methane hydrocarbons, halocarbons, sulphur species) showed clear statistical enhancements (1.1-397×) over the oil sands compared to local background values and, with the exception of CO, were greater over the oil sands than at any other time during the flight. Twenty halocarbons (e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or were minimally enhanced (<10%) over the oil sands. Ozone levels remained low because of titration by NO, and three VOCs (propyne, furan, MTBE) remained below their 3 pptv detection limit throughout the flight. Based on their correlations with one another, the compounds emitted by the oil sands industry fell into two groups: (1) evaporative emissions from the oil sands and its products and/or from the diluent used to lower the viscosity of the extracted bitumen (i.e., C4-C9 alkanes, C5-C6 cycloalkanes, C6-C8 aromatics), together with CO; and (2) emissions associated with the mining effort, such as upgraders (i.e., CO2, CO, CH4, NO, NO2, NOy, SO2, C2-C4 alkanes, C2-C4 alkenes, C9 aromatics, short-lived solvents such as C2Cl4 and C2HCl3, and longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second group, SO2 and NO were remarkably enhanced over the oil sands, with maximum mixing ratios of 38.7 ppbv and 5.0 ppbv, or 383× and 319× the local background, respectively. These SO2 levels are comparable to maximum values measured in heavily polluted megacities such as Mexico City and are attributed to coke combustion. By contrast, relatively poor correlations between CH4, ethane and propane suggest low levels of natural gas leakage despite its heavy use at the surface mining sites. Instead the elevated CH4 levels are attributed to methanogenic tailings pond emissions. In addition to the emission of many trace gases, the natural drawdown of OCS by vegetation was absent above the surface mining operations, presumably because of the widespread land disturbance. Unexpectedly, the mixing ratios of α-pinene and β-pinene were much greater over the oil sands (up to 217 pptv and 610 pptv, respectively) than over vegetation in the background boundary layer (20±7 pptv and 84±24 pptv, respectively), and the pinenes correlated well with several industrial tracers that were elevated in the oil sands plumes. Because so few independent measurements from the oil sands mining industry exist, this study provides an important initial characterization of trace gas emissions from oil sands surface mining operations.

SUPPORT OF GULF OF MEXICO HYDRATE RESEARCH CONSORTIUM: ACTIVITIES TO SUPPORT ESTABLISHMENT OF A SEA FLOOR MONITORING STATION PROJECT

