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Sample records for pseudo-first-order reaction rate

  1. Pseudo-first-order reaction of chemically and biologically formed green rusts with HgII and C₁₅H₁₅N₃O₂: effects of pH and stabilizing agents (phosphate, silicate, polyacrylic acid, and bacterial cells).

    PubMed

    Remy, P-Ph; Etique, M; Hazotte, A A; Sergent, A-S; Estrade, N; Cloquet, C; Hanna, K; Jorand, F P A

    2015-03-01

    The kinetics of Hg(II) and methyl red (MR) reduction by hydroxycarbonate green rust (GR1) and by hydroxysulfate green rust (GR2) were studied in the presence of naturally occurring organic and inorganic ligands (phosphate, polyacrylic acid, bacterial cells, silicate). The reducing ability of biogenic hydroxycarbonate green rust (GR1bio), obtained after microbial reduction of lepidocrocite by Shewanella putrefaciens, was also investigated and compared to those of chemically synthesized GR1 and GR2 (GR1ab and GR2ab). Pseudo first-order rate constants (kobs) of Hg(II) reduction (at pH 7.0, 8.2, and 9.5) and MR reduction (at pH 7.0) were determined and were normalized to the structural Fe(II) content of GRs (kFeII) and to the estimated concentration of surface Fe(II) sites (kS). The kS values ranged from 0.3 L mmol(-1) min(-1) to 43 L mmol(-1) min(-1) for the Hg reduction, and from 0.007 L mmol(-1) min(-1) to 3.4 L mmol(-1) min(-1) for the MR reduction. No significant discrepancy between GRab and GRbio was observed in term of reactivity. However, the reduction kinetics of MR was generally slower than the Hg(II) reduction kinetics for all tested GRs. While a slight difference in Hg(II) reduction rate was noted whatever the pH values (7.0, 8.2, or 9.5), the reduction of MR was significantly affected in the presence of ligands. A decrease by a factor of 2-200, depending on the type of ligand used, was observed. These data give new insights into the reactivity of GRs in the presence of co-occurring organic and inorganic ligands, and have major implications in the characterization of contaminated systems as well as water treatment processes. PMID:25543237

  2. Increasing PCB Radiolysis Rates in Transformer Oil

    SciTech Connect

    Mincher, Bruce Jay

    2002-11-01

    The kinetics of Aroclor 1242 radiolysis in transformer oil, using high-energy electrons, was found to be analogous to that previously measured for individual polychlorinated biphenyl (PCB) congeners irradiated with -rays. The plot of the pseudo-first-order rate constant for PCB decomposition versus initial PCB concentration is a power function, with high rate constants for low concentrations. The addition of alkaline isopropanol to transformer oil was found to increase the pseudo-first-order rate constant for PCB decomposition. The rate constant under these conditions is independent of concentration. This may be explained by the establishment of chain reaction dechlorination in the oil.

  3. Absolute rate constant of the reaction between chlorine /2P/ atoms and hydrogen peroxide from 298 to 424 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1980-01-01

    The absolute rate constant of the reaction between chlorine (2P) atoms and hydrogen peroxide was determined from 298 to 424 K, using the discharge flow resonance fluorescence technique. Pseudo-first-order conditions were used with hydrogen peroxide in large excess. A fast flow-sampling procedure limited hydrogen peroxide decomposition to less than 5% over the temperature range studied. At 298 K, the rate constant is (4.1 plus or minus 0.2) x 10 to the minus 13th cu cm/molecule-sec.

  4. Rate constant for formation of chlorine nitrate by the reaction ClO + NO2 + M

    NASA Technical Reports Server (NTRS)

    Leu, M. T.; Lin, C. L.; Demore, W. B.

    1977-01-01

    The pseudo-first-order decay of ClO in a large excess of NO2 was monitored in a discharge flow/mass-spectrometer apparatus in order to measure the rate constant of the reaction ClO + NO2 + M yields ClONO2 + M for M = He, Ar, and N2 over the temperature range from 248 to 417 K. Numerical results are given for He at 248, 299, 360, and 417 K (1 to 9 torr); for Ar at 298 K (1 to 4 torr); and for N2 at 299, 360, and 417 K (1 to 6 torr). Systematic errors are estimated, and identification of the reaction product is discussed. The results obtained are shown to be in excellent agreement with other recent measurements of the same rate constant.

  5. Faster rates with less catalyst in template-directed reactions

    NASA Technical Reports Server (NTRS)

    Kanavarioti, A.; Baird, E. E.

    1995-01-01

    We have recently shown that the polycytidylic acid-directed polymerization of guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG) is amenable to kinetic study and that rate determinations as a function of 2-MeImpG concentration can reveal much mechanistic detail (Kanavarioti et al. 1993). Here we report kinetic data which show that, once the reaction has been initiated by the formation of dimers, the elongation of dimers to form longer oligomers is accelerated by decreasing polycytidylate (poly(C)) concentration from 0.05 to 0.002 M. This result is consistent with the previously proposed mechanism. The increase in the observed pseudo-first order rate constant for formation of the trimer, k3', and the corresponding constant for formation of oligomers longer than the trimer, ki' (ki' is independent of oligomer length for i > or = 4), with decreasing template concentration for a given monomer concentration is attributed to an increase in template occupancy as template concentration is reduced.

  6. Reaction kinetics of resveratrol with tert-butoxyl radicals

    NASA Astrophysics Data System (ADS)

    Džeba, Iva; Pedzinski, Tomasz; Mihaljević, Branka

    2012-09-01

    The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5×108 M-1s-1. This high value indicates the high reactivity consistent with the strong antioxidant activity of resveratrol.

  7. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it

  8. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

  9. Rate Constant for the OH + CO Reaction at Low Temperatures.

    PubMed

    Liu, Yingdi; Sander, Stanley P

    2015-10-01

    Rate constants for the reaction of OH + CO → products (1) have been measured using laser photolysis/laser-induced fluorescence (LP/LIF) over the temperature range 193–296 K and at pressures of 50–700 Torr of Ar and N2. The reaction was studied under pseudo-first-order conditions, monitoring the decay of OH in the presence of a large excess of CO. The rate constants can be expressed as a combination of bimolecular and termolecular components. The bimolecular component was found to be temperature-independent with an expression given by kbi(T) = (1.54 ± 0.14) × 10(–13)[e(–(13±17)/T)] cm(3) molecule(–1) s(–1), with an error of one standard deviation. The termolecular component was fitted to the expression, kter = k0(T)[M]/[1 + (k0(T)[M]/k∞(T)] × 0.6({1+[log10(k0(T)[M]/k∞(T))]2}−1) where k0(T) = k0(300)(T/300)(−n) and k∞(T) = k∞(300)(T/300)(−m). The parameters for k0(T) were determined to be k0(300) = (6.0±0.5) × 10(−33) cm(6) molecule(–2) s(–1) in N2 and k0(300) = (3.4 ± 0.3) × 10(–33) cm(6) molecule(–2) s(–1) in Ar, with n = 1.9±0.5 and 2.0±0.4 in N2 and Ar, respectively. These parameters were determined using k0(T) and m from the NASA kinetics data evaluation (JPL Publication No. 10-6) since the experimental pressure range was far from the high-pressure limit. Addition of low concentrations of O2 had no discernible effect on the mechanism of the OH + CO reaction but resulted in secondary reactions which regenerated OH. PMID:26305192

  10. Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

    NASA Technical Reports Server (NTRS)

    Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

    1984-01-01

    The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

  11. Rate Coefficients for the OH + (CHO)2 (Glyoxal) Reaction Between 240 and 400 K

    NASA Astrophysics Data System (ADS)

    Feierabend, K. J.; Talukdar, R. K.; Zhu, L.; Ravishankara, A. R.; Burkholder, J. B.

    2006-12-01

    Glyoxal (CHO)2, the simplest dialdehyde, is an end product formed in the atmospheric oxidation of biogenic hydrocarbons, for example, isoprene. As such, glyoxal plays a role in regional air quality and ozone production in certain locations. Glyoxal is lost in the atmosphere via UV photolysis and reaction with OH. However, the currently available rate coefficient data for the OH + glyoxal reaction is limited to a single room- temperature measurement made using the relative rate method. A determination of the rate coefficient temperature dependence is therefore needed for a more complete interpretation of the atmospheric processing of glyoxal. This study reports the rate coefficient for the OH + (CHO)2 reaction measured under pseudo- first-order conditions in OH ([(CHO)2] > 1000 [OH]0). OH radicals were produced using 248 nm pulsed laser photolysis of H2O2 or HNO3 and detected by pulsed laser induced fluorescence. The concentration of glyoxal in the reactor was determined using three independent techniques; gas flow rates as well as in situ UV and IR absorption. The total pressure in the reactor was varied from 40 to 300 Torr (He), and the rate coefficient was found to be independent of pressure over the temperature range studied. The rate coefficient exhibits a negative temperature dependence between 240 and 400 K consistent with the dependence previously observed for many other aldehydes. Our room-temperature rate coefficient is smaller than the relative rate value that is currently recommended for use in atmospheric model calculations. Our measured rate coefficients are discussed with respect to those for other aldehydes. The atmospheric implications of our work will also be discussed.

  12. Polychlorinated ethane reaction with zero-valent zinc: pathways and rate control

    NASA Astrophysics Data System (ADS)

    Arnold, William A.; Ball, William P.; Roberts, A. Lynn

    1999-12-01

    Efficient design of zero-valent metal permeable `barriers' for the reduction of organohalides requires information regarding the pertinent reaction rates as well as an understanding of the resultant distribution of products. In this study, the pathways and kinetics for reaction of polychlorinated ethanes with Zn(0) have been examined in batch reactors. Reductive β-elimination was the only route through which hexachloroethane (HCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA) and 1,2-dichloroethane (1,2-DCA) reacted. Pentachloroethane (PCA) reacted via concurrent reductive β-elimination (93%) and hydrolysis (7%). As previously demonstrated, 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA) reacted predominantly via reductive α-elimination. Attempts to correlate BET surface area-normalized rate constants ( kSA-BET) with one-electron reduction potential ( E1) met with limited success, as HCA, PCA, 1,1,1,2-TeCA, and 1,1,1-TCA reacted at nearly identical rates despite substantial differences in E1 values. Comparison of the pseudo-first-order rate constants ( kobs) for these species with rate constants ( kLa) obtained from a correlation for mass transfer to suspended particles revealed that the reaction of these species was mass transfer limited even though reaction rates were unaffected by mixing speed. Calculations suggest that mass transfer limitations may also play a role in the design of treatment systems for highly reactive species, with overall rate constants predicted to increase with flow velocity.

  13. Reaction rate constants of H-abstraction by OH from large ketones: measurements and site-specific rate rules.

    PubMed

    Badra, Jihad; Elwardany, Ahmed E; Farooq, Aamir

    2014-06-28

    Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (C=O) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (C=O), and the prime is used to differentiate different neighboring environments of a methylene group): PMID:24817270

  14. What Is a Reaction Rate?

    ERIC Educational Resources Information Center

    Schmitz, Guy

    2005-01-01

    The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

  15. Direct measurements of the rate constants of the reactions NCN + NO and NCN + NO2 behind shock waves.

    PubMed

    Dammeier, J; Friedrichs, G

    2011-12-22

    The high-temperature rate constants of the reactions NCN + NO and NCN + NO(2) have been directly measured behind shock waves under pseudo-first-order conditions. NCN has been generated by the pyrolysis of cyanogen azide (NCN(3)) and quantitatively detected by sensitive difference amplification laser absorption spectroscopy at a wavelength of 329.1302 nm. The NCN(3) decomposition initially yields electronically excited (1)NCN radicals, which are subsequently transformed to the triplet ground state by collision-induced intersystem crossing (CIISC). CIISC efficiencies were found to increase in the order of Ar < NO(2) < NO as the collision gases. The rate constants of the NCN + NO/NO(2) reactions can be expressed as k(NCN+NO)/(cm(3) mol(-1)s(-1)) = 1.9 10(12) exp[-26.3 (kJ/mol)/RT] (7%,?E(a) = 1.6 kJ/mol, 764 K < T < 1944 K) and k(NCN+NO(2))/(cm(3) mol(-1)s(-1)) = 4.7 10(12) exp[-38.0(kJ/mol)/RT] (19%,?E(a) = 3.8 kJ/mol, 704 K < T < 1659 K). In striking contrast to reported low-temperature measurements, which are dominated by recombination processes, both reaction rates show a positive temperature dependence and are independent of the total density (1.7 10(-6) mol/cm(3) < ? < 7.6 10(-6) mol/cm(3)). For both reactions, the minima of the total rate constants occur at temperatures below 700 K, showing that, at combustion-relevant temperatures, the overall reactions are dominated by direct or indirect abstraction pathways according to NCN + NO ? CN + N(2)O and NCN + NO(2) ? NCNO + NO. PMID:22066522

  16. The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

    NASA Technical Reports Server (NTRS)

    Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

    2004-01-01

    The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

  17. QSARS FOR PREDICTING REDUCTIVE TRANSFORMATION RATE CONSTANTS OF HALOGENATED AROMATIC HYDROCARBONS IN ANOXIC SEDIMENT SYSTEMS

    EPA Science Inventory

    Quantitative structure-activity relationships (QSARs) are developed relating initial and final pseudo-first-order disappearance rate constants of 45 halogenated aromatic hydrocarbons in anoxic sediments to four readily available molecular descriptors: the carbon-halogen bond stre...

  18. Kinetics of some reactions of atmospheric interest: hydrolysis of carbonyl sulfide, and reaction rates of thermal chlorine atoms with carbonyl sulfide, methanol, hydrogen sulfide, and methyl chloride

    SciTech Connect

    Lu, E.C.C.

    1987-01-01

    The hydrolysis appeared pseudo first order in OCS and showed a rate constant of (1.04 /times/ 10/sup 11/) exp(/minus/10800/T) sec /sup /minus/1/. The hydrolysis of OCS can be increased in rate by the presence of OH/sup /minus// concentration and showed a bimolecular rate constant of (8.12 /times/ 10/sup 9/) exp(/minus/6040/T) 1 mole/sup /minus/1/ sec /sup /minus/1/. The rate corresponds to a lifetime for dissolved OCS of 1.7 days. A two-layer diffusion model with accurate Henry's Law constant and hydrolysis rate constant can obtain air-sea exchange flux. The lifetime for transport of OCS from the troposphere to the ocean with respect to this flux is about 12 years. The ocean is most likely a net source of OCS rather than a sink, but hydrolysis of OCS still occurs in the ocean. The relative rate constants for the gas phase reactions of thermal chlorine atoms have been measured with H/sub 2/S, CH/sub 3/OH, C/sub 2/H/sub 6/, and CH/sub 2/ = CHBr over the temperature range from 232 to 359 K. These data for Cl atoms reaction with H/sub 2/S at a pressure of 4000 Torr of CClF/sub 3/ are consistent with a temperature-dependent rate constant of (10.5 /+-/ 0.4) /times/ 10/sup /minus/11/ cm/sup 3/ molecule/sup /minus/1/ sec/sup /minus/1/. The absolute rate constant for Cl atoms reaction with CH/sub 3/OH is determined to be (9.14 /+-/ 1.02) /times/ 10/sup /minus/11/ cm/sup 3/ molecule/sup /minus/1/ sec/sup /minus/1/ at temperature 295 K. We have carried out a series of competitive runs of OCS with CH/sub 2/ = CHBr and trans-2,3-DCHF-2B. The results of these runs do not indicate any rapid removal of /sup 38/Cl through reaction with OCS with or without the presence of O/sub 2/. An upper limit of 1 /times/ 10/sup /minus/15/ cm/sup 3/ molecule/sup /minus/1/ sec/sup /minus/1/ for the reaction of /sup 38/Cl with OCS.

  19. QSARS FOR PREDICTING BIOTIC AND ABIOTIC REDUCTIVE TRANSFORMATION RATE CONSTANTS OF HALOGENATED HYDROCARBONS IN ANOXIC SEDIMENT SYSTEMS

    EPA Science Inventory

    Quantitative structure-activity relationships (QSARs) are developed relating biotic and abiotic pseudo-first-order disappearance rate constants of halogenated hydrocarbons in anoxic sediments to a number of readily available molecular descriptors. ased upon knowledge of the under...

  20. Bimolecular rate constant and product branching ratio measurements for the reaction of C2H with ethene and propene at 79 K.

    PubMed

    Bouwman, Jordy; Goulay, Fabien; Leone, Stephen R; Wilson, Kevin R

    2012-04-19

    The reactions of the ethynyl radical (C(2)H) with ethene (C(2)H(4)) and propene (C(3)H(6)) are studied under low temperature conditions (79 K) in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by 193 nm photolysis of acetylene (C(2)H(2)) and the reactions are studied in nitrogen as a carrier gas. Reaction products are sampled and subsequently photoionized by the tunable vacuum ultraviolet radiation of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The product ions are detected mass selectively and time-resolved by a quadrupole mass spectrometer. Bimolecular rate coefficients are determined under pseudo-first-order conditions, yielding values in good agreement with previous measurements. Photoionization spectra are measured by scanning the ALS photon energy while detecting the ionized reaction products. Analysis of the photoionization spectra yields-for the first time-low temperature isomer resolved product branching ratios. The reaction between C(2)H and ethene is found to proceed by H-loss and yields 100% vinylacetylene. The reaction between C(2)H and propene results in (85 10)% C(4)H(4) (m/z = 52) via CH(3)-loss and (15 10)% C(5)H(6) (m/z = 66) by H-loss. The C(4)H(4) channel is found to consist of 100% vinylacetylene. For the C(5)H(6) channel, analysis of the photoionization spectrum reveals that (62 16)% is in the form of 4-penten-1-yne, (27 8)% is in the form of cis- and trans-3-penten-1-yne and (11 10)% is in the form of 2-methyl-1-buten-3-yne. PMID:22429068

  1. Method of controlling fusion reaction rates

    DOEpatents

    Kulsrud, Russell M.; Furth, Harold P.; Valeo, Ernest J.; Goldhaber, Maurice

    1988-01-01

    A method of controlling the reaction rates of the fuel atoms in a fusion reactor comprises the step of polarizing the nuclei of the fuel atoms in a particular direction relative to the plasma confining magnetic field. Fusion reaction rates can be increased or decreased, and the direction of emission of the reaction products can be controlled, depending on the choice of polarization direction.

  2. Reaction rate and isomer-specific product branching ratios of C2H + C4H8: 1-butene, cis-2-butene, trans-2-butene, and isobutene at 79 K.

    PubMed

    Bouwman, Jordy; Fournier, Martin; Sims, Ian R; Leone, Stephen R; Wilson, Kevin R

    2013-06-20

    The reactions of C2H radicals with C4H8 isomers 1-butene, cis-2-butene, trans-2-butene, and isobutene are studied by laser photolysis-vacuum ultraviolet mass spectrometry in a Laval nozzle expansion at 79 K. Bimolecular-reaction rate constants are obtained by measuring the formation rate of the reaction product species as a function of the reactant density under pseudo-first-order conditions. The rate constants are (1.9 0.5) 10(-10), (1.7 0.5) 10(-10), (2.1 0.7) 10(-10), and (1.8 0.9) 10(-10) cm(3) s(-1) for the reaction of C2H with 1-butene, cis-2-butene, trans-2-butene, and isobutene, respectively. Bimolecular rate constants for 1-butene and isobutene compare well to values measured previously at 103 K using C2H chemiluminescence. Photoionization spectra of the reaction products are measured and fitted to ionization spectra of the contributing isomers. In conjunction with absolute-ionization cross sections, these fits provide isomer-resolved product branching fractions. The reaction between C2H and 1-butene yields (65 10)% C4H4 in the form of vinylacetylene and (35 10)% C5H6 in the form of 4-penten-1-yne. The cis-2-butene and trans-2-butene reactions yield solely 3-penten-1-yne, and no discrimination is made between cis- and trans-3-penten-1-yne. Last, the isobutene reaction yields (26 15)% 3-penten-1-yne, (35 15)% 2-methyl-1-buten-3-yne, and (39 15)% 4-methyl-3-penten-1-yne. The branching fractions reported for the C2H and butene reactions indicate that these reactions preferentially proceed via CH3 or C2H3 elimination rather than H-atom elimination. Within the experimental uncertainties, no evidence is found for the formation of cyclic species. PMID:23701666

  3. Reaction Order Ambiguity in Integrated Rate Plots

    ERIC Educational Resources Information Center

    Lee, Joe

    2008-01-01

    Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical

  4. Reaction Order Ambiguity in Integrated Rate Plots

    ERIC Educational Resources Information Center

    Lee, Joe

    2008-01-01

    Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical…

  5. pH & Rate of Enzymatic Reactions.

    ERIC Educational Resources Information Center

    Clariana, Roy B.

    1991-01-01

    A quantitative and inexpensive way to measure the rate of enzymatic reaction is provided. The effects of different pH levels on the reaction rate of an enzyme from yeast are investigated and the results graphed. Background information, a list of needed materials, directions for preparing solutions, procedure, and results and discussion are…

  6. Effective reaction rates for diffusion-limited reaction cycles.

    PubMed

    Nałęcz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miękisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%. PMID:26646890

  7. Effective reaction rates for diffusion-limited reaction cycles

    NASA Astrophysics Data System (ADS)

    Nałecz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%.

  8. Kinetic and products study of the gas-phase reaction of Lewisite with ozone under atmospheric conditions.

    PubMed

    Wang, Haitao; Zhang, Yuanpeng; Guo, Xiaodi; Shao, Yusheng; Gao, Runli; Liang, Dejian; Sun, Hao

    2016-02-01

    The rate constant for the gas-phase reaction of O3 and Lewisite was studied in air using the smog chamber technique. The experiments were carried out under pseudo-first-order reaction conditions with [O3]≪[Lewisite]. The observed rate constant of O3 with Lewisite was (7.83±0.38)×10(-19)cm(3)/(molecule·sec) at 298±2K. Lewisite was discussed in terms of reactivity with O3 and its relationship with the ionization potential. Our results show that the rate constant for the gas-phase reaction of O3 with Lewisite is in line with the trend of the rate constants of O3 with haloalkenes. PMID:26969539

  9. Astrophysical Reaction Rates Obtained By Indirect Techniques

    SciTech Connect

    Tribble, R. E.; Al-Abdullah, T.; Alharbi, A.; Banu, A.; Chen, X.; Clark, H. L.; Fu, C.; Gagliardi, C. A.; Hardy, J. C.; Iacob, V. E.; Lui, Y.-W.; McCleskey, M.; Mukhamedzhanov, A.; Nica, N.; Park, H. I.; Roeder, B.; Simmons, E.; Tabacaru, G.; Tokimoto, Y.; Trache, L.

    2010-08-12

    Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short-lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T-REX are discussed.

  10. The Kinetic Rate Law for Autocatalytic Reactions.

    ERIC Educational Resources Information Center

    Mata-Perez, Fernando; Perez-Benito, Joaquin F.

    1987-01-01

    Presented is a method of obtaining accurate rate constants for autocatalytic reactions. The autocatalytic oxidation of dimethylamine by permanganate ion in aqueous solution is used as an example. (RH)

  11. COMPUTERIZED EXTRAPOLATION OF HYDROLYSIS RATE DATA

    EPA Science Inventory

    The program RATE was developed to aid in the extrapolation and interpretation of hydrolysis rate data to a format that is useful for environmental risk assessment. ydrolysis data typically are reported in the literature as pseudo-first-order rate constants at the temperature and ...

  12. Critical reaction rates in hypersonic combustion chemistry

    SciTech Connect

    Oldenborg, R.C.; Harradine, D.M.; Loge, G.W.; Lyman, J.L.; Schott, G.L.; Winn, K.R.

    1989-01-01

    High Mach number flight requires that the scramjet propulsion system operate at a relatively low static inlet pressure and a high inlet temperature. These two constraints can lead to extremely high temperatures in the combustor, yielding high densities of radical species and correspondingly poor chemical combustion efficiency. As the temperature drops in the nozzle expansion, recombination of these excess radicals can produce more product species, higher heat yield, and potentially more thrust. The extent to which the chemical efficiency can be enhanced in the nozzle expansion depends directly on the rate of the radical recombination reactions. A comprehensive assessment of the important chemical processes and an experimental validation of the critical rate parameters is therefore required if accurate predictions of scramjet performance are to be obtained. This report covers the identification of critical reactions, and the critical reaction rates in hypersonic combustion chemistry. 4 refs., 2 figs.

  13. Reaction rates for mesoscopic reaction-diffusion kinetics

    PubMed Central

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2016-01-01

    The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results. PMID:25768640

  14. Reaction rates for mesoscopic reaction-diffusion kinetics

    NASA Astrophysics Data System (ADS)

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-01

    The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

  15. Rate equations of solid-catalyzed reactions

    SciTech Connect

    Mezaki, R.; Inoue, H.

    1991-01-01

    Rate Equations of Solid-Catalyzed Reactions, edited by Mezaki and Inoue, contains a comprehensive compilation of kinetic rate expressions for a large number of relevant catalytic reaction systems. Mezaki and Inoue should be commended for their effort. For the practicing catalytic engineer the book should serve as a quick reference guide for assessing the functional dependence of rate on various operating conditions for a catalytic reaction system of interest. Even in this age of computer-aid literature searches this book should reduce the typically large activation barrier and search time associated with locating kinetic rate expressions for a particular reaction system. It is a recommended reference book for all whom are involved in the business of catalytic reactions. However, its format is not amenable for teaching. The book is structured according to the reaction system type. Chapter (1) focuses on synthesis (e.g., of sulfur trioxide, ammonia, methanol), (2) on hydrogenations (e.g., of carbon monoxide, carbon dioxide, ethylene, cyclohexene), (3) on hydrogenolysis (of low molecular weight alkanes such as ethane and/or pentane), (4) on hydrocracking (of higher molecular weight components such as n-hexane and n-dodecane), (5) on dehydrogenation (e.g., of ethanol, ethane, cyclohexane), (6) on complete oxidation (e.g., of hydrogen, carbon monoxide, alkanes, and olefins), (7) on partial oxidation (e.g., of methanol, ethylene, xylenes, and ammonia), (8) on isomerization (e.g., of methane, ethane, and cyclohexane), (10) on decomposition of ammonia and nitric oxide, (11) on dehydration of various alcohols, (12) on cumene cracking, and (13) on other key reactions such as water-gas shift and nitric oxide reduction.

  16. Universal reaction rates for ultracold molecular collisions

    NASA Astrophysics Data System (ADS)

    Julienne, Paul; Idziaszek, Zbigniew

    2010-03-01

    We offer a simple yet general model of reactive collisions using a quantum defect framework based on the separation of the collision dynamics into long-range and a short-range parts [1]. Two dimensionless quantum defect parameters s and y are used to characterize the S-matrix for a given entrance channel; s represents a phase parameter and y the probability of short-range reaction. The simple analytic expressions we obtain give universal values for s-wave and p-wave collision rates for a van der Waals potential when y approaches unity. In this limit, reaction rates are governed entirely by the threshold laws governing the quantum transmission of the long range potential and depend only on the van der Waals coefficient. The universal rate constants explain the magnitude of the observed rate constants for reactive collisions of fermionic KRb + KRb or K + KRb [2]. In contrast, reaction rates will be non-universal and depend strongly on the phase parameter s if the short range reaction probability is low, y << 1. [1] Z. Idziaszek and P. S. Julienne, arXiv:0912.0370. [2] S. Ospelkaus, K.-K. Ni, D. Wang, M. H. G. de Miranda, B. Neyenhuis, G. Qu'em'ener, P. S. Julienne, J. L. Bohn, D. S. Jin, and J. Ye, arXiv:0912.3854.

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

    PubMed

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

    2015-07-16

    The gas-phase CH3CO + O2 reaction is known to proceed via a chemical activation mechanism leading to the formation of OH and CH3C(O)OO radicals via bimolecular and termolecular reactive channels, respectively. In this work, rate coefficients, k, for the CH3CO + O2 reaction were measured over a range of temperature (241-373 K) and pressure (0.009-600 Torr) with He and N2 as the bath gas and used to characterize the bi- and ter-molecular reaction channels. Three independent experimental methods (pulsed laser photolysis-laser-induced fluorescence (PLP-LIF), pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS), and a very low-pressure reactor (VLPR)) were used to characterize k(T,M). PLP-LIF was the primary method used to measure k(T,M) in the high-pressure regime under pseudo-first-order conditions. CH3CO was produced by PLP, and LIF was used to monitor the OH radical bimolecular channel reaction product. CRDS, a complementary high-pressure method, measured k(295 K,M) over the pressure range 25-600 Torr (He) by monitoring the temporal CH3CO radical absorption following its production via PLP in the presence of excess O2. The VLPR technique was used in a relative rate mode to measure k(296 K,M) in the low-pressure regime (9-32 mTorr) with CH3CO + Cl2 used as the reference reaction. A kinetic mechanism analysis of the combined kinetic data set yielded a zero pressure limit rate coefficient, kint(T), of (6.4 4) 10(-14) exp((820 150)/T) cm(3) molecule(-1) s(-1) (with kint(296 K) measured to be (9.94 1.3) 10(-13) cm(3) molecule(-1) s(-1)), k0(T) = (7.39 0.3) 10(-30) (T/300)(-2.20.3) cm(6) molecule(-2) s(-1), and k?(T) = (4.88 0.05) 10(-12) (T/300)(-0.850.07) cm(3) molecule(-1) s(-1) with Fc = 0.8 and M = N2. A He/N2 collision efficiency ratio of 0.60 0.05 was determined. The phenomenological kinetic results were used to define the pressure and temperature dependence of the OH radical yield in the CH3CO + O2 reaction. The present results are compared with results from previous studies and the discrepancies are discussed. PMID:25803714

  18. The rate constant of the reaction NCN + H2 and its role in NCN and NO modeling in low pressure CH4/O2/N2-flames.

    PubMed

    Faßheber, Nancy; Lamoureux, Nathalie; Friedrichs, Gernot

    2015-06-28

    Bimolecular reactions of the NCN radical play a key role in modeling prompt-NO formation in hydrocarbon flames. The rate constant of the so-far neglected reaction NCN + H2 has been experimentally determined behind shock waves under pseudo-first order conditions with H2 as the excess component. NCN3 thermal decomposition has been used as a quantitative high temperature source of NCN radicals, which have been sensitively detected by difference UV laser absorption spectroscopy at [small nu, Greek, tilde] = 30383.11 cm(-1). The experiments were performed at two different total densities of ρ≈ 4.1 × 10(-6) mol cm(-3) and ρ≈ 7.4 × 10(-6) mol cm(-3) (corresponding to pressures between p = 324 mbar and p = 1665 mbar) and revealed a pressure independent reaction. In the temperature range 1057 K < T < 2475 K, the overall rate constant can be represented by the Arrhenius expression k/(cm(3) mol(-1) s(-1)) = 4.1 × 10(13) exp(-101 kJ mol(-1)/RT) (Δlog k = ±0.11). The pressure independent reaction as well as the measured activation energy is consistent with a dominating H abstracting reaction channel yielding the products HNCN + H. The reaction NCN + H2 has been implemented together with a set of reactions for subsequent HNCN and HNC chemistry into the detailed GDFkin3.0_NCN mechanism for NOx flame modeling. Two fuel-rich low-pressure CH4/O2/N2-flames served as examples to quantify the impact of the additional chemical pathways. Although the overall NCN consumption by H2 remains small, significant differences have been observed for NO yields with the updated mechanism. A detailed flux analysis revealed that HNC, mainly arising from HCN/HNC isomerization, plays a decisive role and enhances NO formation through a new HNC → HNCO → NH2→ NH → NO pathway. PMID:26017854

  19. Reaction rates for a generalized reaction-diffusion master equation

    PubMed Central

    Hellander, Stefan; Petzold, Linda

    2016-01-01

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model, and show in two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is on the order of the reaction radius of a reacting pair of molecules. PMID:26871190

  20. Dehalogenation pathway and rate of chlorinated aromatic compounds in anaerobic sediment

    SciTech Connect

    Masunaga, S.; Nakanishi, J.; Susarla, S.; Yonezawa, Y.

    1995-12-31

    Biodegradation of about 70 haloaromatic compounds were studied in anaerobic sediment. The sediment was collected at the mouth of Tsurumi River that flows into Tokyo Bay. The place is fairly contaminated as the river receives effluent from various industries. Relative rate of degradation among different class of compounds were: chlorophenol > chlorobenzenes > chloroanilines > chlorinated pesticides. Various dehalogenated compounds were detected as intermediates, indicating that most of the biodegradation was due to dehalogenation. For polyhalogenated aromatics, the major and minor dehalogenation pathways were observed. The major pathways could be estimated from the redox potential of the reaction for chlorobenzenes and chloroanilines, but not for chlorophenols. The pseudo-first order reaction rate constant of each compounds was calculated and analyzed by quantitative structure-activity analysis.

  1. Oxidative degradation of decabromodiphenyl ether (BDE 209) by potassium permanganate: reaction pathways, kinetics, and mechanisms assisted by density functional theory calculations.

    PubMed

    Shi, Jiaqi; Qu, Ruijuan; Feng, Mingbao; Wang, Xinghao; Wang, Liansheng; Yang, Shaogui; Wang, Zunyao

    2015-04-01

    This study found that decabromodiphenyl ether (BDE 209) could be oxidized effectively by potassium permanganate (KMnO4) in sulfuric acid medium. A total of 15 intermediate oxidative products were detected. The reaction pathways were proposed, which primarily included cleavage of the ether bond to form pentabromophenol. Direct oxidation on the benzene ring also played an important role because hydroxylated polybrominated diphenyl ethers (PBDEs) were produced during the oxidation process. The degradation occurred dramatically in the first few minutes and fitted pseudo-first-order kinetics. Increasing the water content decelerated the reaction rate, whereas increasing the temperature facilitated the reaction. In addition, density functional theory (DFT) was employed to determine the frontier molecular orbital (FMO) and frontier electron density (FED) of BDE 209 and the oxidative products. The theoretical calculation results confirmed the proposed reaction pathways. PMID:25751737

  2. Kinetics of the reaction O + HO2 yields OH + O2 from 229 to 372 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1982-01-01

    The discharge-flow resonance fluorescence technique has been used to obtain absolute rate data for the O + HO2 reaction from 229 to 372 K at a total pressure of 1 torr. Pseudo-first-order conditions were used with HO2 concentrations in large excess over initial atomic oxygen in order to minimize interference from secondary reactions. The results are independent of the method used to generate HO2 and atomic oxygen. At 299 K, the result is (6.1 + or - 0.4) x 10 to the -11th cu cm/molecule s. The temperature dependence expressed in Arrhenius form is (3.1 + or - 0.3) x 10 to the -11th exp/(+200 + or - 28)/T/. The error limits given are twice the standard deviation; overall experimental error is estimated to be + or - 25%.

  3. Rates of elementary reactions - Measurement and applications

    NASA Technical Reports Server (NTRS)

    Kaufman, F.

    1985-01-01

    Techniques used for characterizing elementary chemical reaction kinetics are explored. Flash- or laser-photolysis (FP) involves producing reactive species on the psec time scale and monitoring the changes spectroscopically. In the discharge flow (DF) method, reactive species are produced continuously in a flow of an inert gas containing the reactants. FP avoids surface and transport effects, while DF allows several reactions to be studied in different regions of one flow. Transport and surface boundary layer models are defined for DF calculations and sample calculations are carried out to illustrate the difficulties inherent in theoretically defining the rate constants for elementary reactions. Applications of the models thus far derived in atmospheric science and combustion studies are discussed.

  4. Kinetics study of the Cl/2P/ + Cl2O yields Cl2 + ClO reaction at 298 K

    NASA Technical Reports Server (NTRS)

    Ray, G. W.; Keyser, L. F.; Watson, R. T.

    1980-01-01

    The kinetics of the Cl + Cl2O reaction, a possible source of ClO(2 Pi) radicals for atmospheric photochemical studies, are investigated at 298 K. The discharge flow/mass spectrometry and discharge flow/resonance fluorescence techniques were used to monitor the decay of C12O in the presence of excess concentrations of atomic chlorine and chlorine monoxide, respectively. The pseudo-first order rate constants obtained from both experiments are found to be in excellent agreement, averaging 9.8 + or - 0.8 x 10 to the -11th cu cm/molecule per sec. Results are consistent with the lower limit obtained by Edgecombe et al. (1957) but differ by a factor of 150 from those of Basco and Dogra (1971). The present value is also noted to be consistent with a lower value for the rate constant of the reaction of oxygen atoms with Cl2O.

  5. Quantum theory of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1994-10-01

    If one wishes to describe a chemical reaction at the most detailed level possible, i.e., its state-to-state differential scattering cross section, then it is necessary to solve the Schroedinger equation to obtain the S-matrix as a function of total energy E and total angular momentum J, in terms of which the cross sections can be calculated as given by equation (1) in the paper. All other physically observable attributes of the reaction can be derived from the cross sections. Often, in fact, one is primarily interested in the least detailed quantity which characterizes the reaction, namely its thermal rate constant, which is obtained by integrating Eq. (1) over all scattering angles, summing over all product quantum states, and Boltzmann-averaging over all initial quantum states of reactants. With the proper weighting factors, all of these averages are conveniently contained in the cumulative reaction probability (CRP), which is defined by equation (2) and in terms of which the thermal rate constant is given by equation (3). Thus, having carried out a full state-to-state scattering calculation to obtain the S-matrix, one can obtain the CRP from Eq. (2), and then rate constant from Eq. (3), but this seems like ``overkill``; i.e., if one only wants the rate constant, it would clearly be desirable to have a theory that allows one to calculate it, or the CRP, more directly than via Eq. (2), yet also correctly, i.e., without inherent approximations. Such a theory is the subject of this paper.

  6. Pycnonuclear reaction rates for binary ionic mixtures

    NASA Technical Reports Server (NTRS)

    Ichimaru, S.; Ogata, S.; Van Horn, H. M.

    1992-01-01

    Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

  7. Maillard reaction rate in various glassy matrices.

    PubMed

    Kawai, Kiyoshi; Hagiwara, Tomoaki; Takai, Rikuo; Suzuki, Toru

    2004-11-01

    The Maillard Reaction (MR) rate below the glass transition temperature (T(g)) for various model glassy food systems was studied at temperatures between 40 degrees C and 70 degrees C. As a sample, freeze-dried glucose and lysine systems embedded in various glassy matrices (e.g., polyvinylpyrrolodone and trehalose) were used, and the MR rate below the T(g) was compared among the various glassy matrices. The extent of MR was estimated spectrophotometrically from the optical density at 280 nm (OD(280)), and the MR rate (k(280)) was determined as a pseudo zero order reaction rate from the time course of OD(280). Although k(280) was described by the Arrhenius plot, the temperature dependence of k(280) was almost the same and the intercept was different among the matrices. From the comparison of k(280), it was suggested that the MR rate in glassy matrix was affected not only by the T(g), but also by the hydrogen bonding between MR reactants and glassy matrix. PMID:15564666

  8. Rate coefficient for the reaction N + NO

    SciTech Connect

    Fox, J.L.

    1994-04-01

    Evidence has been advanced that the rate coefficient for the reaction N + NO {yields} N{sub 2} + O has a small positive temperature dependence at the high temperatures (900-1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch, and at the low temperatures (100-200 K) of the Martian lower thermosphere by Fox. Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation is accurate at 300 K, the authors derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits the Viking 1 measured NO densities. They find that the fit is acceptable for a rate coefficient of about 1.3 x 10{sup {minus}10}(T/300){sup 0.5}exp({minus}400/T) and better for a value of about 2.5 x 10{sup {minus}10}(T/300){sup 0.5}exp({minus}600/T) cm{sup 3}s{sup {minus}1}. 16 refs., 3 figs.

  9. Rate coefficient for the reaction N + NO

    NASA Astrophysics Data System (ADS)

    Fox, J. L.

    1994-04-01

    Evidence has been advanced that the rate coefficient for the reaction N + NO right arrow N2 + O has a small positive temperature dependence at the high temperatures (900 to 1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100 to 200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits the Viking 1 measured NO densities. We find that the fit is acceptable for a rate coefficient of about 1.3 x 10(exp -10)(T/300)(exp 0.5)exp(-400/T) and better for a value of about 2.5 x 10(exp -10)(T/300)(exp 0.5)exp(-600/T)cu cm/s.

  10. Rate coefficient for the reaction N + NO

    NASA Technical Reports Server (NTRS)

    Fox, J. L.

    1994-01-01

    Evidence has been advanced that the rate coefficient for the reaction N + NO right arrow N2 + O has a small positive temperature dependence at the high temperatures (900 to 1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100 to 200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits the Viking 1 measured NO densities. We find that the fit is acceptable for a rate coefficient of about 1.3 x 10(exp -10)(T/300)(exp 0.5)exp(-400/T) and better for a value of about 2.5 x 10(exp -10)(T/300)(exp 0.5)exp(-600/T)cu cm/s.

  11. Mechanisms and rates of plagioclase carbonation reactions

    NASA Astrophysics Data System (ADS)

    Munz, I. A.; Brandvoll, Ø.; Haug, T. A.; Iden, K.; Smeets, R.; Kihle, J.; Johansen, H.

    2012-01-01

    Plagioclase is one of the most abundant sources of calcium in the earth’s crust, and it may play an important role for CO2 storage. This study address’ the carbonation of anorthite-rich plagioclase (An67-An73) in a system with fluid transport, and under stagnant conditions. A combined approach of flow-through column and batch experiments has been used. Experimental conditions ranging from 100 to 250 °C and 20 to 120 bar and different preparations of the starting material were applied. The overall carbonation reaction consists of plagioclase dissolution coupled to a number of precipitation reactions. The flow-through column experiments at 250 °C showed stoichiometric dissolution of the plagioclase. Al-hydroxide (“proto Al-hydroxide”) nucleated on the plagioclase as the first phase to precipitate. A secondary porosity developed between the shrinking plagioclase and the enclosing “proto Al-hydroxide”. Calcite, as the second phase to precipitate, filled the primary pore space. A reaction front was developed separating the zone at the inlet where all the plagioclase had dissolved and the less reacted outlet of the column. Redissolution of the calcite and formation of euhedral boehmite crystals occurred when a sufficient amount of plagioclase had dissolved. Clay minerals were not precipitated in the column experiments. Between 11% and 30% of the plagioclase was dissolved within 72-168 h of reaction. A much higher extent of plagioclase dissolution was observed in the high pressure experiments compared to the low pressure. However, a smaller share of the released Ca was trapped as calcite in the high pressure experiments. Both observations are consistent with a more rapid progression of the dissolution front at high pressure. The batch experiments showed conversion of the plagioclase to a mixture of Al-hydroxide, possibly gibbsite, clays and calcite. A range in conversion from below the detection limit to 91% was observed within reaction periods of 24-72 h. Crystallinity of the feldspar was the most important factor contributing to increased reaction rates. A general positive effect of increasing temperature on the conversion is observed for all materials, whereas pressure and the addition of CaCl2 did not have any effect. The carbonation of plagioclase at stagnant conditions is slow compared to olivine at temperatures around 200 °C. However, industrial operations involving high fluid flows of CO2-water mixtures induce gradients in pH or solute concentrations, which may lead to increased reaction rates and changes in porosity/permeability.

  12. Nuclear reaction rates and the nova outburst

    SciTech Connect

    Starrfield, S.G.; Iliadis, C.

    2000-10-01

    In this paper we examined the consequences of improving the nuclear reaction library on our simulations of TNRs on 1.25M, WD and 1.35M, WDS. We have found that the changes in the rates have affected the nucleosynthesis predictions of our calculations but not, to any great extent, the gross features. In addition, we have used a lower mass accretion rate than in our previous studies in order to accrete (and eject) more material. This has, as expected, caused the peak values of some important parameters to increase over our previous studies at the same WD mass. However, because some important reaction rates have declined in the new compilation this has not increased the abundances for nuclei above aluminum and, in fact, they have declined while the abundances of both {sup 26}Al and {sup 27}Al have increased at both WD masses. In contrast, the abundance of {sup 22}Na has declined at both WD masses over the values predicted in our earlier work. This has important implications with respect to predictions of the observability of novae with INTEGRAL.

  13. Fusion Reaction Rate in an Inhomogeneous Plasma

    SciTech Connect

    S. Son; N.J. Fisch

    2004-09-03

    The local fusion rate, obtained from the assumption that the distribution is a local Maxwellian, is inaccurate if mean-free-paths of fusing particles are not sufficiently small compared with the inhomogeneity length of the plasma. We calculate the first order correction of P0 in terms of the small spatial gradient and obtain a non-local modification of P(sub)0 in a shock region when the gradient is not small. Use is made of the fact that the fusion reaction cross section has a relatively sharp peak as a function of energy.

  14. Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory

    SciTech Connect

    Rauscher, T.

    2010-08-12

    The relevant energy ranges for stellar nuclear reactions are introduced. Low-energy compound direct reactions are discussed. Stellar modifications of the cross sections are presented. Implications for experiments are outlined.

  15. A simple reaction-rate model for turbulent diffusion flames

    NASA Technical Reports Server (NTRS)

    Bangert, L. H.

    1975-01-01

    A simple reaction rate model is proposed for turbulent diffusion flames in which the reaction rate is proportional to the turbulence mixing rate. The reaction rate is also dependent on the mean mass fraction and the mean square fluctuation of mass fraction of each reactant. Calculations are compared with experimental data and are generally successful in predicting the measured quantities.

  16. OH + (E)- and (Z)-1-chloro-3,3,3-trifluoropropene-1 (CF3CH?CHCl) reaction rate coefficients: stereoisomer-dependent reactivity.

    PubMed

    Gierczak, Tomasz; Baasandorj, M; Burkholder, James B

    2014-11-20

    Rate coefficients for the gas-phase reaction of the OH radical with (E)- and (Z)-CF3CH?CHCl (1-chloro-3,3,3-trifluoropropene-1, HFO-1233zd) (k1(T) and k2(T), respectively) were measured under pseudo-first-order conditions in OH over the temperature range 213-376 K. OH was produced by pulsed laser photolysis, and its temporal profile was measured using laser-induced fluorescence. The obtained rate coefficients were independent of pressure between 25 and 100 Torr (He, N2) with k1(296 K) = (3.76 0.35) 10(-13) cm(3) molecule(-1) s(-1) and k2(296 K) = (9.46 0.85) 10(-13) cm(3) molecule(-1) s(-1) (quoted uncertainties are 2? and include estimated systematic errors). k2(T) showed a weak non-Arrhenius behavior over this temperature range. The (E)- and (Z)- stereoisomer rate coefficients were found to have opposite temperature dependencies that are well represented by k1(T) = (1.14 0.15) 10(-12) exp[(-330 10)/T] cm(3) molecule(-1) s(-1) and k2(T) = (7.22 0.65) 10(-19) T(2) exp[(800 20)/T] cm(3) molecule(-1) s(-1). The present results are compared with a previous room temperature relative rate coefficient study of k1, and an explanation for the discrepancy is presented. CF3CHO, HC(O)Cl, and CF3CClO, were observed as stable end-products following the OH radical initiated degradation of (E)- and (Z)-CF3CH?CHCl in the presence of O2. In addition, chemically activated isomerization was also observed. Atmospheric local lifetimes of (E)- and (Z)-CF3CH?CHCl, due to OH reactive loss, were estimated to be ?34 and ?11 days, respectively. Infrared absorption spectra measured in this work were used to estimate radiative efficiencies and well-mixed global warming potentials of ?10 and ?3 for (E)- and (Z)-CF3CH?CHCl, respectively, on the 100-year time horizon. PMID:25333607

  17. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of

  18. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  19. A high-temperature photochemical kinetics study of the O + HCl reaction from 350 to 1,480 K

    SciTech Connect

    Mahmud, K.; Kim, Jongsung; Fontijn, A. )

    1990-04-05

    Rate coefficients for the O + HCl reaction have been measured by using two differently designed high-temperature photochemistry (HTP) reactors. Measurements were made under pseudo-first-order conditions, (O) {much lt} (HCl), at temperatures from 350 to 1,480 K and pressures from 100 to 613 Torr. Ground-state O atoms were generated by flash photolysis of O{sub 2} or CO{sub 2} and monitored by time-resolved atomic resonance fluorescence with pulse counting. Combining the present data with published measurements in the 350-720 K range yields k(T) = 5.6 {times} 10{sup {minus}21} T{sup 2.87} exp({minus}1,766 K/T)cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the 350-1,480 K range with a 2{sigma} confidence interval of 23%, which figure includes a liberal allowance for potential systematic errors.

  20. Modeling of DNA zipper reaction rates

    NASA Astrophysics Data System (ADS)

    Landon, Preston; Sanchez, Casey; Mo, Alexander; Lal, Ratnesh

    2012-02-01

    DNA zippers are a thermodynamically driven system consisting of three DNA oligonucleotides. Two of the strands are designed to create a small helix the third is designed to invade and separated the helix. A zipper system consisting of a normal strand (N), a weak strand (W), and an opening strand (O). N is made up of normal DNA bases, while W is engineered with inosine bases substituted for guanine. Inosine forms one less hydrogen bond with cytosine than guanine. By varying the number and order of inosine, W is engineered to provide less than natural bonding affinities to N in forming the [N:W] helix. When O is introduced (a natural complement of N), it competitively displaces W from [N:W] and forms [N:O]. DNA zippers have been used to create new DNA devices such as springs and tweezers and to create functionalized DNA origami structures. Currently, The basic principles and interactions of DNA zippers are not well understood. Here we will report the results on an investigation of several different DNA zipper constructs designed to aid in the creation of a mathematical prediction of the reaction rate for DNA zippers.

  1. Reaction rates and reaction rate constant conception. One-temperature case

    NASA Astrophysics Data System (ADS)

    Kolesnichenko, Evgeniy G.; Gorbachev, Yuriy E.

    2012-11-01

    The new method of getting a normal solution for the generalized Boltzmann equation for reacting gas mixtures was proposed. It is based on the following items: (i) slow variables are introduced via approximate summational invariants, defined within the method, (ii) kinetic equations are presented in the form of a singularly perturbed system for gas-dynamic (slow) variables and for the "fast" part of the distribution function, (iii) collisional integral is not expanded into the series over the Knudsen number (no assumption is made that the part of the collisional integral, responsible for the chemical reactions, can be treated as the perturbation of its "elastic" part). While deriving the gas-dynamic equations it is shown that the role of non-equilibrium effects is much more essential in our approach, than is generally accepted. By non-equilibrium effects we mean all kind of effects caused by deviation of the distribution function from its quasi-equilibrium value. From several examples it was shown that non-equilibrium corrections and the traditional equilibrium rate constants could be of the same order of magnitude. In this paper we derive expressions for corrections to equilibrium rate constants for arbitrary mixtures and corresponding integral equations for corrections to the quasi-equilibrium distributions. In situations where corrections to the reaction rates are not small non-equilibrium effects dramatically impacts the chemical kinetics of the reacting gas mixture. This leads to the necessity of the revision of the concept of getting information on the reaction rates from the experiments.

  2. In-cell reaction rate distributions and cell-average reaction rates in fast critical assemblies

    SciTech Connect

    Brumbach, S.B.; Gasidlo, J.M.

    1985-08-01

    Measurements are described for determining average values of fission rates in /sup 235/U, /sup 238/U and /sup 239/Pu and capture rates in /sup 238/U for heterogeneous cells used to construct fast critical assemblies. The measurements are based on irradiations of foils of /sup 238/U, /sup 235/U and /sup 239/Pu with counting of fission and capture products using gamma-ray spectroscopy. Both plate and pin cells are considered. Procedures are described for inferring cell-average reaction rate values from a single foil location based on a cell using a quantity called a cell factor. Cell factors are determined from special measurements in which several foils are irradiated within a cell. Comparisons are presented between cell factors determined by measurements and by Monte Carlo calculations which lend credibility to the measurement procedures.

  3. Impact of THM reaction rates for astrophysics

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; Tognelli, E.; Degl'Innocenti, S.; Pizzone, R. G.; Moroni, P. G. Prada; Puglia, S. M. R.; Romano, S.; Sergi, M. L.

    2015-10-01

    Burning reaction S(E)-factor determinations are among the key ingredients for stellar models when one has to deal with energy generation evaluation and the genesis of the elements at stellar conditions. To by pass the still present uncertainties in extrapolating low-energies values, S(E)-factor measurements for charged-particle induced reactions involving light elements have been made available by devote Trojan Horse Method (THM) experiments. The recent results are here discussed together with their impact in astrophysics.

  4. INITIAL TEST OF THE BENCHMARK CHEMICAL APPROACH FOR PREDICTING MICROBIAL TRANSFORMATION RATES IN AQUATIC ENVIRONMENTS

    EPA Science Inventory

    Using 2,4-dichlorophenoxyacetic acid methyl ester (2,4-DME) as a benchmark chemical, we determined relative pseudo-first-order rate coefficients for butoxyethyl ester of 2,4-dichlorophenoxyacetic acid (2,4-DBE), methyl parathion, and methyl-3-chlorobenzoate in a diversity of micr...

  5. Ring-closing metathesis reactions: interpretation of conversion-time data.

    PubMed

    Thiel, Vasco; Wannowius, Klaus-Jürgen; Wolff, Christiane; Thiele, Christina M; Plenio, Herbert

    2013-11-25

    Conversion-time data were recorded for various ring-closing metathesis (RCM) reactions that lead to five- or six-membered cyclic olefins by using different precatalysts of the Hoveyda type. Slowly activated precatalysts were found to produce more RCM product than rapidly activated complexes, but this comes at the price of slower product formation. A kinetic model for the analysis of the conversion-time data was derived, which is based on the conversion of the precatalyst (Pcat) into the active species (Acat), with the rate constant k(act), followed by two parallel reactions: 1) the catalytic reaction, which utilizes Acat to convert reactants into products, with the rate k(cat), and 2) the conversion of Acat into the inactive species (Dcat), with the rate k(dec). The calculations employ two experimental parameters: the concentration of the substrate (c(S)) at a given time and the rate of substrate conversion (-dc(S)/dt). This provides a direct measure of the concentration of Acat and enables the calculation of the pseudo-first-order rate constants k(act), k(cat), and k(dec) and of k(S) (for the RCM conversion of the respective substrate by Acat). Most of the RCM reactions studied with different precatalysts are characterized by fast k(cat) rates and by the k(dec) value being greater than the k(act) value, which leads to quasistationarity for Acat. The active species formed during the activation step was shown to be the same, regardless of the nature of different Pcats. The decomposition of Acat occurs along two parallel pathways, a unimolecular (or pseudo-first-order) reaction and a bimolecular reaction involving two ruthenium complexes. Electron-deficient precatalysts display higher rates of catalyst deactivation than their electron-rich relatives. Slowly initiating Pcats act as a reservoir, by generating small stationary concentrations of Acat. Based on this, it can be understood why the use of different precatalysts results in different substrate conversions in olefin metathesis reactions. PMID:24127335

  6. Photosensitized degradation kinetics of trace halogenated contaminants in natural waters using membrane introduction mass spectrometry as an in situ reaction monitor.

    PubMed

    Letourneau, Dane R; Gill, Chris G; Krogh, Erik T

    2015-11-01

    The photochemically mediated dechlorination of polyhalogenated compounds represents a potential decontamination strategy and a relevant environmental process in chemically reducing media. We report the UV irradiation of natural and artificial waters containing natural dissolved organic matter to effect the photo-sensitized degradation of chlorinated organic compounds, including tetrachloromethane, 1,1,1-tricloroethane, perchloroethene, 1,2-dibromo-3-chloropropane and chlorobenzene at trace (ppb) levels in aqueous solution. The degradation kinetics are followed in situ using membrane introduction mass spectrometry. By re-circulating the reaction mixture in a closed loop configuration over a semi-permeable hollow fiber polydimethylsiloxane membrane in a flow cell interface, volatile and semi-volatile compounds are continuously monitored using a quadrupole ion trap mass spectrometer. The time resolved quantitative information provides useful mechanistic insights, including kinetic data. Pseudo first-order rate constants for the degradation of contaminant mixtures in natural waters are reported. PMID:26439106

  7. Let the microbes explicitly carry out the reactions: a new paradigm to the modeling of soil carbon-nutrient dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Tang, J.; Riley, W. J.; Bouskill, N.; Brodie, E.

    2013-12-01

    Soil carbon-nutrient dynamics are carried out by a broad spectrum of microbial functional guilds through a network of different reactions, all impacted by abiotic factors, including temperature, moisture, pH, redox, and mineralogy. Few existing soil biogeochemical models explicitly represent microbes and the related biotic and abiotic chemical reactions. Rather, these models usually assume microbes are perfectly adaptive such that their ecological impacts on carbon and nutrient dynamics can be sufficiently described by pseudo-first order decay parameters. These decay parameters are empirically formulated as functions of organic matter composition (e.g., lignocellulos index, CN ratio), soil temperature, and soil moisture that are obtained by ad hoc regression fitting to experimental and observational measurements. These pseudo-first order decay models claim predictability at large spatial and long temporal scales; however, their lack of explicit microbial ecology and microbe relevant biogeochemical and biogeophysical interactions have limited these models' capability to mechanistically explain some fundamental patterns, such as the divergent temperature response of decomposition, episodic emissions in drying-rewetting cycles, and predator-prey effects on organic matter decomposition. We here propose a new modeling paradigm that explicitly considers microbial ecology and reactions in modeling soil carbon-nutrient dynamics. We show this approach requires a new formulation of substrate kinetics to properly account for the intrinsic network structure of the biogeochemical processes and that the classical Michaelis-Menten kinetics is of limited use for this purpose. With a simple model based on this new paradigm, we mechanistically explained lignin dynamics in litter decomposition experiments without the ad hoc use of a lignin shielding effect. We further show, using existing experimental results, that decomposition dynamics are co-shaped by litter chemistry and associated microbial ecology. We also show that interactions between soil mineralogy and organic substrates can significantly reduce the microbial decomposition rate. Finally, we will discuss a few open questions and the data necessary to make such a model structure feasible for practical applications.

  8. Kinetic study of flavonoid reactions with stable radicals.

    PubMed

    Butković, Vjera; Klasinc, Leo; Bors, Wolf

    2004-05-19

    The antiradical activities of some flavonols (kaempferol, quercetin, robinetin, quercetagetin, and myricetin), flavones (apigenin, baicalein, and luteolin), flavanones (naringenin and dihydroquercetin), and flavanols [(+)-catechin and (-)-epicatechin] were determined by measuring the reaction kinetics with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and alpha,gamma-bisdiphenylene-beta-phenylallyl (BDPA) radicals. The reactions, which follow the mixed second-order rate law, were investigated under pseudo-first-order conditions by use of a large excess of flavonoids, and their stoichiometry was determined by spectrophotometric titration. The results confirm stoichiometric factors of 1, 2, and 3 for flavonoids with one, two, and three hydroxyl groups in the B-ring, respectively, excluding kaempferol, which, despite a single OH group in the B-ring, has a factor of 2, which is explained by the 3-OH group supporting the reaction with free radicals. Structure-activity considerations indicate for the present series of flavonoids the importance of multiple OH substitutions and conjugation. The logarithms of reaction rate constants with the OH, DPPH, and BDPA radicals correlate well with the reduction potential of the flavonoids. PMID:15137819

  9. DSMC predictions of non-equilibrium reaction rates.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2010-04-01

    A set of Direct Simulation Monte Carlo (DSMC) chemical-reaction models recently proposed by Bird and based solely on the collision energy and the vibrational energy levels of the species involved is applied to calculate nonequilibrium chemical-reaction rates for atmospheric reactions in hypersonic flows. The DSMC non-equilibrium model predictions are in good agreement with theoretical models and experimental measurements. The observed agreement provides strong evidence that modeling chemical reactions using only the collision energy and the vibrational energy levels provides an accurate method for predicting non-equilibrium chemical-reaction rates.

  10. Fermion damping and reaction rates in hot gauge theories

    SciTech Connect

    Weber, Axel

    1999-10-25

    We examine the relation between the damping rate of a fermionic mode propagating in a hot QED or QCD plasma, and the corresponding reaction rate. We show that these two quantities should be equal provided the reaction rate is calculated using properly normalized wave functions for the mode in the medium. We use finite temperature cutting rules to identify the different terms in the expression for the damping rate with physical processes in the plasma.

  11. A review of reaction rates in high temperature air

    NASA Technical Reports Server (NTRS)

    Park, Chul

    1989-01-01

    The existing experimental data on the rate coefficients for the chemical reactions in nonequilibrium high temperature air are reviewed and collated, and a selected set of such values is recommended for use in hypersonic flow calculations. For the reactions of neutral species, the recommended values are chosen from the experimental data that existed mostly prior to 1970, and are slightly different from those used previously. For the reactions involving ions, the recommended rate coefficients are newly chosen from the experimental data obtained more recently. The reacting environment is assumed to lack thermal equilibrium, and the rate coefficients are expressed as a function of the controlling temperature, incorporating the recent multitemperature reaction concept.

  12. On the rate of relativistic surface chemical reactions.

    PubMed

    Veitsman, E V

    2004-07-15

    On the basis of special relativity and the classical theory of chemical reaction rates it is shown how the surface chemical reaction rates vary as v --> c, where v is the velocity of the object under study and c is the velocity of light. PMID:15178286

  13. Rate constants for the reaction of muonium with aromatic compounds

    NASA Astrophysics Data System (ADS)

    Louwrier, P. W. F.; Brinkman, G. A.; Roduner, E.

    1986-12-01

    Rate constants for the reaction of muonium with benzene in water, methanol and n-hexane and for the reaction of muonium with p-difluorobenzene, anilin, hexafluorobenzene and styrene are reported. All rate constants are below the calculated diffusion controlled limit. The activation energy for the reaction of muonium with benzene in n-hexane is very small, indicating the possibility of tunnelling by muonium.

  14. Reaction of Tris(2-chloroethyl)phosphate with Reduced Sulfur Species

    PubMed Central

    Hilaire, Dickens Saint; Ismail, Kamal Z.; Jans, Urs

    2014-01-01

    Tris(2-chloroethyl)phosphates (TCEP) is a widely used flame retardant in the U.S. It has recently been identified as one of the most frequently detected contaminants in U.S. streams. This contaminant is of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn2−), bisulfide (HS−), and thiophenolate (PhS−) present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such a contaminant. The kinetics of reaction of reduced sulfur species with tris(2-chloroethyl)phosphate have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants from the observed pseudo-first order rate constants. The determined second-order rate constant for the reaction of TCEP with polysulfide at 25°C is 5.0 (± 1.4) × 10−4 M−1 s−1, with thiophenolate at 50 °C is 34 (± 2) × 10−4 M−1 s−1 and with bisulfide at 50 °C is 0.9 × 10−4 M−1 s−1, respectively. In addition, the degradation products of hydrolysis and the reactions with polysulfides, thiophenolate, and bisulfide with TCEP were studied with GC-FID and LC-MS-MS and were quantified. PMID:21419471

  15. Kinetic and product studies of the heterogeneous reactions of surface-bound polycyclic aromatic hydrocarbons with selected atmospheric oxidants

    NASA Astrophysics Data System (ADS)

    Kwamena, Nana-Owusua Alecia

    The heterogeneous reaction of surface-bound polycyclic aromatic hydrocarbons (PAHs) and gas-phase ozone was used as a model system to investigate the factors that influence the heterogeneous reactions of organic compounds. The heterogeneous reactions of surface-bound anthracene and benzo[a]pyrene with ozone on different aerosol substrates were determined using an aerosol flow tube apparatus. The kinetics of these reactions displayed pseudo-first order behaviour with respect to ozone. The non-linear dependence of the pseudo-first order rate constant as a function of ozone concentration was consistent with reactions that proceed by the Langmuir---Hinshelwood mechanism for the substrates and PAHs investigated. The variability in the kinetics from substrate to substrate was influenced more by the partitioning of ozone to the aerosol surface than by the surface-phase reaction rate. The product yield of anthraquinone, one of the known products of the reaction between anthracene and ozone, as a function of ozone concentration yielded a non-linear functional dependence that was similar to a Langmuir adsorption profile thus providing the first direct evidence that ozone is involved in the rate-limiting step in the formation of this product. Investigations of the heterogeneous oxidation of anthracene, pyrene and n-hexane soot with the NO3 radical, using a suite of analytical techniques indicated the formation of nitro functional groups on the surface. Carbonyl functionalities were observed in addition to nitro functional groups on the surface of soot surfaces following exposure to a nitrating flow. Absorption experiments indicate that the nitration of PAHs alter the optical properties of the particles to which they are adsorbed, giving rise to absorption intensity in the near UV and visible portions of the spectrum. The experimental results of the kinetic studies were used in a multimedia model that was the first to assess the importance of these heterogeneous reactions in an urban environment. The kinetic, product and modeling studies illustrate that PAHs found on particle surfaces may be lost at a rate greater than by gas-phase loss mechanisms. Further, these studies suggest that the rate of formation of the toxic oxidized PAHs may also be significant in the urban environment.

  16. Empirical rate equation for association reactions and ion-molecule reactions

    NASA Astrophysics Data System (ADS)

    Sato, Shin

    2016-05-01

    Temperature dependence of the rate constants of many association reactions is now available. In order to express the rate constants at temperatures from very low to high, we tried to use the sum of new empirical rate equations for association reactions and Arrhenius equations. Temperature dependence of a number of radical-molecule and some ion-molecule reactions could be successfully demonstrated. A new procedure to analyze ion-molecule reactions was proposed. This might suggest a new viewpoint to understanding chemical reactions.

  17. New determination of 12C(?,?)16O reaction rate

    NASA Astrophysics Data System (ADS)

    Oulebsir, N.

    2015-12-01

    The reaction 12C(?,?)16O was investigated through the direct ?-transfer reaction (7Li,t) at 28 and 34 MeV incident energies. We determined the reduced ?-widths of the sub-threshold 2+ and 1- states of 16O from the DWBA analysis of the transfer reaction 12C(7Li,t)16O performed at two incident energies. The obtained result for the 2+ and 1- sub-threshold resonances as introduced in the R-matrix fitting of radiative capture and elastic-scattering data to determine the E2 and E1 S-factor from 0.01MeV to 4.2MeV in the center-of-mass energy. After determining the astrophysic factor of 12C(?,?)16O S(E) with Pierre Descouvement code, I determined numerically the new reaction rate of this reaction at a different stellar temperature (0.06 Gk-2 GK). The 12C(?,?)16O reaction rate at T9 = 0.2 is [7.21-2.25+2.15] 10-15 cm3 s-1 mol-1. Some comparisons and discussions about our new 12C(?,?)16O reaction rate are presented. The agreements of the reaction rate below T9 = 2 between our results and with those proposed by NACRE indicate that our results are reliable, and they could be included in the astrophysical reaction rate network.

  18. Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft

    NASA Technical Reports Server (NTRS)

    Rizvi, Farheen

    2013-01-01

    A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

  19. Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism

    NASA Astrophysics Data System (ADS)

    Dong, Shipeng; Xiao, Huifang; Huang, Qingguo; Zhang, Jian; Mao, Liang; Gao, Shixiang

    2016-02-01

    The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 μg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS2+ which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination.

  20. Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism.

    PubMed

    Dong, Shipeng; Xiao, Huifang; Huang, Qingguo; Zhang, Jian; Mao, Liang; Gao, Shixiang

    2016-01-01

    The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 μg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS(2+) which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination. PMID:26891761

  1. Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism

    PubMed Central

    Dong, Shipeng; Xiao, Huifang; Huang, Qingguo; Zhang, Jian; Mao, Liang; Gao, Shixiang

    2016-01-01

    The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 μg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS2+ which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination. PMID:26891761

  2. Rate constant for reaction of atomic hydrogen with germane

    NASA Technical Reports Server (NTRS)

    Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

    1990-01-01

    Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

  3. Measured ion-molecule reaction rates for modelling Titan's atmosphere

    NASA Technical Reports Server (NTRS)

    Dheandhanoo, S.; Johnsen, R.; Biondi, M. A.

    1984-01-01

    Rate coefficients for several two- and three-body ion-molecule reactions involving hydrocarbons have been determined at thermal energies and above using drift tube-mass spectrometer techniques. The measured rates for clustering and breakup reactions involving CH5(+) and C2H5(+) ions in methane are found to be strongly temperature dependent in the range from 80 to 240 K. The equilibrium constants determined for these reactions differ somewhat from those of Hiraoka and Kebarle (1975). Rate coefficients for two-body reactions of CH5(+), C2H5(+), N(+), H(+), and D(+) ions with methane and/or ethane have been measured. The results indicate that the product yields of several of the fast ion-molecule reactions depend strongly on ion energy (temperature), and therefore previous room-temperature results may be of limited value for model calculations of Titan's atmosphere.

  4. An Improved Reaction Rate Equation for Simulating the Ignition and Growth of Reaction in High Explosives

    SciTech Connect

    Murphy, M J

    2010-03-08

    We describe an improved reaction rate equation for simulating ignition and growth of reaction in high explosives. It has been implemented into CALE and ALE3D as an alternate to the baseline the Lee-Tarver reactive flow model. The reactive flow model treats the explosive in two phases (unreacted/reactants and reacted/products) with a reaction rate equation to determine the fraction reacted, F. The improved rate equation has fewer parameters, is continuous with continuous derivative, results in a unique set of reaction rate parameters for each explosive while providing the same functionality as the baseline rate equation. The improved rate equation uses a cosine function in the ignition term and a sine function in the growth and completion terms. The improved rate equation is simpler with fewer parameters.

  5. Gas-solid reaction-rate enhancement by pressure cycling

    NASA Astrophysics Data System (ADS)

    Sohn, H. Y.; Aboukheshem, M. B.

    1992-06-01

    An experimental study and mathematical modeling of the effects of external pressure cycling on gas-solid reactions have been conducted using the reduction of nickel oxide pellets by hy-drogen. Experiments were carried out in two phases: In the first phase, the intrinsic kinetic parameters were measured, and in the second phase, the gas-solid reaction was carried out under a constant or cycling external pressure. The effects of the frequency and amplitude of pressure cycling were studied at various reaction conditions. Pressure cycling substantially increases the overall rate of the reaction. A mathematical model was developed from the first principles to establish the extent of the overall reaction-rate enhancement and subsequently to analyze the experimental observations. The calculated values from the mathematical model are in good agreement with the experimental results. The effects are most pronounced when the overall rate under a constant pressure is controlled by diffusion. Depending on the reaction condition, a very large degree of rate enhancement could be achieved. Furthermore, low-amplitude pressure waves, like acoustic waves, could significantly increase the rates of gas-solid reactions.

  6. Heterogeneous reactions between NO 2 and anthracene adsorbed on SiO 2 and MgO

    NASA Astrophysics Data System (ADS)

    Ma, Jinzhu; Liu, Yongchun; He, Hong

    2011-02-01

    The heterogeneous reactions of NO 2 with anthracene adsorbed on SiO 2 and MgO were investigated under dark conditions at 298 K using DRIFTS, GCMS, and UV-Vis. The pseudo-first-order rate constants of anthracene on SiO 2 and MgO were obtained by fitting the exponential decay of adsorbed PAH concentrations versus reaction time. The reaction on SiO 2 was almost two times faster than on MgO when the concentration of NO 2 was 3.69 × 10 12 molecules cm -3. Both 9-nitroanthracene and 9,10-anthraquinone were the products of the nitration of anthracene adsorbed on SiO 2 whereas 9,10-anthraquinone was the only product formed by NO 2 reaction with anthracene adsorbed on MgO. These results suggest that mineral oxides not only control the reaction kinetics of PAHs with NO 2 but also alter the reaction pathway for the heterogeneous reaction of PAHs with NO 2. The difference in the heterogeneous reactivity of NO 2 with anthracene adsorbed on SiO 2 and MgO was ascribed to the formation of HNO 3 on SiO 2, which can catalyze the nitration of PAHs by NO 2. Due to the formation of nitro-anthracene and oxy-anthracene, the heterogeneous reactions of NO 2 with anthracene also altered the optical properties of the mineral oxides on which anthracene were adsorbed.

  7. Reactions of Three Halogenated Organophosphorus Flame Retardants with Reduced Sulfur Species

    PubMed Central

    Saint-Hilaire, Dickens; Jans, Urs

    2014-01-01

    Tris(haloalkyl)phosphates (THAPs) are among the most widely used flame retardants in the U.S. They have been identified as one of the most frequently detected contaminants in U.S. streams. These contaminants are of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn2−) and bisulfide (HS−), present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such contaminants, especially since no significant degradation reactions in the environment (e.g., hydrolysis, biological degradation) is reported for these compounds. The kinetics of the reaction of reduced sulfur species with three structurally related THAPs have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain second-order rate constants from the observed pseudo-first order rate constants. The degradation products were studied with GC-FID and LC-MS. The reactivity of Sn2−, thiophenolate, and HS− were compared and steric, as well as electronic factors are used to explain the relative reactivity of the three THAPs with these three sulfur species. PMID:23948611

  8. Non-resonant triple alpha reaction rate at low temperature

    SciTech Connect

    Itoh, T.; Tamii, A.; Aoi, N.; Fujita, H.; Hashimoto, T.; Miki, K.; Ogata, K.; Carter, J.; Donaldson, L.; Sideras-Haddad, E.; Furuno, T.; Kawabata, T.; Kamimura, M.; Nemulodi, F.; Neveling, R.; Smit, F. D.; Swarts, C.

    2014-05-02

    Our experimental goal is to study the non-resonant triple alpha reaction rate at low temperture (T < 10{sup 8} K). The {sup 13}C(p,d) reaction at 66 MeV has been used to probe the alpha-unbound continuum state in {sup 12}C just below the 2{sup nd} 0{sup +} state at 7.65 MeV. The transition strength to the continuum state is predicted to be sensitive to the non-resonant triple alpha reaction rate. The experiment has been performed at iThemba LABS. We report the present status of the experiment.

  9. Rate of reaction between molecular hydrogen and molecular oxygen

    NASA Technical Reports Server (NTRS)

    Brokaw, R. S.

    1973-01-01

    The shock tube data of Jachimowski and Houghton were rigorously analyzed to obtain rate constants for the candidate initiation reactions H2 + O2 yields H + HO2, H2 + O2 yields H2O + O, and H2 + O2 yields OH + OH. Reaction (01) is probably not the initiation process because the activation energy obtained is less than the endothermicity and because the derived rates greatly exceed values inferred in the literature from the reverse of reaction (01). Reactions (02) and (03) remain as possibilities, with reaction (02) slightly favored on the basis of steric and statistical considerations. The solution of the differential equations is presented in detail to show how the kinetics of other ignition systems may be solved.

  10. A New Approach to Determining Gas-Particle Reaction Probabilities and Application to the Heterogeneous Reaction of Deliquesced Sodium Chloride Particles with Gas-Phase Hydroxyl Radicals

    SciTech Connect

    Laskin, Alexander; Wang, Hai; Robertson, William H.; Cowin, James P.; Ezell, Michael J.; Finlayson-Pitts, Barbara J.

    2006-09-14

    The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (NaClaq) were investigated using a novel experimental approach. The technique utilizes the exposure of substrate-deposited aerosol particles to reactive gases followed by chemical analysis of the particles using computer-controlled scanning electron microscopy with energy-dispersive analysis of X-rays (CCSEM/EDX) capability. Experiments were performed at room temperature and atmospheric pressure with deliquesced NaCl particles in the micron size range at 70-80% RH and with OH concentrations in the range of 1 to 7?109 cm-3. The apparent, pseudo first-order rate constant for the reaction was determined from measurements of changes in the chloride concentration of individual particles upon reaction with OH as a function of the particle loading on the substrate. Quantitative treatment of the data using a model that incorporates both diffusion and reaction kinetics yields a lower-limit to the net reaction probability of ?net > 0.1, with an overall uncertainty of a factor of two.

  11. Tables of Nuclear Cross Sections and Reaction Rates: AN Addendum to the Paper ``ASTROPHYSICAL Reaction Rates from Statistical Model Calculations'' ()

    NASA Astrophysics Data System (ADS)

    Rauscher, Thomas; Thielemann, Friedrich-Karl

    2001-09-01

    In a previous publication (ATOMIC DATAAND NUCLEAR DATA TABLES75, 1 (2000)), we gave seven-parameter analytical fits to theoretical reaction rates derived from nuclear cross sections calculated in the statistical model (Hauser-Feshbach formalism) for targets with 10<=Z<=83 (Ne to Bi) and for a mass range reaching the neutron and proton driplines. Reactions considered were (n,γ), (n,p), (n,α), (p,γ), (p,α), (α,γ), and their inverse reactions. Here, we present the theoretical nuclear cross sections and astrophysical reaction rates from which those rate fits were derived, and we provide these data as on-line electronic files. Corresponding to the fitted rates, two complete data sets are provided, one of which includes a phenomenological treatment of shell quenching for neutron-rich nuclei.

  12. Analysis of reaction schemes using maximum rates of constituent steps.

    PubMed

    Motagamwala, Ali Hussain; Dumesic, James A

    2016-05-24

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps. PMID:27162366

  13. New Astrophysical Reaction Rate for the 12C(?, ?)16O Reaction

    NASA Astrophysics Data System (ADS)

    An, Zhen-Dong; Ma, Yu-Gang; Fan, Gong-Tao; Li, Yong-Jiang; Chen, Zhen-Peng; Sun, Ye-Ying

    2016-01-01

    A new astrophysical reaction rate for 12C(?, ?)16O has been evaluated on the basis of a global R-matrix fitting to the available experimental data. The reaction rates of 12C(?, ?)16O for stellar temperatures between 0.04 ? T9 ? 10 are provided in a tabular form and by an analytical fitting expression. At T9 = 0.2, the reaction rate is (7.83 0.35) 1015 cm3 mol-1 s-1, where stellar helium burning occurs.

  14. Radical formation during autoxidation of 4-dimethylaminophenol and some properties of the reaction products.

    PubMed

    Eyer, P; Lengfelder, E

    1984-04-01

    4-Dimethylaminophenol (DMAP), after intravenous injection, rapidly forms ferrihaemoglobin and has been successfully used in the treatment of cyanide poisoning. Since DMAP produces many equivalents of ferrihaemoglobin, it was of interest to obtain further insight into this catalytic process. DMAP autoxidizes readily at pH regions above neutrality, a process which is markedly accelerated by oxyhaemoglobin. The resulting red-coloured product was identified as the 4-(N,N-dimethylamino) phenoxyl radical by EPR spectroscopy. The same radical was also produced by pulse radiolysis and oxidation with ferricyanide. The 4-(N,N-dimethylamino)phenoxyl radical is quite unstable and decays in a pseudo-first order reaction (k = 0.4 sec-1 at pH 8.5, 22 degrees) with the formation of p-benzoquinone and dimethylamine. This observed decay rate is identical with the rate of hydrolysis of N,N-dimethylquinonimine. When a solution containing the phenoxyl radical was extracted with ether, half the stoichiometric amount of DMAP was recovered. Hence it is apparent that the phenoxyl radical decays by disproportionation yielding DMAP and N,N-dimethylquinonimine. The latter product then quickly hydrolyses. The equilibrium of this disproportionation reaction is far towards the radical side, and the pseudo-first order hydrolysis controls the radical decay rate. p-Benzoquinone rapidly reacts with DMAP (k2 = 2 X 10(4) M-1 sec-1) with the formation of the 4-(N,N-dimethylamino)phenoxyl and the semiquinone radicals. This reaction explains the autocatalytic phenoxyl radical formation during autoxidation of DMAP. DMAP is not oxidized by H2O2 or O-.2 but the 4-(N,N-dimethylamino)phenoxyl radical is very rapidly reduced by O-.2 (k2 = 2 X 10(8) M-1 sec-1). In addition, the phenoxyl radical is quickly reduced by NAD(P)H or GSH with the formation of NAD(P)+ or GSSG. Since DMAP is also able to reduce two equivalents of ferrihaemoglobin (provided that the ferrohaemoglobin produced is trapped by carbon monoxide), electrophilic addition reactions of the phenoxyl radical seem unimportant in contrast to N,N-dimethylquinonimine. Hence, during the catalytic ferrihaemoglobin formation, DMAP is oxidized by oxygen which is activated by haemoglobin, and the phenoxyl radical oxidizes ferrohaemoglobin. This catalytic process is terminated by covalent binding of N,N-dimethylquinonimine to SH groups of haemoglobin (and GSH in red cells). PMID:6324808

  15. Urea degradation by electrochemically generated reactive chlorine species: products and reaction pathways.

    PubMed

    Cho, Kangwoo; Hoffmann, Michael R

    2014-10-01

    This study investigated the transformation of urea by electrochemically generated reactive chlorine species (RCS). Solutions of urea with chloride ions were electrolyzed using a bismuth doped TiO2 (BiOx/TiO2) anode coupled with a stainless steel cathode at applied anodic potentials (Ea) of either +2.2 V or +3.0 V versus the normal hydrogen electrode. In NaCl solution, the current efficiency of RCS generation was near 30% at both potentials. In divided cell experiments, the pseudo-first-order rate of total nitrogen decay was an order of magnitude higher at Ea of +3.0 V than at +2.2 V, presumably because dichlorine radical (Cl2(-)·) ions facilitate the urea transformation primary driven by free chlorine. Quadrupole mass spectrometer analysis of the reactor headspace revealed that N2 and CO2 are the primary gaseous products of the oxidation of urea, whose urea-N was completely transformed into N2 (91%) and NO3(-) (9%). The higher reaction selectivity with respect to N2 production can be ascribed to a low operational ratio of free available chlorine to N. The mass-balance analysis recovered urea-C as CO2 at 77%, while CO generation most likely accounts for the residual carbon. In light of these results, we propose a reaction mechanism involving chloramines and chloramides as reaction intermediates, where the initial chlorination is the rate-determining step in the overall sequence of reactions. PMID:25219459

  16. Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

  17. Heterogeneous photochemical reaction of ozone with anthracene adsorbed on mineral dust

    NASA Astrophysics Data System (ADS)

    Ma, Jinzhu; Liu, Yongchun; Ma, Qingxin; Liu, Chang; He, Hong

    2013-06-01

    The heterogeneous reactions of O3 with anthracene adsorbed on TiO2 and on Asian dust storm particles were investigated in the dark and in the presence of light. The reaction rate constants of the heterogeneous reaction between O3 and anthracene adsorbed on TiO2 were increased by a factor of 1.5 in the presence of light compared to the dark conditions. Anthraquinone, which was identified as the main surface product of anthracene reacted with O3 in the dark, can react with O3 quickly in the presence of light. The reactions on Asian dust storm particles exhibited pseudo-first-order kinetics for anthracene loss, and the reactions between O3 and anthracene adsorbed on Asian dust storm particles proceed by the Langmuir-Hinshelwood mechanism in the dark and in the presence of light. At extremely high ozone concentrations, the degradation of anthracene is enhanced by a factor of 3 in the presence of light compared to the dark conditions.

  18. Benchmark calculations of thermal reaction rates. I - Quantal scattering theory

    NASA Technical Reports Server (NTRS)

    Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

    1991-01-01

    The thermal rate coefficient for the prototype reaction H + H2 yields H2 + H with zero total angular momentum is calculated by summing, averaging, and numerically integrating state-to-state reaction probabilities calculated by time-independent quantum-mechanical scattering theory. The results are very carefully converged with respect to all numerical parameters in order to provide high-precision benchmark results for confirming the accuracy of new methods and testing their efficiency.

  19. The rate of electrochemical electron-transfer reactions

    NASA Astrophysics Data System (ADS)

    Schmickler, W.; Mohr, J.

    2002-08-01

    Electrochemical electron-transfer reactions form the basis of such important devices as fuel cells and sensors. Previous theories of these reactions were limited either to the case of weak electronic interaction between the electrode and the reactants, or to strong interactions. In this work the rate of electron exchange is calculated by a combination of quantum mechanics and computer simulations. This method is valid for all strengths of the electronic interaction, so that the dependence of the reaction rate on the interaction strength could be obtained. Our results encompass three different regimes; in the order of increasing interaction these are: (i) a linear region, in which first-order perturbation theory holds; (ii) a weakly adiabatic region, in which the rate is limited by solvent dynamics; (iii) a strongly adiabatic region, in which the interaction lowers the energy of activation.

  20. Shock tube kinetic study of the CH sub 3 + H sub 2 r equilibrium H + CH sub 4 reaction and the methane dissociation reaction

    SciTech Connect

    Klemm, R.B.; Sutherland, J.W.; Tao, Wen.

    1992-01-01

    In this kinetic study of (1) the reaction of CH{sub 3} radicals with H{sub 2} and (2) the thermal dissociation of methane, primary product H atoms were monitored directly using the sensitive atomic resonance absorption detection technique. The detection limit for the (H) was about 3{times}10{sup 10} atoms cm{sup {minus}3}. Rate constants for both reactions were obtained under pseudo-first-order conditions. In addition, computer simulations verified that kinetic complications were avoided. For the reaction of CH{sub 3}+H{sub 2}, experiments were performed using either acetone or ethane to generate CH{sub 3} radicals rapidly by thermal dissociation in argon. Twenty-four experiments were performed over the temperature range 1346K to 1793K and a rate constant expression derived using linear least-squares analysis: k{sub {minus}2}(T) = (6.0{plus minus}0.7){times}10{sup {minus}12} exp ({minus}5920{plus minus}190K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. 46 refs., 5 figs., 5 tabs.

  1. Shock tube kinetic study of the CH{sub 3} + H{sub 2} {r_equilibrium} H + CH{sub 4} reaction and the methane dissociation reaction

    SciTech Connect

    Klemm, R.B.; Sutherland, J.W.; Tao, Wen

    1992-02-01

    In this kinetic study of (1) the reaction of CH{sub 3} radicals with H{sub 2} and (2) the thermal dissociation of methane, primary product H atoms were monitored directly using the sensitive atomic resonance absorption detection technique. The detection limit for the [H] was about 3{times}10{sup 10} atoms cm{sup {minus}3}. Rate constants for both reactions were obtained under pseudo-first-order conditions. In addition, computer simulations verified that kinetic complications were avoided. For the reaction of CH{sub 3}+H{sub 2}, experiments were performed using either acetone or ethane to generate CH{sub 3} radicals rapidly by thermal dissociation in argon. Twenty-four experiments were performed over the temperature range 1346K to 1793K and a rate constant expression derived using linear least-squares analysis: k{sub {minus}2}(T) = (6.0{plus_minus}0.7){times}10{sup {minus}12} exp ({minus}5920{plus_minus}190K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. 46 refs., 5 figs., 5 tabs.

  2. The Influence of Particle Charge on Heterogeneous Reaction Rate Coefficients

    NASA Technical Reports Server (NTRS)

    Aikin, A. C.; Pesnell, W. D.

    2000-01-01

    The effects of particle charge on heterogeneous reaction rates are presented. Many atmospheric particles, whether liquid or solid are charged. This surface charge causes a redistribution of charge within a liquid particle and as a consequence a perturbation in the gaseous uptake coefficient. The amount of perturbation is proportional to the external potential and the square of the ratio of debye length in the liquid to the particle radius. Previous modeling has shown how surface charge affects the uptake coefficient of charged aerosols. This effect is now included in the heterogeneous reaction rate of an aerosol ensemble. Extension of this analysis to ice particles will be discussed and examples presented.

  3. Revisiting catalytic model reaction p-nitrophenol/NaBH4 using metallic nanoparticles coated on polymeric spheres

    NASA Astrophysics Data System (ADS)

    Li, Maolin; Chen, Guofang

    2013-11-01

    The early reported pseudo-first-order reaction kinetics of the polymer-supported metallic nanocatalysts for the model reaction of p-nitrophenol (p-NP)/NaBH4 were probably oversimplified. Here a detailed study of p-NP reduction by NaBH4 in the presence of the raspberry-like poly(allylamine hydrochloride)-modified polymer poly(glycidyl methacrylate) composite sub-microspheres with tunable gold nanoparticles (PGMA@PAH@AuNPs) was presented. Effects of polyelectrolyte concentration, the ratio of polymer spheres to gold nanoparticles, and the solution pH value for composite synthesis on the induction period, reaction time, average reaction rate and average turnover frequency were systematically investigated. Experimental results in all cases of our study revealed an nth order (n > 1) of the p-NP/NaBH4 catalytic reaction by the prepared polymer composite particles. The apparent order of reaction, n, is dependent on the total surface area of the coated gold nanoparticles on the polymer spheres, which can be closely correlated with the tunable gold nanoparticle surface coverage. The mechanism of the observed catalytic activity enhancement was proposed based on active epoxy groups of the polymer spheres and a large adsorption of p-nitrophenolate anions onto the positively-charged spheres.

  4. Photochemical reactions of 2,4-dinitrotoluene in surfactant solutions

    SciTech Connect

    Diehl, C.A.; Jafvert, C.T.; Larson, R.A.

    1995-12-31

    Photochemical reactions ({lambda}=254 nm) of 2,4-dinitrotoluene were investigated in aqueous solutions containing various additives. These additives were a cationic surfactant (cetyltrimethylammonium bromide; CTAB) or a nonionic surfactant (Brij 58), a hydrogen donor (sodium borohydride; NaBH{sub 4}), and base (sodium hydroxide). All photochemical experiments were performed in a Rayonet RPR-100 photoreactor equipped with a merry-go-round apparatus. Light sources were two phosphor-coated low pressure mercury lamps that emit nearly monochromatic light at 253.7 nm. Illumination of a saturated solution of DNT in solutions containing either 1.9 mM Brij 58 and 1.9 mM NaBH{sub 4}, or 1.8 mM CTAB and 2.5 mM NaBH{sub 4} resulted in pseudo-first order half-lives of 77 minutes and 17 minutes, respectfully. In the presence of BH{sub 4}{sup -}, the reaction rate of 2,4-DNT was enhanced tremendously by addition of CTAB at concentrations above the critical micelle concentration (cmc=0.066 mM with 0.1 M NaCl).

  5. Estimation of the rate of volcanism on Venus from reaction rate measurements

    NASA Technical Reports Server (NTRS)

    Fegley, Bruce, Jr.; Prinn, Ronald G.

    1989-01-01

    Laboratory rate data for the reaction between SO2 and calcite to form anhydrite are presented. If this reaction rate represents the SO2 reaction rate on Venus, then all SO2 in the Venusian atmosphere will disappear in 1.9 Myr unless volcanism replenishes the lost SO2. The required volcanism rate, which depends on the sulfur content of the erupted material, is in the range 0.4-11 cu km of magma erupted per year. The Venus surface composition at the Venera 13, 14, and Vega 2 landing sites implies a volcanism rate of about 1 cu km/yr. This geochemically estimated rate can be used to determine if either (or neither) of two discordant geophysically estimated rates is correct. It also suggests that Venus may be less volcanically active than the earth.

  6. Fusion Reaction Rate Coefficient for Different Beam and Target Scenarios

    NASA Astrophysics Data System (ADS)

    Ou, Wei; Zeng, Xian-Jun; Deng, Bai-Quan; Gou, Fu-Jun

    2015-02-01

    Fusion power output is proportional not only to the fuel particle number densities participating in reaction but also to the fusion reaction rate coefficient (or reactivity), which is dependent on reactant velocity distribution functions. They are usually assumed to be dual Maxwellian distribution functions with the same temperature for thermal nuclear fusion circumstances. However, if high power neutral beam injection and minority ion species ICRF plasma heating, or multi-pinched plasma beam head-on collision, in a converging region are required and investigated in future large scale fusion reactors, then the fractions of the injected energetic fast ion tail resulting from ionization or charge exchange will be large enough and their contribution to the non-Maxwellian distribution functions is not negligible, hence to the fusion reaction rate coefficient or calculation of fusion power. In such cases, beam-target, and beam-beam reaction enhancement effect contributions should play very important roles. In this paper, several useful formulae to calculate the fusion reaction rate coefficient for different beam and target combination scenarios are derived in detail.

  7. Reaction rate uncertainties and the {nu}p-process

    SciTech Connect

    Froehlich, C.; Rauscher, T.

    2012-11-12

    Current hydrodynamical simulations of core collapse supernovae find proton-rich early ejecta. At the same time, the models fail to eject neutron-rich matter, thus leaving the origin of the main r-process elements unsolved. However, the proton-rich neutrino-driven winds from supernovae have been identified as a possible production site for light n-capture elements beyond iron (such as Ge, Sr, Y, Zr) through the {nu}p-process. The detailed nucleosynthesis patterns of the {nu}p-process depend on the hydrodynamic conditions and the nuclear reaction rates of key reactions. We investigate the impact of reaction rate uncertainties on the {nu}p-process nucleosynthesis.

  8. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2002-01-01

    There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

  9. Nuclear Reaction Rates Governing the Nucleosynthesis of 44Ti

    NASA Astrophysics Data System (ADS)

    Jin, Liping; Meyer, Bradley S.; The, Lih-Sin; Clayton, Donald D.

    1997-02-01

    It appears that the main mechanism of 44Ti nucleosynthesis in supernovae involves an alpha-rich freezeout of hot matter. Late assembly of 12C nuclei via triple alpha reactions is followed by a rapid sequence of captures upward to the 44Ti. Considering that radioactive 44Ti is one of the premier targets of gamma astronomy, having already been detected in the Cas A remnant by COMPTEL, and considering that this sequence appears to be responsible for the large 44Ca abundance in solar matter and for the huge 44Ca excesses found within meteoritic SUNOCONs, we have surveyed the nuclear reaction rate uncertainties that govern this abundance. Our purpose is to identify for the nuclear physics community those reaction rates that have the greatest astrophysical importance. Using a large nuclear reaction network, we have systematically varied cross sections and groups of cross sections in an experimental test for astrophysical significance. We will identify these most important nuclear rates and explain our understanding of the overall rate dependencies that we have found.

  10. Reaction rates of graphite with ozone measured by etch decoration

    NASA Technical Reports Server (NTRS)

    Hennig, G. R.; Montet, G. L.

    1968-01-01

    Etch-decoration technique of detecting vacancies in graphite has been used to determine the reaction rates of graphite with ozone in the directions parallel and perpendicular to the layer planes. It consists essentially of peeling single atom layers off graphite crystals without affecting the remainder of the crystal.

  11. Nuclear fusion in dense matter: Reaction rate and carbon burning

    SciTech Connect

    Gasques, L.R.; Afanasjev, A.V.; Beard, M.; Wiescher, M.; Aguilera, E.F.; Chamon, L.C.; Ring, P.; Yakovlev, D.G.

    2005-08-01

    In this paper we analyze the nuclear fusion rates among equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate that covers all cases. The parameters of this formula can be varied to take into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the {sup 12}C+{sup 12}C fusion reaction. This reaction is important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovas, and in accreting neutron stars. The S factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S factor by using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities {rho} > or approx. 10{sup 9} g cm{sup -3}.

  12. Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2010-06-01

    A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  13. Rate coefficients, binding probabilities, and related quantities for area reactivity models

    PubMed Central

    Prüstel, Thorsten; Meier-Schellersheim, Martin

    2014-01-01

    We further develop the general theory of the area reactivity model that describes the diffusion-influenced reaction of an isolated receptor-ligand pair in terms of a generalized Feynman-Kac equation and that provides an alternative to the classical contact reactivity model. Analyzing both the irreversible and reversible reaction, we derive the equation of motion of the survival probability as well as several relationships between single pair quantities and the reactive flux at the encounter distance. Building on these relationships, we derive the equation of motion of the many-particle survival probability for irreversible pseudo-first-order reactions. Moreover, we show that the usual definition of the rate coefficient as the reactive flux is deficient in the area reactivity model. Numerical tests for our findings are provided through Brownian Dynamics simulations. We calculate exact and approximate expressions for the irreversible rate coefficient and show that this quantity behaves differently from its classical counterpart. Furthermore, we derive approximate expressions for the binding probability as well as the average lifetime of the bound state and discuss on- and off-rates in this context. Throughout our approach, we point out similarities and differences between the area reactivity model and its classical counterpart, the contact reactivity model. The presented analysis and obtained results provide a theoretical framework that will facilitate the comparison of experiment and model predictions. PMID:25416882

  14. Rate coefficients, binding probabilities, and related quantities for area reactivity models

    NASA Astrophysics Data System (ADS)

    Prstel, Thorsten; Meier-Schellersheim, Martin

    2014-11-01

    We further develop the general theory of the area reactivity model that describes the diffusion-influenced reaction of an isolated receptor-ligand pair in terms of a generalized Feynman-Kac equation and that provides an alternative to the classical contact reactivity model. Analyzing both the irreversible and reversible reaction, we derive the equation of motion of the survival probability as well as several relationships between single pair quantities and the reactive flux at the encounter distance. Building on these relationships, we derive the equation of motion of the many-particle survival probability for irreversible pseudo-first-order reactions. Moreover, we show that the usual definition of the rate coefficient as the reactive flux is deficient in the area reactivity model. Numerical tests for our findings are provided through Brownian Dynamics simulations. We calculate exact and approximate expressions for the irreversible rate coefficient and show that this quantity behaves differently from its classical counterpart. Furthermore, we derive approximate expressions for the binding probability as well as the average lifetime of the bound state and discuss on- and off-rates in this context. Throughout our approach, we point out similarities and differences between the area reactivity model and its classical counterpart, the contact reactivity model. The presented analysis and obtained results provide a theoretical framework that will facilitate the comparison of experiment and model predictions.

  15. Reaction Kinetics of Catechol (1,2-Benzenediol) and Guaiacol (2-Methoxyphenol) with Ozone.

    PubMed

    Zein, Atallah El; Coeur, Ccile; Obeid, Emil; Lauraguais, Amlie; Fagniez, Thomas

    2015-07-01

    The kinetic reactions of 1,2-benzenediol (catechol) and 2-methoxyphenol (guaiacol) with ozone were studied in a simulation chamber (8 m(3)) under dark conditions. The rate coefficients were measured at 294 2 K, atmospheric pressure and dry conditions (relative humidity, RH < 1%), except for 1,2-benzenediol where they were also measured as a function of relative humidity (RH = 1-80%). The concentrations of organic compounds were followed by a PTR-ToF-MS for a continuous monitoring of gas-phase species. The O3 rate coefficients were obtained using both the pseudo-first-order and relative rate methods. The values (in cm(3) molecule(-1) s(-1)) determined for catechol and guaiacol under dry conditions are (13.5 1.1) 10(-18) and (0.40 0.31) 10(-18), respectively. The rate coefficient of catechol was found to be independent of RH below 20% and above 60%, whereas for RH between 20% and 60% it decreases with increasing RH. The determined rate coefficients have been used to evaluate the atmospheric lifetime of each compound with respect to O3. To our knowledge, this study represents the first determination of the ozone rate coefficient with guaiacol and is also the first kinetic investigation for the influence of the relative humidity on the oxygenated aromatic ozonolysis. PMID:26053029

  16. Reaction rate constant for radiative association of CF+

    NASA Astrophysics Data System (ADS)

    Ã-ström, Jonatan; Bezrukov, Dmitry S.; Nyman, Gunnar; Gustafsson, Magnus

    2016-01-01

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C+) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 11Π → X1Σ+ and rovibrational transitions on the X1Σ+ and a3Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit-Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius-Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10-250 K, the rate constant is about 10-21 cm3 s-1, rising toward 10-16 cm3 s-1 for a temperature of 30 000 K.

  17. Rate of reaction of OH with HNO3

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Ravishankara, A. R.; Kreutter, N. M.; Shah, R. C.; Nicovich, J. M.; Thompson, R. L.; Wuebbles, D. J.

    1981-01-01

    Measurements of the kinetics of the reaction of OH with HNO3, and mechanisms of HNO3 removal from the stratosphere, are reported. Bimolecular rate constants were determined at temperatures between 224 and 366 K by monitoring the concentrations of OH radicals produced by HNO3 photolysis and HNO3 according to their resonance fluorescence and 184.9-nm absorption, respectively. The rate constant measured at 298 K is found to be somewhat faster than previously accepted values, with a negative temperature dependence. Calculations of a one-dimensional transport-kinetic atmospheric model on the basis of the new rate constant indicate reductions in O3 depletion due to chlorofluoromethane release and NOx injection, of magnitudes dependent on the nature of the reaction products.

  18. Nuclear fusion reaction rates for strongly coupled ionic mixtures

    SciTech Connect

    Chugunov, A. I.; DeWitt, H. E.

    2009-07-15

    We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean-field potential of plasma ions. The mean-field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable to multicomponent ion mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in {sup 12}C-{sup 16}O mixtures.

  19. Reaction rate and products for the reaction O/3P/ + H2CO

    NASA Technical Reports Server (NTRS)

    Chang, J. S.; Barker, J. R.

    1979-01-01

    A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

  20. Scaling of geochemical reaction rates via advective solute transport

    NASA Astrophysics Data System (ADS)

    Hunt, A. G.; Ghanbarian, B.; Skinner, T. E.; Ewing, R. P.

    2015-07-01

    Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture.

  1. Scaling of geochemical reaction rates via advective solute transport.

    PubMed

    Hunt, A G; Ghanbarian, B; Skinner, T E; Ewing, R P

    2015-07-01

    Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture. PMID:26232976

  2. Rate of reaction of OH with CS/sub 2/

    SciTech Connect

    Wine, P.H.; Shah, R.C.; Ravishankara, A.R.

    1980-10-02

    The flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction OH + CS/sub 2/ ..-->.. products (k/sub 1/) over the temperature range 251-363 K. Complicating secondary reactions involving CS/sub 2/ photofragments were eliminated only when the photoflash was filtered by 10 torr cm of CS/sub 2/ and SF/sub 6/ was used as the buffer gas. The rate constant was found to be much slower than previous measurements indicated. Based on our experiments, upper limits for k/sub 1/ (in units of 10/sup -15/ cm/sup 3/ molecule/sup -1/s/sup -1/) are 9.9 at 251 K, 1.5 at 297 K, and 1.6 at 363 K. Our results suggest that the title reaction is unimportant as a source for COS in the atmosphere.

  3. Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

    NASA Astrophysics Data System (ADS)

    Farrukh, Muhammad Akhyar; Kauser, Robina; Adnan, Rohana

    2013-09-01

    The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5-4.5) and temperature (15-35°C) in the presence and absence of surfactant were investigated. Activation parameters, Δ E a, Δ H #, Δ S #, Δ G ≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γmax), minimum area per surfactant molecule ( A min), average area occupied by each molecule of surfactant ( a), surface pressure at the CMC (Πmax), Gibb's energy of micellization (Δ G M°), Gibb's energy of adsorption (Δ G ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.

  4. A model for reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Evans, J. S.

    1984-01-01

    To account for the turbulent temperature and species-concentration fluctuations, a model is presented on the effects of chemical reaction rates in computer analyses of turbulent reacting flows. The model results in two parameters which multiply the terms in the reaction-rate equations. For these two parameters, graphs are presented as functions of the mean values and intensity of the turbulent fluctuations of the temperature and species concentrations. These graphs will facilitate incorporation of the model into existing computer programs which describe turbulent reacting flows. When the model was used in a two-dimensional parabolic-flow computer code to predict the behavior of an experimental, supersonic hydrogen jet burning in air, some improvement in agreement with the experimental data was obtained in the far field in the region near the jet centerline. Recommendations are included for further improvement of the model and for additional comparisons with experimental data.

  5. Suppression of excited-state contributions to stellar reaction rates

    NASA Astrophysics Data System (ADS)

    Rauscher, T.

    2013-09-01

    It has been shown in previous work [Kiss , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.191101 101, 191101 (2008); Rauscher , Phys. Rev. C10.1103/PhysRevC.80.035801 80, 035801 (2009)] that a suppression of the stellar enhancement factor (SEF) occurs in some endothermic reactions at and far from stability. This effect is re-evaluated using the ground-state contributions to the stellar reaction rates, which were shown to be better suited to judging the importance of excited-state contributions than the previously applied SEFs. An update of the tables shown in the latter work is given. The new evaluation finds 2350 cases (out of a full set of 57 513 reactions) for which the ground-state contribution is larger in the reaction direction with a negative reaction Q value than in the exothermic direction, thus providing exceptions to the commonly applied Q value rule. The results confirm the Coulomb suppression effect but lead to a larger number of exceptions than previously found. This is due to the fact that often a large variation in the g.s. contribution does not lead to a sizable change in the SEF. On the other hand, several previously identified cases do not appear anymore because it is found that their g.s. contribution is smaller than inferred from the SEF.

  6. Triple-{alpha} reaction rate constrained by stellar evolution models

    SciTech Connect

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2012-11-12

    We investigate the quantitative constraint on the triple-{alpha} reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}25 and in the metallicity range between Z= 0 and Z= 0.02. The revised rate has a significant impact on the evolution of low-and intermediate-mass stars, while its influence on the evolution of massive stars (M > 10M{sub Circled-Dot-Operator }) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-{alpha} reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least {nu} > 10 at T = 1-1.2 Multiplication-Sign 10{sup 8}K where the cross section is proportional to T{sup {nu}}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than {approx} 10{sup -29} cm{sup 6} s{sup -1} mole{sup -2} at Almost-Equal-To 10{sup 7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation.

  7. Reaction Rate Measurements at the National Criticality Experiments Research Center

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Bounds, J. A.; Brooks, G. H., Jr.; Favorite, J. A.; Goda, J. M.; Hayes, D. K.; Jackman, K. R.; Little, R. C.; Macinnes, M. R.; Myers, W. L.; Oldham, W. J.; Rundberg, R. S.; Sanchez, R. G.; Schake, A. R.; White, M. C.; Wilkerson, C. W., Jr.

    2014-09-01

    With the resumption of regular operations of the Los Alamos Critical Assemblies at the National Criticality Experiments Research Center (NCERC), located at the Nevada National Security Site, we have embarked upon a series of campaigns to restore the capability to perform integral reaction rate and fission product yield measurements using historical radiochemical methods. This talk will present an overview of the current and future experimental plans, including results from our experimental campaigns on the Comet/Zeus and Flattop assemblies.

  8. Application of semiclassical methods to reaction rate theory

    SciTech Connect

    Hernandez, R.

    1993-11-01

    This work is concerned with the development of approximate methods to describe relatively large chemical systems. This effort has been divided into two primary directions: First, we have extended and applied a semiclassical transition state theory (SCTST) originally proposed by Miller to obtain microcanonical and canonical (thermal) rates for chemical reactions described by a nonseparable Hamiltonian, i.e. most reactions. Second, we have developed a method to describe the fluctuations of decay rates of individual energy states from the average RRKM rate in systems where the direct calculation of individual rates would be impossible. Combined with the semiclassical theory this latter effort has provided a direct comparison to the experimental results of Moore and coworkers. In SCTST, the Hamiltonian is expanded about the barrier and the ``good`` action-angle variables are obtained perturbatively; a WKB analysis of the effectively one-dimensional reactive direction then provides the transmission probabilities. The advantages of this local approximate treatment are that it includes tunneling effects and anharmonicity, and it systematically provides a multi-dimensional dividing surface in phase space. The SCTST thermal rate expression has been reformulated providing increased numerical efficiency (as compared to a naive Boltzmann average), an appealing link to conventional transition state theory (involving a ``prereactive`` partition function depending on the action of the reactive mode), and the ability to go beyond the perturbative approximation.

  9. Measuring in situ reaction rate constants in wetland sediments.

    PubMed

    Bassein, Emma; Jaffé, Peter R

    2009-12-01

    Wetlands are ecologically important and play a key role in many environmentally significant chemical reactions. However, an accurate way of measuring in situ reaction rates in wetland sediments has yet to be established. This study evaluates the feasibility of adapting the push-pull test often used to measure in situ kinetics in subsurface environments, to wetlands. Experiments comparing the rates obtained with two methods, the push-pull test and a steady-state flow-through reactor, were conducted in a constructed wetland microcosm. First-order kinetic rate constants were determined for both sulfate and chromate reduction using both methods. Chromate reduction rates showed good agreement between the two methods, while sulfate reduction rates determined by the two methods differed significantly. Since the analysis for the push-pull test is based on a first-order kinetic, this discrepancy is likely due to the non-first-order behavior of sulfate reduction under the given environmental conditions. The largest obstacle identified prohibiting the use of this method is the availability of a tracer that is conservative in the presence of plants. PMID:18998226

  10. Calculated third order rate constants for interpreting the mechanisms of hydrolyses of chloroformates, carboxylic Acid halides, sulfonyl chlorides and phosphorochloridates.

    PubMed

    Bentley, T William

    2015-01-01

    Hydrolyses of acid derivatives (e.g., carboxylic acid chlorides and fluorides, fluoro- and chloroformates, sulfonyl chlorides, phosphorochloridates, anhydrides) exhibit pseudo-first order kinetics. Reaction mechanisms vary from those involving a cationic intermediate (SN1) to concerted SN2 processes, and further to third order reactions, in which one solvent molecule acts as the attacking nucleophile and a second molecule acts as a general base catalyst. A unified framework is discussed, in which there are two reaction channels-an SN1-SN2 spectrum and an SN2-SN3 spectrum. Third order rate constants (k3) are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter. These data and kinetic solvent isotope effects, provide the experimental evidence for the SN2-SN3 spectrum (e.g., for chloro- and fluoroformates, chloroacetyl chloride, p-nitrobenzoyl p-toluenesulfonate, sulfonyl chlorides). Deviations from linearity lead to U- or V-shaped plots, which assist in the identification of the point at which the reaction channel changes from SN2-SN3 to SN1-SN2 (e.g., for benzoyl chloride). PMID:26006228

  11. Calculated Third Order Rate Constants for Interpreting the Mechanisms of Hydrolyses of Chloroformates, Carboxylic Acid Halides, Sulfonyl Chlorides and Phosphorochloridates

    PubMed Central

    Bentley, T. William

    2015-01-01

    Hydrolyses of acid derivatives (e.g., carboxylic acid chlorides and fluorides, fluoro- and chloroformates, sulfonyl chlorides, phosphorochloridates, anhydrides) exhibit pseudo-first order kinetics. Reaction mechanisms vary from those involving a cationic intermediate (SN1) to concerted SN2 processes, and further to third order reactions, in which one solvent molecule acts as the attacking nucleophile and a second molecule acts as a general base catalyst. A unified framework is discussed, in which there are two reaction channels—an SN1-SN2 spectrum and an SN2-SN3 spectrum. Third order rate constants (k3) are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter. These data and kinetic solvent isotope effects, provide the experimental evidence for the SN2-SN3 spectrum (e.g., for chloro- and fluoroformates, chloroacetyl chloride, p-nitrobenzoyl p-toluenesulfonate, sulfonyl chlorides). Deviations from linearity lead to U- or V-shaped plots, which assist in the identification of the point at which the reaction channel changes from SN2-SN3 to SN1-SN2 (e.g., for benzoyl chloride). PMID:26006228

  12. Elucidating Latent Mechanistic Complexity in Competing Acid-Catalyzed Reactions of Salicylaldehyde-Derived Baylis-Hillman Adducts.

    PubMed

    Olomola, Temitope O; Klein, Rosalyn; Caira, Mino R; Kaye, Perry T

    2016-01-01

    (1)H NMR-based kinetic studies have revealed the latent mechanistic complexity of deceptively simple hydrochloric acid-catalyzed reactions of salicylaldehyde-derived Baylis-Hillman adducts. Reactions conducted at 0 °C afforded 2-(chloromethyl)cinnamic acid derivatives as the major products and the corresponding 3-(chloromethyl)coumarin derivatives as the minor products. In reactions conducted in refluxing acetic acid, however, the 3-(chloromethyl)coumarin derivatives are the sole products. Variable-temperature (1)H NMR analysis permitted the determination of the rate constants and kinetic parameters involved in the pseudo-first-order formation of (Z)-2-(chloromethyl)-3-(2-hydroxyphenyl)-2-propenoic acid. The kinetic data clearly preclude the operation of classical kinetic versus thermodynamic control and indicate the operation of three independent reaction pathways. Theoretical studies of these pathways undertaken at the B3LYP/6-31G(d) level permitted rationalization of the experimental data and provided insights into the possible mechanism of the enzymic E-Z isomerization and cyclization of (E)-cinnamic acid analogues to afford coumarins. PMID:26655750

  13. Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 Over a Wide Range of Humidity

    SciTech Connect

    Liu, Yong; Gibson, Elizabeth R.; Cain, Jeremy P.; Wang, Hai; Grassian, Vicki H.; Laskin, Alexander

    2008-02-21

    Heterogeneous reaction kinetics of gaseous nitric acid (HNO3) with calcium carbonate (CaCO3) particles was investigated using the Particle-on-Substrate Stagnation Flow Reactor (PS-SFR). The technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO3/H2O/N2 followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiment was conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter pD = 0.85 ?m, particle loading densities 2104 ? Ns ? 6106 cm2 and free stream HNO3 concentrations of 7, 14 and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data using a diffusion-kinetic model yields lower limit to the net reaction probability ?net ? 0.06 (3/2). In the second series of experiments, HNO3 uptake on CaCO3 of the same particle size was examined over a wide range of relative humidity, from 10 to 80%. The lower limit for the net reaction probability was found to increase with an increase in the relative humidity, from ?net ? 0.003 at RH = 10% to 0.21 at 80%.