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

Paul Higley; J. Robert Woolsey; Ralph Goodman

2005-08-01

A Consortium, designed to assemble leaders in gas hydrates research, has been established at the University of Mississippi's Center for Marine Resources and Environmental Technology, CMRET. The primary objective of the group is to design and emplace a remote monitoring station on the sea floor in the northern Gulf of Mexico by the year 2005, in an area where gas hydrates are known to be present at, or just below, the sea floor. This mission necessitates assembling a station that will monitor physical and chemical parameters of the sea water and sea floor sediments on a more-or-less continuous basis overmore » an extended period of time. Development of the station allows for the possibility of expanding its capabilities to include biological monitoring, as a means of assessing environmental health. Establishment of the Consortium has succeeded in fulfilling the critical need to coordinate activities, avoid redundancies and communicate effectively among researchers in this relatively new research arena. Complementary expertise, both scientific and technical, has been assembled to innovate research methods and construct necessary instrumentation. A year into the life of this cooperative agreement, we note the following achievements: (1) Progress on the vertical line array (VLA) of sensors: (A) Software and hardware upgrades to the data logger for the prototype vertical line array, including enhanced programmable gains, increased sampling rates, improved surface communications, (B) Cabling upgrade to allow installation of positioning sensors, (C) Adaptation of SDI's Angulate program to use acoustic slant ranges and DGPS data to compute and map the bottom location of the vertical array, (D) Progress in T''0'' delay and timing issues for improved control in data recording, (E) Successful deployment and recovery of the VLA twice during an October, 2003 cruise, once in 830m water, once in 1305m water, (F) Data collection and recovery from the DATS data logger, (G) Sufficient energy supply and normal functioning of the pressure compensated battery even following recharge after the first deployment, (H) Survival of the acoustic modem following both deployments though it was found to have developed a slow leak through the transducer following the second deployment due, presumably, to deployment in excess of 300m beyond its rating. (2) Progress on the Sea Floor Probe: (A) The Sea Floor Probe and its delivery system, the Multipurpose sled have been completed, (B) The probe has been modified to penetrate the <1m blanket of hemipelagic ooze at the water/sea floor interface to provide the necessary coupling of the accelerometer with the denser underlying sediments, (C) The MPS has been adapted to serve as an energy source for both p- and s-wave studies at the station as well as to deploy the horizontal line arrays and the SFP. (3) Progress on the Electromagnetic Bubble Detector and Counter: (A) Components for the prototype have been assembled, including a dedicated microcomputer to control power, readout and logging of the data, all at an acceptable speed, (B) The prototype has been constructed and preliminary data collected, (C) The construction of the field system is underway. (4) Progress on the Acoustic Systems for Monitoring Gas Hydrates: (A) Video recordings of bubbles emitted from a seep in Mississippi Canyon have been made from a submersible dive and the bubbles analyzed with respect to their size, number, and rise rate. These measurements have been used to determine the parameters to build the system capable of measuring gas escaping at the site of the monitoring station, (B) Laboratory tests performed using the project prototype have produced a conductivity data set that is being used to refine parameters of the field model. (5) Progress on the Mid-Infrared Sensor for Continuous Methane Monitoring: (A) Preliminary designs of mounting pieces for electrical components of ''sphereIR'' have been completed using AutoCAD software, (B) The preliminary design of an electronics baseplate has been completed and aided in the optimization of positioning electrical components inside the instrument housing, (C) First spectroscopic investigations of the highly permeable polymer, poly(trimethylsilyl)propyne (PTMSP), as a potential sensing membrane for methane, have commenced, (D) High-pressure multireflection ATR measurements were continued during this project period to investigate the potential influences of hydrostatic pressure on sensing principles and data evaluation strategies. (6) Progress on the Seismo-acoustic Characterization of Sea Floor Properties and Processes at the Hydrate Monitoring Station: (A) work has concentrated on the design and building of the hardware, bench testing and preliminary field trials, (B) development work to extend the capability of the electronics to allow remote operation on the seabed for up to 3 months at a time done.« less

Fluid inclusion volatile analysis by gas chromatography with photoionization micro-thermal conductivity detectors: Applications to magmatic MoS 2 and other H 2O-CO 2 and H 2O-CH 4 fluids

NASA Astrophysics Data System (ADS)

Bray, C. J.; Spooner, E. T. C.