  14. Alternative nonlinear model for estimating second-order rate coefficients for biodegradation.

    PubMed Central

    Suflita, J M; Smolenski, W J; Robinson, J A

    1987-01-01

    A modification of the second-order model for biodegradation was derived, applied to an example data set, and shown to be superior for describing the anaerobic biodegradation of p-cresol by an enriched bacterial consortium. The modified model circumvents the no-growth assumption implicit in the use of the second-order rate equation, but still requires the assumption of first-order kinetics over the course of substrate depletion. Violation of the no-growth assumption is particularly important since overestimates of the pseudo-first-order rate coefficient lead to underestimates of the time required for the removal of a xenobiotic chemical from a contaminated environment. Our calculations show that the errors introduced into the pseudo-first-order rate coefficient (and the resulting estimates of the second-order rate coefficient) approach 100% if one doubling occurs in activity over the course of substrate depletion. For an exemplary data set, use of a first-order model resulted in a 100% overestimate of the first-order decay coefficient, which would in turn lead to a corresponding overestimate of the second-order rate coefficient. The modified model we describe is a potential alternative to the pseudo-first-order model for the routine estimation of second-order rate coefficients. PMID:3606091

  15. Neutron detectors for fusion reaction-rate measurements

    SciTech Connect

    Lerche, R.A.; Phillion, D.W.; Landen, O.L.; Murphy, T.J.; Jaanimagi, P.A.

    1994-02-10

    Fusion reactions in an inertial-confinement fusion (ICF) target filled with deuterium or a deuterium/tritium fuel release nearly monoenergetic neutrons. Because most the neutrons leave the compressed target without collision, they preserve reaction-rate information as they travel radially outward from their point of origin. Three fast, neutron detector techniques, each capable of measuring the fusion reaction-rate of ICF targets, have been demonstrated. The most advanced detector is based on the fast rise-time of a commercial plastic scintillator material (BC-422) which acts as a neutron-to-light converter. Signals, which are recorded with a fast optical streak camera, have a resolution of 25 ps. Good signals can be recorded for targets producing only 5 x 10{sup 7} DT neutrons. Two other detectors use knock-on collisions between neutrons and protons in a thin polyethylene (CH{sub 2}) converter. In one, the converter is placed in front of the photocathode of an x-ray streak camera. Recoil protons pass through the photocathode and knock out electrons which are accelerated and deflected to produce a signal. Resolutions < 25 ps are possible. In the other, the converter is placed in front of a microchannel plate (MCP) with a gated microstrip. Recoil protons eject electrons from the gold layer forming the microstrip. If a gate pulse is present, the signal is amplified. Present gate times are about 80 ps.

  16. An age extended progress variable for conditioning reaction rates

    NASA Astrophysics Data System (ADS)

    Grout, R. W.

    2007-10-01

    An aging progress variable (APV) is proposed as a convenient tool for conditioning quantities used to calculate reaction rates in premixed turbulent combustion. The APV is defined to obey an advection-diffusion-reaction equation where the source term is linearly related to the fuel consumption rate when the APV is less than a threshold representative of the trailing edge of the fuel consumption layer. Above this threshold, the APV has a constant source term. To test the proposal, three-dimensional fully compressible direct numerical simulation (DNS) is performed in an inflow-outflow configuration with inlet turbulence forcing using a modified version of the DNS code SENGA. A model chemical mechanism involving two steps and four species is used which has an order of magnitude difference between the time scales associated with the two steps. The inlet Taylor scale Reynolds number is 51 and the Damköhler numbers are 2.0 and 0.29 for the two steps. When conditionally averaged on the proposed APV the scalar fluctuations about the conditional average are negligible. Further, it is shown that the probability density function of the APV can be reasonably approximated based on the first two moments of the APV and the fuel mass fraction. The APV probability density function (PDF) is approximated on rectangular slabs of cells normal to the flow direction using only these moments as a test case. Convolution of the PDF so approximated with conditional mean reaction rates—calculated from conditionally averaged scalar fields where the averaging was carried out over the entire domain—leads to an approximation for the unconditional mean reaction rates on each of these slabs typically within 10% of the true value for both steps. That the correlation between the reaction rates and the APV is strong, and that the PDF can be approximated for a situation where approximating the PDF for a product based progress variable is nontrivial, makes the proposed APV a strong alternative to traditional progress variables for both flamelet models and premixed conditional moment closure (CMC) approaches.

  17. Evaluation of plutonium(IV) extraction rate between nitric acid and tri-n-butylphosphate solution using a glass chip microchannel.

    PubMed

    Yamamoto, Masahiko; Taguchi, Shigeo; Sato, Soichi; Surugaya, Naoki

    2015-05-01

    Extraction of Pu(IV) with tri-n-butylphosphate is performed using a glass chip microchannel to evaluate the extraction rate. Two-phase flow forms in the microchannel by introducing a solution of Pu(IV) and tri-n-butylphosphate with flow rates above 5 ?L/min. The Pu(IV) extraction reaction proceeds at the interface between the two phases. To evaluate the extraction rate, the contact time between the two phases is varied from 0.48 to 4.8 s by changing the confluent length of the microchannel and the flow rate. The Pu concentration of each phase collected from the microchannel is measured with an alpha liquid scintillation counter, and the contact time dependence of Pu(IV) extraction is obtained. An extraction model based on diffusion in the microchannel and the reaction at the interface is proposed and applied to determine the extraction rate. The extraction process is assumed to follow pseudo-first-order kinetics, and the extraction rate constant of Pu(IV) is determined to be 1.5 10(-2) cm/s. The investigation demonstrates that a microfluidic device can be a new tool to determine Pu(IV) extraction rates. PMID:25754948

  18. r-PROCESS Reaction Rates for the Actinides and Beyond

    NASA Astrophysics Data System (ADS)

    Panov, I. V.; Korneev, I. Yu.; Rauscher, T.; Thielemann, F.-K.

    2011-10-01

    We discuss the importance of different fission rates for the formation of heavy and superheavy nuclei in the astrophysical r-process. Neutron-induced reaction rates, including fission and neutron capture, are calculated in the temperature range 108 ≤ T(K) ≤ 1010 within the framework of the statistical model for targets with the atomic number 84 ≤ Z ≤ 118 (from Po to Uuo) from the neutron to the proton drip-line for different mass and fission barrier predictions based on Thomas-Fermi (TF), Extended Thomas-Fermi plus Strutinsky Integral (ETFSI), Finite-Range Droplet Model (FRDM) and Hartree-Fock-Bogolyubov (HFB) approaches. The contribution of spontaneous fission as well as beta-delayed fission to the recycling r-process is discussed. We also discuss the possibility of rate tests, based on mini r-processed yields in nuclear explosions.

  19. Critical Anomalies of Two SN1 Hydrolysis Reactions in Critical Binary Solutions.

    PubMed

    Hao, Zhiguo; Yin, Handi; Zheng, Peizhu; Zhao, Jihua; Shen, Weiguo

    2015-08-20

    Rates of SN1 hydrolysis reactions for 2-chloro-2-methylbutane in the critical solution of isobutyric acid + water and for 2-bromo-2-methylpropane in the critical solution of triethylamine + water in the one-phase region and at various temperatures have been determined respectively by conductance measurements. It was found that the reaction rates at different temperatures for those two SN1 reactions were well described by the Arrhenius equation in the noncritical region, whereas near the critical points the critical slowing down was clearly detected. These results are inconsistent with a previous report in the literature (J. Phys. Chem. A 2003, 107, 8435 - 8443). Reanalyzing the literature data, we found that if an Arrhenius equation appropriate to either the one-phase region or the two-phase region being examined was used as the background, a critical slowing down rather than a speeding up was detected for the reaction in both the one-phase region and the two-phase region. The experimental data from different sources were fitted with a simplified crossover formalism characterizing the critical effect on the reactions to determine the critical slowing down exponents, which were found to be about 0.04, showing that only a dynamic critical slowing down could be detected for these reaction systems. This phenomenon was attributed to the fact that the SN1 hydrolysis reaction is neither a first-order nor a pseudo-first-order reaction in the reverse direction and the kinetic measurements were carried out in a region quite far from the equilibrium of the reactions. PMID:26214368

  20. Reaction rate constant for radiative association of CF(.).

    PubMed

    Öström, Jonatan; Bezrukov, Dmitry S; Nyman, Gunnar; Gustafsson, Magnus

    2016-01-28

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C(+)) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 1(1)Π → X(1)Σ(+) and rovibrational transitions on the X(1)Σ(+) and a(3)Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit-Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius-Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10-250 K, the rate constant is about 10(-21) cm(3) s(-1), rising toward 10(-16) cm(3) s(-1) for a temperature of 30 000 K. PMID:26827212

  1. Suitable combination of promoter and micellar catalyst for kilo fold rate acceleration on benzaldehyde to benzoic acid conversion in aqueous media at room temperature: A kinetic approach

    NASA Astrophysics Data System (ADS)

    Ghosh, Aniruddha; Saha, Rumpa; Ghosh, Sumanta K.; Mukherjee, Kakali; Saha, Bidyut

    2013-05-01

    The kinetics of oxidation of benzaldehyde by chromic acid in aqueous and aqueous surfactant (sodium dodecyl sulfate, SDS, alkyl phenyl polyethylene glycol, Triton X-100 and N-cetylpyridinium chloride, CPC) media have been investigated in the presence of promoter at 303 K. The pseudo-first-order rate constants (kobs) were determined from a logarithmic plot of absorbance as a function time. The rate constants were found to increase with introduction of heteroaromatic nitrogen base promoters such as Picolinic acid (PA), 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen). The product benzoic acid has been characterized by conventional melting point experiment, NMR, HRMS and FTIR spectral analysis. The mechanism of both unpromoted and promoted reaction path has been proposed for the reaction. In presence of the anionic surfactant SDS, cationic surfactant CPC and neutral surfactant TX-100 the reaction can undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation in the micellar phase. Both SDS and TX-100 produce normal micellar effect whereas CPC produce reverse micellar effect in the presence of benzaldehyde. The observed net enhancement of rate effects has been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. SDS and bipy combination is the suitable one for benzaldehyde oxidation.

  2. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  3. Metal-silicon reaction rates - The effects of capping

    NASA Technical Reports Server (NTRS)

    Weizer, Victor G.; Fatemi, Navid S.

    1989-01-01

    Evidence is presented showing that the presence of the commonly used anti-reflection coating material Ta2O5 on the free surface of contact metallization can either suppress or enhance, depending on the system, the interaction that takes place at elevated temperatures between the metallization and the underlying Si. The cap layer is shown to suppress both the generation and annihilation of vacancies at the free surface of the metal which are necessary to support metal-Si interactons. Evidence is also presented indicating that the mechanical condition of the free metal surface has a significant effect on the metal-silicon reaction rate.

  4. Novel technique for Constraining r -Process (n , γ ) Reaction Rates

    NASA Astrophysics Data System (ADS)

    Spyrou, A.; Liddick, S. N.; Larsen, A. C.; Guttormsen, M.; Cooper, K.; Dombos, A. C.; Morrissey, D. J.; Naqvi, F.; Perdikakis, G.; Quinn, S. J.; Renstrøm, T.; Rodriguez, J. A.; Simon, A.; Sumithrarachchi, C. S.; Zegers, R. G. T.

    2014-12-01

    A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of 76Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ -ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the 75Ge (n ,γ )76Ge cross section and reaction rate.

  5. Pressure and temperature dependence of the reaction NO2 + NO3 + M yields N2O5 + M

    NASA Technical Reports Server (NTRS)

    Kircher, C. C.; Margitan, J. J.; Sander, S. P.

    1984-01-01

    The pressure and temperature dependences of the reaction NO2 + NO3 + M which yields N2O5 + M are investigated by using the flash photolysis/visible absorption technique in which the pseudo-first-order decay of NO3 is monitored as a function of total pressure (20-700 torr), diluent gas (M = He and N2), and temperature (236-358 K). The reaction is found to be in the falloff region in the 20-700 torr pressure range with collision efficiencies increasing in the order He less than N2. Falloff parameters are obtained by fitting the experimental data to the falloff equation of Troe and co-workers. The expression for k1(N2 concentration, T) is obtained and compared with the evaluations presented in the NASA (DeMore, 1983) and CODATA (Baulch et al., 1982) reviews of kinetic data for atmospheric chemistry. Both evaluations are based on N2O5 thermal decomposition data coupled with estimates of the equilibrium constant. The significance of the reactions for atmospheric chemistry rests not only on their rates but on the extent to which they result in a permanent sink for NOX.

  6. Primordial lithium - New reaction rates, new abundances, new constraints

    NASA Technical Reports Server (NTRS)

    Kawano, Lawrence; Schramm, David; Steigman, Gary

    1988-01-01

    Newly measured nuclear reaction rates for H-3(alpha, gamma)Li-7 (higher than previous values) and Li-7(p, alpha)He-4 (lower than previous values) are shown to increase the Li-7 yield from big band nucleosynthesis for lower baryon-to-photon ratio (less than about 4 x 10 to the 10th). Recent revisions in the He-3(alpha, gamma)Be-7 and the D(p, gamma)He-3 rates enhance the high (greater than 4 x 10 to the 10th) Li-7(Be) production. New, independent determinations of Li abundances in extreme population II stars are in excellent agreement with the work of Spites and give continued confidence in the use of Li-7 in big bang baryon density determinations.

  7. Constraining kinetic rates of mineral reactions using reactive transport models

    NASA Astrophysics Data System (ADS)

    Bolton, E. W.; Wang, Z.; Ague, J.; Bercovici, D.; Cai, Z.; Karato, S.; Oristaglio, M. L.; Qiu, L.

    2012-12-01

    We use a reactive transport model to better understand results of experiments to obtain kinetic rates of mineral reactions in closed systems. Closed system experiments pose special challenges in that secondary minerals may form that modify the fluid composition evolution and may grow on the dissolving minerals thus armoring the surface. Even so, such closed system experiments provide critical data for what minerals would actually form in field applications and how coupled dissolution and precipitation mineral reactions are strongly linked. Comparing to experimental observations can test the reactive transport model, and the experimental observations can be better understood by comparing the results to the modeling. We apply a 0D end member of the model to understand the dissolution of single crystals of forsterite in a variety of settings (low pH, high pH, or NaHCO3 initial fluids, at 100 C and 1 bar, or 200 C and 150 bar). Depending on the initial conditions, we observe the precipitation of talc, brucite, amorphous silica, chrysotile, or magnesite, in various combinations. We compare simulation results to fluid compositions and the presence of secondary minerals experimentally sampled at various times. Insight from the simulations helped create an inverse model to extract the rates of forsterite dissolution and to create a simple forward model useful for exploring the influence of system size, secondary mineral surface areas, etc. Our reactive transport model allows secondary minerals to armor the forsterite surface, which can strongly decrease the dissolution rate as the system evolves. Tuning our model with experimentally derived rates and assuring relevant processes are included so as to reproduce experimental observations is necessary before upscaling to heterogeneous field conditions. The reactive transport model will be used for field-scale sequestration simulations and coupled with a geomechanical model that includes the influence of deformation.

  8. Investigation of the reaction rates between uranium and liquid aluminum

    SciTech Connect

    Strum, M.J.; Sedillo, E.; Smugeresky, J.

    1995-05-05

    A limited study consisting of scoping experiments was carried out to determine if a uranium-niobium alloy was weakly or strongly resistant to penetration by liquid aluminum alloy 6061. Our investigation was limited to temperatures between 700{degrees}and 900{degrees}C and carried out using small cylindrical coupons of U-6wt.%Nb and unalloyed U in unsaturated molten aluminum and aluminum alloy 6061 baths. The results indicate that indeed, significant dissolution of uranium into molten aluminum occurs and in relatively short times. The diameters of U-6wt.%Nb test cylinders immersed in unsaturated Al-6061 decreased linearly with time at 700{degrees}C, 800{degrees}C, and 900{degrees}C at rates of 1.14 mm/h, 3.0 mm/h, and 3.5 mm/h, respectively. However, we have found that the reaction rates were significantly reduced by the alloying elements niobium and magnesium. These results suggest that a more detailed investigation could lead to a predictive capability for control of these reaction rates. In unalloyed U, the rate of U dissolution increased by up to a factor of ten relative to that in U- 6wt.%Nb. In both materials, the dissolution of the U core was found to occur by advance of a continuous intermetallic layer, which redissolves into the unsaturated liquid Al bath. The Nb additions resulted in the formation of a thick transition layer composed of intermetallic and U-saturated liquid. In unalloyed U, however, the transition layer was largely reduced in thickness, allowing unsaturated liquid adjacent to the continuous intermetallic layer. Another important variable identified was the influence of surface condition on interface reactivity. At 900{degrees}C, liquid attack was completely absent over large regions of U-6wt.% Nb samples immersed in Al-6061. Surface analysis by EDX identified the presence of up to 24 at.% Mg in unattacked areas.

  9. Improving the Rate of the Triple Alpha Reaction

    NASA Astrophysics Data System (ADS)

    Tur, C.; Wuosmaa, A.; Austin, S. M.; Lighthall, J.; Marley, S.; Goodman, N.; Bos, J. J.; Heger, A.; Woosley, S. E.; Hoffman, R.

    2006-10-01

    The rate of the triple alpha process is known with an accuracy of about 12%. Variations within those errors can significantly change the size of the iron core in core-collapse supernovae and double the surface abundance of ^12C in light ABG stars. Studies being done using the code KEPLER show that changing the triple alpha rate or the rate of the ^12C (,)^16O reactions can significantly affect the production of the medium weight elements in core-collapse supernova progenitors. Hence, the experiment aims at reducing the uncertainty on this rate to about 6% through an accurate measurement of the pair branch for the Hoyle state excited through inelastic scattering of 10.6 MeV protons from the Tandem accelerator at WMU. The pair branch is given by the ratio of the number of e^+e^- pairs in the plastic scintillators in coincidence with protons scattered at 135 degrees in the lab to the total number of such protons. The gamma ray background is considerably reduced by a coincidence requirement between a thin scintillator tube and the large block of scintillator surrounding it. The experimental status will be presented.

  10. Kinetics of the reaction OH + HO2 yields H2O + O2 from 254 to 382 K

    NASA Technical Reports Server (NTRS)

    Keyser, Leon F.

    1988-01-01

    The discharge-flow resonance fluorescence technique has been used to determine the absolute rate constant for the reaction OH + HO2 yields H2O + O2 from 254 to 382 K at a total pressure of 1 Torr. Pseudo-=first-order conditions were used with HO2 in large excess over OH. The rate constant was obtained directly from observed decays of OH and measured concentrations of HO2. Since the observed rate constant was found to be very sensitive to small background concentrations of O and H atoms, NO2 was used to remove both atom species from the system. With added NO2 the result at 299 K is (1.1 + or - 0.3) x 10 to the -10th cu cm/molecule where the error limits are one standard deviation and include an estimate of overall experimental uncertainty. The temperature dependence expressed in Arrhenius form is (4.8 + or - 0.8) x 10 to the -11th exp (250 + or - 50)/T. The results are independent of the type of reactor surface and the precursor used to produce OH and HO2. The present results agree well with earlier measurements near 1-atm total pressure and suggest that this rate constant exhibits little or no pressure dependence between 1 and 1000 Torr.

  11. Effect of Substrate Character on Heterogeneous Ozone Reaction Rate with Individual PAHs and Their Reaction Mixtures

    NASA Astrophysics Data System (ADS)

    Holmen, B. A.; Stevens, T.

    2009-12-01

    Vehicle exhaust contains many unregulated chemical compounds that are harmful to human health and the natural environment, including polycyclic aromatic hydrocarbons (PAH), a class of organic compounds derived from fuel combustion that can be carcinogenic and mutagenic. PAHs have been quantified in vehicle-derived ultrafine particles (Dp<100nm), which are more toxic than larger particles and are linked to adverse health problems, including respiratory and cardiac disease. Once emitted into the atmosphere, particle-bound PAHs can undergo “aging” reactions with oxidants, such as ozone, to form more polar species. These polar reaction products include species such as quinones that can be more toxic than the parent PAH compounds. Here, 0.4ppm ozone was reacted over a 24-hour period with the 16 EPA priority PAHs plus coronene adsorbed to (i) a quartz fiber filter and (ii) NIST diesel PM. The difference in the PAH/O3 heterogeneous reaction rate resulting from the two substrates will be discussed. The experiments were completed by spiking a known PAH mixture to the solid, reacting the samples with gas-phase ozone, and determining both PAH loss over time and products formed, using thermal-desorption gas chromatography / mass spectrometry (TD-GC/MS). The individual PAHs anthracene, phenanthrene, and fluorene, adsorbed to a QFF were also separately reacted with 0.4 ppm ozone. A volatilization control and the collection of volatilized PAHs using a Tenax-packed thermal desorption vial completed the mass balance and aided determination parent-product relationships. Heterogeneous reaction products analyzed directly without derivatization indicate the formation of 9,10-anthracenedione, 9H-fluoren-9-one, and (1,1’-biphenyl)-2,2’-dicarboxaldehyde from the reaction of ozone with the PAH mix on a QFF, but only 9,10-anthracenedione was detected for the diesel PM reaction. The implications of these results for aging of diesel particulate in urban environments will be discussed.

  12. Transcriptional dynamics with time-dependent reaction rates

    NASA Astrophysics Data System (ADS)

    Nandi, Shubhendu; Ghosh, Anandamohan

    2015-02-01

    Transcription is the first step in the process of gene regulation that controls cell response to varying environmental conditions. Transcription is a stochastic process, involving synthesis and degradation of mRNAs, that can be modeled as a birth-death process. We consider a generic stochastic model, where the fluctuating environment is encoded in the time-dependent reaction rates. We obtain an exact analytical expression for the mRNA probability distribution and are able to analyze the response for arbitrary time-dependent protocols. Our analytical results and stochastic simulations confirm that the transcriptional machinery primarily act as a low-pass filter. We also show that depending on the system parameters, the mRNA levels in a cell population can show synchronous/asynchronous fluctuations and can deviate from Poisson statistics.

  13. The effects of vacuum polarization on thermonuclear reaction rates

    NASA Technical Reports Server (NTRS)

    Gould, Robert J.

    1990-01-01

    Added to the pure Coulomb potential, the contribution from vacuum polarization increases the barrier, reducing the wave function (u) for reacting nuclei within the range of nuclear forces. The cross section and reaction rate are then reduced accordingly by a factor proportional to u squared. The effect is treated by evaluating the vacuum polarization potential as a small correction to the Coulomb term, then computing u in a WKB formulation. The calculation is done analytically employing the small r power-series expansion for the Uehling potential to express the final result in terms of convenient parameters. At a temperature of 1.4 x 10 to the 7th K the (negative) correction is 1.3 percent for the fundamental fusion process p + p yields d + e(+) + nu.

  14. A log derivative formulation of reaction rate theory

    NASA Astrophysics Data System (ADS)

    Manolopoulos, David E.; Light, John C.

    1993-12-01

    The reaction rate theory of Miller, Schwartz and Tromp is reformulated using a complex Bloch boundary value operator to enforce the scattering boundary conditions. This Bloch operator requires a knowledge of the log derivative of the outgoing wave-function on the boundary of the interaction region, and this in turn can be approximated semiclassically from a knowledge of the interaction potential on the boundary. The resulting absorbing log derivative boundary conditions are shown to work well in practice, reducing the range over which the quantum-mechanical problem has to be solved to a narrow region enclosing the relevant turning points. For example they are shown to be at least three times more effective in reducing the required size of the interaction region for a standard barrier tunnelling problem than more conventional absorbing potentials.

  15. In Search of Reaction Rate Scaling Law for Supersonic Combustion

    NASA Astrophysics Data System (ADS)

    Ladeinde, Foluso; Lou, Zhipeng; Li, Wenhai

    2015-11-01

    As a way of employing the flamelet approach, which was developed essentially for incompressible flows, to model supersonic combustion, the role ascribed to pressure has not been very convincing. That is, the reaction rate is often scaled on the square of the pressure in the finite Mach number flow field relative to the usually atmospheric static pressure field used in the generation of the flamelet library. This scaling assumption is quite simple and will therefore be very attractive if it has a sound theoretical basis and it works for a large selection of high-speed combustion flows. We try to find some justifications for different scaling laws, with the hope of coming up with a more universally-acceptable flamelet procedure for supersonic combustion.

  16. Manual choice reaction times in the rate-domain

    PubMed Central

    Harris, Christopher M.; Waddington, Jonathan; Biscione, Valerio; Manzi, Sean

    2014-01-01

    Over the last 150 years, human manual reaction times (RTs) have been recorded countless times. Yet, our understanding of them remains remarkably poor. RTs are highly variable with positively skewed frequency distributions, often modeled as an inverse Gaussian distribution reflecting a stochastic rise to threshold (diffusion process). However, latency distributions of saccades are very close to the reciprocal Normal, suggesting that “rate” (reciprocal RT) may be the more fundamental variable. We explored whether this phenomenon extends to choice manual RTs. We recorded two-alternative choice RTs from 24 subjects, each with 4 blocks of 200 trials with two task difficulties (easy vs. difficult discrimination) and two instruction sets (urgent vs. accurate). We found that rate distributions were, indeed, very close to Normal, shifting to lower rates with increasing difficulty and accuracy, and for some blocks they appeared to become left-truncated, but still close to Normal. Using autoregressive techniques, we found temporal sequential dependencies for lags of at least 3. We identified a transient and steady-state component in each block. Because rates were Normal, we were able to estimate autoregressive weights using the Box-Jenkins technique, and convert to a moving average model using z-transforms to show explicit dependence on stimulus input. We also found a spatial sequential dependence for the previous 3 lags depending on whether the laterality of previous trials was repeated or alternated. This was partially dissociated from temporal dependency as it only occurred in the easy tasks. We conclude that 2-alternative choice manual RT distributions are close to reciprocal Normal and not the inverse Gaussian. This is not consistent with stochastic rise to threshold models, and we propose a simple optimality model in which reward is maximized to yield to an optimal rate, and hence an optimal time to respond. We discuss how it might be implemented. PMID:24959134

  17. An Experiment To Demonstrate How a Catalyst Affects the Rate of a Reaction.

    ERIC Educational Resources Information Center

    Copper, Christine L.; Koubeck, Edward

    1999-01-01

    Describes a chemistry experiment that allows students to calculate rates of reaction, orders of reaction, and activation energies. The activity demonstrates that to increase a reaction's rate, a catalyst need only provide any additional pathway for the reaction, not necessarily a pathway having lower activation energy. (WRM)

  18. Reaction rate theory of radiation exposure:Effects of dose rate on mutation frequency

    NASA Astrophysics Data System (ADS)

    Bando, Masako; Nakamura, Issei; Manabe, Yuichiro

    2014-03-01

    We revisit the linear no threshold (LNT) hypothesis deduced from the prominent works done by H. J. Muller for the DNA mutation induced by the artificial radiation and by W. L. Russell and E. M. Kelly for that of mega-mouse experiments, developing a new kinetic reaction theory. While the existing theoretical models primarily rely on the dependence of the total dose D on the mutation frequency, the key ingredient in our theory is the dose rate d(t) that accounts for decrease in the mutation rate during the time course of the cellular reactions. The general form for the mutation frequency with the constant dose rate d is simply expressed as, dFm(t)/dt = A - BFm(t) , with A =a0 +a1(d +deff) and B =b0 +b1(d +deff) . We discuss the solution for a most likely case with B > 0 ; Fm(t) = [A/B -Fm(0) ] (1 -e-Bt) +Fm(0) with the control value Fm(0) . We show that all the data of mega-mouse experiments by Russel with different dose rates fall on the universal scaling function Φ(τ) ≡ [Fm(τ) -Fm(0) ]/[ A / B -Fm(0) ] = 1 - exp(- τ) with scaled time τ = Bt . The concept of such a scaling rule provides us with a strong tool to study different species in a unified manner.

  19. Products and kinetics of the heterogeneous reaction of suspended vinclozolin particles with ozone.

    PubMed

    Gan, Jie; Yang, Bo; Zhang, Yang; Shu, Xi; Liu, Changgeng; Shu, Jinian

    2010-11-25

    Vinclozolin is a widely used fungicide that can be released into the atmosphere via application and volatilization. This paper reports an experimental investigation on the heterogeneous ozonation of vinclozolin particles. The ozonation of vinclozolin adsorbed on azelaic acid particles under pseudo-first-order conditions is investigated online with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The ozonation products are analyzed with a combination of VUV-ATOFMS and GC/MS. Two main ozonation products are observed. The formation of the ozonation products results from addition of O(3) on the C-C double bond of the vinyl group. The heterogeneous reactive rate constant of vinclozolin particles under room temperature is (2.4 ± 0.4) × 10(-17) cm(3) molecules(-1) s(-1), with a corresponding lifetime at 100 ppbv O(3) of 4.3 ± 0.7 h, which is almost comparable with the estimated lifetime due to the reaction with atmospheric OH radicals (∼1.7 h). The reactive uptake coefficient for O(3) on vinclozolin particles is (6.1 ± 1.0) × 10(-4). PMID:21038901

  20. New insights into atrazine degradation by cobalt catalyzed peroxymonosulfate oxidation: kinetics, reaction products and transformation mechanisms.

    PubMed

    Ji, Yuefei; Dong, Changxun; Kong, Deyang; Lu, Junhe

    2015-03-21

    The widespread occurrence of atrazine in waters poses potential risk to ecosystem and human health. In this study, we investigated the underlying mechanisms and transformation pathways of atrazine degradation by cobalt catalyzed peroxymonosulfate (Co(II)/PMS). Co(II)/PMS was found to be more efficient for ATZ elimination in aqueous solution than Fe(II)/PMS process. ATZ oxidation by Co(II)/PMS followed pseudo-first-order kinetics, and the reaction rate constant (k(obs)) increased appreciably with increasing Co(II) concentration. Increasing initial PMS concentration favored the decomposition of ATZ, however, no linear relationship between k(obs) and PMS concentration was observed. Higher efficiency of ATZ oxidation was observed around neutral pH, implying the possibility of applying Co(II)/PMS process under environmental realistic conditions. Natural organic matter (NOM), chloride (Cl(-)) and bicarbonate (HCO3(-)) showed detrimental effects on ATZ degradation, particularly at higher concentrations. Eleven products were identified by applying solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC/MS) techniques. Major transformation pathways of ATZ included dealkylation, dechlorination-hydroxylation, and alkyl chain oxidation. Detailed mechanisms responsible for these transformation pathways were discussed. Our results reveal that Co(II)/PMS process might be an efficient technique for remediation of groundwater contaminated by ATZ and structurally related s-triazine herbicides. PMID:25544494

  1. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  2. Students' Ideas about Reaction Rate and Its Relationship with Concentration or Pressure

    ERIC Educational Resources Information Center

    Cakmakci, Gultekin; Leach, John; Donnelly, James

    2006-01-01

    This cross-sectional study identifies key conceptual difficulties experienced by upper secondary school and pre-service chemistry teachers (N = 191) in the area of reaction rates. Students' ideas about reaction rates were elicited through a series of written tasks and individual interviews. In this paper, students' ideas related to reaction rate

  3. Fate of nitrogen species in nitrate reduction by nanoscale zero valent iron and characterization of the reaction kinetics.

    PubMed

    Hwang, Y H; Kim, D G; Ahn, Y T; Moon, C M; Shin, H S

    2010-01-01

    This study investigates the fate of nitrogen species during nitrate reduction by nanoscale zero valent iron (NZVI) as well as the related kinetics. The NZVI used for the experiments was prepared by chemical reduction without a stabilizing agent. The pseudo first order kinetic constant of nitrate reduction at 30 degrees C with an NZVI/nitrate ratio of 1.25:1, which were the reference conditions of this study, was 4.08 h(-1) (R(2)=0.955). A nitrogen mass balance was established by quantitative analysis of aqueous-phase and gas-phase nitrogen species. The results confirm that the nitrate was converted to ammonium ion, that ammonia stripping subsequently occurred under a strong alkaline condition, and that the total amount of aqueous nitrogen was consequently reduced. The nitrate reduction rate also increased with a lower pH and a higher temperature when microscale ZVI was used. However, in contrast to the reaction by microscale ZVI, the nitrate reduction rate by NZVI was higher for an unbuffered condition, possibly due to the abundance of surface atoms and the smaller size. PMID:20150707

  4. An Improved Reaction Rate Formulation for Charged-Particle Induced Thermonuclear Reaction of 2H(d,?)4He

    NASA Astrophysics Data System (ADS)

    Aziz, Azni Abdul; Yusof, Norhasliza; Idris, Mahirah; Kassim, Hasan Abu

    2011-03-01

    The reaction rate formula utilized in compilations such as the Nuclear Astrophysics Compilation of Reaction Rates (NACRE) uses low energy approximation due to temperatures in stars are in the region of a few keVs. Most nuclear reaction experiments were done in MeV range and the interior temperatures of massive stars are 109 K. Hence an improved formulation for calculating the nuclear reaction rate that is applicable to high temperatures is discussed in this work. The exact tunneling probability that is applicable for all energies is obtained by solving the Schrdinger equation. This yields an enhanced expression for the astrophysical S-factor for calculating the thermonuclear reaction rate at high temperature. The thermonuclear reaction rate from this work is applied to the 2H(d,?)4He reaction and is compared with the NACRE compilation. This improved reaction rate can be included in the nuclear reaction network in a Big Bang nucleosynthesis (BBN) code or a stellar nuclear network code.

  5. Neutron detector for fusion reaction-rate measurements

    SciTech Connect

    Lerche, R.A.; Phillion, D.W.; Tietbohl, G.L.

    1993-09-03

    We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response < 25-ps FWHM. A thin piece of scintillator material acts as a neutron-to- light converter. A zoom lens images light from the scintillator surface to a high-speed (15 ps) optical streak camera for recording. The zoom lens allows the scintillator to be positioned between 1 and 50 cm from a target. The camera simulaneously records an optical fiducial pulse which allows the camera time base to be calibrated relative to the incident laser power. Bursts of x rays formed by focusing 20-ps, 2.5-TW laser pulses onto gold disk targets demonstrate the detector resolution to be < 25 ps. We have recorded burn histories for deuterium/tritium-filled targets producing as few as 3 {times} 10{sup 7} neutrons.

  6. Enhanced reaction rates in NDP analysis with neutron scattering

    SciTech Connect

    Downing, R. Gregory

    2014-04-15

    Neutron depth profiling (NDP) makes accessible quantitative information on a few isotopic concentration profiles ranging from the surface into the sample a few micrometers. Because the candidate analytes for NDP are few, there is little interference encountered. Furthermore, neutrons have no charge so mixed chemical states in the sample are of no direct concern. There are a few nuclides that exhibit large probabilities for neutron scattering. The effect of neutron scattering on NDP measurements has not previously been evaluated as a basis for either enhancing the reaction rates or as a source of measurement error. Hydrogen is a common element exhibiting large neutron scattering probability found in or around sample volumes being analyzed by NDP. A systematic study was conducted to determine the degree of signal change when neutron scattering occurs during analysis. The relative signal perturbation was evaluated for materials of varied neutron scattering probability, concentration, total mass, and geometry. Signal enhancements up to 50% are observed when the hydrogen density is high and in close proximity to the region of analysis with neutron beams of sub thermal energies. Greater signal enhancements for the same neutron number density are reported for thermal neutron beams. Even adhesive tape used to position the sample produces a measureable signal enhancement. Because of the shallow volume, negligible distortion of the NDP measured profile shape is encountered from neutron scattering.

  7. Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2009-08-01

    This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  8. Laser flash photolysis studies of radical-radical reaction kinetics: The HO{sub 2} + IO reaction

    SciTech Connect

    Cronkhite, J.M.; Stickel, R.E.; Nicovich, J.M.; Wine, P.H.

    1999-04-29

    Reactive iodine as a potential tropospheric O{sub 3} sink has received considerable attention recently. Laser flash photolysis of Cl{sub 2}/CH{sub 3}OH/O{sub 2}/I{sub 2}/NO{sub 2}/SF{sub 6}N{sub 2} mixtures at 308 nm has been coupled with simultaneous time-resolved detection of HO{sub 2} (by infrared tunable diode laser absorption spectroscopy) and IO (by visible absorption spectroscopy) to investigate the kinetics of the atmospherically important reaction HO{sub 2} + IO {r_arrow} products over the temperature range 274--373 K in N{sub 2} buffer gas at pressures of 12 and 25 Torr. All experiments were performed under near pseudo-first-order conditions with HO{sub 2} in excess over IO. At 298 K, the rate coefficient was determined to be (9.7 {+-} 2.9) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1}s{sup {minus}1}, with the primary source of uncertainty being knowledge of the infrared line strength(s) required to convert measured HO{sub 2} absorbances to absolute concentrations. The temperature dependence of the HO{sub 2} + IO rate coefficient was found to be adequately described by the Arrhenius expression k = 9.3 {times} 10{sup {minus}12} exp(680/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The results reported in this study are compared with other recent studies of HO{sub 2} + IO kinetics, and the potential roles of this reaction in atmospheric chemistry are discussed.

  9. On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

    PubMed

    Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

    2016-07-13

    If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data. PMID:27237834

  10. Experimental and density functional theoretical study of the effects of Fenton's reaction on the degradation of Bisphenol A in a high voltage plasma reactor.

    PubMed

    Dai, Fei; Fan, Xiangru; Stratton, Gunnar R; Bellona, Christopher L; Holsen, Thomas M; Crimmins, Bernard S; Xia, Xiaoyan; Mededovic Thagard, Selma

    2016-05-01

    A novel electrical discharge plasma reactor configuration with and without iron ions was evaluated for the degradation of 0.02mM Bisphenol A (BPA). The pseudo-first-order reaction rate constant calculated for the plasma treatment of BPA with a stainless steel electrode in the presence of dissolved ferrous ion (Fe(2+)) salts (termed plasma/Fenton treatment) was higher than in the plasma treatment in the absence of iron salts. At the optimal ferrous ion concentration, longer plasma treatment times resulted in higher BPA degradation rates, likely due to increased hydroxyl (OH) radical concentration formed through the decomposition of H2O2. Replacing the stainless steel with a carbon steel grounded electrode resulted in the release of iron ions from the carbon steel thereby increasing the rate of BPA removal and eliminating the need for iron salts. After the plasma/Fenton treatment, >97% of the residual iron salts were removed by coagulation/flocculation/sedimentation. Byproduct identification coupled with density functional theory (DFT) calculations confirmed that OH radical attack on BPA's hydroxyl group is the primary pathway for byproduct formation. PMID:26874105

  11. Photooxidative removal of the herbicide Acid Blue 9 in the presence of hydrogen peroxide: modeling of the reaction for evaluation of electrical energy per order (E EO).

    PubMed

    Khataee, Ali R; Khataee, Hamid R

    2008-09-01

    The present work deals with photooxidative removal of the herbicide, Acid Blue 9 (AB9), in water in the presence of hydrogen peroxide (H2O2) under UV light illumination (30 W). The influence of the basic operational parameters such as amount of H2O2, irradiation time and initial concentration of AB9 on the photodegradation efficiency of the herbicide was investigated. The degradation rate of AB9 was not appreciably high when the photolysis was carried out in the absence of H2O2 and it was negligible in the absence of UV light. The photooxidative removal of the herbicide was found to follow pseudo-first-order kinetic, and hence the figure-of-merit electrical energy per order (E Eo) was considered appropriate for estimating the electrical energy efficiency. A mathematical relation between the apparent reaction rate constant and H2O2 used was applied for prediction of the electricity consumption in the photooxidative removal of AB9. The results indicated that this kinetic model, based on the initial rates of degradation, provided good prediction of the E Eo values for a variety of conditions. The results also indicated that the UV/H2O2 process was appropriate as the effective treatment method for removal of AB9 from the contaminated wastewater. PMID:18803110

  12. High-temperature photochemistry kinetics study of the reaction of O(/sup 3/P) atoms with ethylene from 290 to 1510 K

    SciTech Connect

    Mahmud, K.; Marshall, P.; Fontijn, A.

    1987-03-12

    The O + C/sub 2/H/sub 4/ reaction has been investigated in a high-temperature photochemistry (HTP) reactor at temperatures from 290 to 1510 K and pressures from 60 to 500 Torr. Ground-state O atoms were generated by flash photolysis of CO/sub 2/ and monitored by time-resolved atomic resonance fluorescence with pulse counting. Measurements were made under pseudo-first-order conditions (O) << (C/sub 2/H/sub 4/). Rate coefficients from 290 to 850 K are in good agreement with the numerous earlier measurements in that range. Above those temperatures a sharp rise in k(T) with increasing T is evident. On the basis of present and other measurements by isolated elementary reaction techniques they recommend k(T) = 1.3 x 10/sup -11/ exp(-830 K/T) + 1.9 x 10/sup -9/ x exp(-6940 K/T) cm/sup 3/ molecule/sup -1/ s/sup -1/ as a fit expression for the 290-1510 K range. Confidence limits are discussed in the text. It is shown that the accepted transition-state treatment for channels significant at T < 850 K cannot account for the sharp upward curvature. Other channels will have to be considered at higher temperatures.

  13. Gas-phase hydrodenitrogenation reactions of polynuclear heteroaromatic nitrogen compounds and selected intermediates with a 50% nickel oxide/aluminate supported on silica-alumina catalyst

    SciTech Connect

    Fish, R.H.; Heinemann, H. ); Michaels, J.N.; Moore, R.S. )

    1990-05-01

    The gas-phase hydrodenitrogenation (HDN) of quinoline, 1,2,3,4-tetrahydroquinoline, 2-propylaniline, and propylbenzene with a 50% nickel oxide/aluminate on SiO{sub 2}-Al{sub 2}O{sub 3} catalyst has been studied at 250{degree}C under 1 atm of hydrogen gas. Under these mild conditions, alkylaromatics are the predominant HDN products. In the reaction network of this catalytic process, quinoline is hydrogenated to 1,2,3,4-tetrahydroquinoline, which subsequently undergoes C-N bond hydrogenolysis to form 2-propylaniline and then propylbenzene. Significant alkyl side-chain hydrogenolysis occurs in parallel to these reactions, producing a mixture of alkylanilines and alkylbenzenes. Small amounts of alkylcyclohexanes are produced by hydrogenation of the alkylbenzenes. This network differs significantly from that of commercial HDN processes in which quinoline is hydrogenated fully to decahydroquinoline prior to C-H bond cleavage. Pseudo-first-order rate constants have been estimated for quinoline hydrogenation, alkylaniline formation, alkylaniline HDN, and alkylbenzene hydrogenation and compared to analogous data for commercial HDN. This comparison indicates that the activity of the nickel oxide/aluminate on SiO{sub 2}-Al{sub 2}O{sub 3} catalyst is within an order of magnitude of the activity of commercial HDN catalysts. The nickel oxide catalyst is irreversibly poisoned by sulfur and slowly deactivates during HDN due to coke formation; the coked catalyst can be regenerated by oxidation in air and subsequent reduction in hydrogen.

  14. Kinetics of tetrabromobisphenol A (TBBPA) reactions with H₂SO₄, HNO₃ and HCl: implication for hydrometallurgy of electronic wastes.

    PubMed

    Zhong, Yin; Li, Dan; Mao, Zhe; Huang, Weilin; Peng, Ping'an; Chen, Pei; Mei, Jun

    2014-04-15

    Hydrometallurgy is an acid leaching based process widely used for recovering precious metals from electronic wastes (e-wastes). The effects of acid leaching on the fate of brominated flame retardants (BFRs) in typical hydrometallurgical processes remain largely unknown. This study was aimed at evaluating the fate of tetrabromobisphenol A (TBBPA), a commonly used BFR, in three acid leaching reagents (i.e. H2SO4, HNO3, and HCl) commonly used in hydrometallurgy. It was found that the reactions of TBBPA with concentrated H2SO4 followed a pseudo-zero-order rate and the reaction rates declined rapidly as the concentrations of H2SO4 decreased. In contrast, TBBPA could be easily transformed in less concentrated HNO3 solutions (<21.7 wt%) and the reactions followed a pseudo-first-order rate. The reaction products identified by GC-MS indicated different transformation pathways of TBBPA in H2SO4 and HNO3. HCl or HCl/H2SO4 mixtures (3:1, v/v) did not appear to react with TBBPA, while aqua regia (3:1 HCl/HNO3, v/v) reacted violently with TBBPA and led to almost complete disappearance of TBBPA within a minute. It suggested that HNO3 significantly affected the fate of TBBPA and the use of HNO3 as leaching reagents in hydrometallurgy of e-wastes should be carefully evaluated. Collectively, our findings of distinct fate of TBBPA in different acid leaching reagents provided fundamental information for design of hydrometallurgical treatment of e-wastes to minimize acid reactions with BFRs within plastics matrix and to maximize acid leaching efficiency for metals recycling processes. PMID:24594840

  15. Students' Ideas about Reaction Rate and Its Relationship with Concentration or Pressure

    ERIC Educational Resources Information Center

    Cakmakci, Gultekin; Leach, John; Donnelly, James

    2006-01-01

    This cross-sectional study identifies key conceptual difficulties experienced by upper secondary school and pre-service chemistry teachers (N = 191) in the area of reaction rates. Students' ideas about reaction rates were elicited through a series of written tasks and individual interviews. In this paper, students' ideas related to reaction rate…

  16. Cross sections and reaction rates of relevance to aeronomy

    SciTech Connect

    Fox, J.L. )

    1991-01-01

    Experimental and theoretical data relevant to models and measurements of the chemical and thermal structures and luminosity of the thermospheres of the earth and planets published during the last four years are surveyed. Among chemical processes, attention is given to ion-molecule reactions, dissociative recombination of molecular ions, and reactions between neutral species. Both reactions between ground state species and species in excited states are considered, including energy transfer and quenching. Measured and calculated cross sections for interactions of solar radiation with atmospheric species, such as photoabsorption, photoionization, and photodissociation and related processes are surveyed.

  17. Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids.

    PubMed

    Gurkan, Burcu E; Gohndrone, Thomas R; McCready, Mark J; Brennecke, Joan F

    2013-05-28

    The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614])-based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22-60 °C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme--a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19,500 L mol(-1) s(-1) ([P66614][Pro]) to 3200 L mol(-1) s(-1) ([P66614][3-CF3pyra]) at 22 °C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol(-1) measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol(-1) for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations. PMID:23598368

  18. The influence of steric hindrance on kinetics and isotope effects in the reaction of 2,2-bis(4-dimethylaminophenyl)-1-nitro-1-(4-nitrophenyl)ethane with DBU base in acetonitrile

    NASA Astrophysics Data System (ADS)

    Nowak, Iwona; Jarczewski, Arnold

    2014-11-01

    The pKa value for 2,2-bis(4-dimethylaminophenyl)-1-nitro-1-(4-nitrophenyl)ethane, (dmap)2 (pKa = 25.11) has been measured spectrophotometrically using buffer solutions of a few strong amine bases: 1,8-diazabicyclo[5.4.0]undec-7-ene, (DBU); 1,1,3,3-tetramethylguanidine, (TMG); 1,5,7-triazabicyclo[4.4.0]dec-5-ene, (TBD); 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, (MTBD) and their salts. The low energy conformers of nitrophenyl nitroalkanes have been determined using the semiempirical PM6 methods, (B3-LYP) density functional theory (DFT) together with the 6-31G(d,p) basis set. The participation of the low energy conformer in the proton transfer reaction to DBU base has been discussed. The kinetic data for proton transfer reactions between (dmap)2 and DBU in acetonitrile (MeCN) at pseudo-first order conditions have been presented. The influence of steric hindrance brought by reacting C-acid and organic base on the stability of the transition state has been discussed. The rates of second-order rate constants for series of nitrophenyl nitroalkanes, NO2PhCHRNO2 (R = Me; Et; iPr; dimethylaminophenyl = (dmap)2) are presented and discussed.

  19. Night-time tropospheric chemistry of the unsaturated alcohols ( Z)-pent-2-en-1-ol and pent-1-en-3-ol: Kinetic studies of reactions of NO 3 and N 2O 5 with stress-induced plant emissions

    NASA Astrophysics Data System (ADS)

    Pfrang, Christian; Baeza Romero, Maria T.; Cabanas, Beatriz; Canosa-Mas, Carlos E.; Villanueva, Florentina; Wayne, Richard P.

    The night-time tropospheric chemistry of two stress-induced volatile organic compounds (VOCs), ( Z)-pent-2-en-1-ol and pent-1-en-3-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO 3) with these pentenols were measured using the discharge-flow technique. Because of the relatively low volatility of these compounds, we employed off-axis continuous-wave cavity-enhanced absorption spectroscopy for detection of NO 3 in order to be able to work in pseudo first-order conditions with the pentenols in large excess over NO 3. The rate coefficients were determined to be (1.53±0.23)×10 -13 and (1.39±0.19)×10 -14 cm 3 molecule -1 s -1 for reactions of NO 3 with ( Z)-pent-2-en-1-ol and pent-1-en-3-ol. An attempt to study the kinetics of these reactions with a relative-rate technique, using N 2O 5 as source of NO 3 resulted in significantly higher apparent rate coefficients. Performing relative-rate experiments in known excesses of NO 2 allowed us to determine the rate coefficients for the N 2O 5 reactions to be (5.0±2.8)×10 -19 cm 3 molecule -1 s -1 for ( Z)-pent-2-en-1-ol, and (9.1±5.8)×10 -19 cm 3 molecule -1 s -1 for pent-1-en-3-ol. We show that these relatively slow reactions can indeed interfere with rate determinations in conventional relative-rate experiments.

  20. "Depletion": A Game with Natural Rules for Teaching Reaction Rate Theory.

    ERIC Educational Resources Information Center

    Olbris, Donald J.; Herzfeld, Judith

    2002-01-01

    Depletion is a game that reinforces central concepts of reaction rate theory through simulation. Presents the game with a set of follow-up questions suitable for either a quiz or discussion. Also describes student reaction to the game. (MM)

  1. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  2. High-temperature photochemistry kinetics study of the reaction of O(/sup 3/P) atoms with acetylene from 290 to 1510 K

    SciTech Connect

    Mahmud, K.; Fontijn, A.

    1987-03-26

    Overall rate coefficients for the O + C/sub 2/H/sub 2/ reaction have been measured in a high-temperature photochemistry (HTP) reactor at temperatures from 290 to 1510 K and pressures from 120 to 630 Torr. Ground-state O atoms were generated from flash photolysis of O/sub 2/ or CO/sub 2/ and monitored by time-resolved atomic resonance fluorescence with pulse counting. Measurements were made under pseudo-first-order conditions (O) << (C/sub 2/H/sub 2/). Rate coefficients from 290 to 1300 K are in good agreement with flow reactor measurements in that range. The strongly curved arrhenius-type plot obtained is contiguous with that found in recent shock tube work from 1500 to 2600 K. A weighted fit to the authors measurements leads to the expression k(T) = 1.1 x 10/sup -19/T/sup 2.6/ exp(-330K/T) cm/sup 3/ molecule/sup -1/ s/sup -1/. Combining the present data set with other experimentally determined k values yields, for the 290 to 2600 K temperature range, k(T) = 3.6 x 10/sup -20/T/sup 2.8/ exp(-250K/T) cm/sup 3/ molecule/sup -1/ s/sup -1/; the accuracy is assessed as 35% at the 1sigma confidence level.

  3. Development of the new approach to the diffusion-limited reaction rate theory

    SciTech Connect

    Veshchunov, M. S.

    2012-04-15

    The new approach to the diffusion-limited reaction rate theory, recently proposed by the author, is further developed on the base of a similar approach to Brownian coagulation. The traditional diffusion approach to calculation of the reaction rate is critically analyzed. In particular, it is shown that the traditional approach is applicable only in the special case of reactions with a large reaction radius and the mean inter-particle distances, and become inappropriate in calculating the reaction rate in the case of a relatively small reaction radius. In the latter case, most important for chemical reactions, particle collisions occur not in the diffusion regime but mainly in the kinetic regime characterized by homogeneous (random) spatial distribution of particles on the length scale of the mean inter-particle distance. The calculated reaction rate for a small reaction radius in three dimensions formally (and fortuitously) coincides with the expression derived in the traditional approach for reactions with a large reaction radius, but notably deviates at large times from the traditional result in the planar two-dimensional geometry. In application to reactions on discrete lattice sites, new relations for the reaction rate constants are derived for both three-dimensional and two-dimensional lattices.

  4. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    NASA Technical Reports Server (NTRS)

    Tsotsis, T. T.; Sane, R. C.

    1987-01-01

    It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.

  5. Quick and Easy Rate Equations for Multistep Reactions

    ERIC Educational Resources Information Center

    Savage, Phillip E.

    2008-01-01

    Students rarely see closed-form analytical rate equations derived from underlying chemical mechanisms that contain more than a few steps unless restrictive simplifying assumptions (e.g., existence of a rate-determining step) are made. Yet, work published decades ago allows closed-form analytical rate equations to be written quickly and easily for

  6. Quick and Easy Rate Equations for Multistep Reactions

    ERIC Educational Resources Information Center

    Savage, Phillip E.

    2008-01-01

    Students rarely see closed-form analytical rate equations derived from underlying chemical mechanisms that contain more than a few steps unless restrictive simplifying assumptions (e.g., existence of a rate-determining step) are made. Yet, work published decades ago allows closed-form analytical rate equations to be written quickly and easily for…

  7. Electric field modulation of electron transfer reaction rates in isotropic systems: Long-distance charge recombination in photosynthetic reaction centers

    SciTech Connect

    Franzen, S.; Goldstein, R.F.; Boxer, S.G. )

    1990-06-14

    A general method is demonstrated for experimentally obtaining the rate constant of electron transfer as a function of the free energy of the reaction in nonoriented systems. An external electric field is used to modulate the energy levels of dipolar states and thereby affect the electron-transfer rate. The method is valid for any electron-transfer system which has a fixed distance between the donor and acceptor. The method is employed to obtain the experimental rate vs applied electric field curve of the charge recombination reaction between the oxidized special pair electron donor and the reduced ubiquinone acceptor in bacterial reaction centers of Rb. sphaeroides at 80 K. The experimental rate vs electric field curve is shown to be equivalent to the rate vs free energy curve when it is linearly scaled by the dipole moment of the charge-transfer state and the local field correction.

  8. The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

    NASA Technical Reports Server (NTRS)

    Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

    1982-01-01

    The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

  9. Kinetics study of heterogeneous reactions of ozone with erucic acid using an ATR-IR flow reactor.

    PubMed

    Leng, Chunbo; Hiltner, Joseph; Pham, Hai; Kelley, Judas; Mach, Mindy; Zhang, Yunhong; Liu, Yong

    2014-03-01

    The ozone initiated heterogeneous oxidation of erucic acid (EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy (ATR-IR) over wide ranges of ozone concentrations (0.25-60 ppm), thin film thickness (0.1-1.0 μm), temperatures (263-298 K), and relative humidities (0-80% RH) for the first time. Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained through changes in the absorbance of C[double bond, length as m-dash]O stretching bands at 1695 cm(-1), which is assigned to the carbonyl group in carboxylic acid. Results showed that the reaction followed the Langmuir-Hinshelwood mechanism and kapp was largely dominated by surface reaction over bulk phase reaction. In addition, both the kapp and the γ values showed very strong temperature dependences (∼two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, the activation energy for the heterogeneous reaction was estimated to be 80.6 kJ mol(-1). Our results have suggested that heterogeneous reactions between ozone and unsaturated solid surfaces likely have a substantially greater temperature dependence than liquid ones. Moreover, the hygroscopic properties of EA thin films before and after exposure to ozone were also studied by measurement of water uptake. Based on the hygroscopicity data, the insignificant RH effect on reaction kinetics was probably due to the relatively weak water uptake by the unreacted and reacted EA thin films. PMID:24457621

  10. The surface reaction kinetics of salicylate on alumina

    SciTech Connect

    Wang, Z.; Ainsworth, C.C.; Friedrich, D.M.; Joly, A.G.; Gassman, P.L.

    1997-12-31

    The kinetics of reaction of salicylate with colloidal alumina in aqueous suspension and with Al(III) in homogeneous aqueous solution were studied by stopped-flow laser fluorescence spectroscopy. The emission spectra confirmed the formation of both monodentate complexes and more stable bidentate chelates. Temporal evolution of the spectra indicated that the reaction was fast (within first few minutes) for both the homogeneous and heterogeneous reactions but slowed down afterwards for the latter. Reactions completed within 10 minutes in homogeneous phase at pH 3.3 but took more than 12 hours in alumina suspension. Analysis of the fluorescence intensity within first four minutes showed that in homogeneous phase the reaction followed a single pseudo-first-order kinetics. In alumina suspension log plots were nonlinear and characteristic of multiple heterogeneous reaction paths. The kinetics are interpreted in terms of the simultaneous formation of multiple species as well as subsequent conversion between species.

  11. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase

    DOE PAGESBeta

    McInerney, Peter; Adams, Paul; Hadi, Masood Z.

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Errormore » rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu , Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition.« less

  12. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase.

    PubMed

    McInerney, Peter; Adams, Paul; Hadi, Masood Z

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Error rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu, Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition. PMID:25197572

  13. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  14. Effect of temperature oscillation on chemical reaction rates in the atmosphere

    NASA Technical Reports Server (NTRS)

    Eberstein, I. J.

    1974-01-01

    The effect of temperature fluctuations on atmospheric ozone chemistry is examined by considering the Chapman photochemical theory of ozone transport to calculate globally averaged ozone production rates from mean reaction rates, activation energies, and recombination processes.

  15. Interlaboratory reaction rate program. 12th progress report, November 1976-October 1979

    SciTech Connect

    Lippincott, E.P.; McElroy, W.N.; Preston, C.C.