1992-01-01

Eighteen fluid inclusion volatile peaks have been detected and identified from 1-2 g samples (quartz) by gas chromatography using heated (~105°C) on-line crushing, helium carrier gas, a single porous polymer column (HayeSep R; 10' × 1/8″: 100/120#; Ni alloy tubing), two temperature programme conditions for separate sample aliquots, micro-thermal conductivity (TCD) and photoionization detectors (PID; 11.7 eV lamp), and off-line digital peak processing. In order of retention time these volatile peaks are: N 2, Ar, CO, CH 4, CO 2, C 2H 4, C 2H 6, C 2H 2, COS, C 3H 6, C 3H 8, C 3H 4 (propyne), H 2O (22.7 min at 80°C), SO 2, ± iso- C4H10 ± C4H8 (1-butene) ± CH3SH, C 4H 8 (iso-butylene), (?) C 4H 6 (1,3 butadiene) and ± n- C4H10 ± C4H8 (trans-2-butene) (80 and -70°C temperature programme conditions combined). H 2O is analysed directly. O 2 can be analysed cryogenically between N 2 and Ar, but has not been detected in natural samples to date in this study. H 2S, SO 2, NH 3, HCl, HCN, and H 2 ca nnot be analysed at present. Blanks determined by crushing heat-treated Brazilian quartz (800-900°C/4 h) are zero for 80°C temperature programme conditions, except for a large, unidentified peak at ~64 min, but contain H 2O, CO 2, and some low molecular weight hydrocarbons at -70°C temperature conditions due to cryogenic accumulation from the carrier gas and subsequent elution. TCD detection limits are ~30 ppm molar in inclusions; PID detection limits are ~ 1 ppm molar in inclusions and lower for unsaturated hydrocarbons (e.g., ~0.2 ppm for C 2H 4; ~ 1 ppb for C 2H 2; ~0.3 ppb for C 3H 6). Precisions (1σ) are ~ ±1-2% and ~ ± 13% for H 2O in terms of total moles detected; the latter value is equivalent to ±0.6 mol% at the 95 mol% H 2O level. Major fluid inclusion volatile species have been successfully analysed on a ~50 mg fluid inclusion section chip (~7 mm × ~10 mm × ~100 μm). Initial inclusion volatile analyses of fluids of interpreted magmatic origin from the Cretaceous Boss Mtn. monzogranite stock-related MoS 2 deposit, central British Columbia of ~97 mol% H 2O, ~3% CO 2, ~ 140-150 ppm N 2, and ~16-39 ppm CH 4 (~300-350°C) are reasonable in comparison with high temperature (~400-900°C) volcanic gas analyses from four, active calc-alkaline volcanoes; e.g., the H 2O contents of volcanic gases from the White Island (New Zealand), Mount St. Helens (Washington, USA), Merapi (Bali, Indonesia), and Momotombo (Nicaragua) volcanoes are 88-95%, >90% (often >95%), 88-95% and ~93%, respectively; CO 2 contents are ~3-10%, 1-10%, 3-8%, and ~3.5%. CO 2/N 2 ratios for the Boss Mtn. MoS 2 fluids of ~ 190-220 are in the range for known volcanic gas ratios (e.g., ~ 150- 240; White Island). The ∑S content of the Boss Mtn. MoS 2 fluid prior to S loss by sulphide precipitation may have been ~2 mol% since CO 2/∑S molar ratios of analysed high-temperature volcanic gases are ~ 1.5. This estimate is supported by ∑S contents for White Island, Merapi and Momotombo volcanic gases of ~2%, ~0.5-2.5%, and ~2%. COS has been determined in H 2O-CO 2 fluid inclusions of interpreted magmatic origin from the Boss Mtn. MoS 2 deposit and the Tanco zoned granitic pegmatite, S.E. Manitoba at ~50-100 ppm molar levels, which are consistent with levels in volcanic gases. It appears that low, but significant, concentrations of C 2-C 4 alkanes (~ 1-20 ppm), C 2-C 4 alkenes (~ 1-480 ppb) and alkynes (e.g., C 3H 4) have been detected in magmatically derived fluids (Boss Mtn. MoS 2 deposit; Tanco granitic pegmatite). Significantly higher, low molecular weight hydrocarbon concentrations have been determined in a CH 4-rich (~ 2%), externally derived fluid of possible metamorphic or deep crustal origin trapped as inclusions in metasomatic wall-rock tourmaline adjacent to the Tanco pegmatite (e.g., 300/470 ppm C 2H 6; 50/90 ppm C 3H 8; 3-60 ppm C 2H 4/C 3H 6 n-C 4H 10).

EDITORIAL: Special issue: CAMOP MOLEC XVI

NASA Astrophysics Data System (ADS)