    1980-09-01

    The Interlaboratory Reaction Rate UILRR) program is establishing the capability to accurately measure neutron-induced reactions and reaction rates for reactor fuels and materials development programs. The goal for the principal fission reactions, /sup 235/U, /sup 238/U and /sup 239/Pu, is an accuracy to within +- 5% at the 95% confidence level. Accurate measurement of other fission and nonfission reactions is also required, but to a lesser accuracy, between +- 5% and 10% at the 95% confidence level. A secondary program objective is improvement in knowledge of the nuclear parameters involved in the standarization of fuels and materials dosimetry measurements of neutron flux, spectra, fluence and burnup.

  16. Upper atmosphere research: Reaction rate and optical measurements

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Allen, J. E., Jr.; Nava, D. F.; Payne, W. A., Jr.

    1990-01-01

    The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

  17. Kinetics of CH2OO reactions with SO2, NO2, NO, H2O and CH3CHO as a function of pressure.

    PubMed

    Stone, Daniel; Blitz, Mark; Daubney, Laura; Howes, Neil U M; Seakins, Paul

    2014-01-21

    Kinetics of CH2OO Criegee intermediate reactions with SO2, NO2, NO, H2O and CH3CHO and CH2I radical reactions with NO2 are reported as a function of pressure at 295 K. Measurements were made under pseudo-first-order conditions using flash photolysis of CH2I2-O2-N2 gas mixtures in the presence of excess co-reagent combined with monitoring of HCHO reaction products by laser-induced fluorescence (LIF) spectroscopy and, for the reaction with SO2, direct detection of CH2OO by photoionisation mass spectrometry (PIMS). Rate coefficients for CH2OO + SO2 and CH2OO + NO2 are independent of pressure in the ranges studied and are (3.42 ± 0.42) × 10(-11) cm(3) s(-1) (measured between 1.5 and 450 Torr) and (1.5 ± 0.5) × 10(-12) cm(3) s(-1) (measured between 25 and 300 Torr), respectively. The rate coefficient for CH2OO + CH3CHO is pressure dependent, with the yield of HCHO decreasing with increasing pressure. Upper limits of 2 × 10(-13) cm(3) s(-1) and 9 × 10(-17) cm(3) s(-1) are placed on the rate coefficients for CH2OO + NO and CH2OO + H2O, respectively. The upper limit for the rate coefficient for CH2OO + H2O is significantly lower than has been reported previously, with consequences for modelling of atmospheric impacts of CH2OO chemistry. PMID:24287566

  18. Putting Reaction Rates and Collision Theory in the Hands of Your Students.

    ERIC Educational Resources Information Center

    Evenson, Andy

    2002-01-01

    Describes a simulation that can be used to give concrete analogies of collision theory and the factors that affect reaction rates including temperature, concentration, catalyst, and molecular orientation. The simulation works best if done as an introduction to the concepts to help prevent misconceptions about reaction rates and collision theory.

  19. Putting Reaction Rates and Collision Theory in the Hands of Your Students.

    ERIC Educational Resources Information Center

    Evenson, Andy

    2002-01-01

    Describes a simulation that can be used to give concrete analogies of collision theory and the factors that affect reaction rates including temperature, concentration, catalyst, and molecular orientation. The simulation works best if done as an introduction to the concepts to help prevent misconceptions about reaction rates and collision theory.…

  20. Absolute rate parameters for the reaction of ground state atomic oxygen with carbonyl sulfide

    NASA Technical Reports Server (NTRS)

    Klemm, R. B.; Stief, L. J.

    1974-01-01

    The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS yields CO + SO, have been determined directly by monitoring O(3P) using the flash photolysis-resonance fluorescence technique. The value for reaction rate was measured over a temperature range of 263-502 K and the data were fitted to an Arrhenius expression with good linearity. A comparison of the present results with those from previous studies of this reaction is also presented.

  1. Reaction rate constants of HO2 + O3 in the temperature range 233-400 K

    NASA Technical Reports Server (NTRS)

    Wang, Xiuyan; Suto, Masako; Lee, L. C.

    1988-01-01

    The reaction rate constants of HO2 + O3 were measured in the temperature range 233-400 K using a discharge flow system with photofragment emission detection. In the range 233-253 K, the constants are approximately a constant value, and then increase with increasing temperature. This result suggests that the reaction may have two different channels. An expression representing the reaction rate constants is presented.

  2. Critical evaluation and rate constants of chemoselective ligation reactions for stoichiometric conjugations in water.

    PubMed

    Saito, Fumito; Noda, Hidetoshi; Bode, Jeffrey W

    2015-04-17

    Chemoselective ligation reactions have contributed immensely to the development of organic synthesis and chemical biology. However, the ligation of stoichiometric amounts of large molecules for applications such as protein-protein conjugates is still challenging. Conjugation reactions need to be fast enough to proceed under dilute conditions and chemoselective in the presence of unprotected functional groups; the starting materials and products must be stable under the reaction conditions. To compare known ligation reactions for their suitability under these conditions, we determined the second-order rate constants of ligation reactions using peptide substrates with unprotected functional groups. The reaction conditions, the chemoselectivity of the reactions, and the stability of the starting materials and products were carefully evaluated. In some cases, the stability could be improved by modifying the substrate structure. These data obtained under the ligation conditions provide a useful guide to choose an appropriate ligation reaction for synthesis of large molecules by covalent ligation reactions of unprotected substrates in water. PMID:25572124

  3. The Gaseous Explosive Reaction : the Effect of Pressure on the Rate of Propagation of the Reaction Zone and upon the Rate of Molecular Transformation

    NASA Technical Reports Server (NTRS)

    Stevens, F W

    1932-01-01

    This study of gaseous explosive reaction has brought out a number of important fundamental characteristics of the explosive reaction indicating that the basal processes of the transformation are much simpler and corresponds more closely to the general laws and principles of ordinary transformations than is usually supposed. The report calls attention to the point that the rate of molecular transformation within the zone was found in all cases to be proportional to pressure, that the transformation within the zone is the result of binary impacts. This result is of unusual interest in the case of the reaction of heavy hydrocarbon fuels and the reaction mechanism proposed by the recent kinetic theory of chain reactions.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  5. Modeling kinetic partitioning of secondary organic aerosol and size distribution dynamics: representing effects of volatility, phase state, and particle-phase reaction

    NASA Astrophysics Data System (ADS)

    Zaveri, R. A.; Easter, R. C.; Shilling, J. E.; Seinfeld, J. H.

    2013-11-01

    This paper describes and evaluates a new formulation for modeling kinetic gas-particle partitioning of secondary organic aerosol (SOA) that takes into account diffusion and chemical reaction within the particle phase. The new formulation uses a combination of: (a) an analytical quasi-steady-state treatment for the diffusion-reaction process within the particle phase for fast-reacting organic solutes, and (b) a two-film theory approach for slow- and non-reacting solutes. The formulation is amenable for use in regional and global atmospheric models, although it currently awaits specification of the actual species and particle-phase reactions that are important for SOA formation. Here, the formulation is applied within the framework of the computationally efficient Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) to investigate the competitive growth dynamics of the Aitken and accumulation mode particles. Results show that the timescale of SOA partitioning and the associated size distribution dynamics depend on the complex interplay between organic solute volatility, particle-phase bulk diffusivity, and particle-phase reactivity (as exemplified by a pseudo-first-order reaction rate constant), each of which can vary over several orders of magnitude. In general, the timescale of SOA partitioning increases with increase in volatility and decrease in bulk diffusivity and rate constant. At the same time, the shape of the aerosol size distribution displays appreciable narrowing with decrease in volatility and bulk diffusivity and increase in rate constant. A proper representation of these physicochemical processes and parameters are needed in the next generation models to reliably predict not only the total SOA mass, but also its composition and number size distribution, all of which together determine its overall optical and cloud-nucleating properties.

  6. The effect of temperature fluctuations of reaction rate constants in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Antaki, P. J.; Kassar, G. M.

    1981-01-01

    Current models of turbulent reacting flows frequently use Arrhenius reaction rate constants obtained from static or laminar flow theory and/or experiments, or from best fits of static, laminar, and turbulent data. By treating the reaction rate constant as a continuous random variable which is temperature-dependent, the present study assesses the effect of turbulent temperature fluctuations on the reaction rate constant. This model requires that a probability density function (PDF) describing the nature of the fluctuations be specified. Three PDFs are examined: the clipped Gaussian, the beta PDF, and the ramp model. All the models indicate that the reaction rate constant is greater in a turbulent flow field than in an equivalent laminar flow. In addition, an amplification ratio, which is the ratio of the turbulent rate constant to the laminar rate constant, is defined and its behavior as a function of the mean temperature fluctuations is described

  7. Chiral Polymerization in Open Systems From Chiral-Selective Reaction Rates

    NASA Astrophysics Data System (ADS)

    Gleiser, Marcelo; Nelson, Bradley J.; Walker, Sara Imari

    2012-08-01

    We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates.

  8. Chiral polymerization in open systems from chiral-selective reaction rates.

    PubMed

    Gleiser, Marcelo; Nelson, Bradley J; Walker, Sara Imari

    2012-08-01

    We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates. PMID:22610131

  9. A simple expression for the apparent reaction rate of large wood char gasification with steam.

    PubMed

    Umeki, Kentaro; Roh, Seon-Ah; Min, Tai-Jin; Namioka, Tomoaki; Yoshikawa, Kunio

    2010-06-01

    A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results. PMID:20144863

  10. Malonic acid concentration as a control parameter in the kinetic analysis of the Belousov-Zhabotinsky reaction under batch conditions.

    PubMed

    Blagojević, Slavica M; Anić, Slobodan R; Cupić, Zeljko D; Pejić, Natasa D; Kolar-Anić, Ljiljana Z

    2008-11-28

    The influence of the initial malonic acid concentration [MA]0 (8.00 x 10(-3) < or = [MA]0 < or = 4.30 x 10(-2) mol dm(-3)) in the presence of bromate (6.20 x 10(-2) mol dm(-3)), bromide (1.50 x 10(-5) mol dm(-3)), sulfuric acid (1.00 mol dm(-3)) and cerium sulfate (2.50 x 10(-3) mol dm(-3)) on the dynamics and the kinetics of the Belousov-Zhabotinsky (BZ) reactions was examined under batch conditions at 30.0 degrees C. The kinetics of the BZ reaction was analyzed by the earlier proposed method convenient for the examinations of the oscillatory reactions. In the defined region of parameters where oscillograms with only large-amplitude relaxation oscillations appeared, the pseudo-first order of the overall malonic acid decomposition with a corresponding rate constant of 2.14 x 10(-2) min(-1) was established. The numerical results on the dynamics and kinetics of the BZ reaction, carried out by the known skeleton model including the Br2O species, were in good agreement with the experimental ones. The already found saddle node infinite period (SNIPER) bifurcation point in transition from a stable quasi-steady state to periodic orbits and vice versa is confirmed by both experimental and numerical investigations of the system under consideration. Namely, the large-amplitude relaxation oscillations with increasing periods between oscillations in approaching the bifurcation points at the beginning and the end of the oscillatory domain, together with excitability of the stable quasi-steady states in their vicinity are obtained. PMID:18989478

  11. Rate variations of a hetero-Diels--Alder reaction in supercritical fluid CO{sub 2}

    SciTech Connect

    Thompson, R.L.; Glaeser, R.; Bush, D.; Liotta, C.L.; Eckert, C.A.

    1999-11-01

    The hetero-Diels-Alder reaction between anthracene and excess 4-phenyl-1,2,4-triazoline-3,5-dione has been investigated in supercritical CO{sub 2} at 40 C and pressures between 75 and 216 bar. Biomolecular reaction rate constants have been measured via fluorescence spectroscopy by following the decrease in anthracene concentration with reaction time. The reaction rate is elevated in the vicinity of the critical pressure. This difference is consistent with local composition enhancement and can be modeled with the Peng-Robinson equation of state.

  12. Improving the rate of the triple alpha reaction

    NASA Astrophysics Data System (ADS)

    Tur, Clarisse; Austin, S. M.; Wuosmaa, A.; Lighthall, J.; Marley, S.; Goodman, N.; Bos, J. J.

    The rate of the triple alpha process, which plays a central role in the production of 12C in stars, is known with an accuracy of about 12%. Variations within the ±12% errors in this rate can cause significant changes in the determination of the mass of the iron core in core-collapse supernovae and the composition of the material later ejected in the interstellar medium, as well as a factor of two change in the surface abundance of 12C in light ABG stars. The triple alpha experiment presented here is a collaborative effort between the Western Michigan University (WMU) and the National Superconducting Cyclotron Laboratory (NSCL) and aims at reducing the uncertainty on the knowledge of this rate to about 6% by measuring more accurately than has been done in the past the pair branch for the 7.654 MeV state in 12C. This state is excited by inelastic proton scattering ( 12C(p, p )12C(7.654MeV ) ), taking advantage of a strong resonance at a bombarding energy of about 10.6 MeV and a scattering angle of 135 degrees in the laboratory. The decay pairs are detected in an almost 4π scintillator system surrounding the target. The protons are produced using the Tandem accelerator at Western Michigan University and detected by silicon detectors at 135 degrees in the lab. The pair branch is given by the ratio of the number of electron-positron pairs detected in the plastic scintillators in coincidence with the protons in the 7.654 MeV silicon spectra to the number of those protons. A reduction in the gamma ray background, mainly due to the cascade gamma decay of the 7.654 MeV state through the 4.44 MeV 2+ state, is achieved by a coincidence requirement between a thin scintillator tube and the large block of plastic scintillator surrounding it. The measurement is expected to take place in the summer of 2006.

  13. Spectrophotometric reaction rate method for determination of barbituric acid by inhibition of the hydrochloric acid-bromate reaction

    NASA Astrophysics Data System (ADS)

    Ensafi, Ali A.; Movahedinia, H.

    2003-11-01

    A new kinetic-spectrophotometric method was developed for the determination of barbituric acid. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.9×10 -7 M and calibration rang is 1×10 -6-6.0×10 -4 M barbituric acid. The linearity range of the calibration graph is depends on bromate concentration. The relative standard deviation of seven replication determination of 5.6×10 -6 M barbituric acid was 1.8%. The influence of potential interfering substance was studied.

  14. Determination of the Temperature Dependence of the Rate Constants for HO2/Acetonylperoxy Reaction and Acetonylperoxy Self-Reaction

    NASA Astrophysics Data System (ADS)

    Darby, E. C.; Grieman, F. J.; Hui, A. O.; Okumura, M.; Sander, S. P.

    2014-12-01

    Reactions of hydroperoxy radical, HO2, with carbonyl containing RO2 can play an important role in the oxidation chemistry of the troposphere. Discovered radical product channels in addition to radical termination channels have resulted in increased study of these important reactions. In our continued study of HO2 reactions with acetonylperoxy and acetylperoxy radicals, we report here our first results on the kinetics of the acetonylperoxy system. Previous studies have resulted in conflicting results and no temperature dependence of the rate constants. Using the Infrared Kinetic Spectroscopy (IRKS) method in which a temperature-controlled slow-flow tube apparatus and laser flash photolysis of Cl2 are used to produce HO2 and CH3C(O)CH2O2 from methanol and acetone, respectively, we studied the chemical kinetics involved over the temperature range of 295 to 240 K. Rates of chemical reaction were determined by monitoring the HO2 concentration as a function of time by sensitive near-IR diode laser wavelength modulation spectroscopy while simultaneously measuring the disappearance of [CH3C(O)CH2O2] in the ultraviolet at 300 nm. The simultaneous fits resulted in the determination of the temperature dependence of the rate constants for the HO2/acetonylperoxy reaction and the acetonylperoxy self-reaction. At the lower temperatures, the reactions of HO2 and CH3C(O)CH2O2 with the adducts HO2•CH3OH and HO2•CH3C(O)CH3 formed in significant concentrations needed to be included in the fitting models.

  15. Viscosity Dependence of Some Protein and Enzyme Reaction Rates: Seventy-Five Years after Kramers.

    PubMed

    Sashi, Pulikallu; Bhuyan, Abani K

    2015-07-28

    Kramers rate theory is a milestone in chemical reaction research, but concerns regarding the basic understanding of condensed phase reaction rates of large molecules in viscous milieu persist. Experimental studies of Kramers theory rely on scaling reaction rates with inverse solvent viscosity, which is often equated with the bulk friction coefficient based on simple hydrodynamic relations. Apart from the difficulty of abstraction of the prefactor details from experimental data, it is not clear why the linearity of rate versus inverse viscosity, k ∝ η(-1), deviates widely for many reactions studied. In most cases, the deviation simulates a power law k ∝ η(-n), where the exponent n assumes fractional values. In rate-viscosity studies presented here, results for two reactions, unfolding of cytochrome c and cysteine protease activity of human ribosomal protein S4, show an exceedingly overdamped rate over a wide viscosity range, registering n values up to 2.4. Although the origin of this extraordinary reaction friction is not known at present, the results indicate that the viscosity exponent need not be bound by the 0-1 limit as generally suggested. For the third reaction studied here, thermal dissociation of CO from nativelike cytochrome c, the rate-viscosity behavior can be explained using Grote-Hynes theory of time-dependent friction in conjunction with correlated motions intrinsic to the protein. Analysis of the glycerol viscosity-dependent rate for the CO dissociation reaction in the presence of urea as the second variable shows that the protein stabilizing effect of subdenaturing amounts of urea is not affected by the bulk viscosity. It appears that a myriad of factors as diverse as parameter uncertainty due to the difficulty of knowing the exact reaction friction and both mode and consequences of protein-solvent interaction work in a complex manner to convey as though Kramers rate equation is not absolute. PMID:26135219

  16. Manganese peroxidase from the lignin-degrading basidiomycete Phanerochaete chrysosporium: Transient state kinetics and reaction mechanism

    SciTech Connect

    Wariishi, Hiroyuki; Gold, M.H. ); Dunford, H.B.; MacDonald, I.D. )

    1989-02-25

    Stopped-flow techniques were used to investigate the kinetics of the formation of manganese peroxidase compound I (MnPI) and of the reactions of MnPI and manganese peroxidase compound II (MnPII) with p-cresol and Mn{sup II}. All of the rate data were obtained from single turnover experiments under pseudo-first order conditions. In the presence of H{sub 2}O{sub 2} the formation of MnPI is independent of pH over the range 3.12-8.29 with a second-order rate constant of (2.0{+-}0.1) {times} 10{sup 6} M{sup {minus}1} s{sup {minus}1}. The activation energy for MnPI formation is 20 kJ mol{sup {minus}1}. MnPI formation also occurs with organic peroxides such as peracetic acid, m-chloroperoxybenzoic acid, and p-nitroperoxybenzoic acid with second-order rate constants of 9.7 x 10{sup 5}, 9.5 {times} 10{sup 4}, and 5.9 {times} 10{sup 4} M{sup {minus}1} s{sup {minus}1}, respectively. The reactions of MnPI and MnPII with p-cresol strictly obeyed second-order kinetics. The second-order rate constant for the reaction of MnPII with p-cresol is extremely low, (9.5{+-}0.5) m{sup {minus}1} s{sup {minus}1}. Kinetic analysis of the reaction of Mn{sup II} with MnPI and MnPII showed a binding interaction with the oxidized enzymes which led to saturation kinetics. The first-order dissociation rate constants for the reaction of Mn{sup II} with MnPI and MnPII are (0.7{+-}0.1) and (0.14{+-}0.01) s{sup {minus}1}, respectively, when the reaction is conducted in lactate buffer. Rate constants are considerably lower when the reactions are conducted in succinate buffer. Single turnover experiments confirmed that Mn{sup II} serves as an obligatory substrate for MnPII and that both oxidized forms of the enzyme form productive complexes with Mn{sup II}. Finally, these results suggest the {alpha}-hydroxy acids such as lactate facilitate the dissociation of Mn{sup II} from the enzyme.

  17. Temperature trends for reaction rates, hydrogen generation, and partitioning of iron during experimental serpentinization of olivine

    NASA Astrophysics Data System (ADS)

    McCollom, Thomas M.; Klein, Frieder; Robbins, Mark; Moskowitz, Bruce; Berquó, Thelma S.; Jöns, Niels; Bach, Wolfgang; Templeton, Alexis

    2016-05-01

    A series of laboratory experiments were conducted to examine how partitioning of Fe among solid reaction products and rates of H2 generation vary as a function of temperature during serpentinization of olivine. Individual experiments were conducted at temperatures ranging from 200 to 320 °C, with reaction times spanning a few days to over a year. The extent of reaction ranged from <1% to ∼23%. Inferred rates for serpentinization of olivine during the experiments were 50-80 times slower than older studies had reported but are consistent with more recent results, indicating that serpentinization may proceed more slowly than previously thought. Reaction products were dominated by chrysotile, brucite, and magnetite, with minor amounts of magnesite, dolomite, and iowaite. The chrysotile contained only small amounts of Fe (XFe = 0.03-0.05, with ∼25% present as ferric Fe in octahedral sites), and displayed little variation in composition with reaction temperature. Conversely, the Fe contents of brucite (XFe = 0.01-0.09) increased steadily with decreasing reaction temperature. Analysis of the reaction products indicated that the stoichiometry of the serpentinization reactions varied with temperature, but remained constant with increasing reaction progress at a given temperature. The observed distribution of Fe among the reaction products does not appear to be entirely consistent with existing equilibrium models of Fe partitioning during serpentinization, suggesting improved models that include kinetic factors or multiple reaction steps need to be developed. Rates of H2 generation increased steeply from 200 to 300 °C, but dropped off at higher temperatures. This trend in H2 generation rates is attributable to a combination of the overall rate of serpentinization reactions and increased partitioning of Fe into brucite rather than magnetite at lower temperatures. The results suggest that millimolal concentration of H2 could be attained in moderately hot hydrothermal systems like Lost City during fluid circulation on timescales of a few years.

  18. Electron-transfer reactions of cobalt(III) complexes. 1. The kinetic investigation of the reduction of various surfactant cobalt(III) complexes by iron(II) in surface active ionic liquids.

    PubMed

    Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian

    2015-05-15

    The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2](3+) (1), cis-[Co(dp)2(C12H25NH2)2](3+) (2), cis-[Co(trien)(C12H25NH2)2](3+) (3), cis-[Co(bpy)2(C12H25NH2)2](3+) (4) and cis-[Co(phen)2(C12H25NH2)2](3+) (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2'-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe(2+) ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH(‡) and entropy of activation ΔS(‡)) of the reaction have been calculated which substantiate the kinetics of the reaction. PMID:25721780

  19. Electron-transfer reactions of cobalt(III) complexes. 1. The kinetic investigation of the reduction of various surfactant cobalt(III) complexes by iron(II) in surface active ionic liquids

    NASA Astrophysics Data System (ADS)

    Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian

    2015-05-01

    The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2]3+ (1), cis-[Co(dp)2(C12H25NH2)2]3+ (2), cis-[Co(trien)(C12H25NH2)2]3+ (3), cis-[Co(bpy)2(C12H25NH2)2]3+ (4) and cis-[Co(phen)2(C12H25NH2)2]3+ (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2‧-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe2+ ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323 K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH‡ and entropy of activation ΔS‡) of the reaction have been calculated which substantiate the kinetics of the reaction.

  20. Evidence of reaction rate influencing cubic and hexagonal phase formation process in CdS nanocrystals

    NASA Astrophysics Data System (ADS)

    Deka, Kuldeep; Kalita, M. P. C.

    2016-05-01

    CdS nanocrystals are synthesized by co-precipitation method using 2-mercaptoethanol (ME) as capping agent. Cubic, hexagonal and their mixture are obtained by varying the ME concentration. Lower (higher) ME concentration results in cubic (hexagonal) phase. The crystallite sizes are in the range 3-7 nm. Increase in ME concentration lead to lower reaction rate between Cd2+ and S2- of the precursors, and slower reaction rate is found to favor hexagonal phase formation over the cubic one in CdS nanocrystals. Role of reaction rate in the phase formation process provides a way to synthesize CdS nanocrystals in desired crystal phase.

  1. Sensitivity study of explosive nucleosynthesis in type Ia supernovae: Modification of individual thermonuclear reaction rates

    NASA Astrophysics Data System (ADS)

    Bravo, Eduardo; Martnez-Pinedo, Gabriel

    2012-05-01

    Background: Type Ia supernovae contribute significantly to the nucleosynthesis of many Fe-group and intermediate-mass elements. However, the robustness of nucleosynthesis obtained via models of this class of explosions has not been studied in depth until now.Purpose: We explore the sensitivity of the nucleosynthesis resulting from thermonuclear explosions of massive white dwarfs with respect to uncertainties in nuclear reaction rates. We put particular emphasis on indentifying the individual reactions rates that most strongly affect the isotopic products of these supernovae.Method: We have adopted a standard one-dimensional delayed detonation model of the explosion of a Chandrasekhar-mass white dwarf and have postprocessed the thermodynamic trajectories of every mass shell with a nucleosynthetic code to obtain the chemical composition of the ejected matter. We have considered increases (decreases) by a factor of 10 on the rates of 1196 nuclear reactions (simultaneously with their inverse reactions), repeating the nucleosynthesis calculations after modification of each reaction rate pair. We have computed as well hydrodynamic models for different rates of the fusion reactions of 12C and of 16O. From the calculations we have selected the reactions that have the largest impact on the supernova yields, and we have computed again the nucleosynthesis using two or three alternative prescriptions for their rates, taken from the JINA REACLIB database. For the three reactions with the largest sensitivity we have analyzed as well the temperature ranges where a modification of their rates has the strongest effect on nucleosynthesis.Results: The nucleosynthesis resulting from the type Ia supernova models is quite robust with respect to variations of nuclear reaction rates, with the exception of the reaction of fusion of two 12C nuclei. The energy of the explosion changes by less than 4% when the rates of the reactions 12C+12C or 16O+16O are multiplied by a factor of 10 or 0.1. The changes in the nucleosynthesis owing to the modification of the rates of these fusion reactions are also quite modest; for instance, no species with a mass fraction larger than 0.02 experiences a variation of its yield larger than a factor of 2. We provide the sensitivity of the yields of the most abundant species with respect to the rates of the most intense reactions with protons, neutrons, and ?. In general, the yields of Fe-group nuclei are more robust than the yields of intermediate-mass elements. Among the species with yields larger than 10-8M?, 35S has the largest sensitivity to the nuclear reaction rates. It is remarkable that the reactions involving elements with Z>22 have a tiny influence on the supernova nucleosynthesis. Among the charged-particle reactions, the most influential on supernova nucleosynthesis are 30Si+p?31P+?, 20Ne+??24Mg+?, and 24Mg+??27Al+p. The temperatures at which a modification of their rate has a larger impact are in the range 2?T?4 GK.Conclusions: The explosion model (i.e., the assumed conditions and propagation of the flame) chiefly determines the element production of type Ia supernovae and derived quantities such as their luminosity, while the nuclear reaction rates used in the simulations have a small influence on the kinetic energy and final chemical composition of the ejecta. Our results show that the uncertainty in individual thermonuclear reaction rates cannot account for discrepancies of a factor of 2 between isotopic ratios in type Ia supernovae and those in the solar system, especially within the Fe group.

  2. Rate constants measured for hydrated electron reactions with peptides and proteins

    NASA Technical Reports Server (NTRS)

    Braams, R.

    1968-01-01

    Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules.

  3. ACTIVE: a program to calculate and plot reaction rates from ANISN calculated fluxes

    SciTech Connect

    Judd, J.L.

    1981-12-01

    The ACTIVE code calculates spatial heating rates, tritium production rates, neutron reaction rates, and energy spectra from particle fluxes calculated by ANISN. ACTIVE has a variety of input options including the capability to plot all calculated spatial distributions. The code was primarily designed for use with fusion first wall/blanket systems, but could be applied to any one-dimensional problem.

  4. Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures

    SciTech Connect

    Newton, J. R.; Longland, R.; Iliadis, C.

    2008-08-15

    We address the problem of extrapolating experimental thermonuclear reaction rates toward high stellar temperatures (T>1 GK) by using statistical model (Hauser-Feshbach) results. Reliable reaction rates at such temperatures are required for studies of advanced stellar burning stages, supernovae, and x-ray bursts. Generally accepted methods are based on the concept of a Gamow peak. We follow recent ideas that emphasized the fundamental shortcomings of the Gamow peak concept for narrow resonances at high stellar temperatures. Our new method defines the effective thermonuclear energy range (ETER) by using the 8th, 50th, and 92nd percentiles of the cumulative distribution of fractional resonant reaction rate contributions. This definition is unambiguous and has a straightforward probability interpretation. The ETER is used to define a temperature at which Hauser-Feshbach rates can be matched to experimental rates. This matching temperature is usually much higher compared to previous estimates that employed the Gamow peak concept. We suggest that an increased matching temperature provides more reliable extrapolated reaction rates since Hauser-Feshbach results are more trustwhorthy the higher the temperature. Our ideas are applied to 21 (p,{gamma}), (p,{alpha}), and ({alpha},{gamma}) reactions on A=20-40 target nuclei. For many of the cases studied here, our extrapolated reaction rates at high temperatures differ significantly from those obtained using the Gamow peak concept.

  5. Astrophysical S-Factors and Reaction Rates of Threshold (p, n)-Reactions on {sup 99-102}Ru

    SciTech Connect

    Skakun, Ye.; Rauscher, T.

    2010-08-12

    Astrophysical S-factors of (p, n) reactions on {sup 99}Ru, {sup 100}Ru, {sup 101}Ru, and {sup 102}Ru were derived from the sum of experimental isomeric and ground states cross sections measured in the incident proton energy range of 5-9 MeV. They were compared with Hauser-Feshbach statistical model predictions of the NON-SMOKER code. Good agreement was found in the majority of cases. Reaction rates were derived up to 8.7 GK stellar temperature by combining experiment and theory.

  6. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

    NASA Technical Reports Server (NTRS)

    Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

    1984-01-01

    The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

  7. One-proton knockout reactions on psd-shell nuclei for relevant reaction rates in explosive Hydrogen burning processes

    NASA Astrophysics Data System (ADS)

    Banu, Adriana

    2012-10-01

    I will discuss the use of one-proton removal reactions at intermediate energies as an indirect method in nuclear astrophysics to infer stellar reaction rates with astrophysical implications for explosive hydrogen burning processes. I will refer in particular to the results of a recent experiment carried out at GANIL for a cocktail of secondary ion beams around 23Al impinging on a carbon target at 50 MeV/nucleon. The longitudinal momentum distributions of one-proton knockout fragments will be reported in comparison with extended Glauber calculations. Determination of corresponding spectroscopic factors and asymptotic normalization coefficients will be presented.

  8. Modeling kinetic partitioning of secondary organic aerosol and size distribution dynamics: representing effects of volatility, phase state, and particle-phase reaction

    NASA Astrophysics Data System (ADS)

    Zaveri, R. A.; Easter, R. C.; Shilling, J. E.; Seinfeld, J. H.

    2014-05-01

    This paper describes and evaluates a new framework for modeling kinetic gas-particle partitioning of secondary organic aerosol (SOA) that takes into account diffusion and chemical reaction within the particle phase. The framework uses a combination of (a) an analytical quasi-steady-state treatment for the diffusion-reaction process within the particle phase for fast-reacting organic solutes, and (b) a two-film theory approach for slow- and nonreacting solutes. The framework is amenable for use in regional and global atmospheric models, although it currently awaits specification of the various gas- and particle-phase chemistries and the related physicochemical properties that are important for SOA formation. Here, the new framework is implemented in the computationally efficient Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) to investigate the competitive growth dynamics of the Aitken and accumulation mode particles. Results show that the timescale of SOA partitioning and the associated size distribution dynamics depend on the complex interplay between organic solute volatility, particle-phase bulk diffusivity, and particle-phase reactivity (as exemplified by a pseudo-first-order reaction rate constant), each of which can vary over several orders of magnitude. In general, the timescale of SOA partitioning increases with increase in volatility and decrease in bulk diffusivity and rate constant. At the same time, the shape of the aerosol size distribution displays appreciable narrowing with decrease in volatility and bulk diffusivity and increase in rate constant. A proper representation of these physicochemical processes and parameters is needed in the next generation models to reliably predict not only the total SOA mass, but also its composition- and number-diameter distributions, all of which together determine the overall optical and cloud-nucleating properties.

  9. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

    2003-04-01

    The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

  10. Nonequilibrium Contribution to the Rate of Reaction. III. Isothermal Multicomponent Systems

    DOE R&D Accomplishments Database

    Shizgal, B.; Karplus, M.

    1970-10-01

    The nonequilibrium contribution to the reaction rate of an isothermal multicomponent system is obtained by solution of the appropriate Chapman-Enskog equation; the system is composed of reactive species in contact with a heat bath of inert atoms M.

  11. Determining astrophysical three-body radiative capture reaction rates from inclusive Coulomb break-up measurements

    NASA Astrophysics Data System (ADS)

    Casal, J.; Rodríguez-Gallardo, M.; Arias, J. M.; Gómez-Camacho, J.

    2016-04-01

    A relationship between the Coulomb inclusive break-up probability and the radiative capture reaction rate for weakly bound three-body systems is established. This direct link provides a robust procedure to estimate the reaction rate for nuclei of astrophysical interest by measuring inclusive break-up processes at different energies and angles. This might be an advantageous alternative to the determination of reaction rates from the measurement of B (E 1 ) distributions through exclusive Coulomb break-up experiments. In addition, it provides a reference to assess the validity of different theoretical approaches that have been used to calculate reaction rates. The procedure is applied to 11Li (9Li+n +n ) and 6He (4He+n +n ) three-body systems for which some data exist.

  12. Shell and explosive hydrogen burning. Nuclear reaction rates for hydrogen burning in RGB, AGB and Novae

    NASA Astrophysics Data System (ADS)

    Boeltzig, A.; Bruno, C. G.; Cavanna, F.; Cristallo, S.; Davinson, T.; Depalo, R.; deBoer, R. J.; Di Leva, A.; Ferraro, F.; Imbriani, G.; Marigo, P.; Terrasi, F.; Wiescher, M.

    2016-04-01

    The nucleosynthesis of light elements, from helium up to silicon, mainly occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative abundances of the synthesized nuclides critically depend on the rates of the nuclear processes involved, often through non-trivial reaction chains, combined with complex mixing mechanisms. In this paper, we summarize the contributions made by LUNA experiments in furthering our understanding of nuclear reaction rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions.

  13. A Unified Equation for the Reaction Rate in Dense Matter Stars

    SciTech Connect

    Gasques, L. R.; Wiescher, M.; Yakovlev, D. G.

    2007-10-26

    We analyze thermonuclear and pycnonuclear reaction rates in multi-component dense stellar plasma. First we describe calculations of the astrophysical S-factor at low energies using the Sao Paulo potential on the basis of the barrier penetration model. Then we present a simple phenomenological expression for a reaction rate. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature.

  14. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    SciTech Connect

    Lindquist, W Brent

    2009-03-03

    The overall goal of the project was to bridge the gap between our knowledge of small-scale geochemical reaction rates and reaction rates meaningful for modeling transport at core scales. The working hypothesis was that reaction rates, determined from laboratory measurements based upon reactions typically conducted in well mixed batch reactors using pulverized reactive media may be significantly changed in in situ porous media flow due to rock microstructure heterogeneity. Specifically we hypothesized that, generally, reactive mineral surfaces are not uniformly accessible to reactive fluids due to the random deposition of mineral grains and to the variation in flow rates within a pore network. Expected bulk reaction rates would therefore have to be correctly up-scaled to reflect such heterogeneity. The specific objective was to develop a computational tool that integrates existing measurement capabilities with pore-scale network models of fluid flow and reactive transport. The existing measurement capabilities to be integrated consisted of (a) pore space morphology, (b) rock mineralogy, and (c) geochemical reaction rates. The objective was accomplished by: (1) characterizing sedimentary sandstone rock morphology using X-ray computed microtomography, (2) mapping rock mineralogy using back-scattered electron microscopy (BSE), X-ray dispersive spectroscopy (EDX) and CMT, (3) characterizing pore-accessible reactive mineral surface area, and (4) creating network models to model acidic CO{sub 2} saturated brine injection into the sandstone rock samples.

  15. Reaction rate and energy-loss rate for photopair production by relativistic nuclei

    NASA Technical Reports Server (NTRS)

    Chodorowski, Michal J.; Zdziarski, Andrzej A.; Sikora, Marek

    1992-01-01

    The process of e(+/-) pair production by relativistic nuclei on ambient photons is considered. The process is important for cosmic-ray nuclei in interstellar and intergalactic space as well as in galactic and extragalactic compact objects. The rate of this process is given by an integral of the cross section over the photon angular and energy distribution. In the case of isotropic photons, the angular integration is performed to provide an expression for the rate at given photon energy in the nucleus rest frame. The total rate then becomes a single integral of that rate over the photon energy distribution. Formulas are also given for the fractional energy loss of a relativistic nucleus colliding with a photon of a given energy in the rest frame. The nucleus energy-loss rate is integrated over the photon angular distribution in the case of isotropic photons, and simple fits are provided.

  16. How imperfect mixing and differential diffusion accelerate the rate of nonlinear reactions in microfluidic channels.

    PubMed

    Niedl, Robert; Berenstein, Igal; Beta, Carsten

    2016-03-01

    In this paper, we show experimentally that inside a microfluidic device, where the reactants are segregated, the reaction rate of an autocatalytic clock reaction is accelerated in comparison to the case where all the reactants are well mixed. We also find that, when mixing is enhanced inside the microfluidic device by introducing obstacles into the flow, the clock reaction becomes slower in comparison to the device where mixing is less efficient. Based on numerical simulations, we show that this effect can be explained by the interplay of nonlinear reaction kinetics (cubic autocatalysis) and differential diffusion, where the autocatalytic species diffuses slower than the substrate. PMID:26861918

  17. Thick target measurement of the 40Ca(alpha,gamma)44Ti reaction rate

    SciTech Connect

    Sheets, S A; Burke, J T; Scielzo, N D; Phair, L; Bleuel, D; Norman, E B; Grant, P G; Hurst, A M; Tumey, S; Brown, T A; Stoyer, M

    2009-02-06

    The thick-target yield for the {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction has been measured for E{sub beam} = 4.13, 4.54, and 5.36 MeV using both an activation measurement and online {gamma}-ray spectroscopy. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than statistical model calculations. This implies a smaller {sup 44}Ti production in supernova compared to recently measured {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction rates.

  18. Review of rate coefficients of ionic reactions determined from measurements made by the atmosphere explorer satellites

    NASA Technical Reports Server (NTRS)

    Torr, D. G.; Torr, M. R.

    1978-01-01

    The large data base of aeronomic parameters measured by the Atmosphere Explorer C, D, and E satellites since December 1973 has been used to determine a number of reaction rate coefficients highly relevant to our understanding of thermospheric chemistry. In this paper the results are reviewed for ionic rate coefficients for recombination of NO(+), O2(+), for reactions of O(+) + N2, N2(+) + O, and O(++) + O, and for various reactions involving O(+)(2D) and O(+)(2P) ions with O and N2.

  19. High-precision (p,t) reaction to determine {sup 25}Al(p,{gamma}){sup 26}Si reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Berg, G. P. A.; Couder, M.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.

    2010-08-15

    Since the identification of ongoing {sup 26}Al production in the universe, the reaction sequence {sup 24}Mg(p,{gamma}){sup 25}Al({beta}{sup +{nu}}){sup 25}Mg(p,{gamma}){sup 26}Al has been studied intensively. At temperatures where the radiative capture on {sup 25}Al (t{sub 1/2}=7.2 s) becomes faster than the {beta}{sup +} decay, the production of {sup 26}Al can be reduced due to the depletion of {sup 25}Al. To determine the resonances relevant for the {sup 25}Al(p,{gamma}){sup 26}Si bypass reaction, we measured the {sup 28}Si(p,t){sup 26}Si reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.

  20. Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(1D) + H2 reaction

    NASA Astrophysics Data System (ADS)

    Jambrina, P. G.; Lara, Manuel; Menéndez, M.; Launay, J.-M.; Aoiz, F. J.

    2012-10-01

    Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S(1D) + H2 → SH + H at total energies up to 1.2 eV using three different theoretical approaches: time-independent quantum mechanics (QM), quasiclassical trajectories (QCT), and statistical quasiclassical trajectories (SQCT). The calculations have been carried out on the widely used potential energy surface (PES) by Ho et al. [J. Chem. Phys. 116, 4124 (2002), 10.1063/1.1431280] as well as on the recent PES developed by Song et al. [J. Phys. Chem. A 113, 9213 (2009), 10.1021/jp903790h]. The results show that the differences between these two PES are relatively minor and mostly related to the different topologies of the well. In addition, the agreement between the three theoretical methodologies is good, even for the highest total angular momenta and energies. In particular, the good accordance between the CRPs obtained with dynamical methods (QM and QCT) and the statistical model (SQCT) indicates that the reaction can be considered statistical in the whole range of energies in contrast with the findings for other prototypical barrierless reactions. In addition, total CRPs and rate coefficients in the range of 20-1000 K have been calculated using the QCT and SQCT methods and have been found somewhat smaller than the experimental total removal rates of S(1D).

  1. Time-Resolved O3 Chemical Chain Reaction Kinetics Via High-Resolution IR Laser Absorption Methods

    NASA Technical Reports Server (NTRS)

    Kulcke, Axel; Blackmon, Brad; Chapman, William B.; Kim, In Koo; Nesbitt, David J.

    1998-01-01

    Excimer laser photolysis in combination with time-resolved IR laser absorption detection of OH radicals has been used to study O3/OH(v = 0)/HO2 chain reaction kinetics at 298 K, (i.e.,(k(sub 1) is OH + 03 yields H02 + 02 and (k(sub 2) is H02 + 03 yields OH + 202). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magnitude higher ozone concentrations ([03] less than or equal to 10(exp 17) molecules/cu cm) than accessible in previous studies. This greater dynamic range permits the full evolution of the chain induction, propagation, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under pseudo- first-order chain reaction conditions is presented, which correctly predicts new kinetic signatures not included in previous OH + 03 kinetic analyses. Specifically, the solutions predict an initial exponential loss (chain "induction") of the OH radical to a steady-state level ([OH](sub ss)), with this fast initial decay determined by the sum of both chain rate constants, k(sub ind) = k(sub 1) + k(sub 2). By monitoring the chain induction feature, this sum of the rate constants is determined to be k(sub ind) = 8.4(8) x 10(exp -14) cu cm/molecule/s for room temperature reagents. This is significantly higher than the values currently recommended for use in atmospheric models, but in excellent agreement with previous results from Ravishankara et al.

  2. Sensitivity of p-Nuclei to (n,g) Reaction Rates

    NASA Astrophysics Data System (ADS)

    Scriven, Dustin; Naqvi, Farheen; Spyrou, Artemis; Simon, Anna; Mayer, Brad

    2015-10-01

    The astrophysical p-process, which is responsible for the creation of the proton-rich p-nuclei, is still not well understood. A sensitivity study of p-nuclei abundances to (n, γ) and (γ,n) reaction rates was conducted at the National Superconducting Cyclotron Laboratory using a nuclear reaction network created at Clemson University. This network simulates the explosive shock front of a Type II supernova passing through the oxygen/neon layer of a 25 M⊙ star. Reaction rates of many (n, γ) reactions and their inverses were increased and decreased by a factor of 3 and the effects were observed. Probing the sensitivity of p-nuclei abundances aids in pointing out reactions important to the p-process. In turn, this information can be used as a tool to drive experimental research, helping to decrease uncertainties and increase the robustness of p-process and other stellar models.

  3. Pore-Scale Process Coupling and Effective Surface Reaction Rates in Heterogeneous Subsurface Materials

    SciTech Connect

    Liu, Chongxuan; Liu, Yuanyuan; Kerisit, Sebastien N.; Zachara, John M.

    2015-09-01

    This manuscript provides a review of pore-scale researches in literature including experimental and numerical approaches, and scale-dependent behavior of geochemical and biogeochemical reaction rates in heterogeneous porous media. A mathematical equation that can be used to predict the scale-dependent behavior of geochemical reaction rates in heterogeneous porous media has been derived. The derived effective rate expression explicitly links the effective reaction rate constant to the intrinsic rate constant, and to the pore-scale variations in reactant concentrations in porous media. Molecular simulations to calculate the intrinsic rate constants were provided. A few examples of pore-scale simulations were used to demonstrate the application of the equation to calculate effective rate constants in heterogeneous materials. The results indicate that the deviation of effective rate constant from the intrinsic rate in heterogeneous porous media is caused by the pore-scale distributions of reactants and their correlation, which are affected by the pore-scale coupling of reactions and transport.

  4. STARLIB: A NEXT-GENERATION REACTION-RATE LIBRARY FOR NUCLEAR ASTROPHYSICS

    SciTech Connect

    Sallaska, A. L.; Iliadis, C.; Champange, A. E.; Goriely, S.; Starrfield, S.; Timmes, F. X.

    2013-07-15

    STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with: (1) theoretical TALYS rates for reactions for which no experimental input is available, and (2) laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest to Z = 83, such as (p, {gamma}), (p, {alpha}), ({alpha}, n), and corresponding reverse rates. Strong rates account for thermal target excitations. Here, we summarize our Monte Carlo formalism, introduce the library, compare methods of correcting rates for stellar environments, and discuss how to implement our library in Monte Carlo nucleosynthesis studies. We also present a method for accessing STARLIB on the Internet and outline updated Monte Carlo-based rates.

  5. STARLIB: A Next-generation Reaction-rate Library for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Sallaska, A. L.; Iliadis, C.; Champange, A. E.; Goriely, S.; Starrfield, S.; Timmes, F. X.

    2013-07-01

    STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with: (1) theoretical TALYS rates for reactions for which no experimental input is available, and (2) laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest to Z = 83, such as (p, γ), (p, α), (α, n), and corresponding reverse rates. Strong rates account for thermal target excitations. Here, we summarize our Monte Carlo formalism, introduce the library, compare methods of correcting rates for stellar environments, and discuss how to implement our library in Monte Carlo nucleosynthesis studies. We also present a method for accessing STARLIB on the Internet and outline updated Monte Carlo-based rates.

  6. Monte Carlo analysis of uncertainty propagation in a stratospheric model. 2: Uncertainties due to reaction rates

    NASA Technical Reports Server (NTRS)

    Stolarski, R. S.; Butler, D. M.; Rundel, R. D.

    1977-01-01

    A concise stratospheric model was used in a Monte-Carlo analysis of the propagation of reaction rate uncertainties through the calculation of an ozone perturbation due to the addition of chlorine. Two thousand Monte-Carlo cases were run with 55 reaction rates being varied. Excellent convergence was obtained in the output distributions because the model is sensitive to the uncertainties in only about 10 reactions. For a 1 ppby chlorine perturbation added to a 1.5 ppby chlorine background, the resultant 1 sigma uncertainty on the ozone perturbation is a factor of 1.69 on the high side and 1.80 on the low side. The corresponding 2 sigma factors are 2.86 and 3.23. Results are also given for the uncertainties, due to reaction rates, in the ambient concentrations of stratospheric species.

  7. Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

    SciTech Connect

    Keek, L.; Cyburt, R. H.; Heger, A.

    2014-06-01

    The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions {sup 15}O(α, γ){sup 19}Ne and {sup 18}Ne(α, p){sup 21}Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the {sup 15}O(α, γ){sup 19}Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true {sup 15}O(α, γ){sup 19}Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on both composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.

  8. Temperature-dependent reaction-rate expression for oxygen recombination at Shuttle entry conditions

    NASA Technical Reports Server (NTRS)

    Zoby, E. V.; Simmonds, A. L.; Gupta, R. N.

    1984-01-01

    A temperature-dependent oxygen surface reaction-rate coefficient has been determined from experimental STS-2 heating and wall temperature data at altitudes of 77.91 km, 74.98 km, and 71.29 km. The coefficient is presented in an Arrhenius form and is shown to be less temperature dependent than previous results. Finite-rate viscous-shock-layer heating rates based on this present expression have been compared with predicted heating rates using the previous rate coefficients and with experimental heating data obtained over an extensive range of STS-2 and STS-3 entry conditions. A substantial improvement is obtained in comparison of experimental data and predicted heating rates using the present oxygen reaction-rate expression.

  9. Formation of OH radicals in the gas-phase reaction of propene, isobutene, and isoprene with O{sub 3}: Yields and mechanistic implications

    SciTech Connect

    Neeb, P.; Moortgat, G.K.

    1999-11-11

    The gas-phase reaction of ozone with alkenes is one of the very few reactions of atmospheric interest that are initiated without free radicals. This tropospheric oxidation pathway for unsaturated compounds has received considerable attention because of the reported formation of OH radicals. OH radicals originating from the alkene-ozone reaction have been proposed as a relevant source of OH radicals in the lower troposphere. Since the reported yields of OH radicals differ considerably, the authors redetermined the OH radical yield for three terminal alkenes by performing a series of pseudo-first-order experiments. Ozonolysis studies were carried out under excess ozone conditions in the presence of different cyclohexane concentrations. The decay rate of the alkene ({kappa}{sub obs}) was followed by long-path FTIR spectroscopy. From the decrease of the effective rate constant ({kappa}{sub obs} = {kappa}{sub eff}[O{sub 3}]) upon addition of cyclohexane, the OH radical yield was determined. The OH radical yields were found to be independent of the concentration of reactants for the Criegee intermediates, which are formed in ozonolysis systems. From these results the authors conclude that OH radicals are formed in a unimolecular process, presumably from the decomposition of the excited Criegee intermediate. Determined yields of OH radical formation in the ozonolysis of propene, isobutene, and isoprene were 0.34, 0.60, and 0.26, respectively. Detailed product studies were performed to verify if the observed stable products can be explained by the assumption that OH radicals are formed via the hydroperoxide channel as proposed by Niki et al. For the isobutene-ozone system, experimental product yields were found to agree well with predictions from a chemical mechanism based on the chemistry of the acetonylperoxy radical CH{sub 3}C(O)CH{sub 2}O{sub 2}, which is formed as an important radical product from the decomposition of the (CH{sub 3}){sub 2}COO Criegee intermediate.

  10. The Effect of Conceptual Change Pedagogy on Students' Conceptions of Rate of Reaction

    ERIC Educational Resources Information Center

    Calik, Muammer; Kolomuc, Ali; Karagolge, Zafer

    2010-01-01

    This paper reports on an investigation of the effect of conceptual change pedagogy on students' conceptions of "rate of reaction" concepts. The study used a pre-test/post-test non-equivalent comparison group design approach and the sample consisted of 72 Turkish grade-11 students (aged 16-18 years) selected from two intact classrooms. The "Rate of…

  11. Teaching Rates of Chemical Reactions and Chemical Equilibrium by Simulation Methods

    ERIC Educational Resources Information Center

    Fogliani, C. L.; Townsend, I. T.

    1977-01-01

    The authors give directions for comparing the rates of zero and first order chemical reactions to the rate of flowing water in simple physical systems. They also show how to compare chemical equilibrium to the level of water in a u-shaped tube. (AJ)

  12. EFFECTS OF RING STRAIN ON GAS-PHASE RATE CONSTANTS. 2. OH RADICAL REACTIONS WITH CYCLOALKENES

    EPA Science Inventory

    Relative rate constants for the gas phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 + or - 2 K, using methyl nitrite photolysis in air as a source of OH radicals. The data show that the rate constants for the nonconjugated cycloalkenes stu...

  13. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y. (Pasco, WA); Wang, Yong (Richland, WA); Wegeng, Robert S. (Richland, WA); Gao, Yufei (Kennewick, WA)

    2006-05-16

    Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

  14. The Effect of Conceptual Change Pedagogy on Students' Conceptions of Rate of Reaction

    ERIC Educational Resources Information Center

    Calik, Muammer; Kolomuc, Ali; Karagolge, Zafer

    2010-01-01

    This paper reports on an investigation of the effect of conceptual change pedagogy on students' conceptions of "rate of reaction" concepts. The study used a pre-test/post-test non-equivalent comparison group design approach and the sample consisted of 72 Turkish grade-11 students (aged 16-18 years) selected from two intact classrooms. The "Rate of

  15. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y.; Wang, Yong; Wegeng, Robert S.; Gao, Yufei

    2003-09-09

    Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

  16. Reevaluation of the O(+)(2P) reaction rate coefficients derived from Atmosphere Explorer C observations

    NASA Technical Reports Server (NTRS)

    Chang, T.; Torr, D. G.; Richards, P. G.; Solomon, S. C.

    1993-01-01

    O(+)(2P) is an important species for studies of the ionosphere and thermosphere: its emission at 7320 A can be used as a diagnostic of the thermospheric atomic oxygen density. Unfortunately, there are no laboratory measurements of the O and N2 reaction rates which are needed to determine the major sinks of (O+)(2p). We have recalculated the O and N2 reaction rates for O(+) (2P) using recent improvements in the solar EUV flux, cross sections, and photoelectron fluxes. For the standard solar EUV flux, the new N2 reaction rate of 3.4 +/- 1.5 x 10 exp -10 cu cm/s is close to the value obtained by Rusch et al. (1977), but the new O reaction rate of 4.0 +/- 1.9 x 10 exp -10 cu cm/sec is about 8 times larger. These new reaction rates are derived using neutral densities, electron density, and solar EUV fluxes measured by Atmosphere Explorer C in 1974 during solar minimum. The new theoretical emission rates are in good agreement with the data for the two orbits studied by Rusch et al.

  17. Field measurement of slow metamorphic reaction rates at temperatures of 500 degrees to 600 degrees C

    PubMed

    Baxter; DePaolo

    2000-05-26

    High-temperature metamorphic reaction rates were measured using strontium isotopic ratios of garnet and whole rock from a field site near Simplon Pass, Switzerland. For metamorphic conditions of cooling from 612 degrees +/- 17 degrees C to 505 degrees +/- 15 degrees C at pressures up to 9.1 kilobars, the inferred bulk fluid-rock exchange rate is 1.3(-0.4)(+1.1) x 10(-7) grams of solid reacted per gram of solid per year, several orders of magnitude lower than laboratory-based estimates. The inferred reaction rate suggests that mineral chemistry may lag the evolving conditions in Earth's crust during mountain building. PMID:10827949

  18. Venus volcanism: Rate estimates from laboratory studies of sulfur gas-solid reactions

    NASA Technical Reports Server (NTRS)

    Ehlers, K.; Fegley, B., Jr.; Prinn, R. G.

    1989-01-01

    Thermochemical reactions between sulfur-bearing gases in the atmosphere of Venus and calcium-, iron-, magnesium-, and sulfur-bearing minerals on the surface of Venus are an integral part of a hypothesized cycle of thermochemical and photochemical reactions responsible for the maintenance of the global sulfuric acid cloud cover on Venus. SO2 is continually removed from the Venus atmosphere by reaction with calcium bearing minerals on the planet's surface. The rate of volcanism required to balance SO2 depletion by reactions with calcium bearing minerals on the Venus surface can therefore be deduced from a knowledge of the relevant gas-solid reaction rates combined with reasonable assumptions about the sulfur content of the erupted material (gas + magma). A laboratory program was carried out to measure the rates of reaction between SO2 and possible crustal minerals on Venus. The reaction of CaCO3(calcite) + SO2 yields CaSO4 (anhydrite) + CO was studied. Brief results are given.

  19. Simulation of chemical reaction via particle tracking: Diffusion-limited versus thermodynamic rate-limited regimes

    NASA Astrophysics Data System (ADS)

    Benson, David A.; Meerschaert, Mark M.

    2008-12-01

    Chemical reactions may be simulated without regard to local concentrations by applying simple probabilistic rules of particle interaction and combination. The forward reaction A + B→ C is coded by calculating the probability that any A and B particles will occupy the same volume over some time interval. This becomes a convolution of the location densities of the two particles. The backward reaction is a simple exponential decay of C particles into A and B particles. When the mixing of reactants is not a limiting process, the classical thermodynamic reaction rates are reproduced. When low mixing (as by diffusion) limits the reaction probabilities, the reaction rates drop significantly, including the rate of approach to global equilibrium. At long enough times, the law of mass action is reproduced exactly in the mean, with some irreducible deviation in the local equilibrium saturations (the equilibrium constant divided by the mass action expression) away from unity. The saturation variability is not sensitive to numerical parameters but depends strongly on how far from equilibrium the system is initiated. This is simply due to a relative paucity of particles of some species as the reaction moves far to one side or the other.

  20. Rate Coefficient Measurements of the Reaction CH3 + O2 = CH3O + O

    NASA Technical Reports Server (NTRS)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, sub -0.47 ) x 10(exp 13) e(-15813 +/- 587 K/T)/cubic cm.mol.s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  1. Rate Coefficient Measurements of the Reaction CH3+O2+CH3O+O

    NASA Technical Reports Server (NTRS)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, -0.47)) X 10(exp 13) exp(- 15813 +/- 587 K/T)cc/mol s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  2. Controlling the rates of biochemical reactions and signaling networks by shape and volume changes

    PubMed Central

    Lizana, L.; Bauer, B.; Orwar, O.

    2008-01-01

    In biological systems, chemical activity takes place in micrometer- and nanometer-sized compartments that constantly change in shape and volume. These ever-changing cellular compartments embed chemical reactions, and we demonstrate that the rates of such incorporated reactions are directly affected by the ongoing shape reconfigurations. First, we show that the rate of product formation in an enzymatic reaction can be regulated by simple volume contraction–dilation transitions. The results suggest that mitochondria may regulate the dynamics of interior reaction pathways (e.g., the Krebs cycle) by volume changes. We then show the effect of shape changes on reactions occurring in more complex and structured systems by using biomimetic networks composed of micrometer-sized compartments joined together by nanotubes. Chemical activity was measured by implementing an enzymatic reaction–diffusion system. During ongoing reactions, the network connectivity is changed suddenly (similar to the dynamic tube formations found inside Golgi stacks, for example), and the effect on the reaction is registered. We show that spatiotemporal properties of the reaction–diffusion system are extremely sensitive to sudden changes in network topology and that chemical reactions can be initiated, or boosted, in certain nodes as a function of connectivity. PMID:18337513

  3. Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles

    NASA Astrophysics Data System (ADS)

    Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-02-01

    We investigate the kinetics of the ubiquitous phosphorylation-dephosphorylation cycle on biological membranes by means of kinetic Monte Carlo simulations on the triangular lattice. We establish the dependence of effective macroscopic reaction rate coefficients as well as the steady-state phosphorylated substrate fraction on the diffusion coefficient and concentrations of opposing enzymes: kinases and phosphatases. In the limits of zero and infinite diffusion, the numerical results agree with analytical predictions; these two limits give the lower and the upper bound for the macroscopic rate coefficients, respectively. In the zero-diffusion limit, which is important in the analysis of dense systems, phosphorylation and dephosphorylation reactions can convert only these substrates which remain in contact with opposing enzymes. In the most studied regime of nonzero but small diffusion, a contribution linearly proportional to the diffusion coefficient appears in the reaction rate. In this regime, the presence of opposing enzymes creates inhomogeneities in the (de)phosphorylated substrate distributions: The spatial correlation function shows that enzymes are surrounded by clouds of converted substrates. This effect becomes important at low enzyme concentrations, substantially lowering effective reaction rates. Effective reaction rates decrease with decreasing diffusion and this dependence is more pronounced for the less-abundant enzyme. Consequently, the steady-state fraction of phosphorylated substrates can increase or decrease with diffusion, depending on relative concentrations of both enzymes. Additionally, steady states are controlled by molecular crowders which, mostly by lowering the effective diffusion of reactants, favor the more abundant enzyme.

  4. Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

    PubMed Central

    Piccini, GiovanniMaria; Alessio, Maristella

    2016-01-01

    Abstract The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide‐and‐conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction‐type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre‐exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  5. The rate of the reaction between CN and C2H2 at interstellar temperatures

    NASA Technical Reports Server (NTRS)

    Woon, D. E.; Herbst, E.

    1997-01-01

    The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures.

  6. Unbound states of (32)Cl andthe (31)S(p,gamma)(32)Cl reaction rate

    SciTech Connect

    Matos, M.; Blackmon, Jeff C; Linhardt, Laura; Bardayan, Daniel W; Nesaraja, Caroline D; Clark, Jason; Diebel, C.; O'Malley, Patrick; Parker, P.D.

    2011-01-01

    The {sup 31}S(p,{gamma}){sup 32}Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the {sup 32}S(3He,t){sup 32}Cl charge-exchange reaction to determine properties of proton-unbound levels in {sup 32}Cl that have previously contributed significant uncertainties to the {sup 31}S(p,{gamma}){sup 32}Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in {sup 32}Cl. Proton-branching ratios were obtained by detecting decay protons from unbound {sup 32}Cl states in coincidence with tritons. An improved {sup 31}S(p,{gamma}){sup 32}Cl reaction rate was calculated including robust statistical and systematic uncertainties.

  7. Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

    PubMed

    Piccini, GiovanniMaria; Alessio, Maristella; Sauer, Joachim

    2016-04-18

    The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre-exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  8. Ultrasound promoted reaction of Rhodamine B with sodium hypochlorite using sonochemical and dental ultrasonic instruments.

    PubMed

    Tiong, T Joyce; Price, Gareth J

    2012-03-01

    The sonochemical acceleration of bleaching of Rhodamine B by sodium hypochlorite has been studied using ultrasound intensities in the range 0-7 W cm(-2). Using a 20 kHz ultrasonic horn, it was shown that ultrasound could significantly shorten the treatment time and/or the concentration of hypochlorite required for the reaction. A number of intermediate species formed during the reaction have been identified. It was demonstrated that the same sonochemical reactions occur during the use of dental ultrasound instruments of the type used in endodontics where hypochlorite solutions act as disinfectants. Results showed pseudo-first order degradation kinetics for the degradation of Rhodamine B for both types of source. Both the distribution of cavitation and the resulting bleaching reactions were dependent on the design of the tips. The bleaching reaction can therefore be used to characterise the behaviour of dental instruments and aid in the optimisation of their performance. PMID:21868274

  9. NUCLEAR PHYSICS: Determination of the stellar reaction rate for 12C(α, γ)16O: using a new expression with the reaction mechanism

    NASA Astrophysics Data System (ADS)

    Xu, Yi; Xu, Wang; Ma, Yu-Gang; Cai, Xiang-Zhou; Chen, Jin-Gen; Fan, Gong-Tao; Fan, Guang-Wei; Guo, Wei; Luo, Wen; Pan, Qiang-Yan; Shen, Wen-Qing; Yang, Li-Feng

    2009-04-01

    The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9 = 0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α, γ)16O reaction rates are calculated in the temperature range from T9 = 0.3 to 2 according to all the available cross section data. A new analytic expression of the 12C(α, γ)16O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9 = 0.3 to 2. Using the fit results, the analytic expression of 12C(α, γ)16O reaction rate is extrapolated down to T9 = 0.05 based on the underlying physics. The 12C(α, γ)16O reaction rate at T9 = 0.2 is (8.78 ± 1.52) × 1015 cm's-1 mol-1. Some comparisons and discussions about our new 12C(α, γ)16O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9 = 2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α, γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α, γ)16O reaction rates.

  10. Depletion: A Game with Natural Rules for Teaching Reaction Rate Theory

    NASA Astrophysics Data System (ADS)

    Olbris, Donald J.; Herzfeld, Judith

    2002-10-01

    Depletion is a game that reinforces central concepts of reaction rate theory through simulation. Each player buys chemicals and guides them through a series of reactions, thereby earning money to buy more chemicals. The reactions occur when players roll a high enough value on two dice to overcome an activation barrier. The reactions may be accelerated by buying heat (which allows the player to roll three dice instead of two) or catalysts (which lower the activation barrier). The value of acceleration derives from the increasing price of fresh chemicals as resources are depleted and waste products accumulate. The player who nets the most money wins the game. The details of the game are presented, with a set of follow-up questions suitable for either a quiz or discussion. Student reaction to the game is also described.

  11. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  12. Considerations Based on Reaction Rate on Char Gasification Behavior in Two-stage Gasifier for Biomass

    NASA Astrophysics Data System (ADS)

    Taniguchi, Miki; Nishiyama, Akio; Sasauchi, Kenichi; Ito, Yusuke; Akamatsu, Fumiteru

    In order to develop a small-scale gasifier in which biomass can be converted to energy with high efficiency, we planned a gasification process that consists of two parts: pyrolysis part (rotary kiln) and gasification part (downdraft gasifier). We performed fundamental experiments on gasification part and discussed the appropriate conditions such as air supply location, air ratio, air temperature and hearth load. We considered the results by calculating reaction rates of representative reactions on char gasification part and found that water gas reaction is dominant in the reduction area and its behavior gives important information to decide the adequate length of the char layer.

  13. Rate constants for chemical reactions in high-temperature nonequilibrium air

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  14. A simple recipe for modeling reaction-rate in flows with turbulent-combustion

    NASA Technical Reports Server (NTRS)

    Girimaji, Sharath S.

    1991-01-01

    A computationally viable scheme to account for chemical reaction in turbulent flows is presented. The multivariate beta-pdf model for multiple scalar mixing forms the basis of this scheme. Using the model scalar joint pdf and a general form of the instantaneous reaction-rate, the unclosed chemical reaction terms are expressed as simple functions of scalar means and the turbulent scalar energy. The calculation procedure requires that the mean scalar equations and only one other transport equation - for the turbulent scalar energy - be solved.

  15. Reaction kinetics and oxidation product formation in the degradation of acetaminophen by ferrate (VI).

    PubMed

    Wang, Hongyu; Liu, Yibing; Jiang, Jia-Qian

    2016-07-01

    This paper investigates the degradation of acetaminophen (AAP) in aqueous solutions by ferrate (VI), aiming to propose the kinetics, pathways and the oxidation products' formation in the AAP degradation. A series of jar tests were undertaken over ferrate (VI) dosages (molar ratios of ferrate (VI):AAP, 5:1 to 25:1) and pH values (4-11). The effects of co-existing ions (0.2-5 mM) and humic acid (10-50 mg l(-1)) on the AAP removal were investigated. Ferrate (VI) can remove 99.6% AAP (from 1000 μg l(-1)) in 60 min under study conditions when majority of the AAP reduction occurred in the first 5 min. The treatment performance depended on the ferrate(VI) dosage, pH and the type and strength of co-existing ions and humic acid. Raising ferrate (VI) dosage with optimal pH 7 improved the AAP degradation. In the presence of humic acid, the AAP degradation by ferrate (VI) was promoted in a short period (<30 min) but then inhibited with increasing in humic acid contents. The presence of Al(3+), CO3(2-) and PO4(3-) ions declined but the existence of K(+), Na(+), Mg(2+) and Ca(2+) ions can improve the AAP removal. The catalytic function of Al(3+) on the decomposition of ferrate (VI) in aqueous solution was found. The kinetics of the reaction between ferrate (VI) and AAP was pseudo first-order for ferrete (VI) and pseudo second-order for AAP. The pseudo rate constant of ferrate (VI) with AAP was 1.4 × 10(-5) L(2) mg(-2) min(-1). Three oxidation products (OPs) were identified and the AAP degradation pathways were proposed. PMID:27155474

  16. Kinetics of the benzyl + O(3P) reaction: a quantum chemical/statistical reaction rate theory study.

    PubMed

    da Silva, Gabriel; Bozzelli, Joseph W

    2012-12-14

    The resonance stabilized benzyl radical is an important intermediate in the combustion of aromatic hydrocarbons and in polycyclic aromatic hydrocarbon (PAH) formation in flames. Despite being a free radical, benzyl is relatively stable in thermal, oxidizing environments, and is predominantly removed through bimolecular reactions with open-shell species other than O(2). In this study the reaction of benzyl with ground-state atomic oxygen, O((3)P), is examined using quantum chemistry and statistical reaction rate theory. C(7)H(7)O energy surfaces are generated at the G3SX level, and include several novel pathways. Transition state theory is used to describe elementary reaction kinetics, with canonical variational transition state theory applied for barrierless O atom association with benzyl. Apparent rate constants and branching ratios to different product sets are obtained as a function of temperature and pressure from solving the time-dependent master equation, with RRKM theory for microcanonical k(E). These simulations indicate that the benzyl + O reaction predominantly forms the phenyl radical (C(6)H(5)) plus formaldehyde (HCHO), with lesser quantities of the C(7)H(6)O products benzaldehyde, ortho-quinone methide, and para-quinone methide (+H), along with minor amounts of the formyl radical (HCO) + benzene. Addition of O((3)P) to the methylene site in benzyl produces a highly vibrationally excited C(7)H(7)O* adduct, the benzoxyl radical, which can β-scission to benzaldehyde + H and phenyl + HCHO. In order to account for the experimental observation of benzene as the major reaction product, a roaming radical mechanism is proposed that converts the nascent products phenyl and HCHO to benzene + HCO. Oxygen atom addition at the ortho and para ring sites in benzyl, which has not been previously considered, is shown to lead to the quinone methides + H; these species are less-stable isomers of benzaldehyde that are proposed as important combustion intermediates, but are yet to be identified experimentally. Franck-Condon simulations of the benzaldehyde, o-quinone methide, and p-quinone methide photoelectron spectra suggest that these C(7)H(6)O isomers could be distinguished using tunable VUV photoionization mass spectrometry. PMID:23108328

  17. Determination of the rate constant of hydroperoxyl radical reaction with phenol

    NASA Astrophysics Data System (ADS)

    Kozmér, Zsuzsanna; Arany, Eszter; Alapi, Tünde; Takács, Erzsébet; Wojnárovits, László; Dombi, András

    2014-09-01

    The rate constant of HO2rad reaction with phenol (kHO2rad +phenol) was investigated. The primary radical set produced in water γ radiolysis (rad OH, eaq- and Hrad ) was transformed to HO2rad /O2rad - by using dissolved oxygen and formate anion (in the form of either formic acid or sodium formate). The concentration ratio of HO2rad /O2rad - was affected by the pH value of the solution: under acidic conditions (using HCOOH) almost all radicals were converted to HO2rad , while under alkaline conditions (using HCOONa) to O2rad -. The degradation rate of phenol was significantly higher using HCOOH. From the ratio of reaction rates under the two reaction conditions kHO2rad +phenol was estimated to be (2.7±1.2)×103 L mol-1 s-1.

  18. Calculations on the rate of the ion-molecule reaction between NH3(+) and H2

    NASA Technical Reports Server (NTRS)

    Herbst, Eric; Defrees, D. J.; Talbi, D.; Pauzat, F.; Koch, W.

    1991-01-01

    The rate coefficient for the ion-molecule reaction NH3(+) + H2 yields NH4(+) + H has been calculated as a function of temperature with the use of the statistical phase space approach. The potential surface and reaction complex and transition state parameters used in the calculation have been taken from ab initio quantum chemical calculations. The calculated rate coefficient has been found to mimic the unusual temperature dependence measured in the laboratory, in which the rate coefficient decreases with decreasing temperature until 50-100 K and then increases at still lower temperatures. Quantitative agreement between experimental and theoretical rate coefficients is satisfactory given the uncertainties in the ab initio results and in the dynamics calculations. The rate coefficient for the unusual three-body process NH3(+) + H2 + He yields NH4(+) + H + He has also been calculated as a function of temperature and the result found to agree well with a previous laboratory determination.

  19. Triple-alpha reaction rate studied with the Faddeev three-body formalism

    SciTech Connect

    Ishikawa, Souichi

    2012-11-12

    The triple-alpha (3{alpha}) reaction, {sup 4}He+{sup 4}He+{sup 4}He{yields}{sup 12}C+{gamma}, which plays a significant role in the stellar evolution scenarios, is studied in terms of a three-alpha (3-{alpha}) model. The reaction rate of the process is calculated via an inverse process, 3-{alpha} photodisintegration of a {sup 12}C nucleus. Both of 3-{alpha} bound and-continuum states are calculated by a Faddeev method with accommodating the long range Coulomb interaction. With being adjusted to the empirical E2-strength for {sup 12}C(0{sub 2}{sup +}){yields}{sup 12}C(2{sub 1}{sup +}) transition, results of the 3{alpha} reaction rate <{alpha}{alpha}{alpha}> at higher temperature (T > 10{sup 8} K), where the reaction proceeds mainly through the {sup 8}Be and {sup 12}C(0{sub 2}{sup +}) resonant states, almost agree with those of the Nuclear Astrophysics Compilation of Reaction Rates (NACRE). On the other hand, calculated values of <{alpha}{alpha}{alpha}> are about 10{sup 3} times larger than the NACRE rate at a low temperature (T= 10{sup 7} K), which means our results are remarkably smaller than recent CDCC results.

  20. Ferrous iron oxidation rates in the pycnocline of a permanently stratified lake.

    PubMed

    Díez, Sergi; Noonan, Gregory O; MacFarlane, John K; Gschwend, Philip M

    2007-01-01

    Ferrous iron was found year round at 2-4 mM in the anoxic hypolimnion of the Halls Brook Holding Area (HBHA), a small lake in eastern Massachusetts. Oxygenated epilimnion waters always had total iron concentrations of <80 nanomolar, implying nearly complete oxidation of ferrous iron as it mixed upward across the lake's pycnocline. Assuming conductivity was a conservative parameter, and using data on the lake's water balance, upward advection rates (0.02-0.05 m d(-1)) and vertical eddy diffusion coefficients (0.007-0.05 m2 d(-1)) were determined for the lake's pycnocline on five dates. Using the same advection and diffusion parameters, corresponding pseudo first-order rate coefficients for ferrous iron oxidation, k(ox) (s(-1)), on those dates were calculated (0.0004-0.007 s(-1)). The values of k(ox) (s(-1)) were always too large to reflect only homogeneous solution reactions; and on at least four dates they appeared too fast to be due to heterogeneous catalysis on iron oxyhydroxides. This suggested that ferrous iron oxidation in this lake's pycnocline was primarily due to catalysis by microorganisms, and this was supported by comparison of azide-poisoned vs. untreated batch tests. As a result of their continuous production, iron oxyhydroxide precipitates and any associated sorbates/coprecipitates are most likely continuously settling back into the lake's deep water and bed sediments, except when episodic storm events flush these solids out of the pycnocline and downstream via the Aberjona River. PMID:17049963

  1. Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence

    NASA Technical Reports Server (NTRS)

    Manzanares, E. R.; Suto, Masako; Lee, Long C.; Coffey, Dewitt, Jr.

    1986-01-01

    A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

  2. Hydrophobic catalytic Janus motors: Slip boundary condition and enhanced catalytic reaction rate

    NASA Astrophysics Data System (ADS)

    Manjare, Manoj; Ting Wu, Yuan; Yang, Bo; Zhao, Y.-P.

    2014-02-01

    A hydrophobic front surface in Janus catalytic motors could introduce two effects to the motion kinetics: a partially slippery surface and a change in catalytic reaction rate. Experimentally, the hydrophobic Janus motors have been observed to move appreciably faster than the hydrophilic ones for large size motors with high fuel concentrations. Numerical investigation and experimental data reveal that the slippery surface has an insignificant effect on motor kinetics compared to an enhanced catalytic reaction rate, which could result from the water depletion layer around the hydrophobic surface and the strong hydrophobic interaction between the generated O2 and the hydrophobic surface.

  3. Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars

    NASA Astrophysics Data System (ADS)

    Dixon, Emily M.; Elwood Madden, Andrew S.; Hausrath, Elisabeth M.; Elwood Madden, Megan E.

    2015-04-01

    Jarosite flow-through dissolution experiments were conducted in ultrapure water (UPW), pH 2 sulfuric acid, and saturated NaCl and CaCl2 brines at 295-298 K to investigate how hydrologic variables may affect jarosite preservation and reaction products on Mars. K+-based dissolution rates in flowing UPW did not vary significantly with flow rate, indicating that mineral surface reactions control dissolution rates over the range of flow rates investigated. In all of the solutions tested, hydrologic variables do not significantly affect extent of jarosite alteration; therefore, jarosite is equally likely to be preserved in flowing or stagnant waters on Mars. However, increasing flow rate did affect the mineralogy and accumulation of secondary reaction products. Iron release rates in dilute solutions increased as the flow rate increased, likely due to nanoscale iron (hydr)oxide transport in flowing water. Anhydrite formed in CaCl2 brine flow-through experiments despite low temperatures, while metastable gypsum and bassanite were observed in batch experiments. Therefore, observations of the hydration state of calcium sulfate minerals on Mars may provide clues to unravel past salinity and hydrologic conditions as well as temperatures and vapor pressures.

  4. Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

    2013-03-15

    Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

  5. Modeling of atmospheric OH reaction rates using newly developed variable distance weighted zero order connectivity index

    NASA Astrophysics Data System (ADS)

    Markelj, Jernej; Pompe, Matevž

    2016-04-01

    A new variable distance weighted zero order connectivity index was used for development of structure-activity relationship for modeling reactivity of OH radical with alkanes and non-conjugated alkenes in the atmosphere. The proposed model is based on the assumptions that the total reaction rate can be obtained by summing all partial reaction rates and that all reaction sites are interrelated by influencing each other. The results suggest that these assumptions are justified. The model was compared with the EPA implemented model in the studied application domain and showed superior prediction capabilities. Further, optimized values of the weights that were used in our model permit some insight into mechanisms that govern the reaction OH + alkane/alkene. The most important conclusion is that the branching degree of the forming radical seems to play a major role in site specific reaction rates. Relative qualitative structural interpretation is possible, e.g. allylic site is suggested to be much more reactive than even tertiary sp3 carbon. Novel modeling software MACI, which was developed in our lab and is now available for research purposes, was used for calculations. Various variable topological indices that are again starting to be recognized because of their great potentials in simplicity, fast calculations, very good correlations and structural information, were implemented in the program.

  6. Photochemistry of Solutes in Different Locations in/on Ice. Part II: Reaction Rate Measurements

    NASA Astrophysics Data System (ADS)

    Hullar, T.; Anastasio, C.

    2014-12-01

    Particularly in polar regions, photochemical reactions in snowpacks can be an important mechanism for transforming organic and inorganic compounds. Chemicals within snow and ice are found in three different compartments: distributed in the bulk ice, concentrated in liquid-like regions (LLRs) within the ice matrix (such as at grain boundaries), or in quasi-liquid layers at the air-ice interface. While some experiments suggest reaction rates may vary in these different compartments, it is not clear if the reaction rates are different or if the changes are due to variations in the reaction environment (such as photon flux). A companion presentation discusses our work identifying solute location in laboratory ice samples; here, we describe experimental measurements of reaction rates in different ice compartments. Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow and ice. We first prepared aqueous solutions of a single PAH. We then froze these samples using various methods that segregate the solute into different locations in the ice matrix. With simulated sunlight, we illuminated these samples and measured photon flux (using 2-nitrobenzaldehyde) and the photodecay of the PAH. We will discuss differences in PAH photochemistry as a function of location in the ice sample and the implications of these results for environmental snow and ice.

  7. Evaluation of reaction rates in streambed sediments with seepage flow: a novel code

    NASA Astrophysics Data System (ADS)

    Boano, Fulvio; De Falco, Natalie; Arnon, Shai

    2015-04-01

    Streambed interfaces represent hotspots for nutrient transformations because they host different microbial species which perform many heterotrophic and autotrophic reactions. The evaluation of these reaction rates is crucial to assess the fate of nutrients in riverine environments, and it is often performed through the analysis of concentrations from water samples collected along vertical profiles. The most commonly employed evaluation tool is the Profile code developed by Berg et al. (1998), which determines reaction rates by fitting observed concentrations to a diffusion-reaction equation that neglects the presence of water flow within sediments. However, hyporheic flow is extremely common in streambeds, where solute transport is often controlled by advection rather than diffusion. There is hence a pressing need to develop new methods that can be applied even to advection-dominated sediments. This contribution fills this gap by presenting a novel approach that extends the method proposed by Berg et al. (1998). This new approach includes the influence of vertical solute transport by upwelling or downwelling water, and it is this suited to the typical flow conditions of stream sediments. The code is applied to vertical profiles of dissolved oxygen from a laboratory flume designed to mimic the complex flow conditions of real streams. The results show that it is fundamental to consider water flow to obtain reliable estimates of reaction rates in streambeds. Berg, P., N. Risgaard-Petersen, and S. Rysgaard, 1998, Interpretation of measured concentration profiles in the sediment porewater, Limnology and Oceanography, 43:1500-1510.

  8. Acid–base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer

    PubMed Central

    Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L.; Eisele, Fred L.; Siepmann, J. Ilja; Hanson, David R.; Zhao, Jun; McMurry, Peter H.

    2012-01-01

    Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid–base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta. PMID:23091030

  9. Pore and Continuum Scale Study of the Effect of Subgrid Transport Heterogeneity on Redox Reaction Rates

    SciTech Connect

    Liu, Yuanyuan; Liu, Chongxuan; Zhang, Changyong; Yang, Xiaofan; Zachara, John M.

    2015-08-01

    A micromodel system with a pore structure for heterogeneous flow and transport was used to investigate the effect of subgrid transport heterogeneity on redox reaction rates. Hematite reductive dissolution by injecting a reduced form of flavin mononucleotide (FMNH2) at variable flow rates was used as an example to probe the variations of redox reaction rates in different subgrid transport domains. Experiments, pore-scale simulations, and macroscopic modeling were performed to measure and simulate in-situ hematite reduction and to evaluate the scaling behavior of the redox reaction rates from the pore to macroscopic scales. The results indicated that the measured pore-scale rates of hematite reduction were consistent with the predictions from a pore scale reactive transport model. A general trend is that hematite reduction followed reductant transport pathways, starting from the advection-dominated pores toward the interior of diffusion-dominated domains. Two types of diffusion domains were considered in the micromodel: a micropore diffusion domain, which locates inside solid grains or aggregates where reactant transport is limited by diffusion; and a macropore diffusion domain, which locates at wedged, dead-end pore spaces created by the grain-grain contacts. The rate of hematite reduction in the advection-dominated domain was faster than those in the diffusion-controlled domains, and the rate in the macropore diffusion domain was faster than that in the micropore domain. The reduction rates in the advection and macropore diffusion domains increased with increasing flow rate, but were affected by different mechanisms. The rate increase in the advection domain was controlled by the mass action effect as a faster flow supplied more reactants, and the rate increase in the macropore domain was more affected by the rate of mass exchange with the advection domain, which increased with increasing flow rate. The hematite reduction rate in the micropore domain was, however, not affected by the flow rate because molecular diffusion limits reductant supply to the micropore domain interior. Domain-based macroscopic models were evaluated to scale redox reaction rates from the pore to macroscopic scales. A single domain model, which ignores subgrid transport heterogeneity deviated significantly from the pore-scale results. Further analysis revealed that the rate expression for hematite reduction was not scalable from the pore to porous media using the single domain model. A three-domain model, which effectively considers subgrid reactive diffusion in the micropore and macropore domains, significantly improved model description. Overall this study revealed the importance of subgrid transport heterogeneity in the manifestation of redox reaction rates in porous media and in scaling reactions from the pore to porous media. The research also supported that the domain-based scaling approach can be used to directly scale redox reactions in porous media with subgrid transport heterogeneity.

  10. Pore and continuum scale study of the effect of subgrid transport heterogeneity on redox reaction rates

    NASA Astrophysics Data System (ADS)

    Liu, Yuanyuan; Liu, Chongxuan; Zhang, Changyong; Yang, Xiaofan; Zachara, John M.

    2015-08-01

    A micromodel system, which corresponds to one or part of a numerical grid in the continuum model, was used to investigate the effect of subgrid transport heterogeneity on redox reaction rates. Hematite reductive dissolution by injecting a reduced form of flavin mononucleotide (FMNH2) at variable flow rates was used as an example to probe the variations of redox reaction rates in different subgrid transport domains. Experiments, pore-scale simulations, and macroscopic continuum modeling were performed to measure and simulate in-situ hematite reduction and to evaluate the scaling behavior of the redox reaction rates from the pore to continuum scales. The results indicated that the measured pore-scale rates of hematite reduction were consistent with the predictions from a pore-scale reactive transport model. A general trend is that hematite reduction followed reductant transport pathways, starting from the advection-dominated pores toward the interior of diffusion-dominated domains. Two types of diffusion domains were considered in the micromodel: a micropore diffusion domain, which locates inside solid grains or aggregates where reactant transport is limited by diffusion; and a macropore diffusion domain, which locates at wedged, dead-end pore spaces created by the grain-grain contacts. The rate of hematite reduction in the advection-dominated domain was faster than those in the diffusion-controlled domains, and the rate in the macropore diffusion domain was faster than that in the micropore domain. The reduction rates in the advection and macropore diffusion domains increased with increasing flow rate, but were affected by different mechanisms. The rate increase in the advection domain was controlled by the mass action effect as a faster flow supplied more reactants, and the rate increase in the macropore domain was more affected by the rate of mass exchange with the advection domain, which increased with increasing flow rate. The hematite reduction rate in the micropore domain was, however, not affected by the flow rate because molecular diffusion limits reductant supply to the micropore domain interior. Domain-based macroscopic models were evaluated to scale redox reaction rates from the pore to continuum scales. Simulation results from the single domain model, which ignores subgrid transport heterogeneity, deviated significantly from the pore-scale results. Further analysis revealed that the rate expression for hematite reduction was not scalable from the pore to porous media using the single domain model. A three-domain model, which effectively considers subgrid reactive diffusion in the micropore and macropore domains, significantly improved model description. Overall this study revealed the importance of subgrid transport heterogeneity in the manifestation of redox reaction rates in porous media and in scaling reactions from the pore to porous media. The research also supported that the domain-based scaling approach can be used to directly scale redox reactions in porous media with subgrid transport heterogeneity.

  11. Solid-gas reaction with adsorption as the rate limiting step.

    PubMed

    Wróbel, Rafał; Arabczyk, Walerian

    2006-07-27

    The model of nucleation where adsorption of reactant is a rate-limiting step has been considered. Assuming the adsorption range model, a numerical simulation has been made. The dependency of bulk concentration and surface coverage versus time and thermogravimetric curves are presented. The crystallite size is suggested to be the key factor of the nucleation rate. Theoretical considerations have been compared with the experimental results of the iron nitriding reaction. PMID:16854036

  12. A kinetics study of the O( sup 3 P) + CH sub 3 Cl reaction over the 556-1485 K range by the HTP and LP-ST techniques

    SciTech Connect

    Ko, Taeho; Fontijn, A. . High-Temperature Reaction Kinetics Lab.); Lim, K.P.; Michael, J.V. )

    1991-12-01

    The high-temperature photochemistry (HTP) and laser photolysis-shock tube (LP-ST) techniques have been combined to study the kinetics of the reaction between ground-state oxygen atoms with CH{sub 3}Cl over the temperature range, 556--1485 K. In the HTP reactor, used for the 556--1291 K range, O atoms were generated by flash photolysis of O{sub 2}, CO{sub 2} or SO{sub 2}, and the atom concentrations were monitored by resonance fluorescence, while with the LP-ST technique, used for the 916--1485 K range, O atoms were generated by the photolysis of either SO{sub 2} or NO with the 193 nm light from a pulsed ArF excimer laser, and atomic resonance absorption spectroscopy (ARAS) was used to monitor (O){sub t}. In both studies, rate coefficients were derived from the (O) profiles under the pseudo-first-order condition, (O){much lt}(CH{sub 3}Cl). The data obtained by the two techniques are in excellent agreement and are best represented by the expression, k(T) = 2.57 {times} 10{sup {minus}11} (T/K){sup 0.31} exp({minus}5633 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} with a 2{sigma} precision varying from {plus minus}6 {plus minus}22% and an estimated 2{sigma} accuracy of {plus minus}21% to {plus minus}30%, depending on temperature. The rate coefficients for the title reaction are essentially identical to those for the O + CH{sub 4} reaction over the observed temperature range, the reasons for which are discussed.

  13. A kinetics study of the O({sup 3}P) + CH{sub 3}Cl reaction over the 556-1485 K range by the HTP and LP-ST techniques

    SciTech Connect

    Ko, Taeho; Fontijn, A.; Lim, K.P.; Michael, J.V.

    1991-12-01

    The high-temperature photochemistry (HTP) and laser photolysis-shock tube (LP-ST) techniques have been combined to study the kinetics of the reaction between ground-state oxygen atoms with CH{sub 3}Cl over the temperature range, 556--1485 K. In the HTP reactor, used for the 556--1291 K range, O atoms were generated by flash photolysis of O{sub 2}, CO{sub 2} or SO{sub 2}, and the atom concentrations were monitored by resonance fluorescence, while with the LP-ST technique, used for the 916--1485 K range, O atoms were generated by the photolysis of either SO{sub 2} or NO with the 193 nm light from a pulsed ArF excimer laser, and atomic resonance absorption spectroscopy (ARAS) was used to monitor [O]{sub t}. In both studies, rate coefficients were derived from the [O] profiles under the pseudo-first-order condition, [O]{much_lt}[CH{sub 3}Cl]. The data obtained by the two techniques are in excellent agreement and are best represented by the expression, k(T) = 2.57 {times} 10{sup {minus}11} (T/K){sup 0.31} exp({minus}5633 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} with a 2{sigma} precision varying from {plus_minus}6 {plus_minus}22% and an estimated 2{sigma} accuracy of {plus_minus}21% to {plus_minus}30%, depending on temperature. The rate coefficients for the title reaction are essentially identical to those for the O + CH{sub 4} reaction over the observed temperature range, the reasons for which are discussed.

  14. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    NASA Astrophysics Data System (ADS)

    Vorotilin, V. P.; Yanovskii, Yu. G.

    2015-07-01

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities-the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  15. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    SciTech Connect

    Vorotilin, V. P. Yanovskii, Yu. G.

    2015-07-15

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities–the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  16. New Approach for Investigating Reaction Dynamics and Rates with Ab Initio Calculations.

    PubMed

    Fleming, Kelly L; Tiwary, Pratyush; Pfaendtner, Jim

    2016-01-21

    Herein, we demonstrate a convenient approach to systematically investigate chemical reaction dynamics using the metadynamics (MetaD) family of enhanced sampling methods. Using a symmetric SN2 reaction as a model system, we applied infrequent metadynamics, a theoretical framework based on acceleration factors, to quantitatively estimate the rate of reaction from biased and unbiased simulations. A systematic study of the algorithm and its application to chemical reactions was performed by sampling over 5000 independent reaction events. Additionally, we quantitatively reweighed exhaustive free-energy calculations to obtain the reaction potential-energy surface and showed that infrequent metadynamics works to effectively determine Arrhenius-like activation energies. Exact agreement with unbiased high-temperature kinetics is also shown. The feasibility of using the approach on actual ab initio molecular dynamics calculations is then presented by using Car-Parrinello MD+MetaD to sample the same reaction using only 10-20 calculations of the rare event. Owing to the ease of use and comparatively low-cost of computation, the approach has extensive potential applications for catalysis, combustion, pyrolysis, and enzymology. PMID:26690335

  17. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  18. Rate constant for the reaction of O(3P) with diacetylene from 210 to 423 K

    NASA Technical Reports Server (NTRS)

    Mitchell, M. B.; Nava, D. F.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction of O(3P) with diacetylene (C4H2) has been measured as a function of pressure and temperature by the flash-photolysis/resonance-fluorescence method. At 298 K and below, no pressure dependence of the rate constant was observed, but at 423 K a moderate (factor-of-2) increase was detected in the range 3 to 75 torr Ar.Results at or near the high-pressure limit are represented by an Arrhenius expression over the temperature range 210 to 423 K. The results are compared with previous determinations, all of which employed the discharge-flow/mass-spectrometry technique. The mechanism of the reaction is considered, including both primary and secondary processes. The heats of formation of the reactants, adducts, and products for the O(3P) + C4H2 reaction are discussed and contrasted with those for O(3P) + C2H2.

  19. Reaction rates and kinetic isotope effects of H2 + OH → H2O + H

    NASA Astrophysics Data System (ADS)

    Meisner, Jan; Kästner, Johannes

    2016-05-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling were applied using a fitted potential energy surface [J. Chen et al., J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval 4 ṡ 10-20 to 4 ṡ 10-17 cm3 s-1, demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures.

  20. Reaction rates and kinetic isotope effects of H2 + OH → H2O + H.

    PubMed

    Meisner, Jan; Kästner, Johannes

    2016-05-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling were applied using a fitted potential energy surface [J. Chen et al., J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval 4 ⋅ 10(-20) to 4 ⋅ 10(-17) cm(3) s(-1), demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures. PMID:27155636

  1. Toward a reaction rate model of condensed-phase RDX decomposition under high temperatures

    NASA Astrophysics Data System (ADS)

    Schweigert, Igor

    2015-06-01

    Shock ignition of energetic molecular solids is driven by microstructural heterogeneities, at which even moderate stresses can result in sufficiently high temperatures to initiate material decomposition and chemical energy release. Mesoscale modeling of these ``hot spots'' requires a reaction rate model that describes the energy release with a sub-microsecond resolution and under a wide range of temperatures. No such model is available even for well-studied energetic materials such as RDX. In this presentation, I will describe an ongoing effort to develop a reaction rate model of condensed-phase RDX decomposition under high temperatures using first-principles molecular dynamics, transition-state theory, and reaction network analysis. This work was supported by the Naval Research Laboratory, by the Office of Naval Research, and by the DoD High Performance Computing Modernization Program Software Application Institute for Multiscale Reactive Modeling of Insensitive Munitions.

  2. Calibration of reaction rates for the CREST reactive-burn model

    NASA Astrophysics Data System (ADS)

    Handley, Caroline

    2015-06-01

    In recent years, the hydrocode-based CREST reactive-burn model has had success in modelling a range of shock initiation and detonation propagation phenomena in polymer bonded explosives. CREST uses empirical reaction rates that depend on a function of the entropy of the non-reacted explosive, allowing the effects of initial temperature, porosity and double-shock desensitisation to be simulated without any modifications to the model. Until now, the sixteen reaction-rate coefficients have been manually calibrated by trial and error, using hydrocode simulations of a subset of sustained-shock initiation gas-gun experiments and the detonation size-effect curve for the explosive. This paper will describe the initial development of an automatic method for calibrating CREST reaction-rate coefficients, using the well-established Particle Swarm Optimisation (PSO) technique. The automatic method submits multiple hydrocode simulations for each ``particle'' and analyses the results to determine the ``misfit'' to gas-gun and size-effect data. Over ~40 ``generations,'' the PSO code finds a best set of reaction-rate coefficients that minimises the misfit. The method will be demonstrated by developing a new CREST model for EDC32, a conventional high explosive.

  3. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  4. Effect of Conceptual Change Approach on Students' Understanding of Reaction Rate Concepts

    ERIC Educational Resources Information Center

    Kingir, Sevgi; Geban, Omer

    2012-01-01

    The purpose of the present study was to investigate the effect of conceptual change text oriented instruction compared to traditional instruction on 10th grade students' understanding of reaction rate concepts. 45 students from two classes of the same teacher in a public high school participated in this study. Students in the experimental group

  5. Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions

    ERIC Educational Resources Information Center

    Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

    2007-01-01

    Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free

  6. Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions

    ERIC Educational Resources Information Center

    Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

    2007-01-01

    Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free…

  7. Measurement of proton transfer reaction rates in a microwave cavity discharge flowing afterglow

    NASA Astrophysics Data System (ADS)

    Brooke, George M., IV

    The reaction rate coefficients between the hydronium ion and the molecules ethene (C2H4), propene (C 3H6), 1-butene (C4H8) and hydrogen sulfide (H2S) were measured at 296 K. The measured reaction rates were compared to collision rates calculated using average dipole orientation (ADO) theory. Reaction efficiency depends primarily upon the proton affinity of the molecules. All the measurements were obtained using the newly developed microwave cavity discharge flowing afterglow (MCD-FA) apparatus. This device uses an Asmussen-type microwave cavity discharge ion source that is spatially separated from the flow tube, eliminating many of the problems inherent with the original FA devices. In addition to measuring reaction rate coefficients, the MCD-FA was shown to be an effective tool for measuring trace compounds in atmospheric air. This method has many advantages over current detection techniques since compounds can be detected in almost real time, large mass ranges can be scanned quickly, and repeated calibration is not required. Preliminary measurements were made of car exhaust and exhaled alveolar air. Car exhaust showed the presence of numerous hydrocarbons, such as butene, benzene and toluene while the exhaled alveolar air showed the presence of various volatile organic compounds such as methanol and acetone.

  8. Should thermostatted ring polymer molecular dynamics be used to calculate thermal reaction rates?

    NASA Astrophysics Data System (ADS)

    Hele, Timothy J. H.; Suleimanov, Yury V.

    2015-08-01

    We apply Thermostatted Ring Polymer Molecular Dynamics (TRPMD), a recently proposed approximate quantum dynamics method, to the computation of thermal reaction rates. Its short-time transition-state theory limit is identical to rigorous quantum transition-state theory, and we find that its long-time limit is independent of the location of the dividing surface. TRPMD rate theory is then applied to one-dimensional model systems, the atom-diatom bimolecular reactions H + H2, D + MuH, and F + H2, and the prototypical polyatomic reaction H + CH4. Above the crossover temperature, the TRPMD rate is virtually invariant to the strength of the friction applied to the internal ring-polymer normal modes, and beneath the crossover temperature the TRPMD rate generally decreases with increasing friction, in agreement with the predictions of Kramers theory. We therefore find that TRPMD is approximately equal to, or less accurate than, ring polymer molecular dynamics for symmetric reactions, and for certain asymmetric systems and friction parameters closer to the quantum result, providing a basis for further assessment of the accuracy of this method.

  9. Effect of Conceptual Change Approach on Students' Understanding of Reaction Rate Concepts

    ERIC Educational Resources Information Center

    Kingir, Sevgi; Geban, Omer

    2012-01-01

    The purpose of the present study was to investigate the effect of conceptual change text oriented instruction compared to traditional instruction on 10th grade students' understanding of reaction rate concepts. 45 students from two classes of the same teacher in a public high school participated in this study. Students in the experimental group…

  10. Reaction Rate Acceleration and Tg Depression of Polycyanurate Under Nanopore Confinement

    NASA Astrophysics Data System (ADS)

    Lopez, Evelyn; Simon, Sindee L.

    2015-03-01

    Material properties such as Tg and the reaction kinetics are known to deviate from the bulk when subjected to nano-sized confinement. Previous work from our laboratory on the trimerization of cyanate esters found that the reaction kinetics were faster for a monofunctional reactant compared to a difunctional monomer, whereas the Tg depression was greater for the crosslinked product of the latter compared to the low molecular weight trimer of the former. The origin of the changes in nanoconfined reaction rates differs from those that govern changes in the Tg. The research objective is to further explore the effect that confinement has on reaction kinetics and Tg using a mixture consisting of mono- and di- cyanate ester monomers. The product is an uncrosslinked polycyanurate with Mn = 5240 g/mol and PDI = 1.78. The confinement mediums are controlled pore glasses with diameters ranging from 8.1 to 111.1 nm. The nanopore-confined material was synthesized in-situ and the reaction kinetics are followed by DSC; after the reaction, the Tg values of the nanoconfined polymer where also measured by DSC. An acceleration factor of 13 and a Tg depression of 38 °C are observed for the material confined in the smallest 8.1 nm-diameter pores. The Tg depression is between those of the trimer and network previously studied, while the acceleration of the reaction rate is lower. Our results are consistent with the reaction acceleration arising from packing effects at the pore wall and the Tg depression arising from intrinsic size effects.

  11. New empirical rate expression for reactions without a barrier: Analysis of the reaction of CN with O2

    NASA Astrophysics Data System (ADS)

    Hessler, Jan P.

    1999-09-01

    The rate coefficients of reactions that occur on potential energy surfaces without a barrier often exhibit a negative temperature dependence at low temperatures. Generally, this behavior is modeled with either the Harcourt-Essen equation, k(T)=AT-m, or a "negative" activation energy, k(T)=ATm exp{ΔE/kBT}. Neither of these expressions is consistent with the Wigner threshold law. The general expression k(T)=(1+T/TW)-m∑l=0∞Al(1+T/TW)-l(T/TW)l is proposed where the relative angular momentum of the reacting species is l, TW and m are independent parameters to be extracted from the data, and the amplitude of each partial wave is Al. This expression may be approximated by k(T)=A0(1+T/TW)-m exp[(T/TW)/(1+T/TW)]. For CN+O2→ NCO+O and CO+NO the above expression reproduces the rate data, the branching ratio to the CO+NO channel, and the reactive cross section for the NCO+O channel. The rate coefficient for the NCO+O channel is given by k(cm3 s-1)=1.79×10-10(+T/21.7)-1.38{exp[(T/21.7)/(1+T/21.7)]-1}+4.62×10-12 exp[(T/21.7)/(1+T/21.7)] while for CO+NO we obtain k(cm3 s-1)=1.79×10-10(1+T/21.7)-1.38. An analytic form of the C-O bonding potential and the electric dipole-quadrupole interaction is used to show that the quantum threshold region extends up to 7 K. These results demonstrate the need of a complete quantum treatment for reactions that proceed on potential surfaces without a barrier.

  12. Product distributions, rate constants, and mechanisms of LiH +H reactions

    NASA Astrophysics Data System (ADS)

    Defazio, Paolo; Petrongolo, Carlo; Gamallo, Pablo; González, Miguel

    2005-06-01

    We present a quantum-mechanical investigation of the LiH depletion reaction LiH +H→Li+H2 and of the H exchange reaction LiH +H'→LiH'+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The H21 nuclear-spin statistics and progressions of vib-rotational states (v',j') rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j' preferred with respect to even j'. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results.

  13. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    PubMed

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles. PMID:26938837

  14. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    USGS Publications Warehouse

    Green, C.T.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O 2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample-based estimates of "apparent" parameters with "true" (intrinsic) values. For this aquifer, non-Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2 threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport. ?? 2010 by the American Geophysical Union.

  15. Reaction and internal energy relaxation rates in viscous thermochemically non-equilibrium gas flows

    NASA Astrophysics Data System (ADS)

    Kustova, E. V.; Oblapenko, G. P.

    2015-01-01

    In the present paper, reaction and energy relaxation rates as well as the normal stress are studied for viscous gas flows with vibrational and chemical non-equilibrium. Using the modified Chapman-Enskog method, multi-temperature models based on the Treanor and Boltzmann vibrational distributions are developed for the general case taking into account all kinds of vibrational energy transitions, exchange reactions, dissociation, and recombination. Integral equations specifying the first-order corrections to the normal mean stress and reaction rates are derived, as well as approximate systems of linear equations for their numerical computation. Generalized thermodynamic driving forces associated with all non-equilibrium processes are introduced. It is shown that normal stresses and rates of non-equilibrium processes can be expressed in terms of the same driving forces; the symmetry of kinetic coefficients in these expressions is proven. The developed general model is applied to a particular case of a pure N2 viscous flow with slow VT relaxation. Normal stress and rates of vibrational relaxation are studied for various ratios of vibrational and translational temperatures. The cross effects between different vibrational transitions in viscous flows are evaluated, along with the influence of anharmonicity and flow compressibility on the first-order corrections to the relaxation rate. Limits of validity for the widely used Landau-Teller model of vibrational relaxation are indicated.

  16. Rate Constant and Reaction Coordinate of Trp-Cage Folding in Explicit Water

    PubMed Central

    Juraszek, Jarek; Bolhuis, Peter G.

    2008-01-01

    We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the protein maintains its compact configuration, while a (de)increase of secondary structure is observed. The calculated folding rate agrees reasonably with experiment, while the unfolding rate is 10 times higher. We discuss possible origins for this mismatch. We recomputed the rates with the forward flux sampling method, and found a discrepancy of four orders of magnitude, probably caused by the method's higher sensitivity to the choice of order parameter with respect to transition interface sampling. Finally, we used the previously computed transition path-sampling ensemble to screen combinations of many order parameters for the best model of the reaction coordinate by employing likelihood maximization. We found that a combination of the root mean-square deviation of the helix and of the entire protein was, of the set of tried order parameters, the one that best describes the reaction coordination. PMID:18676648

  17. Reaction and internal energy relaxation rates in viscous thermochemically non-equilibrium gas flows

    SciTech Connect

    Kustova, E. V.; Oblapenko, G. P.

    2015-01-15

    In the present paper, reaction and energy relaxation rates as well as the normal stress are studied for viscous gas flows with vibrational and chemical non-equilibrium. Using the modified Chapman-Enskog method, multi-temperature models based on the Treanor and Boltzmann vibrational distributions are developed for the general case taking into account all kinds of vibrational energy transitions, exchange reactions, dissociation, and recombination. Integral equations specifying the first-order corrections to the normal mean stress and reaction rates are derived, as well as approximate systems of linear equations for their numerical computation. Generalized thermodynamic driving forces associated with all non-equilibrium processes are introduced. It is shown that normal stresses and rates of non-equilibrium processes can be expressed in terms of the same driving forces; the symmetry of kinetic coefficients in these expressions is proven. The developed general model is applied to a particular case of a pure N{sub 2} viscous flow with slow VT relaxation. Normal stress and rates of vibrational relaxation are studied for various ratios of vibrational and translational temperatures. The cross effects between different vibrational transitions in viscous flows are evaluated, along with the influence of anharmonicity and flow compressibility on the first-order corrections to the relaxation rate. Limits of validity for the widely used Landau–Teller model of vibrational relaxation are indicated.

  18. Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

    2008-04-01

    Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

  19. Simplified Representation of Partial and Total Rate Constants of Complex-Forming Bimolecular Reactions.

    PubMed

    Troe, J

    2015-12-17

    The temperature and pressure dependence of partial and total rate constants of complex-forming bimolecular reactions are investigated with the goal to obtain simplified and compact rate constant expressions suitable for data compilations. The transition of the reactions from low pressure chemical activation to high pressure association character is analyzed. The two processes are modeled separately first by solving master equations, leading to "inverse" and "normal" falloff curves, respectively, and allowing for a compact representation of the separated rate constants. It is shown that broadening factors of the two falloff curves are different, and those of chemical activation often approaching unity. Coupling of the two separate processes then is modeled in a simplified manner. Finally, thermal redissociation of the adducts formed by association is accounted for. PMID:26334454

  20. Quantum three-body calculation of nonresonant triple-{alpha} reaction rate at low temperatures

    SciTech Connect

    Ogata, Kazuyuki; Kan, Masataka; Kamimura, Masayasu

    2010-08-12

    Triple-{alpha} reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the {alpha}-{alpha} nonresonant states significantly quenches the Coulomb barrier between the first two {alpha}-particles and the third {alpha}-particle. Consequently, the{alpha}-{alpha} nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-{alpha} reaction rate by about 20 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.

  1. Rate constant for the reaction of atomic chlorine with formaldehyde from 200 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.

    1979-01-01

    The absolute rate constant for the reaction of atomic chlorine with formaldehyde has been measured from 200 to 500 K using the flash photolysis-resonance fluorescence technique. The results were independent of substantial variations in (H2CO), total pressure (Ar), and flash intensity (i.e., initial (Cl)). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being k-sub-1 = (7.48 + or - 0.50) times 10 to the -11 cu cm/molecule sec, where the error is one standard deviation. This result is compared with the only previous determination of k-sub-1, which was a relative value obtained at 298 K. The rate constant is theoretically discussed, and the potential importance of the reaction in stratospheric chemistry is considered.

  2. Estimating Reaction Rate Coefficients Within a Travel-Time Modeling Framework

    SciTech Connect

    Gong, R; Lu, C; Luo, Jian; Wu, Wei-min; Cheng, H.; Criddle, Craig; Kitanidis, Peter K.; Gu, Baohua; Watson, David B; Jardine, Philip M; Brooks, Scott C

    2011-03-01

    A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

  3. Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Wilson, E., Jr.

    1998-01-01

    Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

  4. Reaction rate kinetics for in situ combustion retorting of Michigan Antrim oil shale

    USGS Publications Warehouse

    Rostam-Abadi, M.; Mickelson, R.W.

    1984-01-01

    The intrinsic reaction rate kinetics for the pyrolysis of Michigan Antrim oil shale and the oxidation of the carbonaceous residue of this shale have been determined using a thermogravimetric analysis method. The kinetics of the pyrolysis reaction were evaluated from both isothermal and nonisothermal rate data. The reaction was found to be second-order with an activation energy of 252.2 kJ/mole, and with a frequency factor of 9.25 ?? 1015 sec-1. Pyrolysis kinetics were not affected by heating rates between 0.01 to 0.67??K/s. No evidence of any reactions among the oil shale mineral constituents was observed at temperatures below 1173??K. However, it was found that the presence of pyrite in oil shale reduces the primary devolatilization rate of kerogen and increases the amount of residual char in the spent shale. Carbonaceous residues which were prepared by heating the oil shale at a rate of 0.166??K/s to temperatures between 923??K and 1073??K, had the highest reactivities when oxidized at 0.166??K/s in a gas having 21 volume percent oxygen. Oxygen chemisorption was found to be the initial precursor to the oxidation process. The kinetics governing oxygen chemisorption is (Equation Presented) where X is the fractional coverage. The oxidation of the carbonaceous residue was found also to be second-order. The activation energy and the frequency factor determined from isothermal experiments were 147 kJ/mole and 9.18??107 sec-1 respectively, while the values of these parameters obtained from a nonisothermal experiment were 212 kJ/mole and 1.5??1013 sec-1. The variation in the rate constants is attributed to the fact that isothermal and nonisothermal analyses represent two different aspects of the combustion process.

  5. Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.

    PubMed

    Fleming, Donald G; Cottrell, Stephen P; McKenzie, Iain; Ghandi, Khashayar

    2015-08-14

    The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect. PMID:26165545

  6. Benchmark experiments for validation of reaction rates determination in reactor dosimetry

    NASA Astrophysics Data System (ADS)

    Rataj, J.; Huml, O.; Heraltova, L.; Bily, T.

    2014-11-01

    The precision of Monte Carlo calculations of quantities of neutron dosimetry strongly depends on precision of reaction rates prediction. Research reactor represents a very useful tool for validation of the ability of a code to calculate such quantities as it can provide environments with various types of neutron energy spectra. Especially, a zero power research reactor with well-defined core geometry and neutronic properties enables precise comparison between experimental and calculated data. Thus, at the VR-1 zero power research reactor, a set of benchmark experiments were proposed and carried out to verify the MCNP Monte Carlo code ability to predict correctly the reaction rates. For that purpose two frequently used reactions were chosen: He-3(n,p)H-3 and Au-197(n,γ)Au-198. The benchmark consists of response measurement of small He-3 gas filled detector in various positions of reactor core and of activated gold wires placed inside the core or to its vicinity. The reaction rates were calculated in MCNP5 code utilizing a detailed model of VR-1 reactor which was validated for neutronic calculations at the reactor. The paper describes in detail the experimental set-up of the benchmark, the MCNP model of the VR-1 reactor and provides a comparison between experimental and calculated data.

  7. Rapid heartbeat, but dry palms: reactions of heart rate and skin conductance levels to social rejection

    PubMed Central

    Iffland, Benjamin; Sansen, Lisa M.; Catani, Claudia; Neuner, Frank

    2014-01-01

    Background: Social rejection elicits negative mood, emotional distress, and neural activity in networks that are associated with physical pain. However, studies assessing physiological reactions to social rejection are rare and results of these studies were found to be ambiguous. Therefore, the present study aimed to examine and specify physiological effects of social rejection. Methods: Participants (n = 50) were assigned to either a social exclusion or inclusion condition of a virtual ball-tossing game (Cyberball). Immediate and delayed physiological [skin conductance level (SCL) and heart rate] reactions were recorded. In addition, subjects reported levels of affect, emotional states, and fundamental needs. Results: Subjects who were socially rejected showed increased heart rates. However, social rejection had no effect on subjects' SCLs. Both conditions showed heightened arousal on this measurement. Furthermore, psychological consequences of social rejection indicated the validity of the paradigm. Conclusions: Our results reveal that social rejection evokes an immediate physiological reaction. Accelerated heart rates indicate that behavior activation rather than inhibition is associated with socially threatening events. In addition, results revealed gender-specific response patterns suggesting that sample characteristics such as differences in gender may account for ambiguous findings of physiological reactions to social rejection. PMID:25221535

  8. Low-temperature rate coefficients for the reaction of ethynyl radical (C2H) with benzene.

    PubMed

    Goulay, Fabien; Leone, Stephen R

    2006-02-01

    The reaction of the C2H radical with benzene is studied at low temperature using a pulsed Laval nozzle apparatus. The C2H radical is prepared by 193-nm photolysis of acetylene, and the C2H concentration is monitored using CH(A2Delta) chemiluminescence from the C2H + O2 reaction. Measurements at very low photolysis energy are performed using CF3C2H as the C2H precursor to study the influence of benzene photodissociation on the rate coefficient. Rate coefficients are obtained over a temperature range between 105 and 298 K. The average rate coefficient is found to be five times greater than the estimated value presently used in the photochemical modeling of Titan's atmosphere. The reaction exhibits a slight negative temperature dependence which can be fitted to the expression k(cm3 molecule(-1) s(-1)) = 3.28(+/-1.0) x 10(-10) (T/298)(-0.18(+/-0.18)). The results show that this reaction has no barrier and may play an important role in the formation of large molecules and aerosols at low temperature. Our results are consistent with the formation of a short lifetime intermediate that decomposes to give the final products. PMID:16451020

  9. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  10. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; Jim Fredrickson; Ken Kemner; Shelly Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  11. Involvement of an arginyl residue in the nucleotide-binding site of Ca(2+)-ATPase from sarcoplasmic reticulum as seen by reaction with phenylglyoxal.