Ascenzi, Daniela; Franceschi, Pietro; Tosi, Paolo

2007-09-01

In this special issue of CAMOP/Physica Scripta we would like to present a picture of the state-of-the-art in the field of the dynamics of molecular systems. It contains a collection of papers submitted in association with the most recent MOLEC meeting (MOLEC XVI), which was held in September 2006 in Levico Terme (Italy) to celebrate the 30th anniversary of the MOLEC conference series. The series of biennial European Conferences on the Dynamics of Molecular Systems (MOLEC) started in 1976, when the first meeting was held in Trento (Italy). Successive conferences were organized in Brandbjerg Højskole (Denmark, 1978), Oxford (UK, 1980), Nijmegen (The Netherlands, 1982), Jerusalem (Israel, 1984), Aussois (France, 1986), Assisi (Italy, 1988), Bernkastel-Kues (Germany, 1990), Prague (Czech Republic, 1992), Salamanca (Spain, 1994), Nyborg Strand (Denmark, 1996), Bristol (UK, 1998), Jerusalem (Israel, 2000), Istanbul (Turkey, 2002) and Nunspeet (The Netherlands, 2004). This is the second time that Physica Scripta has hosted a special issue dedicated to MOLEC. The previous issue ( Physica Scripta (2006) 73 C1-C89) was edited by Steven Stolte and Harold Linnartz following the MOLEC 2004 conference. Following the philosophy of CAMOP, we have asked invited speakers to summarize important problems in their research area, with the objective of setting forth the current thinking of leading researchers in atomic, molecular and optical physics. This comprises discussions of open questions, important new applications, new theoretical and experimental approaches and also predictions of where the field is heading. In addition to being authoritative contributions of acknowledged experts, we hope that the papers also appeal to non-specialists as each work contains a clear and broad introduction and references to the accessible literature. The present special issue comprises 17 papers, which are arranged according to the following topics: theoretical and experimental studies of molecular collisions and chemically reactive systems (papers by Toennies, Cavalli et al, Varandas, Nyman, Allan et al, Liu et al, Boxford et al); cooling and alignment of molecular systems (papers by Kumarappan et al, van de Meerakker et al); photon-matter interactions, spectroscopy and photodissociation (papers by Fárník and Buck, Golan et al, Borghesani et al, Coreno et al); theory of complex systems (papers by Villarreal et al, Bodo et al, Yurtsever and Calvo). The final contribution concerns the dynamics of systems of biological relevance (paper by Denicke et al). The paper by Toennies, one of the founding fathers of the MOLEC conference and winner of the MOLEC award in 1996, presents a comprehensive account of the experimental developments in the field of low energy collisions over the last 30 years, and provides a short outlook on how the most recent cooling and ultra cooling techniques (helium droplets and electro-magnetic laser traps) could open up new perspectives in the field of chemical reaction dynamics. Cavalli et al present a theoretical interpretation of overlapping resonances in the reactive cross section for the benchmark reaction F + H2→HF + H, explained by the formation of a short-lived state located in the transition state region and of a van der Waals metastable state in the exit valley. The subject of accurate ab initio calculations for potential energy surfaces is addressed by Varandas in a paper describing suitable modelling strategies to obtain intermolecular potentials at near spectroscopic resolution. In the following paper, Nyman gives an overview of how thermal rate constants for polyatomic chemical reactions can be calculated from first principles: the reaction H2 + CH3→CH4 + H is used as an example and theoretical results are compared with experimental ones. The `uncharted territory' of collision dynamics at the gas-liquid interface is explored in the pioneering contribution by Allan et al, in which experimental results on the reactivity of O atoms with long chain liquid hydrocarbons are interpreted with the aid of molecular dynamics calculations. The contribution of Liu et al shifts towards the reactivity of charged systems, by presenting results of crossed beam experiments on the reaction dynamics of ethylene with OD+ and D2O+ ions. Boxford et al continue with an experimental and theoretical study of the systematics of multiply-charged anion fragmentation in dianion-cation contact ion pairs. The next two contributions present the latest findings in the field of cooling and alignment of molecular systems. Kumarappan et al provide an overview of adiabatic and non-adiabatic laser-induced alignment of linear and asymmetric top molecules. van de Meerakker and Meijer discuss the state-of-the-art of Stark deceleration of OH radicals and the prospects for future applications of such tools in scattering experiments are presented. The third section of this issue comprises spectroscopy and photodissociation studies. Fárník and Buck discuss the photodissociation of HBr molecules in three different cluster environments: pure hydrogen bonded (HBr)n clusters, large van der Waals bonded HBr.Arn and HBr.(H2O)n clusters. Differences in the photofragmentation of rovibrationally excited methylamine and propyne molecules are taken as an example by Golan et al to demonstrate the importance of vibrationally mediated photodissociation for understanding energy flows in molecular systems. A study of the IR luminescence in excited and weakly bound rare gas complexes is reported in the contribution by Borghesani et al. Coreno et al discuss the generation of core hole states by soft x-ray absorption of molecules by presenting results on the visible and UV fluorescence decay from H2O, NH3 and CH4 molecules following core electron excitation and by proposing a mechanism of molecular dissociation. The fourth section includes three theoretical contributions. In the first one, by Villarreal et al, the simulation of IR spectra of molecules solvated in atomic clusters is reviewed by presenting a method to obtain energies and wave functions for systems composed of a molecular impurity immersed in He clusters. Bodo et al continue with an application of variational and diffusion Monte Carlo calculation procedure to the `solvation' of molecular and atomic ions in small He clusters. Yurtsever and Calvo describe the influence of a central point defect on the structure of 2D clusters consisting of point charge particles that are confined by an isotropic trap. Finally, Denicke et al review the imaging technique of single-beam and multi-beam two-photon laser-scanning microscopy for biomedical research by showing applications to the study of cell metabolism via NADH imaging. We are grateful to all the authors who participated with their contributions to this issue. We thank Physica Scripta for providing us with a platform for the publication of the MOLEC special issue and we hope that such a recently established tradition will continue to bring to readers new insights into the advances in the field of molecular dynamics.