    PubMed Central

    Corbalán-García, S; Teruel, J A; Gómez-Fernández, J C

    1996-01-01

    1. Chemical modification of the Ca(2+)-ATPase with phenylglyoxal, as a modifier of arginine residues, leads to an almost total loss of the ATPase activity. The presence of nucleotides in the reaction medium protects against the binding of 18 nmol of phenylglyoxal/mg of protein and this reduction in the binding of phenylglyoxal is accompanied by a substantial retention of ATPase activity. The incorporation of phenylglyoxal to the protein alters neither calcium binding nor phosphorylation from inorganic phosphate. Nevertheless the binding of nucleotides is dramatically inhibited and, consequently, so is phosphorylation from ATP. Fluorescein 5'-isothiocyanate labelling of the phenylglyoxal-modified ATPase is not affected but, on the other hand, phenylglyoxal is not able to modify the fluorescein 5'-isothiocyanate-prelabelled ATPase. The way in which ATPase inhibition depends on the presence of phenylglyoxal indicates that this process occurs in a pseudo-first-order reaction. However, the dependence of the apparent first-order rate constant on phenylglyoxal concentration appears to be more complex and an inhibition mechanism of two steps, with phenylglyoxal binding, has to be taken into account. 2. We have found that phenylglyoxal labels both A and B tryptic fragments, but only B fragment labelling is prevented by ATP. The sequencing of peptides from mild acid hydrolysis of phenylglyoxal-labelled ATPase shows that phenylglyoxal is located in the Ala506-Gly595 peptide that is a part of the B fragment. 3. We conclude that phenylglyoxal inactivates the calcium pump in a two-step mechanism in which the second step is irreversible. Phenylglyoxal labels an arginyl residue in the Ala506-Gly595 peptide that can be protected by the binding of ATP to its site. PMID:8761469

  12. Rates for neutron-capture reactions on tungsten isotopes in iron meteorites. [Abstract only

    NASA Technical Reports Server (NTRS)

    Masarik, J.; Reedy, R. C.

    1994-01-01

    High-precision W isotopic analyses by Harper and Jacobsen indicate the W-182/W-183 ratio in the Toluca iron meteorite is shifted by -(3.0 +/- 0.9) x 10(exp -4) relative to a terrestrial standard. Possible causes of this shift are neutron-capture reactions on W during Toluca's approximately 600-Ma exposure to cosmic ray particles or radiogenic growth of W-182 from 9-Ma Hf-182 in the silicate portion of the Earth after removal of W to the Earth's core. Calculations for the rates of neutron-capture reactions on W isotopes were done to study the first possibility. The LAHET Code System (LCS) which consists of the Los Alamos High Energy Transport (LAHET) code and the Monte Carlo N-Particle(MCNP) transport code was used to numerically simulate the irradiation of the Toluca iron meteorite by galactic-cosmic-ray (GCR) particles and to calculate the rates of W(n, gamma) reactions. Toluca was modeled as a 3.9-m-radius sphere with the composition of a typical IA iron meteorite. The incident GCR protons and their interactions were modeled with LAHET, which also handled the interactions of neutrons with energies above 20 MeV. The rates for the capture of neutrons by W-182, W-183, and W-186 were calculated using the detailed library of (n, gamma) cross sections in MCNP. For this study of the possible effect of W(n, gamma) reactions on W isotope systematics, we consider the peak rates. The calculated maximum change in the normalized W-182/W-183 ratio due to neutron-capture reactions cannot account for more than 25% of the mass 182 deficit observed in Toluca W.

  13. Electrochemical degradation of sulfonamides at BDD electrode: kinetics, reaction pathway and eco-toxicity evaluation.

    PubMed

    Fabiańska, Aleksandra; Białk-Bielińska, Anna; Stepnowski, Piotr; Stolte, Stefan; Siedlecka, Ewa Maria

    2014-09-15

    The investigation dealt with electrochemical oxidation of five sulfonamides (SNs): sulfadiazine (SDZ), sulfathiazole (STZ), sulfamerazine (SMR), sulfamethazine (SMN) and sulfadimethoxine (SDM) in aqueous solution at boron-doped diamond (BDD) electrode. All studied sulfonamides were degraded according to a pseudo first order kinetics. The structure of SNs had no significant effect on the values of pseudo first order rate constants. Increased degradation efficiency was observed in higher temperature and in acidic pH. Due to the presence of chlorine and nitrate SNs were more effectively oxidized from municipal wastewater treatment plant (WWTP) effluents than from pure supporting electrolyte Na2SO4. The intermediates identified by LC-MS and GC-MS analysis suggested that the hydroxyl radicals attack mainly the SN bond, but also the aromatic ring systems (aniline, pyrimidine or triazole) of SNs. Finally, the toxicity of the SNs solutions and effluents after electrochemical treatment was assessed through the measurement of growth inhibition of green algae (Scenedesmus vacualatus) and duckweed (Lemna minor). Toxicity of SMR, STZ, SMN solutions before and after electrochemical oxidation and SDM solution after the process in L. minor test was observed. No significant toxicity of studied SNs was observed in algae test. PMID:25215656

  14. Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

    NASA Technical Reports Server (NTRS)

    Payne, W. A.; Nava, D. F.; Brunning, J.; Stief, L. J.

    1986-01-01

    The first-order, diffusion, and bimolecular rate constants for the reaction Br + C2H2 yields C2H3Br are evaluated. The rate constants are measured at 210, 248, 298, and 393 K and at pressures between 15-100 torr Ar using flash photolysis combined with time-resolved detection of atomic bromine via Br resonance radiation. It is observed that the reaction is not affected by pressure or temperature and the bimolecular constant = (4.0 + or - 0.8) x 10 to the -15th cu cm/sec with an error of two standard deviations. The C2H2 + Br reaction rates are compared with reactions of C2H2 with Cl, OH, NH2, and H. The loss rates for atmospheric C2H2 for reactions with OH, Cl, O, and Br are calculated as a function of altitude.

  15. Accurate label-free reaction kinetics determination using initial rate heat measurements

    PubMed Central

    Ebrahimi, Kourosh Honarmand; Hagedoorn, Peter-Leon; Jacobs, Denise; Hagen, Wilfred R.

    2015-01-01

    Accurate label-free methods or assays to obtain the initial reaction rates have significant importance in fundamental studies of enzymes and in application-oriented high throughput screening of enzyme activity. Here we introduce a label-free approach for obtaining initial rates of enzyme activity from heat measurements, which we name initial rate calorimetry (IrCal). This approach is based on our new finding that the data recorded by isothermal titration calorimetry for the early stages of a reaction, which have been widely ignored, are correlated to the initial rates. Application of the IrCal approach to various enzymes led to accurate enzyme kinetics parameters as compared to spectroscopic methods and enabled enzyme kinetic studies with natural substrate, e.g. proteases with protein substrates. Because heat is a label-free property of almost all reactions, the IrCal approach holds promise in fundamental studies of various enzymes and in use of calorimetry for high throughput screening of enzyme activity. PMID:26574737

  16. On OH and O3 Reaction Rates with Isoprene-Derived Hydroxy Nitrates

    NASA Astrophysics Data System (ADS)

    Lee, L.; Teng, A.; Crounse, J.; Wennberg, P. O.; Cohen, R. C.

    2013-12-01

    3 of the 8 primary isoprene hydroxy nitrate isomers ((E & Z)-2-methyl-4-nitrooxybut-2-ene-1-ol and 2-methyl-1-nitrooxybut-3-ene-2-ol) were synthesized. The purity of these isomers was confirmed with proton NMR spectroscopy. Oxidation of these unsaturated nitrates by OH and O3 were studied in an environmental chamber equipped with both Chemical Ionization Mass Spectrometer (CIMS) and Thermo-Dissociation Laser Induced Fluorescence (TD-LIF) instrument for continuous monitoring of reactants and products. The OH reaction rates of the individual isomers were measured relative to propene resulting in rate constants for each isomer, in the same order as above, of: 1.1×10-10, 1.1×10-10 and 4.2×10-11 cm3/s. For the O3 reaction rate constant of 2-methyl-1-nitrooxybut-3-ene-2-ol, we report an interval of (2.5~5)×10-19 cm3/s. The precision of our estimate on this very slow process was limited by the chamber wall loss. For (E) and (Z)-2-methyl-4-nitrooxybut-2-ene-1-ol the O3 rate constants are 2.7×10-17 and 2.9×10-17 cm3/s, respectively. Reaction pathways, product yields and implications for atmospheric chemistry are discussed.

  17. Rate constant for the reaction SO + BrO yields SO2 + Br

    NASA Technical Reports Server (NTRS)

    Brunning, J.; Stief, L.

    1986-01-01

    The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

  18. Determination of relative rate constants for in vitro RNA processing reactions by internal competition.

    PubMed

    Lin, Hsuan-Chun; Yandek, Lindsay E; Gjermeni, Ino; Harris, Michael E

    2014-12-15

    Studies of RNA recognition and catalysis typically involve measurement of rate constants for reactions of individual RNA sequence variants by fitting changes in substrate or product concentration to exponential or linear functions. A complementary approach is determination of relative rate constants by internal competition, which involves quantifying the time-dependent changes in substrate or product ratios in reactions containing multiple substrates. Here, we review approaches for determining relative rate constants by analysis of both substrate and product ratios and illustrate their application using the in vitro processing of precursor transfer RNA (tRNA) by ribonuclease P as a model system. The presence of inactive substrate populations is a common complicating factor in analysis of reactions involving RNA substrates, and approaches for quantitative correction of observed rate constants for these effects are illustrated. These results, together with recent applications in the literature, indicate that internal competition offers an alternate method for analyzing RNA processing kinetics using standard molecular biology methods that directly quantifies substrate specificity and may be extended to a range of applications. PMID:25173512

  19. Photooxidative degradation of Acid Red 27 (AR27): modeling of reaction kinetic and influence of operational parameters.

    PubMed

    Daneshvar, Nezameddin; Rabbani, Mohammad; Modirshahla, Nasser; Behnajady, Mohammad-Ali

    2004-01-01

    The decolorization and mineralization of Acid Red 27 (AR27), an anionic monoazo dye of acid class, were studied by UV/H202 process in laboratory and real samples. Effects of different process parameters such as initial H2O2 and AR27 concentrations, pH and EtOH as an electron scavenger have been studied. H2O2 and UV light have a negligible effect when they were used on their own. The decolorization rate follows pseudo-first order kinetic with respect to the dye concentration. The rate constant of the attack of *OH radicals to the AR27 has been estimated through the adoption of a simplified kinetic model (1.03 x 10(8)M(-1)s(-1)). This model allows predicting the pseudo-first order rate constant and concentration of AR27 in different illumination times for different initial concentrations of H2O2. Mineralization studies showed, the formation of sulfate ions, the decrease of pH and 85% of COD reduction occur in less than 60 min. In the real wastewater color removal could be achieved after only 75 min, whereas 45% of COD reduction occurs after 105 min of illumination. PMID:15478925

  20. Substituent effects on the reaction rates of hydrogen abstraction in the pyrolysis of phenethyl phenyl ethers

    SciTech Connect

    Beste, Ariana; Buchanan III, A C

    2010-01-01

    We report reaction profiles and forward rate constants for hydrogen abstraction reactions occurring in the pyrolysis of methoxy-substituted derivatives of phenethyl phenyl ether (PhCH{sub 2}CH{sub 2}OPh, PPE), where the substituents are located on the aryl ether ring (PhCH{sub 2}CH{sub 2}OPh-X). We use density functional theory in combination with transition-state theory, and anharmonic corrections are included within the independent mode approximation. PPE is the simplest model of the abundant {beta}-O-4 linkage in lignin. The mechanism of PPE pyrolysis and overall product selectivities have been studied experimentally by one of us, which was followed by computational analysis of key individual hydrogen-transfer reaction steps. In the previous work, we have been able to use a simplified kinetic model based on quasi-steady-state conditions to reproduce experimental {alpha}/{beta} selectivities for PPE and PPEs with substituents on the phenethyl ring (X-PhCH{sub 2}CH{sub 2}OPh). This model is not applicable to PPE derivatives where methoxy substituents are located on the phenyl ring adjacent to the ether oxygen because of the strongly endothermic character of the hydrogen abstraction by substituted phenoxy radicals as well as the decreased kinetic chain lengths resulting from enhanced rates of the initial C?O homolysis step. Substituents decelerate the hydrogen abstraction by the phenoxy radical, while the influence on the benzyl abstraction is less homogeneous. The calculations provide insight into the contributions of steric and polar effects in these important hydrogen-transfer steps. We emphasize the importance of an exhaustive conformational space search to calculate rate constants and product selectivities. The computed rate constants will be used in future work to numerically simulate the pyrolysis mechanism, pending the calculation of the rate constants of all participating reactions.

  1. VizieR Online Data Catalog: Neutron-induced astrophysical reaction rates (Panov+, 2010)

    NASA Astrophysics Data System (ADS)

    Panov, I. V.; Korneev, I. Yu.; Rauscher, T.; Martinez-Pinedo, G.; Kelic-Heil, A.; Zinner, N. T.; Thielemann, F.-K.

    2010-01-01

    The organization of Tables 3-6 with calculated rates for 24 different values of T9 is extremely simple - all data are in 8 columns. The columns give, in this order, the target element, the atomic mass number A of the target, the temperature in T9, partition function of the target, neutron-induced fission rate for the ground state, neutron-induced fission rate with thermally populated target states, neutron capture rate for the ground state, neutron capture rate with thermally populated target states. The rates in Tables 3-6 were calculated on the basis of different mass and fission barrier predictions: ETFSI, TF and FRDM(masses)+TF(barriers), respectively (see main text of the paper for details). The fitting coefficients for the (n,g), (g,n), and neutron-induced fission rates (n,f) with different mass and fission-barrier predictions are placed in the Tables 7-18 (see example on how to use them in Appendix A of the main paper). The columns in Tables 7-18 are organized as follows: target element, atomic mass number A of the target, target charge number Z, the number of fitting curves i_{fit}, seven coefficients of the forward reaction a_i, and the mean square error for direct reactions. A value i{fit}=0 means that there is only one seven-parameter set to fit the rate. Values i_{fit}>1 give the number of parameter sets which have to be added up to yield the final rate, i.e. the rate r is calculated as r={sum.on.i}ri, with each ri computed from the i-th parameter set and using Eq. ri=exp(a0+a1/T9+a2/T91/3+a3*T91/3+a4*T9+a5*T95/3^+a6*ln(T9)) (4). (16 data files).

  2. Cooperation between bound waters and hydroxyls in controlling isotope-exchange rates

    NASA Astrophysics Data System (ADS)

    Panasci, Adele F.; McAlpin, J. Gregory; Ohlin, C. André; Christensen, Shauna; Fettinger, James C.; Britt, R. David; Rustad, James R.; Casey, William H.

    2012-02-01

    Mineral oxides differ from aqueous ions in that the bound water molecules are usually attached to different metal centers, or vicinal, and thus separated from one another. In contrast, for most monomeric ions used to establish kinetic reactivity trends, such as octahedral aquo ions (e.g., Al(H 2O) 63+), the bound waters are closely packed, or geminal. Because of this structural difference, the existing literature about ligand substitution in monomer ions may be a poor guide to the reactions of geochemical interest. To understand how coordination of the reactive functional groups might affect the rates of simple water-exchange reactions, we synthesized two structurally similar Rh(III) complexes, [Rh(phen) 2(H 2O) 2] 3+ [ 1] and [Rh(phen) 2(H 2O)Cl] 2+ [ 2] where (phen) = 1,10-phenanthroline. Complex [ 1] has two adjacent, geminal, bound waters in the inner-coordination sphere and [ 2] has a single bound water adjacent to a bound chloride ion. We employed Rh(III) as a trivalent metal rather than a more geochemically relevant metal like Fe(III) or Al(III) to slow the rate of reaction, which makes possible measurement of the rates of isotopic substitution by simple mass spectrometry. We prepared isotopically pure versions of the molecules, dissolved them into isotopically dissimilar water, and measured the rates of exchange from the extents of 18O and 16O exchange at the bound waters. The pH dependency of rates differ enormously between the two complexes. Pseudo-first-order rate coefficients at 298 K for water exchanges from the fully protonated molecules are close: k0298 = 5 × 10 -8(±0.5 × 10 -8) s -1 for [ 1] and k0298 = 2.5 × 10 -9(±1 × 10 -9) for [ 2]. Enthalpy and entropy activation parameters (Δ H‡ and Δ S‡) were measured to be 119(±3) kJ mol -1, and 14(±1) J mol -1 K -1, respectively for [ 1]. The corresponding parameters for the mono-aquo complex, [ 2], are 132(±3) kJ mol -1 and 41.5(±2) J mol -1 K -1. Rates increase by many orders of magnitude upon deprotonation of one of the bound waters in complex [ 1] because of the close proximity of a transferable proton that can convert the bound hydroxyl to a bound water. This interconversion allows the oxygen to exchange as a bound water, rather than as a bound hydroxyl, which is slow at near-neutral pH conditions.

  3. Reaction Rates for H-burning in Stars from Experiments with Radioactive Nuclear Beams

    SciTech Connect

    Trache, Livius

    2008-01-24

    In this lecture some of the indirect methods for nuclear astrophysics that can be applied to extract reaction rates for H-burning in stars are treated. Instead of reviewing all methods, I chose for exemplification four different experiments of our Texas A and M group, each involving a different method, but all related to the study of the proton rich nucleus {sup 23}Al. They involve the use of radioactive nuclear beams. I will describe the use of one-nucleon transfer reactions (the ANC method), breakup reactions at intermediate energies, {beta}-decay and {beta}-delayed proton-decay to extract nuclear structure information that is then used for nuclear astrophysics. I will show the specificities of each method, talk about their complementarities and redundancies.

  4. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    SciTech Connect

    Lamia, L.; Spitaleri, C.; La Cognata, M.; Palmerini, S.; Sergi, M. L.; Puglia, S. M. R.

    2015-02-24

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium ({sup 2}H), for the two lithium {sup 6,7}Li isotopes, for the {sup 9}Be and the one for the two boron {sup 10,11}B isotopes will be discussed.

  5. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; La Cognata, M.; Palmerini, S.; Puglia, S. M. R.; Sergi, M. L.

    2015-02-01

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium (2H ), for the two lithium 6,7Li isotopes, for the 9Be and the one for the two boron 10,11B isotopes will be discussed.

  6. Rate coefficients of hydroxyl radical reactions with pesticide molecules and related compounds: A review

    NASA Astrophysics Data System (ADS)

    Wojnrovits, Lszl; Takcs, Erzsbet

    2014-03-01

    Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2109-11010 mol-1 dm3 s-1. The rate coefficients show some variation with the electron withdrawing-donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5109 mol-1 dm3 s-1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C-H bonds may also be above 1109 mol-1 dm3 s-1. However, the values for molecules without C=C double bonds or several C-H bonds are in the 1107-1109 mol-1 dm3 s-1 range.

  7. The Effects of Tempur Insoles on Ground Reaction Forces and Loading Rates in Running

    PubMed Central

    RUANO, CRYSTAL; POWELL, DOUGLAS; CHALAMBAGA, ELIZABETH T.; RENSHAW, DOUG

    2009-01-01

    Runners often experience over-use injuries. Ground reaction force (GRFs) patterns have been associated with these over-use injuries; however, it is not solely the magnitude of GRFs, but also the rate at which they are applied that lead to lower extremity injury. Many recreational runners will use over-the-counter insoles as a method of treating or preventing injury. Therefore, the purpose of this study was to examine the efficacy of two insoles on peak GRFs and loading rates. It was hypothesized that no differences in peak GRFs or loading rates would exist with the addition of two insoles during running. Twelve subjects (7 females; 5 males) performed seven running trials in each of the following conditions: no insoles (NORM), over-the-counter insoles (OTC) and memory-foam insoles (TEMPUR). GRFs were recorded using a force plate (1440Hz; AMTI) while subjects ran across a 15 meter lab. A 2 x 3 (gender x insole) repeated measures ANOVA was used to compare the effects of insoles on loading rate and ground reaction forces. Alpha level was set at p <0.05. The current study found no statistical differences in loading rate or GRFs between the insole and no insole conditions. Furthermore, there was no gender effect in any condition. The findings of the current study suggest that insoles do not attenuate shock or decrease loading rate. The lack of shock attenuation associated with insoles suggests they do not protect the lower extremity from injury.

  8. Kinetics of Several Oxygen-Containing Carbon-Centered Free Radical Reactions with Nitric Oxide.

    PubMed

    Rissanen, Matti P; Ihlenborg, Marvin; Pekkanen, Timo T; Timonen, Raimo S

    2015-07-16

    Kinetics of four carbon-centered, oxygen-containing free radical reactions with nitric oxide (NO) were investigated as a function of temperature at a few Torr pressure of helium, employing flow tube reactors coupled to a laser-photolysis/resonance-gas-discharge-lamp photoionization mass spectrometer (LP-RPIMS). Rate coefficients were directly determined from radical (R) decay signals under pseudo-first-order conditions ([R]0 ≪ [NO]). The obtained rate coefficients showed negative temperature dependences, typical for a radical-radical association process, and can be represented by the following parametrizations (all in units of cm(3) molecule(-1) s(-1)): k(CH2OH + NO) = (4.76 × 10(-21)) × (T/300 K)(15.92) × exp[50700/(RT)] (T = 266-363 K, p = 0.79-3.44 Torr); k(CH3CHOH + NO) = (1.27 × 10(-16)) × (T/300 K)(6.81) × exp[28700/(RT)] (T = 241-363 K, p = 0.52-3.43 Torr); k(CH3OCH2 + NO) = (3.58 ± 0.12) × 10(-12) × (T/300 K)(-3.17±0.14) (T = 221-363 K, p = 0.50-0.80 Torr); k(T)3 = 9.62 × 10(-11) × (T/300 K)(-5.99) × exp[-7100/(RT)] (T = 221-473 K, p = 1.41-2.95 Torr), with the uncertainties given as standard errors of the fits and the overall uncertainties estimated as ±20%. The rate of CH3OCH2 + NO reaction was measured in two density ranges due to its observed considerable pressure dependence, which was not found in the studied hydroxyalkyl reactions. In addition, the CH3CO + NO rate coefficient was determined at two temperatures resulting in k298K(CH3CO + NO) = (5.6 ± 2.8) × 10(-13) cm(3) molecule(-1) s(-1). No products were found during these experiments, reasons for which are briefly discussed. PMID:26000890

  9. Rates of hydration reactions in crustal shear zones and their implications for temporal variations in rheology

    NASA Astrophysics Data System (ADS)

    Yardley, B. W. D.; Harlov, D. E.; Heinrich, W.

    2009-04-01

    Crustal shear zones are commonly accompanied by retrograde metamorphism of pre-existing higher grade rocks. The retrograde reactions involve hydration, but the localisation of the retrogression suggests that reaction is limited by either the availability of water or the effect of deformation on reaction kinetics. Depending on the rate of retrograde hydration reactions, shear zones may either be uniformly wet for long periods of time during their deformation history, or may be dry for much of the time, experiencing brief periods where free water is present. If the latter scenario is correct, their strength will fluctuate markedly according to the presence or absence of water. In order to evaluate the likely residence time of water in mid-crustal shear zones, we have carried out experiments to investigate the rate of hydration of a natural granulite under greenschist to amphibolite facies metamorphic conditions (300-500C, 3-5 kbar). Seived and cleaned grains of powdered hornblende granulite were loaded in gold capsules with weighed amounts of water and reacted for periods of between 3 days and 12 weeks. The water consumed by hydration reactions was determined by weighing at the end of the run and combined with estimated surface areas to calculate the rate at which water was lost during the reaction. Results are of the order 10-7 to 10-8 g/s/m2 surface area, and are comparable to previous published data for the rate of hydration of K-feldspar + andalusite. SEM observation of the run charges shows that retrograde minerals including actinolite and sheet silicates were produced. There are no obvious differences in reaction rate between experiments at different P-T conditions. These reaction rates imply that if water infiltrates along a fracture surface in high grade rocks under mid-crustal conditions, forming a film with a half thickness of 100 microns, it will survive for around 10-100 years only before being consumed by hydration reactions. The film thickness has been estimated based on thicknesses of secondary fluid inclusion planes (normally less than 50 microns) and of mineral growth zones in secondary minerals. These times are short even relative to the repeat rate of earthquakes on major fault systems and suggest that a free water phase is absent from shear zone rocks for most of their history. We propose that shear zones are dry and relatively strong for much of their history but become weakened and deform when water is able to gain access from water-bearing fractures in overlying crust or, possibly, overpressured reservoirs at depth. Each episode of strain in response to water infiltration lasts for times of the order of tens to hundreds of years, and terminates when all the water has been consumed in hydrous minerals, thereby inhibiting further deformation by water-assisted mechanisms. We conclude that strain localisation in shear zones is normally the result of focussed introduction of water from an external source such as a fault at higher levels.

  10. The effects of physical and geochemical heterogeneities on hydro-geochemical transport and effective reaction rates

    NASA Astrophysics Data System (ADS)

    Atchley, Adam L.; Navarre-Sitchler, Alexis K.; Maxwell, Reed M.

    2014-09-01

    The role of coupled physical and geochemical heterogeneities in hydro-geochemical transport is investigated by simulating three-dimensional transport in a heterogeneous system with kinetic mineral reactions. Ensembles of 100 physically heterogeneous realizations were simulated for three geochemical conditions: 1) spatially homogeneous reactive mineral surface area, 2) reactive surface area positively correlated to hydraulic heterogeneity, and 3) reactive surface area negatively correlated to hydraulic heterogeneity. Groundwater chemistry and the corresponding effective reaction rates were calculated at three transverse planes to quantify differences in plume evolution due to heterogeneity in mineral reaction rates and solute residence time (τ). The model is based on a hypothetical CO2 intrusion into groundwater from a carbon capture utilization and storage (CCUS) operation where CO2 dissolution and formation of carbonic acid created geochemical dis-equilibrium between fluids and the mineral galena that resulted in increased aqueous lead (Pb2 +) concentrations. Calcite dissolution buffered the pH change and created conditions of galena oversaturation, which then reduced lead concentrations along the flow path. Near the leak kinetic geochemical reactions control the release of solutes into the fluid, but further along the flow path mineral solubility controls solute concentrations. Simulation results demonstrate the impact of heterogeneous distribution of geochemical reactive surface area in coordination with physical heterogeneity on the effective reaction rate (Krxn,eff) and Pb2 + concentrations within the plume. Dissimilarities between ensemble Pb2 + concentration and Krxn,eff are attributed to how geochemical heterogeneity affects the time (τeq) and therefore advection distance (Leq) required for the system to re-establish geochemical equilibrium. Only after geochemical equilibrium is re-established, Krxn,eff and Pb2 + concentrations are the same for all three geochemical conditions. Correlation between reactive surface area and hydraulic conductivity, either positive or negative, results in variation in τeq and Leq.

  11. The effects of physical and geochemical heterogeneities on hydro-geochemical transport and effective reaction rates.

    PubMed

    Atchley, Adam L; Navarre-Sitchler, Alexis K; Maxwell, Reed M

    2014-09-01

    The role of coupled physical and geochemical heterogeneities in hydro-geochemical transport is investigated by simulating three-dimensional transport in a heterogeneous system with kinetic mineral reactions. Ensembles of 100 physically heterogeneous realizations were simulated for three geochemical conditions: 1) spatially homogeneous reactive mineral surface area, 2) reactive surface area positively correlated to hydraulic heterogeneity, and 3) reactive surface area negatively correlated to hydraulic heterogeneity. Groundwater chemistry and the corresponding effective reaction rates were calculated at three transverse planes to quantify differences in plume evolution due to heterogeneity in mineral reaction rates and solute residence time (τ). The model is based on a hypothetical CO2 intrusion into groundwater from a carbon capture utilization and storage (CCUS) operation where CO2 dissolution and formation of carbonic acid created geochemical dis-equilibrium between fluids and the mineral galena that resulted in increased aqueous lead (Pb(2+)) concentrations. Calcite dissolution buffered the pH change and created conditions of galena oversaturation, which then reduced lead concentrations along the flow path. Near the leak kinetic geochemical reactions control the release of solutes into the fluid, but further along the flow path mineral solubility controls solute concentrations. Simulation results demonstrate the impact of heterogeneous distribution of geochemical reactive surface area in coordination with physical heterogeneity on the effective reaction rate (Krxn,eff) and Pb(2+) concentrations within the plume. Dissimilarities between ensemble Pb(2+) concentration and Krxn,eff are attributed to how geochemical heterogeneity affects the time (τeq) and therefore advection distance (Leq) required for the system to re-establish geochemical equilibrium. Only after geochemical equilibrium is re-established, Krxn,eff and Pb(2+) concentrations are the same for all three geochemical conditions. Correlation between reactive surface area and hydraulic conductivity, either positive or negative, results in variation in τeq and Leq. PMID:25113426

  12. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    SciTech Connect

    Peters, Catherine A

    2013-02-28

    Geochemical reactions in deep subsurface environments are complicated by the consolidated nature and mineralogical complexity of sedimentary rocks. Understanding the kinetics of these reactions is critical to our ability to make long-term predictions about subsurface processes such as pH buffering, alteration in rock structure, permeability changes, and formation of secondary precipitates. In this project, we used a combination of experiments and numerical simulation to bridge the gap between our knowledge of these reactions at the lab scale and rates that are meaningful for modeling reactive transport at core scales. The focus is on acid-driven mineral dissolution, which is specifically relevant in the context of CO2-water-rock interactions in geological sequestration of carbon dioxide. The project led to major findings in three areas. First, we modeled reactive transport in pore-network systems to investigate scaling effects in geochemical reaction rates. We found significant scaling effects when CO2 concentrations are high and reaction rates are fast. These findings indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. Second, we used mathematical modeling to investigate the extent to which SO2, if co-injected with CO2, would acidify formation brines. We found that there exist realistic conditions in which the impact on brine acidity will be limited due to diffusion rate-limited SO2 dissolution from the CO2 phase, and the subsequent pH shift may also be limited by the lack of availability of oxidants to produce sulfuric acid. Third, for three Viking sandstones (Alberta sedimentary basin, Canada), we employed backscattered electron microscopy and energy dispersive X-ray spectroscopy to statistically characterize mineral contact with pore space. We determined that for reactive minerals in sedimentary consolidated rocks, abundance alone is not a good predictor of mineral accessible surface area, and should not be used in reactive transport modeling. Our work showed that reaction rates would be overestimated by three to five times.

  13. Transition path sampling with quantum/classical mechanics for reaction rates.

    PubMed

    Grter, Frauke; Li, Wenjin

    2015-01-01

    Predicting rates of biochemical reactions through molecular simulations poses a particular challenge for two reasons. First, the process involves bond formation and/or cleavage and thus requires a quantum mechanical (QM) treatment of the reaction center, which can be combined with a more efficient molecular mechanical (MM) description for the remainder of the system, resulting in a QM/MM approach. Second, reaction time scales are typically many orders of magnitude larger than the (sub-)nanosecond scale accessible by QM/MM simulations. Transition path sampling (TPS) allows to efficiently sample the space of dynamic trajectories from the reactant to the product state without an additional biasing potential. We outline here the application of TPS and QM/MM to calculate rates for biochemical reactions, by means of a simple toy system. In a step-by-step protocol, we specifically refer to our implementation within the MD suite Gromacs, which we have made available to the research community, and include practical advice on the choice of parameters. PMID:25330957

  14. Identifying Nuclear Reaction Rates That Are Important For (44) TI Supernova Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    The, L.-S.; Meyer, B. S.; Clayton, D. D.

    1997-05-01

    Large excesses of (44) Ca in certain presolar graphite and silicon carbide grains give strong evidence for (44) Ti production in supernovae. Furthermore, recent detection of the (44) Ti gamma -line from the Cas A SNR by CGRO/COMPTEL shows that radioactive (44) Ti is produced in supernovae. In this work we study the conditions needed for (44) Ti production in alpha-rich freezeouts in core-collapse supernovae as a function of peak temperature and density. We survey the key nuclear reactions governing (44) Ti production by varying their cross sections. We identify and rank their importance. We find (44) Ti production is most sensitive to variations in the rates of the reactions (44) Ti(alpha ,p)(47) V, alpha (2alpha ,gamma )(12) C, and (45) V(p,gamma )(46) Cr. Because many of these rates are unknown experimentally, our results suggest the most important targets for future cross section measurements.

  15. Rate of reactions between D 2O and Ca xAl yO z

    NASA Astrophysics Data System (ADS)

    Christensen, A. Nørlund; Lehmann, M. S.

    1984-02-01

    The rate of the reaction between D 2O and the calcium aluminum oxides Ca 3Al 2O 6, Ca 5Al 6O 14, CaAl 2O 4, and CaAl 4O 7 was investigated by on-line neutron diffraction powder methods at temperatures from room temperature to 100°C. The rate of the reaction increases with increasing calcium content of the compounds and with increasing temperature for each of the compounds. The crystallographic stable hydrate Ca 3Al 2(OD) 12 is obtained from CaAl 4O 7 and CaAl 2O 4 at temperatures above 63°C, from Ca 5Al 6O 14 at temperatures above 49°C, and from Ca 3Al 2O 6 at temperatures as low as 7°C.

  16. Hydrolysis of lanthanide dicarbides: Rates of reaction of cubic and tetragonal solid solutions with water

    SciTech Connect

    McColm, I.J. )

    1993-05-01

    Two series of solid solutions, Ho[sub 1[minus]x]La[sub x]C[sub 2] and Nd[sub 1[minus]x]LaC[sub 2], have been made and their X-ray unit cell parameters measured. The Ho[sub 1[minus]x]La[sub x]C[sub 2] series contains two tetragonal phases and a cubic solid solution series which has enabled the reaction rate constants for the water hydrolysis reaction of a cubic dicarbide phase to be determined for the first time. By comparing the linear rate constants and the activation energies across the two series the nature of bonding in general and the structure of the cubic phase are elucidated. A comparison with microhardness data is made and the change in M-C[sub 2] bonding as a function of composition is considered. 10 refs., 9 figs., 3 tabs.

  17. Reacting gas mixtures in the state-to-state approach: The chemical reaction rates

    SciTech Connect

    Kustova, Elena V.; Kremer, Gilberto M.

    2014-12-09

    In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.

  18. Modelling of silicon oxynitridation by nitrous oxide using the reaction rate approach

    NASA Astrophysics Data System (ADS)

    Dominique Krzeminski, Christophe

    2013-12-01

    Large technological progress in oxynitridation processing leads to the introduction of silicon oxynitride as ultra-thin gate oxide. On the theoretical side, few studies have been dedicated to the process modelling of oxynitridation. Such an objective is a considerable challenge regarding the various atomistic mechanisms occurring during this fabrication step. In this article, some progress performed to adapt the reaction rate approach for the modelling of oxynitride growth by a nitrous ambient are reported. The Ellis and Buhrman's approach is used for the gas phase decomposition modelling. Taking into account the mass balance of the species at the interface between the oxynitride and silicon, a minimal kinetic model describing the oxide growth has been calibrated and implemented. The influence of nitrogen on the reaction rate has been introduced in an empirical way. The oxidation kinetics predicted with this minimal model compares well with several experiments.

  19. 23Na (?,p )26Mg Reaction Rate at Astrophysically Relevant Energies

    NASA Astrophysics Data System (ADS)

    Howard, A. M.; Munch, M.; Fynbo, H. O. U.; Kirsebom, O. S.; Laursen, K. L.; Diget, C. Aa.; Hubbard, N. J.

    2015-07-01

    The production of 26Al in massive stars is sensitive to the 23Na (?,p )26Mg cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of 40 . We present here differential cross sections for the 23Na (?,p )26Mg reaction measured in the energy range Ec .m .=1.7 - 2.5 MeV . Concurrent measurements of Rutherford scattering provide absolute normalizations that are independent of variations in target properties. Angular distributions are measured for both p0 and p1 permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates by a factor of 40, impacting the 26Al yield from massive stars by more than a factor of 3.

  20. Absolute rate of the reaction of bromine atoms with ozone from 200 to 360 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Lee, J. H.; Payne, W. A.; Stief, L. J.

    1978-01-01

    The rate constant for the reaction Br + O3 yields BrO + O2 has been measured from 200 to 360 K by the technique of flash photolysis coupled to time resolved detection of bromine atoms by resonance fluorescence (FP-RF). Br atoms were produced by the flash photolysis of CH3Br at a wavelength of 165 nm. O3 concentration was monitored continuously under reaction conditions by absorption at 253.7 nm. At each of five temperatures the results were independent of substantial variations in O3 concentration, total pressure (Ar), and limited variations in flash intensity (i.e., initial Br concentration). The measured rate constants obey the Arrhenius expression, k = (7.74 plus or minus 0.50) x 10 to the -12th exp(-603 plus or minus 16/T) cu cm/molecule/sec, where the error quoted is two standard deviations.

  1. Absolute rate of the reaction of bromine atoms with ozone from 200-360 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Lee, J. H.; Payne, W. A.; Stief, L. J.

    1978-01-01

    The rate constant for the reaction Br + O3 yields BrO + O2 was measured from 200 to 360 K by the technique of flash photolysis coupled to time resolved detection of bromine atoms by resonance fluorescence (FP-RF). Br atoms were produced by the flash photolysis of CH3Br at lambda 165nm.O3 was monitored continuously under reaction conditions by absorption at 253.7 nm. At each of five temperatures the results were independent of substantial variations in O3, total pressure and limited variations in flash intensity. The measured rate constants obeyed the Arrhenius expression, where the error quoted is two standard deviations. Results are compared with previous determinations which employed the discharge flow-mass spectrometric technique.

  2. Reaction rates of α-tocopheroxyl radicals confined in micelles and in human plasma lipoproteins.

    PubMed

    Vanzani, Paola; Rigo, Adelio; Zennaro, Lucio; Di Paolo, Maria Luisa; Scarpa, Marina; Rossetto, Monica

    2014-08-01

    α-Tocopherol, the main component of vitamin E, traps highly reactive radicals which otherwise might react with lipids present in plasmatic lipoproteins or in cell membranes. The α-tocopheroxyl radicals generated by this process have also a pro-oxidant action which is contrasted by their reaction with ascorbate or by bimolecular self-reaction (dismutation). The kinetics of this bimolecular self-reaction were explored in solution such as ethanol, and in heterogeneous systems such as deoxycholic acid micelles and in human plasma. According to ESR measurements, the kinetic rate constant (2k(d)) of the bimolecular self-reaction of α-tocopheroxyl radicals in micelles and in human plasma was calculated to be of the order of 10(5) M(-1) s(-1) at 37 °C. This value was obtained considering that the reactive radicals are confined into the micellar pseudophase and is one to two orders of magnitude higher than the value we found in homogeneous phase. The physiological significance of this high value is discussed considering the competition between bimolecular self-reaction and the α-tocopheroxyl radical recycling by ascorbate. PMID:24995727

  3. Quantitative determination of the steady-state kinetics of multienzyme reactions using the algebraic rate equations for the component single-enzyme reactions.

    PubMed Central

    Stoner, C D

    1993-01-01

    Methods are given whereby the steady-state kinetic characteristics of multienzyme reactions consisting of individual single-enzyme reactions linked by freely diffusible intermediates can be determined quantitatively from the experimentally determined complete algebraic rate equations for the individual reactions. The approach is based on the fact that a valid steady-state rate equation for such a multienzyme reaction, in terms of the rate equations for the individual reactions, can be obtained simply from knowledge of the relative rates of the individual reactions when the multienzyme reaction is in the steady state. A number of model multienzyme reactions, which differ as to structural arrangement of the individual reactions, are examined by this approach. Simple mathematical methods which are applicable to most of these models are given for direct calculation of dependent variables. It is either pointed out or demonstrated with Mathematica that the rate equations for all of these models can be handled very easily with the aid of a personal computer equipped with appropriate equation-solving software. Since the approach permits evaluation of all dependent variables for any specific combination of values for the kinetic parameters and independent variables, numerical values for the flux control coefficients of the individual enzymes can be obtained by direct calculation for a wide variety of conditions and can be compared with those obtained according to the methods of Metabolic Control Analysis. Several such comparisons have been made and in all cases identical results were obtained. The intuitive notion that the individual enzymes of a multienzyme reaction would be equally rate limiting if the total amount of enzyme were being used with maximum efficiency is tested and shown to be incorrect. In the course of this test the flux control coefficient for the individual enzymes were found to be appropriate indicators of relative rate limitation or control by the enzymes and to account properly for differences in specific activity among the enzymes. PMID:8484738

  4. Turnover rate, reaction order, and elementary steps for the hydrodechlorination of chlorofluorocarbon compounds on palladium catalysts

    SciTech Connect

    Thompson, C.D.; Rioux, R.M.; Chen, N.; Ribeiro, F.H.

    2000-04-13

    The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H{sub 2}, and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H{sub 2}, gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF{sub 3}-CF{sub 2}Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF{sub 3}-CFClH), 1,1-dichlorotetrafluoroethane (CF{sub 3}-CFCl{sub 2}), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF{sub 3}-CCl{sub 3}).

  5. Actinide complexation kinetics: rate and mechanism of dioxoneptunium (V) reaction with chlorophosphonazo III

    SciTech Connect

    Fugate, G.; Feil-Jenkins, J.F.; Sullivan, J.C.; Nash, K.L.

    1996-12-01

    Rates of complex formation and dissociation in NpO{sub 2}{sup +}- Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La{sup 3+}, Eu{sup 3+}, Dy{sup 3+}, and Fe{sup 3+} with CLIII. Rate determining step in each system is an intramolecular process, the NpO{sub 2}{sup +}-CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are {Delta}H=46.2{+-}0.3 kJ/m and {Delta}S=7{+-} J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are {Delta}H=38.8{+-}0.6 kJ/m, {Delta}S=-96{+-}18 J/mK, {Delta}H=70.0{+-} kJ/m, and {Delta}S=17{+-}1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, and Zr{sup 4+}. Rates of CLIII complex formation reactions for Fe{sup 3+}, Zr{sup 4+}, NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, La{sup 3+}, Eu{sup 3+}, and Dy{sup 3+} correlate with cation radius rather than charge/radius ratio.

  6. A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air

    NASA Technical Reports Server (NTRS)

    Hansen, C Frederick; Heims, Steve P

    1958-01-01

    Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

  7. Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1978-01-01

    Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219-360 K by the flash photolysis-resonance fluorescence technique. The results can be expressed in Arrhenius form by K = (1.33 plus or minus 0.32)x10 to the minus 10 power exp (-449 plus or minus 58/T) cu cm/molecule/s (two standard deviations). The present work is compared to two previous determinations and is discussed theoretically.

  8. Investigating rare events with nonequilibrium work measurements. II. Transition and reaction rates.

    PubMed

    Moradi, Mahmoud; Sagui, Celeste; Roland, Christopher

    2014-01-21

    We present a formalism for investigating transition pathways and transition probabilities for rare events in biomolecular systems. The formalism is based on combining Transition Path Theory with the results of nonequilibrium work relations, and shows that the equilibrium and nonequilibrium transition rates are in fact related. Aside from its fundamental importance, this allows for the calculation of relative equilibrium reaction rates with driven nonequilibrium simulations such as Steered Molecular Dynamics. The workings of the formalism are illustrated with a few typical numerical examples. PMID:25669371

  9. Rate coefficients for reaction of OH with acetone between 202 and 395 K

    SciTech Connect

    Wollenhaupt, M.; Carl, S.A.; Horowitz, A.; Crowley, J.N.

    2000-03-30

    The kinetics of the title reaction were investigated between 202 and 395 K and at 20, 50, and 100 Torr of Ar or N{sub 2} bath gas using pulsed laser photolysis (PLP) generation of OH combined with both resonance fluorescence (RF) and laser-induced fluorescence (LIF) detection. OH was generated either by the sequential 439 nm, two-photon dissociation of NO{sub 2} in the presence of H{sub 2}, or by HONO photolysis at 351 nm. The accuracy of the rate constants obtained was enhanced by optical absorption measurements of acetone concentrations both before and after the photolysis reactor. The temperature dependence is not describe by a simple Arrhenius expression but by k{sub 1} (202--395 K) = 8.8 x 10{sup {minus}12} exp({minus}1,320/T) + 1.7 x 10{sup {minus}14} exp(423/T) cm{sup 3} s{sup {minus}1}, indicating that a simple H atom abstraction may not be the only reaction mechanism. The estimated total error (95% confidence) associated wit the rate coefficient derived from this expression is estimated as 5% and is independent of temperature. The curvature in the Arrhenius plot results in a significantly larger rate coefficient at low temperatures than obtained by extrapolation of the previous measurement and implies greater significance for the reaction with OH as a sink for acetone in the upper troposphere than presently assumed.

  10. Material interactions with the low earth orbital environment Accurate reaction rate measurements

    NASA Technical Reports Server (NTRS)

    Visentine, J. T.; Leger, L. J.

    1985-01-01

    Interactions between spacecraft surfaces and atomic oxygen within the low earth orbital (LEO) environment have been observed and measured during Space Shuttle flights over the past 3 yr. The results of these experiments have demonstrated that interaction rates for many materials proposed for spacecraft applications are high and that protective coatings must be developed to enable long-lived operation of spacecraft structures in the LEO environment. A flight experiment discussed herein uses the Space Shuttle as an orbiting exposure laboratory to obtain accurate reaction rate measurements for materials typically used in spacecraft construction. An ion-neutral mass spectrometer, installed in the Orbiter cargo bay, will measure diurnal ambient oxygen densities while material samples are exposed at low altitude (222 km) to the orbital environment. From in situ atomic oxygen density information and postflight material recession measurements, accurate reaction rates can be derived to update the Space Station materials interaction data base. Additionally, gases evolved from a limited number of material surfaces subjected to direct oxygen impingement will be identified using the mass spectrometer. These measurements will aid in mechanistic definitions of chemical reactions which cause atom-surface interactions and in validating results of upcoming degradation studies conducted in ground-based neutral beam laboratories.

  11. Rates and mechanisms of the atomic oxygen reaction with nickel at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1973-01-01

    The oxidation of nickel by atomic oxygen at pressure from 1 to 45 N/sq m between 1050 and 1250 K was investigated. In these ranges, the oxidation was found to follow the parobolic rate law, viz., K sub p = 0.0000114 exp(-13410/T) g squared/cm4/sec for films of greater than 1 micron thickness and was pressure independent. The activation enthalpy for the oxidation reaction was 112 + or - 11 kj/mole (27 + or - 3 kcal/mole). Of a number of possible mechanisms and defect structures considered, it was shown that the most likely was a saturated surface defect model for atomic oxidation, based on reaction activation enthalpies, impurity effects, pressure independence, and magnitudes of rates. A model judged somewhat less likely was one having doubly ionized cationic defects rate controlling in both atomic and molecular oxygen. From comparisons of the appropriate processes, the following enthalpy values were derived: enthalpy of activation (Ni diffusion in Ni0) = 110 + or - 30 kj/mole and standard enthalpy change for reaction formation (doubly ionized cation vacancies in Ni0 from atomic oxygen)= -9 + or - 25 kj/mole.

  12. Rate and product measurements for the reactions of OH with I/sub 2/ and ICl at 298 K: separation of gas-phase and surface reaction components

    SciTech Connect

    Loewenstein, L.M.; Anderson, J.G.

    1985-12-05

    The kinetic behavior of OH with I/sub 2/ and ICl is reported within the context of a series of radical-halogen reactions to investigate the mechanism of such reactions through studies of reactivity trends. Atomic I and Cl products of the title reactions are measured by resolved resonance fluorescence vapor lamps. IO and ClO are detected by chemically converting them, using NO, to I and Cl, respectively. The rate constant of the reaction H + ICl has been measured at 298 K; its only product channel is I + HCl. Magnitudes of the rate constants of these OH reactions substantiate the reactivity trends in the OH-halogen system based on an electron-transfer mechanism from the highest occupied molecular orbital of the halogen to the lowest unoccupied orbital of the hydroxyl. The rapidity of the OH + I/sub 2/ reaction makes it a possible source of HOI for photochemical studies. 31 references, 11 figures, 2 tables.

  13. The Rate of the Phosphorous Reaction Between Liquid Iron and Slag

    NASA Astrophysics Data System (ADS)

    Manning, Christopher P.; Fruehan, Richard J.

    2013-02-01

    In the current study, the rates of dephosphorization and rephosphorization of liquid iron with simulated steelmaking slags were investigated at 1873 K (1600° C). The experiments were conducted in an induction furnace with supplemental heating to maintain a consistent temperature within both the metal and slag phases. An integrated form of the rate equation was used to evaluate the results, assuming mass transfer in both the slag and metal was rate controlling. The results of the current and previous studies indicate that the mass transfer parameter, the slag-metal surface area, and the overall mass transfer coefficient ( A* k 0), decreased as the reaction proceeded. It is proposed that initially when the rate and oxygen flux are high, the interfacial energy decreases, and the interfacial fluid velocity increases causing disruption of the slag metal interface. The consequent increases in interfacial area and interfacial fluid flow cause A* k 0 to be high initially and then decrease as the oxygen flux decreases.

  14. Relative rate constants for the reactions of OH with methane and methyl chloroform

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1992-01-01

    Atmospheric lifetimes of methane and methyl chloroform are largely determined by the rates of their reactions with hydroxyl radical. The relative lifetimes for this loss path are inversely proportional to the ratio of the corresponding rate coefficients. The relative rate constants were measured in a slow-flow, temperature-controlled photochemical reactor, and were based on rates of disappearance of the parent compounds as measured by FTIR spectroscopy. The temperature range was 277-356 K. Hydroxyl radicals were generated by 254 nm photolysis of O3 in the presence of water vapor. The preferred Arrhenius expression for the results is k(CH3CCl3)/k(CH4) = 0.62 exp (291/T), corresponding to a value of 1.65 at 298 K and 1.77 at 277 K. The respective uncertainties are 5 and 7 percent.

  15. Reaction rate and collisional efficiency of the rhodopsin-transducin system in intact retinal rods.

    PubMed Central

    Kahlert, M; Hofmann, K P

    1991-01-01

    A model of transducin activation is constructed from its partial reactions (formation of metarhodopsin II, association, and dissociation of the rhodopsin-transducin complex). The kinetic equations of the model are solved both numerically and, for small photoactivation, analytically. From data on the partial reactions in vitro, rate and activation energy profile of amplified transducin turnover are modeled and compared with measured light-scattering signals of transducin activation in intact retinal rods. The data leave one free parameter, the rate of association between transducin and rhodopsin. Best fit is achieved for an activation energy of 35 kJ/mol, indicating lateral membrane diffusion of the proteins as its main determinant. The absolute value of the association rate is discussed in terms of the success of collisions to form the catalytic complex. It is greater than 30% for the intact retina and 10 times lower after permeabilization with staphylococcus aureus alpha-toxin. Dissociation rates for micromolar guanosinetriphosphale (GTP) (Kohl, B., and K. P. Hofmann, 1987. Biophys. J. 52:271-277) must be extrapolated linearly up to the millimolar range to explain the rapid transducin turnover in situ. This is interpreted by an unstable rhodopsin-transducin-GTP transient state. At the time of maximal turnover after a flash, the rate of activation is determined as 30, 120, 800, 2,500, and 4,000 activated transducins per photoactivated rhodopsin and second at 5, 10, 20, 30, 37 degrees C, respectively. PMID:1901231

  16. Insights into solar photo-Fenton reaction parameters in the oxidation of a sanitary landfill leachate at lab-scale.

    PubMed

    Silva, Tânia F C V; Ferreira, Rui; Soares, Petrick A; Manenti, Diego R; Fonseca, Amélia; Saraiva, Isabel; Boaventura, Rui A R; Vilar, Vítor J P

    2015-12-01

    This work evaluates the effect of the main photo-Fenton (PF) reaction variables on the treatment of a sanitary landfill leachate collected at the outlet of a leachate treatment plant, which includes aerated lagooning followed by aerated activated sludge and a final coagulation-flocculation step. The PF experiments were performed in a lab-scale compound parabolic collector (CPC) photoreactor using artificial solar radiation. The photocatalytic reaction rate was determined while varying the total dissolved iron concentration (20-100 mg Fe(2+)/L), solution pH (2.0-3.6), operating temperature (10-50 °C), type of acid used for acidification (H2SO4, HCl and H2SO4 + HCl) and UV irradiance (22-68 W/m(2)). This work also tries to elucidate the role of ferric hydroxides, ferric sulphate and ferric chloride species, by taking advantage of ferric speciation diagrams, in the efficiency of the PF reaction when applied to leachate oxidation. The molar fraction of the most photoactive ferric species, FeOH(2+), was linearly correlated with the PF pseudo-first order kinetic constants obtained at different solution pH and temperature values. Ferric ion speciation diagrams also showed that the presence of high amounts of chloride ions negatively affected the PF reaction, due to the decrease of ferric ions solubility and scavenging of hydroxyl radicals for chlorine radical formation. The increment of the PF reaction rates with temperature was mainly associated with the increase of the molar fraction of FeOH(2+). The optimal parameters for the photo-Fenton reaction were: pH = 2.8 (acidification agent: H2SO4); T = 30 °C; [Fe(2+)] = 60 mg/L and UV irradiance = 44 WUV/m(2), achieving 72% mineralization after 25 kJUV/L of accumulated UV energy and 149 mM of H2O2 consumed. PMID:26342264

  17. Atmospheric degradation of saturated alcohols: Room temperature rate coefficients for NO3 radical reactions

    NASA Astrophysics Data System (ADS)

    Moreno, Alberto; Salgado, Sagrario; Taccone, Raul; Martín, Pilar; Cabañas, Beatriz

    2014-10-01

    Rate coefficients for the reactions of NO3 radicals with a series of saturated alcohols are reported here using the relative rate technique. Experiments were performed using air as bath gas in a 50 L glass-pyrex reaction chamber at room temperature (298 ± 2) K with long-path FTIR spectroscopy used to monitor the reaction at atmospheric pressure (708 ± 8) Torr. The reference compounds used and their rate coefficients are: propanal kNO3 = (6.0 ± 0.6) × 10-15, methyl methacrylate kNO3 = (3.55 ± 0.62) × 10-15, acetaldehyde kNO3 = (2.62 ± 0.29) × 10-15 and propene kNO3 = (9.50 ± 1.9) × 10-15, in cm3 molecule-1 s-1. Rate coefficients obtained were (in units cm3 molecule-1 s-1): (1.87 ± 0.14) × 10-15, (2.39 ± 0.20) × 10-15, (2.28 ± 0.17) × 10-15, (1.80 ± 0.13) × 10-15 and (3.52 ± 0.19) × 10-15 for 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3,3-dimethyl-1-butanol and 3,3-dimethyl-2-butanol respectively. Reactivity trend can be explained in terms of the different types of hydrogen inside the hydrocarbon chain. The reaction occurs by an initial H-atom abstraction mainly from C-H groups of the alcohols by the NO3 radical being NO3 more reactive towards an H atom attached to a tertiary carbon than that attached to a secondary or primary carbon. Reactivity trend is compared with their similar structural 2-butanol and with the corresponding alkanes. Atmospheric implications are also discussed calculating lifetimes of the saturated alcohols studied here due to the reaction with NO3 radicals in comparison to their reactions with the other major atmospheric oxidants.

  18. Temperature dependence of the electric field modulation of electron-transfer rates. Charge recombination in photosynthetic reaction centers

    SciTech Connect

    Franzen, S.; Boxer, S.G. )

    1993-06-10

    The rates of electron-transfer reactions can be systematically varied by application of external electric fields. The electric field effect on the charge recombination rate constant of the state P[sup +]Q[sub A][sup [minus

  19. Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

    2013-12-01

    Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  20. Assessing the Effects of New Reaction Rates and Convection Theory on Studies of Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Starrfield, Sumner

    We request funding to carry out a systematic evaluation of nuclear reaction rates and convection on the pre-explosion evolution of core-collapse (SN II) and thermonuclear (SN Ia) supernovae. We will use MESA (Modules for Experiments in Stellar Astrophysics) a new stellar evolution computer code that is co-authored by Co-PI Timmes. One goal of this proposal is to determine the effects of new thermonuclear reaction rates, taken from the next-generation library STARLIB developed by Co-PI Iliadis, on the resulting evolution. Another goal is to test the effects of the latest convection theory, microphysics changes, and numerical techniques on the results. STARLIB is a first-of-its-kind nuclear reaction rate library and, unlike all other libraries, it contains the full reaction rate probability densities at all stellar temperatures. It is publicly available as of June 2013. Consequently, we are now in a unique position to model stellar evolution and nucleosynthesis in a quantitative manner that makes predictions for key observations by NASA ground-based and satellite observatories. We will use two complementary strategies. First, we will take the modern and multiple prescriptions of convection that are implemented in MESA, together with the recommended thermonuclear reaction rates provided by STARLIB, to generate new hydrodynamic simulations of SN Ia and SN II progenitor evolution. Second, we will take the temperature-density-time trajectories from the evolutionary results and do Monte Carlo post-processing nucleosynthesis calculations by sampling over the reaction rate probability densities. This procedure could not be applied previously and has only become feasible with the availability of STARLIB. Calculations of pre-supernova evolution with the STARLIB reaction rates and new convection prescriptions will provide, for the first time, statistically rigorous estimates for both their evolutionary structures and resulting nucleosynthesis. Significant insight into pre-supernova evolution will be obtained from the comparison of our simulations to the large amount of spectroscopic and photometric data available to us from both NASA satellites and ground-based observatories. We will use these data, combined with our simulations, to make predictions that can be tested against both archival and new observations from NASA ground-based and satellite observatories and thereby advance our understanding of supernovae. This proposal is directly relevant to two of the top three recommendations (Cosmic Dawn and Physics of the Universe) in the 2010 Decadel Survey of Astronomy and Astrophysics New Worlds, New Horizons. It is also directly relevant to part of the Science Goals in the 2014 ROSES Call for Proposals (page 41): ``Astrophysics: Discover how the universe works and explore how the universe began and evolved''. We also cover the following Topic Categories (listed on page D.4-2): 2) Stellar Astrophysics and Exoplanets, 3) Collapsed Objects and X-ray Astrophysics, and 4) Supernovae and Gamma Ray Bursts.

  1. A study of the photocatalytic effects of aqueous suspensions of platinized semiconductor materials on the reaction rates of candidate redox reactions

    NASA Technical Reports Server (NTRS)

    Miles, A. M.

    1982-01-01

    The effectiveness of powdered semiconductor materials in photocatalyzing candidate redox reactions was investigated. The rate of the photocatalyzed oxidation of cyanide at platinized TiO2 was studied. The extent of the cyanide reaction was followed directly using an electroanalytical method (i.e. differential pulse polarography). Experiments were performed in natural or artificial light. A comparison was made of kinetic data obtained for photocatalysis at platinized powders with rate data for nonplatinized powders.

  2. Probabilistic models and uncertainty quantification for the ionization reaction rate of atomic Nitrogen

    NASA Astrophysics Data System (ADS)

    Miki, K.; Panesi, M.; Prudencio, E. E.; Prudhomme, S.

    2012-05-01

    The objective in this paper is to analyze some stochastic models for estimating the ionization reaction rate constant of atomic Nitrogen (N + e- → N+ + 2e-). Parameters of the models are identified by means of Bayesian inference using spatially resolved absolute radiance data obtained from the Electric Arc Shock Tube (EAST) wind-tunnel. The proposed methodology accounts for uncertainties in the model parameters as well as physical model inadequacies, providing estimates of the rate constant that reflect both types of uncertainties. We present four different probabilistic models by varying the error structure (either additive or multiplicative) and by choosing different descriptions of the statistical correlation among data points. In order to assess the validity of our methodology, we first present some calibration results obtained with manufactured data and then proceed by using experimental data collected at EAST experimental facility. In order to simulate the radiative signature emitted in the shock-heated air plasma, we use a one-dimensional flow solver with Park's two-temperature model that simulates non-equilibrium effects. We also discuss the implications of the choice of the stochastic model on the estimation of the reaction rate and its uncertainties. Our analysis shows that the stochastic models based on correlated multiplicative errors are the most plausible models among the four models proposed in this study. The rate of the atomic Nitrogen ionization is found to be (6.2 ± 3.3) × 1011 cm3 mol-1 s-1 at 10,000 K.

  3. Equation of state and reaction rate for condensed-phase explosives

    NASA Astrophysics Data System (ADS)

    Wescott, B. L.; Stewart, D. Scott; Davis, W. C.

    2005-09-01

    The wide-ranging equation of state is a nonideal equation of state based on empirical fitting forms argued from thermodynamic considerations that yield the proper physical features of detonation. The complete equation of state forms are presented and the equation of state and a reaction rate are calibrated for the condensed-phase explosive PBX-9502. Experimental overdriven Hugoniot data are used to calibrate the products equation of state off the principal isentrope passing through the Chapman-Jouguet state. Shock Hugoniot data are used to calibrate the reactants equation of state. The normal detonation shock speed-shock curvature data (Dn-κ) from rate-stick measurements and shock initiation data from wedge tests are used to calibrate the reaction rate. Simulations are carried out that predict detailed particle velocity transients that are measured experimentally with embedded electromagnetic gauge measurements from gas-gun experiments. Multidimensional simulations of steady detonation in a right circular cylinder rate stick are carried out and compared with experiment.

  4. Groundwater ages and reaction rates during seawater circulation in the Dead Sea aquifer

    NASA Astrophysics Data System (ADS)

    Kiro, Yael; Weinstein, Yishai; Starinsky, Abraham; Yechieli, Yoseph

    2013-12-01

    The Dead Sea system provides a unique opportunity to study flow velocities and reaction rates during seawater circulation in the aquifer. We present here a novel application of calculating groundwater age and velocity along the flow path of the hypersaline water from the Dead Sea into the aquifer using the buildup rate of 228Ra in this water. The calculated circulation velocities are 1-10 m/y, which is in agreement with estimates based on the Na/Cl ratios in this water (1.5-4 m/y). The latter is unique to the Dead Sea-aquifer system, where the Na/Cl ratio has been decreasing during the past 50 years due to the precipitation of halite in the lake. The velocity estimates facilitated the calculation of the rates of water-rock interactions in the Dead Sea aquifer. SO4 is removed relatively fast (k=0.8 y-1) due to gypsum precipitation while barite or celestine precipitation removes 226Ra and Ba in a time scale of years (k=0.22 y-1). Similar rates were found for redox-driven reactions, such as U removal (k=0.4 y-1) and Fe and Mn contribution due to the dissolution of oxides (k=0.15 y-1). In the fresh-saline groundwater transition zone, gypsum which precipitated from hypersaline water in higher lake stands, is now being dissolved and enrich the water with SO4.

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

    NASA Technical Reports Server (NTRS)

    DeMore, W.B.

    1996-01-01

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

  6. Charge-exchange reactions and electron-capture rates for presupernova stellar evolution

    NASA Astrophysics Data System (ADS)

    Zegers, Remco

    2015-04-01

    Weak reaction rates such as electron captures and beta decays play major roles in a variety of astrophysical phenomena, such as core-collapse and thermonuclear supernovae and accreting neutron stars. Consequently, the use of accurate weak reaction rates in astrophysical simulations to understand these phenomena is important. Unfortunately, the number of relevant nuclei is typically very large, and, except for a few special cases, it is impossible to rely on experimental results only: theoretical models must be used to estimate the weak reaction rates. These models can then be benchmarked and improved on the basis of a limited number of experimental data. The most important nuclear structure input that is required for calculating weak reaction rates are Gamow-Teller transition strengths. Although these can be extracted from beta and electron-capture decay data, the energy window accessible by such experiments is limited, if accessible at all. However, at the high temperatures and densities that occur in massive stars prior to the cataclysmic demise, transitions to final states at high excitation energies are important. In addition, to properly test theory, full Gamow-Teller transition strength distributions are very valuable. Fortunately, nature is kind: charge-exchange experiments at intermediate energies can provide the relevant strength distributions over a wide energy window and a variety of charge-exchange probes, such as (p,n), (n,p), (d,2 He) and (t,3 He) have been used to extract strengths of relevance for astrophysics (and for other purposes). This presentation will focus on efforts to validate electron capture rates calculated based on nuclear structure models for nuclei with masses ranging from A ~ 40-65, and on studies aimed at testing astrophysical sensitivities to uncertainties/deviations in the theoretical rates. These efforts include experiments with unstable isotopes, and special gamma-ray coincidence techniques to localize very weak, but astrophysically important, low-lying Gamow-Teller transitions. Future efforts will focus on heavier nuclei (A>65) and nuclei further from stability. For the latter, opportunities provided at the Facility for Rare Isotope Beams (FRIB) will be critically important. In particular, experiments enables by the construction of a High Rigidity Spectrometer will strongly enhance the impact of the data for the validation and improvements of novel theoretical approaches. This work was supported by the US National Science Foundation (under Grants PHY-1102511 and PHY-0822648 [JINA]) and the US Department Of Energy under Grant DE- 334 AC02-05CH11231 (LBNL).

  7. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.

    1986-01-01

    A computationally-viable model describing the interaction between fluid-mechanical turbulence and finite-rate combustion reactions, principally in high-speed flows was developed. Chemical kinetic mechanisms, complete and global, were developed describing the finite rate reaction of fuels of interest to NASA. These fuels included principally hydrogen and silane, although a limited amount of work involved hydrocarbon fuels as well.

  8. Measuring OH Reaction Rate Constants and Estimating the Atmospheric Lifetimes of Trace Gases.

    NASA Astrophysics Data System (ADS)

    Orkin, Vladimir; Kurylo, Michael

    2015-04-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound's residence time in the atmosphere for a majority of trace gases. In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound's impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound. We have demonstrated the ability to conduct very high accuracy determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of kinetic data to 2-3%. The atmospheric lifetime of a well-mixed compound due to its reaction with tropospheric hydroxyl radicals can be estimated by using a simple scaling procedure that is based on the results of field observations of methyl chloroform concentrations and detailed modeling of the OH distribution in the atmosphere. The currently available modeling results of the atmospheric fate of various trace gases allow for an improved understanding of the ability and accuracy of simplified semi-empirical estimations of atmospheric lifetimes. These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

  9. Rate coefficients for the H + NH sub 3 reaction over a wide temperature range

    SciTech Connect

    Ko, Taeho; Marshall, P.; Fontijn, A. )

    1990-02-22

    The temperature dependence of the rate coefficients for the H + NH{sub 3} {yields} NH{sub 2} + H{sub 2} reaction is measured by the high-temperature photochemistry (HTP) technique. For the 490-960 K range, we find k{sub 1}(T) = 1.21 {times} 10{sup {minus}10} exp({minus}4920 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. When combined with two other sets of direct measurements, a best fit gives k{sub 1}(T) = 9.0 {times} 10{sup {minus}19} (T/K){sup 2.40} exp({minus}4991 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the 490-1780 K range. It is shown that these data can be more closely fitted by a calculation based on conventional transition-state theory plus an Eckart tunneling model than with other current transition-state models considered. Using the potential energy surface for the H + NH{sub 3} reaction, several tunneling models fit the results for the D + ND{sub 3} reaction. The kinetic isotope effect for these two reactions is compared to results from different theoretical models, with the Eckart model giving the best approximation.

  10. Absolute rate of the reaction of Cl(p-2) with molecular hydrogen from 200 - 500 K

    NASA Technical Reports Server (NTRS)

    Whytock, D. A.; Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1976-01-01

    Rate constants for the reaction of atomic chlorine with hydrogen are measured from 200 - 500 K using the flash photolysis-resonance fluorescence technique. The results are compared with previous work and are discussed with particular reference to the equilibrium constant for the reaction and to relative rate data for chlorine atom reactions. Theoretical calculations, using the BEBO method with tunneling, give excellent agreement with experiment.

  11. Reaction kinetics, P-T-t paths and rates of tectonic processes

    SciTech Connect

    Bohlen, S.R.; Hankins, W.B.; Eckert, J.O. Jr.; Kirby, S.H.; Liu, J. ); Hacker, B.R.; Mosenfelder, J.L. . Dept. of Geology)

    1992-01-01

    The interpretation of portions of P-T-time (t) paths in metamorphic rocks assumes that continuous and discontinuous reactions record local equilibrium as P-T conditions change, implying that the kinetics of many reactions are rapid relative to dT/dt and dP/dt. Occurrence of eclogite veins in granulites from Bergen, Norway as well as occurrences of coesite and diamond in crustal rocks imply that, under certain conditions, this assumption is wrong. Knowledge of the kinetics of important reactions under appropriate conditions would provide limits on the duration of relatively narrowly defined P-T conditions, allow inference of the rates of exhumation of rocks containing high-pressure phases, and allow the calculation of the time required for the conversion of gabbro to eclogite in the lower crust as a function of P-T-t. The authors are currently assessing the rates of key phase transformations: calcite to aragonite, albite to jadeite + quartz, coesite to quartz, opx[sub Fs[sup 80

  12. ABCRATE: A program for the calculation of atom-diatom reaction rates

    NASA Astrophysics Data System (ADS)

    Garrett, Bruce C.; Lynch, Gillian C.; Allison, Thomas C.; Truhlar, Donald G.

    1998-03-01

    ABCRATE is a computer program for the calculation of atom-diatom chemical reaction rates for systems with collinear-dominated dynamics. The dynamical methods used are conventional or generalized transition state theory (GTST) and multidimensional semiclassical approximations for tunneling and nonclassical reflection. The GTST methods included in this version of the program are the canonical and improved canonical variational transition state theory (VTST) and the canonical unified statistical (CUS) method. Rate constants may be calculated for canonical ensembles or for specific vibrational states of selected modes with translational, rotational, and other vibrational modes treated thermally. The potential energy surface required by the program may be a global or semiglobal analytic function. The reaction path is calculated as the path of steepest descent in mass-scaled coordinates from a collinear saddle point, and vibrations transverse to the reaction path are treated by curvilinear internal coordinates. The vibrational modes are quantized, and anharmonicity may be included by various options, including the WKB approximation for bond stretches and the centrifugal oscillator approximation through quartic terms for the curvilinear bend coordinate. Tunneling probabilities are calculated by a variety of semiclassical methods, in particular zero-curvature tunneling (ZCT), small-curvature tunneling (SCT), large-curvature tunneling (LCT), least-action tunneling (LAT), and the microcanonical optimized multidimensional tunneling (?OMT) methods.

  13. Effective reaction rate for porous surfaces under strong shear: Beyond Damkohler

    NASA Astrophysics Data System (ADS)

    Shaqfeh, Eric S. G.; Shah, Preyas

    2014-11-01

    Traditonally, surface reactive porous media are modeled via an effective reaction/mass transfer rate based on the original ansatz of Damkohler, i.e, reaction limited transport at the microscale in the absence of flow. We are interested in modeling the microscale mass transfer to porous surfaces occuring in leaky tumor vasculature, where the Damkohler number can be O(1) and the Peclet number may be large. We model it as a uniform bath of a species in unbound shear flow over a wall with first order reactive circular patches (pores). We analyze the flux through a single pore using both analytic and boundary element simulations and observe the formation of a 3-D depletion region (wake) downstream of the pore. Wake sharing between adjacent pores in a multibody setting such as 2 pores aligned in the shear direction leads to a smaller flux per pore. Obtaining this interaction length scale and using the renormalized periodic Green's function, we study the flux through a periodic and disordered distribution of pores. This flux appears as the reaction rate in an effective boundary condition, valid up to non-dilute pore area fractions, and applicable at a wall-normal effective slip distance. It replaces the details of the surface and can be used directly in large scale physics simulations.

  14. Absolute rate constants of alkoxyl radical reactions in aqueous solution. [Tert-butyl hydroperoxide

    SciTech Connect

    Erben-Russ, M.; Michel, C.; Bors, W.; Saran, M.

    1987-04-23

    The pulse radiolysis technique was used to generate the alkoxyl radical derived from tert-butyl hydroperoxide (/sup t/BuOOH) in aqueous solution. The reactions of this radical with 2,2'-azinobis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) and promethazine were monitored by kinetic spectroscopy. The unimolecular decay rate constant of the tert-butoxyl radical (/sup t/BuO) was determined to be 1.4 x 10/sup 6/ s/sup -1/. On the basis of this value, the rate constants for /sup t/BuO attack on quercetin, crocin, crocetin, ascorbate, isoascorbate, trolox c, glutathione, thymidine, adenosine, guanosine, and unsaturated fatty acids were determined. In addition, the reaction of /sup t/BuO with the polyunsaturated fatty acids (PUFA) was observed by directly monitoring the formation of the fatty acid pentadienyl radicals. Interestingly, the attack of /sup t/BuO on PUFA was found to be faster by about one order of magnitude as compared to the same reaction in a nonpolar solvent.

  15. THE IMPACT OF HELIUM-BURNING REACTION RATES ON MASSIVE STAR EVOLUTION AND NUCLEOSYNTHESIS

    SciTech Connect

    West, Christopher; Heger, Alexander; Austin, Sam M. E-mail: alexander.heger@monash.edu

    2013-05-20

    We study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. The current solar abundances from Lodders are used for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the {sup 12}C({alpha}, {gamma}){sup 16}O and 3{alpha} reaction rates, denoted R{sub {alpha},12} and R{sub 3{alpha}}, respectively. The production factors of both the intermediate-mass elements (A = 16-40) and the s-only isotopes along the weak s-process path ({sup 70}Ge, {sup 76}Se, {sup 80}Kr, {sup 82}Kr, {sup 86}Sr, and {sup 87}Sr) were found to be in reasonable agreement with predictions for variations of R{sub 3{alpha}} and R{sub {alpha},12} of {+-}25%; the s-only isotopes, however, tend to favor higher values of R{sub 3{alpha}} than the intermediate-mass isotopes. The experimental uncertainty (one standard deviation) in R{sub 3{alpha}}(R{sub {alpha},12}) is approximately {+-}10%({+-}25%). The results show that a more accurate measurement of one of these rates would decrease the uncertainty in the other as inferred from the present calculations. We also observe sharp changes in production factors and standard deviations for small changes in the reaction rates, due to differences in the convection structure of the star. The compactness parameter was used to assess which models would likely explode as successful supernovae, and hence contribute explosive nucleosynthesis yields. We also provide the approximate remnant masses for each model and the carbon mass fractions at the end of core-helium burning as a key parameter for later evolution stages.

  16. Quantifying metabolic rates in submarine hydrothermal vent chimneys: A reaction transport model

    NASA Astrophysics Data System (ADS)

    LaRowe, D.; Dale, A.; Aguilera, D.; Amend, J. P.; Regnier, P.

    2012-12-01

    The fluids emanating from active submarine hydrothermal vent chimneys provide a window into subseafloor processes and, through mixing with seawater, are responsible for steep thermal and compositional gradients that provide the energetic basis for diverse biological communities. Although several models have been developed to better understand the dynamic interplay of seawater, hydrothermal fluid, minerals and microorganisms inside chimney walls, none provide a fully integrated approach to quantifying the biogeochemistry of these hydrothermal systems. In an effort to remedy this, a fully coupled biogeochemical reaction transport model of a hydrothermal vent chimney has been developed that explicitly quantifies the rate of microbial catalysis while taking into account geochemical processes such as fluid flow, solute transport and oxidation-reduction reactions associated with fluid mixing as a function of temperature. Methanogenesis, hydrogen oxidation by oxygen and sulfate, sulfide oxidation by oxygen and methane oxidation by oxygen and sulfate are the metabolisms included in the reaction network. Model results indicate that microbial catalysis is fastest in the hottest habitable portion of the vent chimney except for methane oxidation by oxygen, which peaks near the seawater-side of the chimney at 20 nmol /cm^3 yr. The dominant metabolisms in the chimney are hydrogen oxidation by sulfate and oxygen and sulfide oxidation at peak rates 3200 , 300 and 900 nmol /cm^3 yr, respectively. The maximum rate of hydrogenotrophic methanogensis is just under 0.07 nmol /cm^3 yr, the slowest of the metabolisms considered. Due to thermodynamic inhibition, there is no anaerobic oxidation of methane by sulfate (AOM). The model developed here provides a quantitative approach to understanding the rates of biogeochemical transformations in hydrothermal systems and can be used to better understand the role of microbial activity in the deep subsurface.

  17. Modeling microbial reaction rates in a submarine hydrothermal vent chimney wall

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Aguilera, David R.; L'Heureux, Ivan; Amend, Jan P.; Regnier, Pierre

    2014-01-01

    The fluids emanating from active submarine hydrothermal vent chimneys provide a window into subseafloor processes and, through mixing with seawater, are responsible for steep thermal and compositional gradients that provide the energetic basis for diverse biological communities. Although several models have been developed to better understand the dynamic interplay of seawater, hydrothermal fluid, minerals and microorganisms inside chimney walls, none provide a fully integrated approach to quantifying the biogeochemistry of these hydrothermal systems. In an effort to remedy this, a fully coupled biogeochemical reaction-transport model of a hydrothermal vent chimney has been developed that explicitly quantifies the rates of microbial catalysis while taking into account geochemical processes such as fluid flow, solute transport and oxidation-reduction reactions associated with fluid mixing as a function of temperature. The metabolisms included in the reaction network are methanogenesis, aerobic oxidation of hydrogen, sulfide and methane and sulfate reduction by hydrogen and methane. Model results indicate that microbial catalysis is generally fastest in the hottest habitable portion of the vent chimney (77-102 °C), and methane and sulfide oxidation peak near the seawater-side of the chimney. The fastest metabolisms are aerobic oxidation of H2 and sulfide and reduction of sulfate by H2 with maximum rates of 140, 900 and 800 pmol cm-3 d-1, respectively. The maximum rate of hydrogenotrophic methanogenesis is just under 0.03 pmol cm-3 d-1, the slowest of the metabolisms considered. Due to thermodynamic inhibition, there is no anaerobic oxidation of methane by sulfate (AOM). These simulations are consistent with vent chimney metabolic activity inferred from phylogenetic data reported in the literature. The model developed here provides a quantitative approach to describing the rates of biogeochemical transformations in hydrothermal systems and can be used to constrain the role of microbial activity in the deep subsurface.

  18. Evaluation of electron capture reaction rates in Ni isotopes in stellar environments

    SciTech Connect

    Suzuki, Toshio; Honma, Michio; Mao, Helene; Otsuka, Takaharu; Kajino, Toshitaka

    2011-04-15

    Electron capture rates in Ni isotopes are studied in stellar environments, that is, at high densities and high temperatures during the core-collapse and postbounce explosive nucleosynthesis in supernovae. Reaction rates in {sup 58}Ni and {sup 60}Ni, as well as in {sup 56}Ni, {sup 62}Ni, and {sup 64}Ni, are evaluated by shell-model calculations with the use of a new shell-model Hamiltonian in the fp shell, GXPF1J. While the previous shell-model calculations failed to reproduce the measured peaks of Gamow-Teller strength in {sup 58}Ni and {sup 60}Ni, the present new Hamiltonian is found to reproduce them very well, as well as the capture rates obtained from the observed strengths. Strengths and energies of the Gamow-Teller transitions in {sup 56}Ni, {sup 62}Ni, and {sup 64}Ni are also found to be consistent with the observations.

  19. Channel specific rate constants for reactions of O(1D) with HCl and HBr

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Wells, J. R.; Ravishankara, A. R.

    1986-01-01

    The absolute rate coefficients and product yields for reactions of O(1D) with HCl(1) and HBr(2) at 287 K are presently determined by means of the time-resolved resonance fluorescence detection of O(3P) and H(2S) in conjunction with pulsed laser photolysis of O3/HX/He mixtures. Total rate coefficients for O(1D) removal are found to be, in units of 10 to the -10th cu cm/molecule per sec, k(1) = 1.50 + or - 0.18 and k(2) 1.48 + or - 0.16; the absolute accuracy of these rate coefficients is estimated to be + or - 20 percent.

  20. Rates of hydroxyl radical reactions with some HFCs. [HydroFluoroCarbons

    NASA Technical Reports Server (NTRS)

    Demore, William B.

    1993-01-01

    Relative rate constants for OH reactions with some HFCs have been determined at 298 K by a technique which measures the loss of HFC greater than OH. The following ratios were determine: k(152a)/k(CH4) = 5.2 +/- 0.5, k(CH4)/k(125) = 3.9 +/- 0.5, k(CH4)/k(134a) = 2.1 +/- 0.2, k(134a)/k(125) = 2.0 +/- 0.2, and k(C2H6)/k(152a) = 6.2 +/- 1.0. These results are in good agreement with literature values for the absolute rate constants except for HFC 134a, where a slower rate constant is indicated.

  1. Development of the GEM-MSTPC for studies of astrophysical nuclear reaction rates

    SciTech Connect

    Yamaguchi, K.; Arai, I.; Ishiyama, H.; Watanabe, Y. X.; Tanaka, M. H.; Miyatake, H.; Hirayama, Y.; Imai, N.; Fuchi, Y.; Jeong, S. C.; Nomura, T.; Mizoi, Y.; Das, S. K.; Fukuda, T.; Hashimoto, T.; Yamaguchi, H.; Kubono, S.; Hayakawa, S.; Makii, H.; Mitsuoka, S.

    2010-08-12

    We have developed an active-target type gas-detector, a Gas Electron Multiplier Multiple-Sampling and Tracking Proportional Chamber (GEM-MSTPC) operating with low-pressure He-base mixed gas, where He is used as a target for studies of astrophysical nuclear reaction rates. Different kinds of 400 {mu}m thick GEMs were examined. The gain stability was examined with a configuration of GEMs of 400 {mu}m in thickness fabricated in different ways, against the injection rate of low-energy heavy ions of 10{sup 5} particles per second. The gain of GEM with Cu electrodes coated by Au was observed to be stable up to the injection rate of 10{sup 5} particles per second.

  2. Sonochemical and sonophotocatalytic degradation of malachite green: the effect of carbon tetrachloride on reaction rates.

    PubMed

    Bejarano-Pérez, Néstor Javier; Suárez-Herrera, Marco Fidel

    2008-04-01

    A comparative study between the sonolytic, photocatalytic and sonophotocatalytic oxidation processes of aqueous solutions of malachite green was carried out in the presence of carbon tetrachloride, under a low power ultrasonic field (<15 W) and using titanium dioxide as a photocatalyst. The effect of a number of parameters such as ultrasonic intensity, TiO2 crystalline structure and the presence of CCl4 were studied using an inexpensive reactor. Enhanced rates of sonolytic degradation of malachite green in the presence of CCl4 were demonstrated. On the other hand, the simultaneous use of sonolysis and photocatalysis in the presence of CCl4 does not improve the degradation rate of malachite green in comparison with the one obtained using only sonolysis, but it makes possible a faster oxidative degradation of some reaction intermediaries. Finally, in air saturated solutions both processes, the sonolytic and the photocatalytic one, follow a first-order rate law. PMID:17977775

  3. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Foy, E.; Ronan, G.; Chinitz, W.

    1982-01-01

    A principal element to be derived from modeling turbulent reacting flows is an expression for the reaction rates of the various species involved in any particular combustion process under consideration. A temperature-derived most-likely probability density function (pdf) was used to describe the effects of temperature fluctuations on the Arrhenius reaction rate constant. A most-likely bivariate pdf described the effects of temperature and species concentrations fluctuations on the reaction rate. A criterion is developed for the use of an "appropriate" temperature pdf. The formulation of models to calculate the mean turbulent Arrhenius reaction rate constant and the mean turbulent reaction rate is considered and the results of calculations using these models are presented.

  4. A kinetic-theory approach for computing chemical-reaction rates in upper-atmosphere hypersonic flows.

    PubMed

    Gallis, Michael A; Bond, Ryan B; Torczynski, John R

    2009-09-28

    Recently proposed molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction-rate information) are investigated for chemical reactions occurring in upper-atmosphere hypersonic flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases. PMID:19791885

  5. The use of the magnetic field effect for studying a chemiluminescent chemical reaction in aqueous solution. Reaction rate constants and lifetimes of intermediate molecules

    NASA Astrophysics Data System (ADS)

    Triebel, Michael M.; Totrov, Maxim M.; Zorinyants, George E.; Frankevich, Eugene L.

    1993-11-01

    The phase shift magnetic field effect technique is applied for investigation of the chemiluminescent (ChL) reaction of luminol oxidation by potassium ferricyanide in aqueous alkali solution. The external modulated magnetic field changed the rate constant of recombination of luminol radicals. Rate constants of intermediate stages of the reaction are obtained: 10 8 M -1 s -1 for diazaquinone reaction with hydrogen peroxide, 2 X 10 6 M -1 s -1 for diazaquinone hydrolysis and 2 X 10 5 s -1 for the decomposition of hydroperoxide, which is a precursor of the light emitter.

  6. Heterogeneous photocatalysis of real textile wastewater: evaluation of reaction kinetics and characterization.

    PubMed

    Sahoo, Chittaranjan; Gupta, Ashok K; Pillai, Indu M Sasidharan

    2012-01-01

    Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag(+) doped TiO(2) (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis. PMID:22871009

  7. Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers

    SciTech Connect

    Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.

    1993-08-03

    A method is described for substantially completely oxidizing combustible materials in which an aqueous stream bearing the combustible materials is reacted in the presence of an oxidant comprising diatomic oxygen and at a temperature greater than the critical temperature of water and at a pressure greater than about 25 bar, within a reactor for a period of less than about 5 minutes to produce a reaction product stream, wherein the reaction is initiated in the presence of a rate enhancer comprising at least one oxidizing agent in addition to said oxidant selected from the group consisting of ozone, hydrogen peroxide, salts containing persulfate, salts containing permanganate, nitric acid, salts containing nitrate, oxyacids of chlorine and their corresponding salts, hypochlorous acid, salts containing hypochlorite, chlorous acid, salts containing chlorite, chloric acid, salts containing chlorate, perchloric acid, and salts containing perchlorate.

  8. Structural and dynamical control of the reaction rate in protein electron transfer

    NASA Astrophysics Data System (ADS)

    Balabin, Ilya A.

    Electron transfer (ET) reactions in proteins are key steps in many vital bioenergetic processes, and the reaction rate is known to be highly sensitive to the protein structure in some cases. For most bioenergetic reactions, as described by the Fermi Golden rule, the rate is proportional to a product of the average square of the effective electronic donor to acceptor coupling and a Franck-Condon factor, which accounts for the nuclear control of the energy gap. The nuclear factor is reasonably well described in Marcus theory and its modifications, and this work is focused on the mechanisms that control the effective coupling. About ten years ago, the Pathways model described for the first time how protein environment may control the effective coupling. In this work, a novel theoretical approach is developed to explore the mechanisms of structural and dynamical control beyond the qualitative level of the Pathways model. In Chapter 1, the assumptions of the Pathways model, its limitations and effects of the structure and the electronic Hamiltonian are investigated for model chain-like bridges using the Dyson's equations. In Chapter II, the framework to explore the sensitivity of the effective coupling to quality of the electronic Hamiltonian, the interference among the dominant pathways and the bridge dynamics is presented. This analysis employs the Green's function technique and includes combined molecular dynamics and electronic structure calculations. Finally, in Chapter III, this framework is tested on the bacterial photosynthetic reaction center, and the mechanisms of the structural and dynamical control for different ET steps are discussed.

  9. Temperature dependent rate coefficients for the reaction of OH radicals with dimethylbenzoquinones

    NASA Astrophysics Data System (ADS)

    Bejan, Iustinian; Barnes, Ian; Wiesen, Peter; Wenger, John C.

    2015-10-01

    Rate coefficients for the gas-phase reaction of hydroxyl (OH) radicals with two methylated benzoquinones have been measured at atmospheric pressure over the temperature range 284-313 K using the relative rate method. The following Arrhenius expressions (in cm3 molecule-1 s-1) have been obtained: k(25DMBQ) = (8.59 ± 4.70) × 10-12exp[(228 ± 163)/T] and k(26DMBQ) = (5.11 ± 2.79) × 10-12exp[(399 ± 165)/T] for 2,5-dimethylbenzoquinone (2,5DMBQ) and 2,6-dimethylbenzoquinone (2,6DMBQ), respectively, with corresponding values at 298 K: k(25DMBQ) = (2.05 ± 0.46) × 10-11 and k(26DMBQ) = (1.93 ± 0.12) × 10-11. The rate coefficients are compared to those reported for similar compounds and discussed in terms of structure-activity relationships. The results are also used to calculate atmospheric lifetimes for 2,5DMBQ and 2,6DMBQ with respect to reaction with OH radicals.

  10. Nuclear reaction rates and their influence on nucleosynthesis in the neutrino-p-process

    NASA Astrophysics Data System (ADS)

    Hatcher, Daniel; Frohlich, Carla; Perdikakis, Georgios

    2015-10-01

    The synthesis of elements heavier than iron in the early stages of galactic evolution is commonly attributed to Type II (core collapse) supernova explosions. However, the currently accepted mechanisms of heavy element synthesis through neutron capture processes (r-process and s-process) cannot explain the abundance patterns seen in very old galactic halo stars. A proposed solution to this problem is the neutrino-p-process, which takes place in the strong neutrino winds of core-collapse supernovae. In the neutrino-p-process, antineutrinos absorbed by protons yield neutrons that are quickly captured by the surrounding, proton-rich nuclei through (n,p) reactions. Such interactions allow for the nucleosynthesis of elements with atomic mass numbers greater than 64 (this includes Sr, Y, Zr and others possibly up to Sn). We study the sensitivity of the νp-process abundance pattern to (n,p), (p, γ), and (n, γ) rates for nuclei between Ni and Sn. We illustrate our findings for three different initial electron fractions and two representative trajectories. We discuss how these rates influence the abundance pattern and the nuclear flow. We observe the effects of predicted reaction rates on the abundance pattern and nuclear flow.

  11. Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans

    PubMed Central

    Lizama, Hector M.; Suzuki, Isamu

    1989-01-01

    Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 μM Fe2+ per min per FeS2 percent pulp density for the spontaneous pyrite dissolution, 10 μM Fe2+ per min per mM Fe3+ for the indirect leaching with Fe3+, 90 μM O2 per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 μM O2 per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The Km values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a Ki value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe2+ production from Fe3+ plus pyrite. PMID:16348054

  12. New reaction rates for improved primordial D /H calculation and the cosmic evolution of deuterium

    NASA Astrophysics Data System (ADS)

    Coc, Alain; Petitjean, Patrick; Uzan, Jean-Philippe; Vangioni, Elisabeth; Descouvemont, Pierre; Iliadis, Christian; Longland, Richard

    2015-12-01

    Primordial or big bang nucleosynthesis (BBN) is one of the three historically strong evidences for the big bang model. Standard BBN is now a parameter-free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background radiation. There is a good agreement between the primordial abundances of 4He, D, 3He, and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D /H , to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we reevaluate the d (p ,γ )3He, d (d ,n ) 3H3, and d (d ,p ) 3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D /H =(2.45 ±0.10 )×10-5 (2 σ ), in agreement with observations.

  13. Rate equations and kinetic parameters of the reactions involved in pyrite oxidation by Thiobacillus ferrooxidans

    SciTech Connect

    Lizama, H.M.; Suzuki, Isamu )

    1989-11-01

    Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 {mu}M Fe{sup 2+} per min per FeS{sub 2} percent pulp density for the spontaneous pyrite dissolution, 10 {mu}M Fe{sup 2+} per min per mM Fe{sup 3+} for the indirect leaching with Fe{sup 3+}, 90 {mu}M O{sub 2} per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washing pyrite, and 250 {mu}M O{sub 2} per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K{sub m} values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K{sub i} value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe{sup 2+} production from Fe{sup 3+} plus pyrite.

  14. Theory and simulation of the time-dependent rate coefficients of diffusion-influenced reactions.

    PubMed Central

    Zhou, H X; Szabo, A

    1996-01-01

    A general formalism is developed for calculating the time-dependent rate coefficient k(t) of an irreversible diffusion-influenced reaction. This formalism allows one to treat most factors that affect k(t), including rotational Brownian motion and conformational gating of reactant molecules and orientation constraint for product formation. At long times k(t) is shown to have the asymptotic expansion k(infinity)[1 + k(infinity) (pie Dt)-1/2 /4 pie D + ...], where D is the relative translational diffusion constant. An approximate analytical method for calculating k(t) is presented. This is based on the approximation that the probability density of the reactant pair in the reactive region keeps the equilibrium distribution but with a decreasing amplitude. The rate coefficient then is determined by the Green function in the absence of chemical reaction. Within the framework of this approximation, two general relations are obtained. The first relation allows the rate coefficient for an arbitrary amplitude of the reactivity to be found if the rate coefficient for one amplitude of the reactivity is known. The second relation allows the rate coefficient in the presence of conformational gating to be found from that in the absence of conformational gating. The ratio k(t)/k(0) is shown to be the survival probability of the reactant pair at time t starting from an initial distribution that is localized in the reactive region. This relation forms the basis of the calculation of k(t) through Brownian dynamics simulations. Two simulation procedures involving the propagation of nonreactive trajectories initiated only from the reactive region are described and illustrated on a model system. Both analytical and simulation results demonstrate the accuracy of the equilibrium-distribution approximation method. PMID:8913584

  15. Unimolecular reaction rate constants of NO{sub 2} just above D{sub 0}

    SciTech Connect

    Bezel, I.; Stolyarov, D.; Wittig, C.

    1999-12-09

    Photoinitiated unimolecular decomposition on a barrierless potential energy surface (PES) has been studied for the reaction NO{sub 2} {yields} O({sup 3}P{sub 2}) + NO(X{sup 2}{Pi}{sub 1/2}, {nu} = 0) for excess energies up to approximately 17 cm{sup {minus}1} above the dissociation threshold (i.e., D{sub 0} for nonrotating molecules) by using expansion-cooled samples and the time-resolved pump-probe technique. To examine the threshold region with enough energy resolution to discern abrupt changes in the rate constant, should they occur, a pump-probe cross-correlation temporal width of {approximately}25 ps and a pump line width {le}2 cm{sup {minus}1} has been used. These are the first direct observations of the reaction rate constants in this energy regime. The rate constant was found to increase by an order of magnitude, varying from {approximately}2 x 10{sup 10} s{sup {minus}1} to {ge}10{sup 11} s{sup {minus}1}, the latter being a rough lower bound imposed by the experimental arrangement. The rate constant does not display the energy dependence predicted by using phase space theory, at least in detail. Rather, it appears to reflect the highly complex nature of the levels and the multiple PESs that are believed to be responsible for the anomalously high vibronic level density which has been observed just below D{sub 0}. These results bridge the gap between spectroscopic studies which have been carried out at energies just above D{sub 0} and ultrafast experiments which have measured rate constants in this energy region with pump laser spectral widths of {approximately}30 cm{sup {minus}1}.

  16. Pyrite oxidation in unsaturated aquifer sediments. Reaction stoichiometry and rate of oxidation.

    PubMed

    Andersen, M S; Larsen, F; Postma, D

    2001-10-15

    The oxidation of pyrite (FeS2) contained in unsaturated aquifer sediment was studied by sediment incubation in gas impermeable polymer laminate bags. Reaction progress was followed over a period of nearly 2 months by monitoring the gas composition within the laminate bag. The gas phase in the incubation bags became depleted in O2 and enriched in CO2 and N2 and was interpreted as due to pyrite oxidation in combination with calcite dissolution. Sediment incubation provides a new method to estimate low rates of pyrite oxidation in unsaturated zone aquifer sediments. Oxidation rates of up to 9.4 x 10(-10) mol FeS2/g x s are measured, and the rates are only weakly correlated with the sediment pyrite content. The reactivity of pyrite, including the inhibition by FeOOH layers formed on its surface, apparently has a major effect on the rate of oxidation. The code PHREEQC 2.0 was used to calculate the reaction stoichiometry and partitioning of gases between the solution and the gas phase. Pyrite oxidation with concurrent calcite dissolution was found to be consistent with the experimental data while organic carbon oxidation was not. The reaction involves changes in the total volume of the gas phase. The reaction scheme predicts the volume of O2 gas consumed to be larger than of CO2 produced. In addition the solubility of CO2 in water is about 30 times larger than of O2 causing a further decrease in total gas volume. The change in total gas volume therefore also depends on the gas/water volume ratio and the lower the ratio the more pronounced the loss of volume will be. Under field conditions the change in total volume may amount up to 20% in the absence of calcite and over 10% in the presence of calcite. Such changes in gas volume during the oxidation of pyrite are expected to result in pressure gradients causing advective transport of gaseous oxygen. PMID:11686369

  17. Chemical reaction rates using the semiclassical Van-Vleck initialvalue representation

    SciTech Connect

    Venkataraman, Charulatha; Miller, William H.

    2006-11-29

    A semiclassical IVR formulation using the Van-Vleck propagator has been used to calculate the flux correlation function and thereby reaction rate constants. This Van-Vleck formulation of the flux-flux correlation function is computationally as simple as the classical Wigner model. However unlike the latter, it has the ability to capture quantum interference/coherence effects. Classical trajectories are evolved starting from the dividing surface that separates reactants and products, and are evolved negatively in time. This formulation has been tested on model problems ranging from the Eckart barrier, double well to the collinear H + H{sub 2}.

  18. Novel technique for constraining r-process (n, γ) reaction rates.

    PubMed

    Spyrou, A; Liddick, S N; Larsen, A C; Guttormsen, M; Cooper, K; Dombos, A C; Morrissey, D J; Naqvi, F; Perdikakis, G; Quinn, S J; Renstrøm, T; Rodriguez, J A; Simon, A; Sumithrarachchi, C S; Zegers, R G T

    2014-12-01

    A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,γ)^{76}Ge cross section and reaction rate. PMID:25526121

  19. Redox reaction rates in shallow aquifers: Implications for nitrate transport in groundwater and streams

    USGS Publications Warehouse

    Tesoriero, Anthony J.

    2012-01-01

    Groundwater age and water chemistry data along flow paths from recharge areas to streams were used to evaluate the trends and transformations of agricultural chemicals. Results from this analysis indicate that median nitrate recharge concentrations in these agricultural areas have increased markedly over the last 50 years from 4 mg N/L in samples collected prior to 1983 to 7.5 mg N/L in samples collected since 1983. The effect that nitrate accumulation in shallow aquifers will have on drinking water quality and stream ecosystems is dependent on the rate of redox reactions along flow paths and on the age distribution of nitrate discharging to supply wells and streams.

  20. Rates of reaction and process design data for the Hydrocarb Process

    SciTech Connect

    Steinberg, M.; Kobayashi, Atsushi ); Tung, Yuanki )

    1992-08-01

    In support of studies for developing the coprocessing of fossil fuels with biomass by the Hydrocarb Process, experimental and process design data are reported. The experimental work includes the hydropryolysis of biomass and the thermal decomposition of methane in a tubular reactor. The rates of reaction and conversion were obtained at temperature and pressure conditions pertaining to a Hydrocarb Process design. A Process Simulation Computer Model was used to design the process and obtain complete energy and mass balances. Multiple feedstocks including biomass with natural gas and biomass with coal were evaluated. Additional feedstocks including green waste, sewage sludge and digester gas were also evaluated for a pilot plant unit.

  1. Irreversible bimolecular reactions with inertia: from the trapping to the target setting at finite densities

    NASA Astrophysics Data System (ADS)

    Piazza, Francesco; Foffi, Giuseppe; De Michele, Cristiano

    2013-06-01

    We investigate numerically pseudo-first-order irreversible bimolecular reactions of the type A + B → B between hard spheres undergoing event-driven Brownian dynamics. We study the encounter rate and the survival probability of A particles as functions of the packing fraction ϕ in the trapping (a single particle diffusing among static non-overlapping traps) and target (many traps diffusing in the presence of a single static target particle) settings, as well as in the case of diffusing traps and particles (full mobility). We show that, since inertial effects are accounted for in our simulation protocol, the standard Smoluchowski theory of coagulation of non-interacting colloids is recovered only at times greater than a characteristic time Δt, marking the transition from the under-damped to the over-damped regime. We show that the survival probability S(t) decays exponentially during this first stage, with a rate 1/τ0 ∝ ϕ. Furthermore, we work out a simple analytical expression that is able to capture to an excellent extent the numerical results for t < Δt at low and intermediate densities. Moreover, we demonstrate that the time constant of the asymptotic exponential decay of S(t) for diffusing traps and particles is {k}_{{S}}^{-1}, where kS = 4π(DA + DB)Rρ is the Smoluchowski rate. Detailed analyses of the effective decay exponent β = d [log(-logS(t))]/d (logt) and of the steady-state encounter rate reveal that the full mobility and trapping problem are characterized by very similar kinetics, rather different from the target problem. Our results do not allow one to ascertain whether the prediction S(t) ∝ exp(-at3/2) (a = const.) as t → ∞ for the trapping problem in 3D is indeed recovered. In fact, at high density, S(t) is dominated by short encounter times, which makes it exceedingly hard to record the events corresponding to the exploration of large, trap-free regions. As a consequence, at high densities the steady-state rate simply tends to 1/τ0. Finally, we work out an analytical formula for the rate that shows a remarkable agreement with the numerics up ϕ = 0.4.

  2. Can interstellar H2S be formed via gas-phase reactions? - Calculations concerning the rates of the ternary and radiative association reactions between HS(+) and H2

    NASA Astrophysics Data System (ADS)

    Herbst, Eric; Defrees, D. J.; Koch, W.

    1989-04-01

    Based on laboratory work involving the ternary association reaction of HS+ and H2 at 80 K, we have estimated the rate of the analogous radiative association reaction under interstellar conditions. Both the ternary and radiative association reactions appear to occur via a mechanism in which the electronic spin of the H3S+ complex changes before the complex is stabilized. Although this spin change is of low probability, it leads to a radiative association rate coefficient at 80 K of 7 × 10-16 cm3 s-1 if radiative stabilization occurs at a rate of 103 s-1. This value of the radiative association rate coefficient at 80 K is large enough to lead to the observed abundance of H2S in the ambient ridge source in Orion.

  3. Immediate effects of Suryanamaskar on reaction time and heart rate in female volunteers.

    PubMed

    Bhavanani, Ananda Balayogi; Ramanathan, Meena; Balaji, R; Pushpa, D

    2013-01-01

    Suryanamaskar (SN), a yogic technique is composed of dynamic muscular movements synchronised with deep rhythmic breathing. As it may have influence on CNS, this study planned to investigate immediate effects of SN on reaction time (RT) and heart rate (HR). 21 female volunteers attending yoga classes were recruited for study group and 19 female volunteers not participating in yoga were recruited as external-controls. HR, auditory reaction time (ART) and visual reaction time (VRT) were recorded before and after three rounds of SN in study group as well as 5 minutes of quiet sitting in both groups. Performance of SN produced immediate decrease in both VRT and ART (P < 0.001). This was significant when compared to self-control period (P < 0.001) and compared to external-control group, it decreased significantly in ART (p = 0.02). This was pronounced when delta% was compared between groups (P < 0.001). HR increased significantly following SN compared with both self-control (p = 0.025) and external-control group (p = 0.032). Faster reactivity may be due to intermediate level of arousal by conscious synchronisation of dynamic movements with breathing. Rise in HR is attributed to sympathetic arousal and muscular exertion. We suggest that SN may be used as an effective training means to improve neuro-muscular abilities. PMID:24617172

  4. Elementary reaction rate measurements at high temperatures by tunable-laser flash-absorption

    SciTech Connect

    Hessler, J.P.

    1993-12-01

    The major objective of this program is to measure thermal rate coefficients and branching ratios of elementary reactions. To perform these measurements, the authors constructed an ultrahigh-purity shock tube to generate temperatures between 1000 and 5500 K. The tunable-laser flash-absorption technique is used to measure the rate of change of the concentration of species which absorb below 50,000 cm{sup {minus}1} e.g.: OH, CH, and CH{sub 3}. This technique is being extended into the vacuum-ultraviolet spectral region where one can measure atomic species e.g.: H, D, C, O, and N; and diatomic species e.g.: O{sub 2}, CO, and OH.

  5. Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

    1979-01-01

    Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.

  6. PH-dependence of the steady-state rate of a two-step enzymic reaction.

    PubMed

    Brocklehurst, K; Dixon, H B

    1976-04-01

    1. The pH-dependence is considered of a reaction between E and S that proceeds through an intermediate ES under "Briggs-Haldane' conditions, i.e. there is a steady state in ES and [S]o greater than [E]T, where [S]o is the initial concentration of S and [E]T is the total concentration of all forms of E. Reactants and intermediates are assumed to interconvert in three protonic states (E equilibrium ES; EH equilibrium EHS; EH2 equilibrium EH2S), but only EHS provides products by an irreversible reaction whose rate constant is kcat. Protonations are assumed to be so fast that they are all at equilibrium. 2. The rate equation for this model is shown to be v = d[P]/dt = (kcat.[E]T[S]o/A)/[(KmBC/DA) + [S]o], where Km is the usual assembly of rate constants around EHS and A-D are functions of the form (1 + [H]/K1 + K2/[H]), in which K1 and K2 are: in A, the molecular ionization constants of ES; in B, the analogous constants of E; in C and D, apparent ionization constants composed of molecular ionization constants (of E or ES) and assemblies of rate constants. 3. As in earlier treatments of this type of reaction which involve either the assumption that the reactants and intermediate are in equilibrium or the assumption of Peller & Alberty [(1959) J. Am. Chem. Soc. 81, 5907-5914] that only EH and EHS interconvert directly, the pH-dependence of kcat. is determined only by A. 4. The pH-dependence of Km is determined in general by B-C/A-D, but when reactants and intermediate are in equilibrium, C identical to D and this expression simplifies to B/A. 5. The pH-dependence of kcat./Km, i.e. of the rate when [S]o less than Km, is not necessarily a simple bell-shaped curve characterized only by the ionization constants of B, but is a complex curve characterized by D/B-C. 6. Various situations are discussed in which the pH-dependence of kcat./Km is determined by assemblies simpler than D/B-C. The special situation in which a kcat./Km-pH profile provides the molecular pKa values of the intermediate ES complex is delineated. PMID:7241

  7. Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR.

    PubMed

    Balzan, Riccardo; Fernandes, Laetitia; Comment, Arnaud; Pidial, Laetitia; Tavitian, Bertrand; Vasos, Paul R

    2016-01-01

    The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of metabolic transformations. Hyperpolarization via dissolution DNP circumvents part of the sensitivity issues thanks to the large out-of-equilibrium nuclear magnetization stemming from the electron-to-nucleus spin polarization transfer. The high NMR signal obtained can be used to monitor chemical reactions in real time. The downside of hyperpolarized NMR resides in the limited time window available for signal acquisition, which is usually on the order of the nuclear spin longitudinal relaxation time constant, T1, or, in favorable cases, on the order of the relaxation time constant associated with the singlet-state of coupled nuclei, TLLS. Cellular uptake of endogenous molecules and metabolic rates can provide essential information on tumor development and drug response. Numerous previous hyperpolarized NMR studies have demonstrated the relevancy of pyruvate as a metabolic substrate for monitoring enzymatic activity in vivo. This work provides a detailed description of the experimental setup and methods required for the study of enzymatic reactions, in particular the pyruvate-to-lactate conversion rate in presence of lactate dehydrogenase (LDH), by hyperpolarized NMR. PMID:26967906

  8. Oxygen consumption rates in subseafloor basaltic crust derived from a reaction transport model.

    PubMed

    Orcutt, Beth N; Wheat, C Geoffrey; Rouxel, Olivier; Hulme, Samuel; Edwards, Katrina J; Bach, Wolfgang

    2013-01-01

    Oceanic crust is the largest potential habitat for life on Earth and may contain a significant fraction of Earth's total microbial biomass; yet, empirical analysis of reaction rates in basaltic crust is lacking. Here we report the first assessment of oxygen consumption in young (~8 Ma) and cool (<25 °C) basaltic crust, which we calculate from modelling dissolved oxygen and strontium pore water gradients in basal sediments collected during Integrated Ocean Drilling Program Expedition 336 to 'North Pond' on the western flank of the Mid-Atlantic Ridge. Dissolved oxygen is completely consumed within the upper to middle section of the sediment column, with an increase in concentration towards the sediment-basement interface, indicating an upward supply from oxic fluids circulating within the crust. A parametric reaction transport model of oxygen behaviour in upper basement suggests oxygen consumption rates of 1 nmol  cm(-3)ROCK d(-1) or less in young and cool basaltic crust. PMID:24071791

  9. Temperature and Pressure-Dependent Rate Coefficients for the Reaction of Vinyl Radical with Molecular Oxygen.

    PubMed

    Goldsmith, C Franklin; Harding, Lawrence B; Georgievskii, Yuri; Miller, James A; Klippenstein, Stephen J

    2015-07-16

    State-of-the-art calculations of the C2H3O2 potential energy surface are presented. A new method is described for computing the interaction potential for R + O2 reactions. The method, which combines accurate determination of the quartet potential along the doublet minimum energy path with multireference calculations of the doublet/quartet splitting, decreases the uncertainty in the doublet potential and thence the rate constants by more than a factor of 2. The temperature- and pressure-dependent rate coefficients are computed using variable reaction coordinate transition-state theory, variational transition-state theory, and conventional transition-state theory, as implemented in a new RRKM/ME code. The main bimolecular product channels are CH2O + HCO at lower temperatures and CH2CHO + O at higher temperatures. Above 10 atm, the collisional stabilization of CH2CHOO directly competes with these two product channels. CH2CHOO decomposes primarily to CH2O + HCO. The next two most significant bimolecular products are OCHCHO + H and (3)CHCHO + OH, and not C2H2 + HO2. C2H3 + O2 will be predominantly chain branching above 1700 K. Uncertainty analysis is presented for the two most important transition states. The uncertainties in these two barrier heights result in a significant uncertainty in the temperature at which CH2CHO + O overtakes all other product channels. PMID:25978112

  10. Rate constants and products of the OH reaction with isoprene-derived epoxides.

    PubMed

    Jacobs, Michael I; Darer, Adam I; Elrod, Matthew J

    2013-11-19

    Recent laboratory and field work has shown that isoprene-derived epoxides (IEPOX) are crucial intermediates that can explain the existence of a variety of compounds found in ambient secondary organic aerosol (SOA). However, IEPOX species are also able to undergo gas phase oxidation, which competes with the aerosol phase processing of IEPOX. In order to better quantify the atmospheric fate of IEPOX, the gas phase OH reaction rate constants and product formation mechanisms have been determined using a flow tube chemical ionization mass spectrometry technique. The new OH rate constants are generally larger than previous estimations and some features of the product mechanism are well predicted by the Master Chemical Mechanism Version 3.2 (MCM v3.2), while other features are at odds with MCM v3.2. Using a previously proposed kinetic model for the quantitative prediction of the atmospheric fate of IEPOX, it is found that gas phase OH reaction is an even more dominant fate for chemical processing of IEPOX than previously suggested. The present results suggest that aerosol phase processing of IEPOX will be competitive with gas phase OH oxidation only under SOA conditions of high liquid water content and low pH. PMID:24144330

  11. Reaction Rate Theory of Radiation Exposure and Scaling Hypothesis in Mutation Frequency

    NASA Astrophysics Data System (ADS)

    Manabe, Yuichiro; Nakamura, Issei; Bando, Masako

    2014-11-01

    We have developed a kinetic reaction model for cells with irradiated DNA molecules due to ionizing radiation exposure. Our theory simultaneously accounts for the time-dependent reactions of DNA damage, DNA mutation and DNA repair, and the proliferation and apoptosis of cells in a tissue with a minimal set of model parameters. In contrast to existing theories of radiation exposition, we do not assume the relationships between the total dose and the induced mutation frequency. Our theory provides a universal scaling function that reasonably explains the mega-mouse experiments by Russell and Kelly [Proc. Natl. Acad. Sci. U.S.A. 79, 542 (1982)] with different dose rates. Furthermore, we have estimated the effective dose rate, which is biologically equivalent to the ionizing effects other than those caused by artificial irradiation. This value is 1.11 × 10-3 Gy/h, which is significantly larger than the effect caused by natural background radiation.

  12. Relationship between the surface coverage of spectator species and the rate of electrocatalytic reactions.

    SciTech Connect

    Strmcnik, D. S.; Rebec, P.; Gaberscek, M.; Tripkovic, D.; Stamenkovic, V.; Lucas, C.; Markovic, N. M.; Materials Science Division; Univ. of Chicago; National Inst. of Chemistry; Univ. of Liverpool

    2007-12-20

    Relationships between the surface coverage of spectator (blocking) species and the rate of the hydrogen oxidation reaction (HOR), the oxygen reduction reaction (ORR), and the bulk oxidation of dissolved CO on Pt(100) and Pt(111) single crystals in acidic electrolytes has been probed by cyclic voltammetry, in situ surface X-ray scattering (SXS), and ex situ scanning tunneling microscopy (STM) techniques. It is shown that the surface coverage by spectator species during the HOR and the ORR are the same as for the corresponding coverage obtained in the inert (Ar-saturated) environment. This observation is consistent with the proposition that the availability of active sites for H{sub 2} and O{sub 2} is determined almost entirely by the coverage of adsorbates from the supporting electrolyte and not by the active intermediates. Related electrochemical-SXS studies undertaken for bulk CO oxidation reveal that the maximum rate above the ignition potential is reached on a surface that is covered by {approx}90% of an ordered CO adlayer. The nature of the active sites in this case is determined by a combination of electrochemical and STM results. It is found that the active sites in this potential region are steps, which appear to be active sites for OH adsorption. To get insight into the relationship between the diffusion-limiting current and the surface coverage by the inactive CO adlayer, we introduce the concept of a partially blocked electrode surface with active and inactive areas. On the basis of the calculations and experimental results, it is proposed that the active sites for given electrochemical reactions on Pt electrodes are arrays of adsorbate-free nanoscale patches embedded in an inactive adlayer of nonreactive molecular species.

  13. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  14. Reaction rate theory: What it was, where is it today, and where is it going?

    NASA Astrophysics Data System (ADS)

    Pollak, Eli; Talkner, Peter

    2005-06-01

    A brief history is presented, outlining the development of rate theory during the past century. Starting from Arrhenius [Z. Phys. Chem. 4, 226 (1889)], we follow especially the formulation of transition state theory by Wigner [Z. Phys. Chem. Abt. B 19, 203 (1932)] and Eyring [J. Chem. Phys. 3, 107 (1935)]. Transition state theory (TST) made it possible to obtain quick estimates for reaction rates for a broad variety of processes even during the days when sophisticated computers were not available. Arrhenius' suggestion that a transition state exists which is intermediate between reactants and products was central to the development of rate theory. Although Wigner gave an abstract definition of the transition state as a surface of minimal unidirectional flux, it took almost half of a century until the transition state was precisely defined by Pechukas [Dynamics of Molecular Collisions B, edited by W. H. Miller (Plenum, New York, 1976)], but even this only in the realm of classical mechanics. Eyring, considered by many to be the father of TST, never resolved the question as to the definition of the activation energy for which Arrhenius became famous. In 1978, Chandler [J. Chem. Phys. 68, 2959 (1978)] finally showed that especially when considering condensed phases, the activation energy is a free energy, it is the barrier height in the potential of mean force felt by the reacting system. Parallel to the development of rate theory in the chemistry community, Kramers published in 1940 [Physica (Amsterdam) 7, 284 (1940)] a seminal paper on the relation between Einstein's theory of Brownian motion [Einstein, Ann. Phys. 17, 549 (1905)] and rate theory. Kramers' paper provided a solution for the effect of friction on reaction rates but left us also with some challenges. He could not derive a uniform expression for the rate, valid for all values of the friction coefficient, known as the Kramers turnover problem. He also did not establish the connection between his approach and the TST developed by the chemistry community. For many years, Kramers' theory was considered as providing a dynamic correction to the thermodynamic TST. Both of these questions were resolved in the 1980s when Pollak [J. Chem. Phys. 85, 865 (1986)] showed that Kramers' expression in the moderate to strong friction regime could be derived from TST, provided that the bath, which is the source of the friction, is handled at the same level as the system which is observed. This then led to the Mel'nikov-Pollak-Grabert-Hänggi [Mel'nikov and Meshkov, J. Chem. Phys. 85, 1018 (1986); Pollak, Grabert, and Hänggi, J. Chem. Phys. 91, 4073 (1989)] solution of the turnover problem posed by Kramers. Although classical rate theory reached a high level of maturity, its quantum analog leaves the theorist with serious challenges to this very day. As noted by Wigner [Trans. Faraday Soc. 34, 29 (1938)], TST is an inherently classical theory. A definite quantum TST has not been formulated to date although some very useful approximate quantum rate theories have been invented. The successes and challenges facing quantum rate theory are outlined. An open problem which is being investigated intensively is rate theory away from equilibrium. TST is no longer valid and cannot even serve as a conceptual guide for understanding the critical factors which determine rates away from equilibrium. The nonequilibrium quantum theory is even less well developed than the classical, and suffers from the fact that even today, we do not know how to solve the real time quantum dynamics for systems with "many" degrees of freedom.

  15. Reaction rate theory: what it was, where is it today, and where is it going?

    PubMed

    Pollak, Eli; Talkner, Peter

    2005-06-01

    A brief history is presented, outlining the development of rate theory during the past century. Starting from Arrhenius [Z. Phys. Chem. 4, 226 (1889)], we follow especially the formulation of transition state theory by Wigner [Z. Phys. Chem. Abt. B 19, 203 (1932)] and Eyring [J. Chem. Phys. 3, 107 (1935)]. Transition state theory (TST) made it possible to obtain quick estimates for reaction rates for a broad variety of processes even during the days when sophisticated computers were not available. Arrhenius' suggestion that a transition state exists which is intermediate between reactants and products was central to the development of rate theory. Although Wigner gave an abstract definition of the transition state as a surface of minimal unidirectional flux, it took almost half of a century until the transition state was precisely defined by Pechukas [Dynamics of Molecular Collisions B, edited by W. H. Miller (Plenum, New York, 1976)], but even this only in the realm of classical mechanics. Eyring, considered by many to be the father of TST, never resolved the question as to the definition of the activation energy for which Arrhenius became famous. In 1978, Chandler [J. Chem. Phys. 68, 2959 (1978)] finally showed that especially when considering condensed phases, the activation energy is a free energy, it is the barrier height in the potential of mean force felt by the reacting system. Parallel to the development of rate theory in the chemistry community, Kramers published in 1940 [Physica (Amsterdam) 7, 284 (1940)] a seminal paper on the relation between Einstein's theory of Brownian motion [Einstein, Ann. Phys. 17, 549 (1905)] and rate theory. Kramers' paper provided a solution for the effect of friction on reaction rates but left us also with some challenges. He could not derive a uniform expression for the rate, valid for all values of the friction coefficient, known as the Kramers turnover problem. He also did not establish the connection between his approach and the TST developed by the chemistry community. For many years, Kramers' theory was considered as providing a dynamic correction to the thermodynamic TST. Both of these questions were resolved in the 1980s when Pollak [J. Chem. Phys. 85, 865 (1986)] showed that Kramers' expression in the moderate to strong friction regime could be derived from TST, provided that the bath, which is the source of the friction, is handled at the same level as the system which is observed. This then led to the Mel'nikov-Pollak-Grabert-Hanggi [Mel'nikov and Meshkov, J. Chem. Phys. 85, 1018 (1986); Pollak, Grabert, and Hanggi, ibid. 91, 4073 (1989)] solution of the turnover problem posed by Kramers. Although classical rate theory reached a high level of maturity, its quantum analog leaves the theorist with serious challenges to this very day. As noted by Wigner [Trans. Faraday Soc. 34, 29 (1938)], TST is an inherently classical theory. A definite quantum TST has not been formulated to date although some very useful approximate quantum rate theories have been invented. The successes and challenges facing quantum rate theory are outlined. An open problem which is being investigated intensively is rate theory away from equilibrium. TST is no longer valid and cannot even serve as a conceptual guide for understanding the critical factors which determine rates away from equilibrium. The nonequilibrium quantum theory is even less well developed than the classical, and suffers from the fact that even today, we do not know how to solve the real time quantum dynamics for systems with "many" degrees of freedom. PMID:16035918

  16. Ground Reaction Forces and Loading Rates Associated with Parkour and Traditional Drop Landing Techniques

    PubMed Central

    Puddle, Damien L.; Maulder, Peter S.

    2013-01-01

    Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76) and landing loading rate (54%, p < 0.01, ES = 1.22). Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04) and landing loading rate (63%, p < 0.01, ES = 1.54) were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced. Key points Parkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates. Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios. The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life. PMID:24149735

  17. Ground reaction forces and loading rates associated with parkour and traditional drop landing techniques.

    PubMed

    Puddle, Damien L; Maulder, Peter S

    2013-01-01

    Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76) and landing loading rate (54%, p < 0.01, ES = 1.22). Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04) and landing loading rate (63%, p < 0.01, ES = 1.54) were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced. Key pointsParkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates.Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios.The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life. PMID:24149735

  18. RATE CONSTANTS FOR THE REACTION OF OH RADICALS WITH A SERIES OF ALKENES AND DIALKENES AT 295 + OR - 1 K

    EPA Science Inventory

    Using a relative rate technique, rate constants for the gas phase reactions of the OH radical with n-butane, n-hexane and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 + or - 1K. The resulting rate constant d...

  19. Theoretical study and rate constant calculation of the CH2O+CH3 reaction

    NASA Astrophysics Data System (ADS)

    Liu, Jing-yao; Li, Ze-sheng; Wu, Jia-yan; Wei, Zhi-gang; Zhang, Gang; Sun, Chia-chung

    2003-10-01

    The potential energy surface of the CH2O+CH3 reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P1 CHO+CH4 (R1), while the addition process leading to P2H+CH3CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH3CH2O and CH3OCH2 radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect plays a significant role in the rate constant calculation; and as a result, the CVT/SCT rate constants exhibit typical non-Arrhenius behavior over a wide temperature range 300-2000 K. The three parameter expression is k=6.35×10-26 T4.4 exp(-2450/T) cm3 molecule-1 s-1.

  20. Rate and reaction probability of the surface reaction between ozone and dihydromyrcenol measured in a bench scale reactor and a room-sized chamber

    NASA Astrophysics Data System (ADS)

    Shu, Shi; Morrison, Glenn C.

    2012-02-01

    Low volatility terpenoids emitted from consumer products can react with ozone on surfaces and may significantly alter concentrations of ozone, terpenoids and reaction products in indoor air. We measured the reaction probability and a second-order surface-specific reaction rate for the ozonation of dihydromyrcenol, a representative indoor terpenoid, adsorbed onto polyvinylchloride (PVC), glass, and latex paint coated spheres. The reaction probability ranged from (0.06-8.97) × 10 -5 and was very sensitive to humidity, substrate and mass adsorbed. The average surface reaction probability is about 10 times greater than that for the gas-phase reaction. The second-order surface-specific rate coefficient ranged from (0.32-7.05) × 10 -15 cm 4 s -1 molecule -1and was much less sensitive to humidity, substrate, or mass adsorbed. We also measured the ozone deposition velocity due to adsorbed dihydromyrcenol on painted drywall in a room-sized chamber, Based on that, we calculated the rate coefficient ((0.42-1.6) × 10 -15 cm 4 molecule -1 s -1), which was consistent with that derived from bench-scale experiments for the latex paint under similar conditions. We predict that more than 95% of dihydromyrcenol oxidation takes place on indoor surfaces, rather than in building air.

  1. Shock tube measurements of specific reaction rates in the branched chain CH4-CO-O2 system

    NASA Technical Reports Server (NTRS)

    Brabbs, T. A.; Brokaw, R. S.

    1974-01-01

    Rate constants of two elementary bimolecular reactions involved in the oxidation of methane have been determined by monitoring the exponential growth of CO flame band emission behind incident shocks in three suitably chosen gas mixtures. The data do not support a mechanism which invokes the four center process CH3 + O2 yields CH2O + OH for the reaction of methyl with oxygen.

  2. Mixed quantum classical calculation of proton transfer reaction rates: From deep tunneling to over the barrier regimes

    SciTech Connect

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-07

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

  3. Stress-associated cardiovascular reaction masks heart rate dependence on physical load in mice.

    PubMed

    Andreev-Andrievskiy, A A; Popova, A S; Borovik, A S; Dolgov, O N; Tsvirkun, D V; Custaud, M; Vinogradova, O L

    2014-06-10

    When tested on the treadmill mice do not display a graded increase of heart rate (HR), but rather a sharp shift of cardiovascular indices to high levels at the onset of locomotion. We hypothesized that under test conditions cardiovascular reaction to physical load in mice is masked with stress-associated HR increase. To test this hypothesis we monitored mean arterial pressure (MAP) and heart rate in C57BL/6 mice after exposure to stressful stimuli, during spontaneous locomotion in the open-field test, treadmill running or running in a wheel installed in the home cage. Mice were treated with β1-adrenoblocker atenolol (2mg/kg ip, A), cholinolytic ipratropium bromide (2mg/kg ip, I), combination of blockers (A+I), anxiolytic diazepam (5mg/kg ip, D) or saline (control trials, SAL). MAP and HR in mice increased sharply after handling, despite 3weeks of habituation to the procedure. Under stressful conditions of open field test cardiovascular parameters in mice were elevated and did not depend on movement speed. HR values did not differ in I and SAL groups and were reduced with A or A+I. HR was lower at rest in D pretreated mice. In the treadmill test HR increase over speeds of 6, 12 and 18m/min was roughly 1/7-1/10 of HR increase observed after placing the mice on the treadmill. HR could not be increased with cholinolytic (I), but was reduced after sympatholytic (A) or A+I treatment. Anxiolytic (D) reduced heart rate at lower speeds of movement and its overall effect was to unmask the dependency of HR on running speed. During voluntary running in non-stressful conditions of the home cage HR in mice linearly increased with increasing running speeds. We conclude that in test situations cardiovascular reactions in mice are governed predominantly by stress-associated sympathetic activation, rendering efforts to evaluate HR and MAP reactions to workload unreliable. PMID:24802359

  4. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Foy, E.; Rowan, G.; Goldstein, D.

    1982-01-01

    The use of probability theory to determine the effects of turbulent fluctuations on reaction rates in turbulent combustion systems is briefly reviewed. Results are presented for the effect of species fluctuations in particular. It is found that turbulent fluctuations of species act to reduce the reaction rates, in contrast with the temperature fluctuations previously determined to increase Arrhenius reaction rate constants. For the temperature fluctuations, a criterion is set forth for determining if, in a given region of a turbulent flow field, the temperature can be expected to exhibit ramp like fluctuations. Using the above results, along with results previously obtained, a model is described for testing the effects of turbulent fluctuations of temperature and species on reaction rates in computer programs dealing with turbulent reacting flows. An alternative model which employs three variable probability density functions (temperature and two species) and is currently being formulated is discussed as well.

  5. Shock tube measurements of specific reaction rates in branched chain CH4-CO-O2 system

    NASA Technical Reports Server (NTRS)

    Brabbs, T. A.; Brokaw, R. S.

    1974-01-01

    Rate constants of two elementary bimolecular reactions involved in the oxidation of methane were determined by monitoring the exponential growth of CO flame band emission behind incident shocks in three suitably chosen gas mixtures.

  6. Revised Production Rates for Na-22 and Mn-54 in Meteorites Using Cross Sections Measured for Neutron-induced Reactions

    NASA Technical Reports Server (NTRS)

    Sisterson, J. M.; Kim, K. J.; Reedy, R. C.

    2004-01-01

    The interactions of galactic cosmic rays (GCR) with extraterrestrial bodies produce small amounts of radionuclides and stable isotopes. The production rates of many relatively short-lived radionuclides, including 2.6-year Na-22 and 312-day Mn-54, have been measured in several meteorites collected very soon after they fell. Theoretical models used to calculate production rates for comparison with the measured values rely on input data containing good cross section measurements for all relevant reactions. Most GCR particles are protons, but secondary neutrons make most cosmogenic nuclides. Calculated production rates using only cross sections for proton-induced reactions do not agree well with measurements. One possible explanation is that the contribution to the production rate from reactions initiated by secondary neutrons produced in primary GCR interactions should be included explicitly. This, however, is difficult to do because so few of the relevant cross sections for neutron-induced reactions have been measured.

  7. The role of advanced reactive surface area characterization in improving predictions of mineral reaction rates

    NASA Astrophysics Data System (ADS)

    Beckingham, L. E.; Zhang, S.; Mitnick, E.; Cole, D. R.; Yang, L.; Anovitz, L. M.; Sheets, J.; Swift, A.; Kneafsey, T. J.; Landrot, G.; Mito, S.; Xue, Z.; Steefel, C. I.; DePaolo, D. J.; Ajo Franklin, J. B.

    2014-12-01

    Geologic sequestration of CO2 in deep sedimentary formations is a promising means of mitigating carbon emissions from coal-fired power plants but the long-term fate of injected CO2 is challenging to predict. Reactive transport models are used to gain insight over long times but rely on laboratory determined mineral reaction rates that have been difficult to extrapolate to field systems. This, in part, is due to a lack of understanding of mineral reactive surface area. Many models use an arbitrary approximation of reactive surface area, applying orders of magnitude scaling factors to measured BET or geometric surface areas. Recently, a few more sophisticated approaches have used 2D and 3D image analyses to determine mineral-specific reactive surface areas that account for the accessibility of minerals. However, the ability of these advanced surface area estimates to improve predictions of mineral reaction rates has yet to be determined. In this study, we fuse X-ray microCT, SEM QEMSCAN, XRD, SANS, and SEM-FIB analysis to determine mineral-specific accessible reactive surface areas for a core sample from the Nagaoka pilot CO2 injection site (Japan). This sample is primarily quartz, plagioclase, smectite, K-feldspar, and pyroxene. SEM imaging shows abundant smectite cement and grain coatings that decrease the fluid accessibility of other minerals. However, analysis of FIB-SEM images reveals that smectite nano-pores are well connected such that access to underlying minerals is not occluded by smectite coatings. Mineral-specific accessible surfaces are determined, accounting for the connectivity of the pore space with and without connected smectite nano-pores. The large-scale impact of variations in accessibility and dissolution rates are then determined through continuum scale modeling using grid-cell specific information on accessible surface areas. This approach will be compared with a traditional continuum scale model using mineral abundances and common surface area estimates. Ultimately, the effectiveness of advanced surface area characterization to improve mineral dissolution rates will be evaluated by comparison of model results with dissolution rates measured from a flow-through column experiment.

  8. Transformation and removal of tetrabromobisphenol A from water in the presence of natural organic matter via laccase-catalyzed reactions: reaction rates, products, and pathways.

    PubMed

    Feng, Yiping; Colosi, Lisa M; Gao, Shixiang; Huang, Qingguo; Mao, Liang

    2013-01-15

    The widespread occurrence of the brominated flame retardant tetrabromobisphenol A (TBBPA) makes it a possible source of concern. Our experiments suggest that TBBPA can be effectively transformed by the naturally occurring laccase enzyme from Trametes versicolor. These reactions follow second-order kinetics, whereby apparent removal rate is a function of both substrate and enzyme concentrations. For reactions at different initial concentrations and with or without natural organic matter (NOM), reaction products are identified using liquid or gas chromatography with mass spectrometry. Detailed reaction pathways are proposed. It is postulated that two TBBPA radicals resulting from a laccase-mediated reaction are coupled together via interaction of an oxygen atom on one radical and a propyl-substituted aromatic carbon atom on the other. A 2,6-dibromo-4-isopropylphenol carbocation is then eliminated from the radical dimer. All but one of the detected products arise from either substitution or proton elimination of the 2,6-dibromo-4-isopropylphenol carbocation. Three additional products are identified for reactions in the presence of NOM, which suggests that reaction occurs between NOM and TBBPA radical. Data from acute immobilization tests with Daphnia confirm that TBBPA toxicity is effectively eliminated by laccase-catalyzed TBBPA removal. These findings are useful for understanding laccase-mediated TBBPA reactions and could eventually lead to development of novel methods to control TBBPA contamination. PMID:23256593

  9. The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments

    NASA Astrophysics Data System (ADS)

    Lansdown, K.; Heppell, C. M.; Trimmer, M.; Binley, A.; Heathwaite, A. L.; Byrne, P.; Zhang, H.

    2015-06-01

    Anthropogenic nitrogen fixation and subsequent use of this nitrogen as fertilizer have greatly disturbed the global nitrogen cycle. Rivers are recognized hot spots of nitrogen removal in the landscape as interaction between surface water and sediments creates heterogeneous redox environments conducive for nitrogen transformations. Our understanding of riverbed nitrogen dynamics to date comes mainly from shallow sediments or hyporheic exchange flow pathways with comparatively little attention paid to groundwater-fed, gaining reaches. We have used 15N techniques to quantify in situ rates of nitrate removal to 1 m depth within a groundwater-fed riverbed where subsurface hydrology ranged from strong upwelling to predominantly horizontal water fluxes. We combine these rates with detailed hydrologic measurements to investigate the interplay between biogeochemical activity and water transport in controlling nitrogen attenuation along upwelling flow pathways. Nitrate attenuation occurred via denitrification rather than dissimilatory nitrate reduction to ammonium or anammox (range = 12 to >17,000 nmol 15N L-1 h-1). Overall, nitrate removal within the upwelling groundwater was controlled by water flux rather than reaction rate (i.e., Damköhler numbers <1) with the exception of two hot spots of biogeochemical activity. Deep sediments were as important a nitrate sink as shallow sediments with fast rates of denitrification and short water residence time close to the riverbed surface balanced by slower rates of denitrification and water flux at depth. Within this permeable riverbed >80% of nitrate removal occurs within sediments not exposed to hyporheic exchange flows under base flow conditions, illustrating the importance of deep sediments as nitrate sinks in upwelling systems.

  10. Measurement of enzyme reaction rates using advanced pH control system: application of repetitive PF system.

    PubMed

    Shimizu, H; Sada, E; Shioya, S; Suga, K

    1989-09-01

    The aim of this article is to develop the on-line measurement system of enzyme reaction rates, using an advanced pH controller, which is called a repetitive PF(Programmed Controller/Feedback Compensator) System. In the esterolysis reaction of the N-acetyltyrosine ethyl ester by alpha-chymotrypsin, the enzyme reaction rate could be calculated from the amount of base required for keeping the pH constant. The proposed controller has a learning mechanism in which the knowledge is obtained from the former results of the repetition, and pH was controlled much more successfully by the proposed repetitive PF System than by the conventional on-off controller, PI controller, and the adaptive controller. The enzyme reaction rate could be evaluated each time as accurately as possible based on the result of the controlled batch reaction. Using Lineweaver-Burk plots of the estimated reaction rates, kinetic parameters, such as the enzyme activity and Michaelis-Menten constant, could be estimated more accurately and from fewer experiments by the repetitive PF system than by initial reaction rates using on-off pH-stat. PMID:18588166

  11. Analysis of turbulent free jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.

    1978-01-01

    The nonequilibrium flow field resulting from the turbulent mixing and combustion of a supersonic axisymmetric hydrogen jet in a supersonic parallel coflowing air stream is analyzed. Effective turbulent transport properties are determined using the (K-epsilon) model. The finite-rate chemistry model considers eight reactions between six chemical species, H, O, H2O, OH, O2, and H2. The governing set of nonlinear partial differential equations is solved by an implicit finite-difference procedure. Radial distributions are obtained at two downstream locations of variables such as turbulent kinetic energy, turbulent dissipation rate, turbulent scale length, and viscosity. The results show that these variables attain peak values at the axis of symmetry. Computed distributions of velocity, temperature, and mass fraction are also given. A direct analytical approach to account for the effect of species concentration fluctuations on the mean production rate of species (the phenomenon of unmixedness) is also presented. However, the use of the method does not seem justified in view of the excessive computer time required to solve the resulting system of equations.

  12. Actinometric measurement of solar ultraviolet and development of a weighted solar UV integral. [photochemical reaction rate determination

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Coulbert, C.

    1978-01-01

    An actinometer has been developed to measure outdoor irradiance in the range 295-400 nm. Actinometric measurements of radiation are based on determination of photochemical reaction rates for reactions of known quantum efficiency. Actinometers have the advantage of providing irradiance data over surfaces of difficult accessibility; in addition, actinometrically determined irradiance data are wavelength weighted and therefore provide a useful means of assessing the degradation rates of polymers employed in solar energy systems.

  13. Early diagenetic processes, fluxes, and reaction rates in sediments of the South Atlantic

    SciTech Connect

    Schulz, H.D.; Dahmke, A.; Schinzel, U.; Wallmann, K.; Zabel, M. )

    1994-05-01

    Porewaters recovered from sediment cores (gravity corers, box corers, and multicorers) from various subregions of the South Atlantic (Amazon River mouth, equatorial upwelling, Congo River mouth, Benguela coastal upwelling area, and Angola Basin) were investigated geochemically. Objectives included determination of Eh, pH, oxygen, nitrate, sulfate, alkalinity, phosphate, ammonium, fluoride, sulfide, Ca, Mg, Sr, Fe, Mn, and Si, in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes. Porewater profiles from the eastern upwelling areas of the South Atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation, whereas organic matter degradation by sulfate reduction is restricted to the near-surface sediments. Further, a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m, far below the zone of bioturbation or bioirrigation. Because other sedimentological reasons seem to fail as explanations, an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed. Porewater profiles from the sediments of the Amazon fan area are mainly influenced by reactions with Fe(III)-phases. The remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments. In contrast to the upwelling sediments, the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5.3 m, probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals. A comparison of organic matter degradation rates from the different areas of the South Atlantic show the expected relationship to primary productivity.

  14. Path-integral virial estimator for reaction rate calculation basedon the quantum instanton aproximation

    SciTech Connect

    Yang, Sandy; Yamamoto, Takeshi; Miller, William H.

    2005-11-28

    The quantum instanton approximation is a type of quantum transition state theory that calculates the chemical reaction rate using the reactive flux correlation function and its low order derivatives at time zero. Here we present several path-integral estimators for the latter quantities, which characterize the initial decay profile of the flux correlation function. As with the internal energy or heat capacity calculation, different estimators yield different variances (and therefore different convergence properties) in a Monte Carlo calculation. Here we obtain a virial(-type) estimator by using a coordinate scaling procedure rather than integration by parts, which allows more computational benefits. We also consider two different methods for treating the flux operator, i.e., local-path and global-path approaches, in which the latter achieves a smaller variance at the cost of using second-order potential derivatives. Numerical tests are performed for a one-dimensional Eckart barrier and a model proton transfer reaction in a polar solvent, which illustrates the reduced variance of the virial estimator over the corresponding thermodynamic estimator.

  15. Pressure dependence on the reaction propagation rate of PETN at high pressure

    SciTech Connect

    Foltz, M.F.

    1993-04-01

    The reaction propagation rate (RPR) of the sensitive high explosive pentaerythritol tetranitrate (PETN) was measured in a diamond anvil cell (DAC) over the pressure range of 2--20 GPa. The experimental technique used is the same as that previously reported. The RPR data shows that it burns one to two orders of magnitude faster in the DAC than 1,3,5,-triamino-2,4,6-trinitrobenzene (TATB) and nitromethane (CH{sub 3}NO{sub 2}) respectively. The PETN RPR curve did not show sample pressure-dependent behavior like that of nitromethane, but instead varied abruptly like the RPR curve of TATB. In order to interpret these changes, static-pressure DAC mid-IR FTIR spectra were taken of micro-pellets of PETN embedded in KBr. The relationship between changes in the spectra, the RPR curve, and published single crystal PETN wedge test data are discussed.

  16. Rate constants for oxidation reactions by radical cations from methyl iodide

    SciTech Connect

    Mohan, H.; Asmus, K.D.

    1988-01-14

    Radical cations from methyl iodide CH/sub 3/I/sup .+/, and (CH/sub 3/I therefore ICH/sub 3/)/sup +/ are shown to be excellent oxidants with a one-electron redox potential presumably greater than or equal to +2 V. Absolute rate constants in the order of 10/sup 9/ M/sup -1/ have been determined for their reactions with various organic sulfides, disulfides, thiols, phenothiazines, and inorganic metal and halide ions. A similarly high reactivity has also been found for the hydroxyl radical adduct to methyl iodide, CH/sub 3/I(OH)/sup ./. The results are discussed in view of the electronic and steric structure of these oxidizing radical species and the substrates to be oxidized.

  17. Temperature dependence of the NO + O3 reaction rate from 195 to 369 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Allen, J. E., Jr.; Brobst, W. D.

    1981-01-01

    The temperature dependence of the NO + O3 reaction rate was examined by means of the fast flow technique. Several different experimental conditions and detection schemes were employed. With excess NO or excess O3, NO2 chemiluminescence was monitored. In addition, with excess O3, NO was followed by fluorescence induced by an NO microwave discharge lamp. The results of the three independent sets of data are compared and found to agree within experimental error, indicating the absence of secondary chemistry which might complicate the kinetics. The data exhibit curvature on an Arrhenius plot; however, the simple Arrhenius expression k = (2.6 + or - 0.8) x 10 to the -12th exp(-1435 + or - 64/T) cu cm/molecule s is an adequate description for T between 195 and 369 K. This result is compared to earlier determinations.

  18. Cybersickness provoked by head-mounted display affects cutaneous vascular tone, heart rate and reaction time.

    PubMed

    Nalivaiko, Eugene; Davis, Simon L; Blackmore, Karen L; Vakulin, Andrew; Nesbitt, Keith V

    2015-11-01

    Evidence from studies of provocative motion indicates that motion sickness is tightly linked to the disturbances of thermoregulation. The major aim of the current study was to determine whether provocative visual stimuli (immersion into the virtual reality simulating rides on a rollercoaster) affect skin temperature that reflects thermoregulatory cutaneous responses, and to test whether such stimuli alter cognitive functions. In 26 healthy young volunteers wearing head-mounted display (Oculus Rift), simulated rides consistently provoked vection and nausea, with a significant difference between the two versions of simulation software (Parrot Coaster and Helix). Basal finger temperature had bimodal distribution, with low-temperature group (n=8) having values of 23-29 °C, and high-temperature group (n=18) having values of 32-36 °C. Effects of cybersickness on finger temperature depended on the basal level of this variable: in subjects from former group it raised by 3-4 °C, while in most subjects from the latter group it either did not change or transiently reduced by 1.5-2 °C. There was no correlation between the magnitude of changes in the finger temperature and nausea score at the end of simulated ride. Provocative visual stimulation caused prolongation of simple reaction time by 20-50 ms; this increase closely correlated with the subjective rating of nausea. Lastly, in subjects who experienced pronounced nausea, heart rate was elevated. We conclude that cybersickness is associated with changes in cutaneous thermoregulatory vascular tone; this further supports the idea of a tight link between motion sickness and thermoregulation. Cybersickness-induced prolongation of reaction time raises obvious concerns regarding the safety of this technology. PMID:26340855

  19. Comparison of Nernst-Planck and reaction rate models for multiply occupied channels.

    PubMed Central

    Levitt, D G

    1982-01-01

    The Nernst-Planck continuum equation for a channel that can be occupied by at most two ions is solved for two different physical cases. The first case is for the assumption that the water and ion cannot get around each other anywhere in the channel, so that if there are two ions in the channel the distance between them is fixed by the number of water molecules between them. The second case is for the assumption that there are regions at he ends of the channel where the ions and water can get around each other. For these two cases, the validity of the simple two-site reaction-rate approximation when there is a continuously varying central energy barrier was evaluated by comparing it with the exact Nernst-Planck solution. For the first continuum case, the kinetics for the continuum and reaction-rate models are nearly identical. For the second case, the agreement depends on the strength of the ion-ion interaction energy. For a low interaction energy (large channel diameter) a high ion concentrations, there is a large difference in the flux as a function of voltage for the two models-with the continuum flux becoming more than four times larger at 250 mV. Simple analytical expressions are derived for the two-ion continuum channel for the case where the ends are in equilibrium with the bulk solution and for the case where ion mobility becomes zero when there are two ions in the channel. The implications of these results for biological channels are discussed. PMID:6280783

  20. Kinetics and Mechanism of the Reaction of Hydoxyl Radicals with Acetonitrile under Atmospheric Conditions

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH3CN (1) and its isotopic variants, OH + CD3CN (2), OD + CH3CN (3), and OD + CD3CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N2, N2/O2, and He buffer gases. In the absence of O2 all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-first rate constants which were proportional to substrate concentration. Data obtained in N2 over the range 50-700 Torr at 298 K are consistent with k(sub 1), showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures in k(sub 1)(T) = (1.1(sup +0.5)/(sub -0.3)) x 10(exp -12) exp[(-1130 +/- 90)/T] cu cm /(molecule s). The kinetics of reaction 2 are found to be pressure dependent with k(sub 2) (298 K) increasing from (1.21 +/- 0.12) x 10(exp -14) to (2.16 +/- 0.11) x 10(exp -14) cm(exp 3)/ (molecule s) over the pressure range 50-700 Torr of N2 at 298 K. Data at pressures greater than 600 Torr give k(sub 2)(T) = (9.4((sup +13.4)(sub -5.0))) x 10(exp -13) exp[(-1180 +/- 250)/T] cu cm/(molecule s). The rates of reactions 3 and 4 are found to be independent of pressure over the range 50-700 Torr of N2 with 298 K rate coefficient given by k(sub 3) =(3.18 +/- 0.40) x 10(exp -14) cu cm/(molecule s) and k(sub 4) = (2.25 +/-0.28) x 10(exp -14) cu cm/(molecule s). In the presence of O2 each reaction shows complex (non-pseudo-first-order) kinetic behavior and/or an apparent decrease in the observed rate constant with increasing [O2], indicating the presence of significant OH or OD regeneration. Observation of regeneration of OH in (2) and OD in (3) is indicative of a reaction channel which proceeds via addition followed by reaction of the adduct, or one of its decomposition products, with O2. The observed OH and OD decay profiles have been modeled by using a simple mechanistic scheme to extract kinetic information about the adduct reations with O2 and branching ratios for OH regeneration. A plausible mechanism for OH regeneration in (2) involves OH addition to the nitrogen atom followed by O2 addition to the cyano carbon atom, isomeriazation and decomposition to D2CO + DOCN + OH. Our results suggest that the OH + CH3CN reaction occurs via a complex mechanism involving both bimolecular and termolecular pathways, analogous to the mechanisms for the the important atmospheric reactions of OH with CO and HNO3.

  1. On the use of chemical reaction rates with discrete internal energies in the direct simulation Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Gimelshein, S. F.; Gimelshein, N. E.; Levin, D. A.; Ivanov, M. S.; Wysong, I. J.

    2004-07-01

    The conventional chemical reaction models of the direct simulation Monte Carlo method developed with the assumption of continuous rotational or vibrational modes that are shown to exhibit systematic errors when used with discrete energy modes. A reaction model is proposed that is consistent with the use of discrete energy distributions of rotational and vibrational modes, and is equally applicable to diatomic and polyatomic systems. The sensitivity of the model to variations of different reaction rate parameters is examined. The revised chemical reaction model is then applied to the modeling of hypersonic flows over spacecraft in the Martian and Earth atmospheres.

  2. High-precision {sup 28}Si(p,t){sup 26}Si reaction to determine {sup 22}Mg({alpha},p){sup 25}Al reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Beard, M.; Berg, G. P. A.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.

    2011-08-15

    The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of ({alpha},p) reactions via high-lying resonances in sd-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the ({alpha},p) reaction to natural parity states. We measured the {sup 28}Si(p,t){sup 26}Si reaction with a high-resolution spectrometer to identify resonance levels in {sup 26}Si above the {alpha}-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the {sup 22}Mg({alpha},p){sup 25}Al reaction and to test the validity of the statistical assumption.

  3. Helium effects on microstructural change in RAFM steel under irradiation: Reaction rate theory modeling

    NASA Astrophysics Data System (ADS)

    Watanabe, Y.; Morishita, K.; Nakasuji, T.; Ando, M.; Tanigawa, H.

    2015-06-01

    Reaction rate theory analysis has been conducted to investigate helium effects on the formation kinetics of interstitial type dislocation loops (I-loops) and helium bubbles in reduced-activation-ferritic/martensitic steel during irradiation, by focusing on the nucleation and growth processes of the defect clusters. The rate theory model employs the size and chemical composition dependence of thermal dissociation of point defects from defect clusters. In the calculations, the temperature and the production rate of Frenkel pairs are fixed to be T = 723 K and PV = 10-6 dpa/s, respectively. And then, only the production rate of helium atoms was changed into the following three cases: PHe = 0, 10-7 and 10-5 appm He/s. The calculation results show that helium effect on I-loop formation quite differs from that on bubble formation. As to I-loops, the loop formation hardly depends on the existence of helium, where the number density of I-loops is almost the same for the three cases of PHe. This is because helium atoms trapped in vacancies are easily emitted into the matrix due to the recombination between the vacancies and SIAs, which induces no pronounced increase or decrease of vacancies and SIAs in the matrix, leading to no remarkable impact on the I-loop nucleation. On the other hand, the bubble formation depends much on the existence of helium, in which the number density of bubbles for PHe = 10-7 and 10-5 appm He/s is much higher than that for PHe = 0. This is because helium atoms trapped in a bubble increase the vacancy binding energy, and suppress the vacancy dissociation from the bubble, resulting in a promotion of the bubble nucleation. And then, the helium effect on the promotion of bubble nucleation is very strong, even the number of helium atoms in a bubble is not so large.

  4. Reaction rates, depositional history and sources of indium in sediments from Appalachian and Canadian Shield lakes

    NASA Astrophysics Data System (ADS)

    Tessier, André; Gobeil, Charles; Laforte, Lucie

    2014-07-01

    Sediment cores were collected at the deepest site of twelve headwater lakes from the Province of Québec, Canada that receive contaminants only from atmospheric deposition, either directly to the lake surface or indirectly from the watershed. Several of the lakes are located within relatively short distance (<40 km) and others at more than 200 km from potential sources of contamination. The sediments were dated and analyzed for In and other elements including Fe, Mn, Al and organic C. Fe-rich authigenic material was collected on Teflon sheets inserted vertically into the sediments at the only study site whose hypolimnion remains perennially oxic. Porewater samples collected at the coring site of four of the lakes were also analyzed for In and other solutes including sulfide, sulfate, Fe, Mn, inorganic and organic C and major ions. The porewater In profiles display concentration gradients at or below the sediment-water interface. Modeling these profiles with a one-dimensional transport-reaction equation assuming steady state allows definition of depth intervals (zones) where In is either released to or removed from porewater and quantification of net In reactions rates in each zone. The position of the In consumption zones, the shape of the vertical profiles of dissolved In, sulfide and iron, as well as thermodynamic calculations of saturation states collectively suggest that In(OH)3(s) and In2S3(s) do not precipitate in the sediments and that adsorption of In onto sedimentary FeS(s) does not occur. However, similarities in the In and Fe porewater profiles, and the presence of In in the authigenic Fe-rich solids, reveal that part of the In becomes associated with authigenic Fe oxyhydroxides in the perennially oxic lake and is coupled to the Fe redox cycling. Comparison of the In/Corg and In/Fe molar ratios in the authigenic Fe-rich material and in surface sediments (0-0.5 cm) of this lake suggests that most non-lithogenic In was bound to humic substances. From the magnitude of the net In reaction rates, we infer that the post-depositional redistribution of this element is quantitatively not important and that the In sedimentary record represents accurately In deposition at the sampling sites. Reconstructed chronologies of the anthropogenic In deposition and comparison of In inventories among lakes point to non-ferrous metal smelters as a past significant source of atmospheric In contamination and to a significant reduction of industrial In emissions into the North American atmosphere in recent decades.

  5. Rate Coefficient for the (4)Heμ + CH4 Reaction at 500 K: Comparison between Theory and Experiment.

    PubMed

    Arseneau, Donald J; Fleming, Donald G; Li, Yongle; Li, Jun; Suleimanov, Yury V; Guo, Hua

    2016-03-01

    The rate constant for the H atom abstraction reaction from methane by the muonic helium atom, Heμ + CH4 → HeμH + CH3, is reported at 500 K and compared with theory, providing an important test of both the potential energy surface (PES) and reaction rate theory for the prototypical polyatomic CH5 reaction system. The theory used to characterize this reaction includes both variational transition-state (CVT/μOMT) theory (VTST) and ring polymer molecular dynamics (RPMD) calculations on a recently developed PES, which are compared as well with earlier calculations on different PESs for the H, D, and Mu + CH4 reactions, the latter, in particular, providing for a variation in atomic mass by a factor of 36. Though rigorous quantum calculations have been carried out for the H + CH4 reaction, these have not yet been extended to the isotopologues of this reaction (in contrast to H3), so it is important to provide tests of less rigorous theories in comparison with kinetic isotope effects measured by experiment. In this regard, the agreement between the VTST and RPMD calculations and experiment for the rate constant of the Heμ + CH4 reaction at 500 K is excellent, within 10% in both cases, which overlaps with experimental error. PMID:26484648

  6. The rate of the reaction between C2H and C2H2 at interstellar temperatures

    NASA Technical Reports Server (NTRS)

    Herbst, E.; Woon, D. E.

    1997-01-01

    The reaction between the radical C2H and the stable hydrocarbon C2H2 is one of the simplest neutral-neutral hydrocarbon reactions in chemical models of dense interstellar clouds and carbon-rich circumstellar shells. Although known to be rapid at temperatures > or = 300 K, the reaction has yet to be studied at lower temperatures. We present here ab initio calculations of the potential surface for this reaction and dynamical calculations to determine its rate at low temperature. Despite a small potential barrier in the exit channel, the calculated rate is large, showing that this reaction and, most probably, more complex analogs contribute to the formation of complex organic molecules in low-temperature sources.

  7. Influence of salts, including amino acids, on the rate and outcome of the in-water prebiotic reactions

    NASA Astrophysics Data System (ADS)

    Kolb, Vera M.

    2013-09-01

    Most prebiotic reactions are hypothesized to have occurred in water. However, organic compounds in general are not water-soluble. This has created a great problem for prebiotic chemistry. However, it has been shown recently that many organic materials which are not soluble in water are still capable of reacting in water, often at faster rates than in the organic solvents. This has provided a new era in the study of the prebiotic reactions. Simulated prebiotic reactions are typically performed in water. However, presence of inorganic salts and the amino acids was ubiquitous in the aqueous media on the prebiotic Earth. We thus address the influence of common salts and selected water-soluble amino acids on the rate and outcome of selected prebiotic reactions in water. We focus on Diels-Alder (DA) reaction and multicomponent Passerini reaction (PR), as models for other prebiotic reactions. Some of the results came from our laboratory, and others are from the literature. DA reaction is influenced by salts and by selected water-soluble amino acids, but generally not to a large extent. The PR is also influenced by salts, but not dramatically. However, concentrations of salts and amino acids could have been extremely high in various local niches on the early Earth, and the influence of such concentrations on these prebiotic reactions awaits further study.

  8. The reaction O((3)P) + HOBr: Temperature dependence of the rate constant and importance of the reaction as an HOBr stratospheric loss process

    NASA Technical Reports Server (NTRS)

    Nesbitt, F. L.; Monks, P. S.; Payne, W. A.; Stief, L. J.; Toumi, R.

    1995-01-01

    The absolute rate constant for the reaction O((3)P) + HOBr has been measured between T = 233K and 423K using the discharge-flow kinetic technique coupled to mass spectrometric detection. The value of the rate coefficient at room temperature is (2.5 +/- 0.6) x 10(exp -11)cu cm/molecule/s and the derived Arrhenius expression is (1.4 +/- 0.5) x 10(exp -10) exp((-430 +/- 260)/T)cu cm/molecule/s. From these rate data the atmospheric lifetime of HOBr with respect to reaction with O((3)P) is about 0.6h at z = 25 km which is comparable to the photolysis lifetime based on recent measurements of the UV cross section for HOBr. Implications for HOBr loss in the stratosphere have been tested using a 1D photochemical box model. With the inclusion of the rate parameters and products for the O + HOBr reaction, calculated concentration profiles of BrO increase by up to 33% around z = 35 km. This result indicates that the inclusion of the O + HOBr reaction in global atmospheric chemistry models may have an impact on bromine partitioning in the middle atmosphere.

  9. The TDF System for Thermonuclear Plasma Reaction Rates, Mean Energies and Two-Body Final State Particle Spectra

    SciTech Connect

    Warshaw, S I

    2001-07-11

    The rate of thermonuclear reactions in hot plasmas as a function of local plasma temperature determines the way in which thermonuclear ignition and burning proceeds in the plasma. The conventional model approach to calculating these rates is to assume that the reacting nuclei in the plasma are in Maxwellian equilibrium at some well-defined plasma temperature, over which the statistical average of the reaction rate quantity {sigma}v is calculated, where {sigma} is the cross-section for the reaction to proceed at the relative velocity v between the reacting particles. This approach is well-understood and is the basis for much nuclear fusion and astrophysical nuclear reaction rate data. The Thermonuclear Data File (TDF) system developed at the Lawrence Livermore National Laboratory (Warshaw 1991), which is the topic of this report, contains data on the Maxwellian-averaged thermonuclear reaction rates for various light nuclear reactions and the correspondingly Maxwellian-averaged energy spectra of the particles in the final state of those reactions as well. This spectral information closely models the output particle and energy distributions in a burning plasma, and therefore leads to more accurate computational treatments of thermonuclear burn, output particle energy deposition and diagnostics, in various contexts. In this report we review and derive the theoretical basis for calculating Maxwellian-averaged thermonuclear reaction rates, mean particle energies, and output particle spectral energy distributions for these reactions in the TDF system. The treatment of the kinematics is non-relativistic. The current version of the TDF system provides exit particle energy spectrum distributions for two-body final state reactions only. In a future report we will discuss and describe how output particle energy spectra for three- and four-body final states can be developed for the TDF system. We also include in this report a description of the algorithmic implementation of the TDF system, which is in two parts: the code which generates the data file itself from the nuclear reaction cross-sections, and the lookup utilities (bundled in a Fortran 77 subroutine library) which are used to retrieve the appropriate thermonuclear data from the file on demand. Unique approaches to generating, retrieving and looking up the data that were developed will be described in some detail. These developments resulted in an unusually compact data file which can be quickly generated, and from which an enormous amount of thermonuclear reaction rate, output particle energy and particle energy spectrum data can be rapidly retrieved. It is this compactness, speed and relative platform independence that distinguishes the LLNL TDF system from others.

  10. Analysis of turbulent free-jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.; Evans, J. S.

    1979-01-01

    A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

  11. Rate constant for the OH + CO reaction - Pressure dependence and the effect of oxygen

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1984-01-01

    The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10 percent. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40 percent at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

  12. Evaporation Rate Study and NDMA Formation from UDMH/NO2 Reaction Products

    NASA Technical Reports Server (NTRS)

    Buchanan, Vanessa D.; Dee, Louis A.; Baker, David L.

    2003-01-01

    Laboratory samples of uns-dimethylhydrazine (UDMH) fuel/oxidizer (nitrogen dioxide) non-combustion reaction products (UFORP) were prepared using a unique permeation tube technology. Also, a synthetic UFORP was prepared from UDMH, N-nitrosodimethylamine (NDMA), dimethylammonium nitrate, sodium nitrite and purified water. The evaporation rate of UFORP and synthetic UFORP was determined under space vacuum (approx 10(exp -3) Torr) at -40 ?C and 0 ?C. The material remaining was analyzed and showed that the UFORP weight and NDMA concentration decreased over time; however, NDMA had not completely evaporated. Over 85% of the weight was removed by subjecting the UFORP to 10(-3) Torr for 7 hours at -40 ?C and 4 hours at 0 ?C. A mixture of dimethylammonium nitrate and sodium nitrite formed NDMA at a rapid rate in a moist air environment. A sample of UFORP residue was analyzed for formation of NDMA under various conditions. It was found that NDMA was not formed unless nitrite was added.

  13. Chemical mechanisms and reaction rates for the initiation of hot corrosion of IN-738

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1984-01-01

    Sodium-sulfate-induced hot corrosion of preoxidized IN-738 was studied at 975 C with special emphasis placed on the processes occurring during the long induction period. Thermogravimetric tests were run for predetermined periods of time, and then one set of specimens was washed with water. Chemical analysis of the wash solutions yielded information about water soluble metal salts and residual sulfate. A second set of samples was cross sectioned dry and polished in a nonaqueous medium. Element distributions within the oxide scale were obtained from electron microprobe X-ray micrographs. Evolution of SO was monitored throughout the thermogravimetric tests. Kinetic rate studies were performed for several pertinent processes; appropriate rate constants were obtained from the following chemical reactions: Cr2O3 + 2 Na2SO4(1) + 3/2 O2 yields 2 Na2CrO4(1) + 2 SO3(g)n TiO2 + Na2SO4(1) yields Na2O(TiO2)n + SO3(g)n TiO2 + Na2CrO4(1) yields Na2O(TiO2)n + CrO3(g).

  14. Potential chlorofluorocarbon replacements: OH reaction rate constants between 250 and 315 K and infrared absorption spectra

    SciTech Connect

    Garland, N.L.; Medhurst, L.J.; Nelson, H.H.

    1993-12-20

    The authors measured the rate constant for reactions of the OH radical with several potential chlorofluorocarbon replacements over the temperature range 251-314 K using laser photolysis laser-induced fluorescence techniques. The compounds studied and Arrhenius parameters determined from fits to the measured rate constants are as follows: CHF{sub 2}OCHF{sub 2} (E 134), k(T) = (5.4 {+-} 3.5) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}3.1 {+-} 0.4 kcal mol{sup {minus}1})/RT]; CF{sub 3}CH{sub 2}CF{sub 3} (FC 236fa), k(T) = (2.0 {+-} 1.0) x 10{sup {minus}14} cm{sup 3} s{sup {minus}1} exp [({minus}1.8 {+-} 0.3 kcal mol{sup {minus}1})/RT]; CF{sub 3}CHFCHF{sub 2} (FC 236ea), k(T) = (2.0 {+-} 0.9) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.0 {+-} 0.3 kcal mol{sup {minus}1})/RT]; and CF{sub 3}CF{sub 2}CH{sub 2}F (FC 236cb), k(T) = (2.6 {+-} 1.6) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.2 {+-} 0.4 kcal mol{sup {minus}1})/RT]. The measured activation energies (2-3 kcal mol{sup {minus}1}) are consistent with a mechanism of H atom abstraction. The tropospheric lifetimes, estimated from the measured OH reaction rates, and measured integrated infrared absorption cross sections over the range 770 to 1430 cm{sup {minus}1} suggest that E 134 and FC 236fa may have significant global warming potential, while FC 236ea and FC 236cb do not. 17 refs., 4 figs., 3 tabs.

  15. A New 13N(p,{gamma})14O Reaction Rate And Its Influence In Novae Nucleosynthesis

    SciTech Connect

    Tang, X.; Azhari, A.; Fu Changbo; Gagliardi, C.A.; Mukhamedzhanov, A.M.; Pirlepesov, F.; Trache, L.; Tribble, R.E.; Burjan, V.; Kroha, V.; Carstoiu, F.; Irgaziev, B.F.

    2005-04-05

    The direct capture contribution for 13N(p,{gamma})14O has been determined more precisely with the peripheral transfer reaction, 14N(13N,14O)13C at the energy of 11.8 MeV/nucleon using the ANC technique. The updated 13N(p,{gamma})14O reaction rate is about 2.5 times larger than the standard REACLIB rate in the temperature range 0.1 < T9 < 0.3. The transition condition from the cold to hot CNO cycles has been determined with this updated rate. The influences incurred by this update have been investigated with two one-zone nova models.

  16. A sensitivity study of s-process: the impact of uncertainties from nuclear reaction rates

    NASA Astrophysics Data System (ADS)

    Vinyoles, N.; Serenelli, A.

    2016-01-01

    The slow neutron capture process (s-process) is responsible for the production of about half the elements beyond the Fe-peak. The production sites and the conditions under which the different components of s-process occur are relatively well established. A detailed quantitative understanding of s-process nucleosynthesis may yield light in physical processes, e.g. convection and mixing, taking place in the production sites. For this, it is important that the impact of uncertainties in the nuclear physics is well understood. In this work we perform a study of the sensitivity of s-process nucleosynthesis, with particular emphasis in the main component, on the nuclear reaction rates. Our aims are: to quantify the current uncertainties in the production factors of s-process elements originating from nuclear physics and, to identify key nuclear reactions that require more precise experimental determinations. In this work we studied two different production sites in which s-process occurs with very different neutron exposures: 1) a low-mass extremely metal-poor star during the He-core flash (nn reaching up to values of ∼ 1014cm-3); 2) the TP-AGB phase of a M⊙, Z=0.01 model, the typical site of the main s-process component (nn up to 108 — 109cm-3). In the first case, the main variation in the production of s-process elements comes from the neutron poisons and with relative variations around 30%-50%. In the second, the neutron poison are not as important because of the higher metallicity of the star that actually acts as a seed and therefore, the final error of the abundances are much lower around 10%-25%.

  17. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    NASA Astrophysics Data System (ADS)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of representative acceptor and donor molecules.

  18. Influence of changing particle structure on the rate of gas-solid gasification reactions. Final report, July 1981-March 1984

    SciTech Connect

    Not Available

    1984-04-04

    The objetive of this work is to determine the changes in the particle structure of coal as it undergoes the carbon/carbon dioxide reaction (C + CO/sub 2/ ..-->.. 2CO). Char was produced by heating the coal at a rate of 25/sup 0/C/min to the reaction temperatures of 800/sup 0/C, 900/sup 0/C, 1000/sup 0/C and 1100/sup 0/C. The changes in surface area and effective diffusivity as a result of devolitization were determined. Changes in effective diffusivity and surface area as a function of conversion have been measured for reactions conducted at 800, 900, 1000 and 1100/sup 0/C for Wyodak coal char. The surface areas exhibit a maximum as a function of conversion in all cases. For the reaction at 1000/sup 0/C the maximum in surface area is greater than the maxima determined at all other reaction temperatures. Thermogravimetric rate data were obtained for five coal chars; Wyodak, Wilcox, Cimmeron, Illinois number 6 and Pittsburgh number 6 over the temperature range 800-1100/sup 0/C. All coal chars exhibit a maximum in reaction rate. Five different models for gas-solid reactions were evaluated. The Bhatia/Perlmutter model seems to best represent the data. 129 references, 67 figures, 37 tables.

  19. Mixing Limited Reaction Rates in Radial Groundwater Flow Upscaled by the Lamella Approach at Continuum-Scales.

    NASA Astrophysics Data System (ADS)

    Ali, A. A. M.; Ginn, T. R.; Le Borgne, T.; Dentz, M.

    2014-12-01

    Upscaling mixing-limited reactive transport of injectates involved in in-situ groundwater treatment schemes remains challenging due to the non-commutation between averaging approaches and nonlinearities in the reaction rate expressions and due to the difficulty in quantifying mixing. The Eulerian effective plume model (macrodispersion model) generally overestimates the reaction rate due to the overestimated mixing of the plume, whereas Lagrangian particle or streamtube approaches do not provide an explicit means for keeping track of mixing extent. The lamella approach is a new modeling tool that overcomes the abovementioned shortcomings by combining mixing measures such as the scalar dissipation rate with a Lagrangian modeling focus on front-tracking. This approach involves dividing the moving interface between the displacing-displaced solutions into approximately linear segments (set of lamellae) on which the mixing-limited reactions take place and studying the transport mechanisms and the chemical reactions on them. This approach is summarized in application to idealized radial injection, where mixing between the injected and displaced solutions leads to calcite precipitation..The theoretical reaction rate found via the simplified lamella approach is compared with explicit simulation using a finite elements (COMSOL) framework fitted with the representative multicomponent equilibrium reaction network.

  20. Investigations of solvent properties and solvent effects on chemical equilibria and reaction rates

    NASA Astrophysics Data System (ADS)

    Defeo, Laura Lynn Thomas

    Thermodynamic and structural properties computed via simulations of pure liquids and dilute solutions are routinely used as a metric of accuracy for condensed-phase force fields and in the development and testing of new methodology. Additionally, reliable modeling of solvent systems is critical to investigations of physical phenomena, such as the elucidation of solvent effects on chemical equilibria and reaction rates. This dissertation highlights a series of studies that span these topics. The Lennard-Jones 12-6 functional form, often invoked to model van der Waals interactions, has been argued to be too repulsive at short internuclear separations. Monte Carlo simulations of organic liquids at various temperatures and pressures show that this function, in conjunction with OPLS parameters, is capable of reproducing experimental densities. In order to address potential cumulative deviations of computed properties and conformational differences between the gas phase and pure liquids, Monte Carlo simulations have been carried out for the homologous n-alkane series C4H10-C12H26 using the OPLS-AA force field. Favorable structural motifs of longer alkanes were also investigated to study self solvation in the gas phase. Next, an overview of the computation of free energy changes in solution using perturbation theory, overlap sampling, and related approximate methods is presented. Results are provided for free energies of hydration of OPLS-AA substituted benzenes in TIP4P water. For comparable amounts of computer time, the double-wide and overlap sampling methods yield very similar results. QM/MM simulations of the Diels-Alder reactions of cyclopentadiene with 1,4-naphthoquinone, methyl vinyl ketone, and acrylonitrile have been carried out at the water-vacuum interface and in the gas phase. The relative free energies of activation and transition structure geometries at the interface were intermediate between those calculated in the gas phase and in bulk water, consistent with estimated experimental rate constants. Energy pair distributions reveal a loss of slightly favorable solute-solvent pair contacts but retention of stronger interactions upon transition from bulk to surface hydration. These strong interactions cause the methyl vinyl ketone transition structure to preferentially orient its carbonyl toward the surface, while the other transition structures prefer orientations parallel to the surface.

  1. Experimental measurements of low temperature rate coefficients for neutral-neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: reactions of the CN radical.

    PubMed

    Morales, Sébastien B; Le Picard, Sébastien D; Canosa, André; Sims, Ian R

    2010-01-01

    The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions. Temperature dependences, different for each reaction, are compared to those used in the most recent photochemical models of Titan's atmosphere. PMID:21302546

  2. Chromo-fluorogenic detection of nerve-agent mimics using triggered cyclization reactions in push-pull dyes.

    PubMed

    Costero, Ana M; Parra, Margarita; Gil, Salvador; Gotor, Raúl; Mancini, Pedro M E; Martínez-Máñez, Ramón; Sancenón, Félix; Royo, Santiago

    2010-07-01

    A family of azo and stilbene derivatives (1-9) are synthesized, and their chromo-fluorogenic behavior in the presence of nerve-agent simulants, diethylchlorophosphate (DCP), diisopropylfluorophosphate (DFP), and diethylcyanophosphate (DCNP) in acetonitrile and mixed solution of water/acetonitrile (3:1 v/v) buffered at pH 5.6 with MES, is investigated. The prepared compounds contain 2-(2-N,N-dimethylaminophenyl)ethanol or 2-[(2-N,N-dimethylamino)phenoxy]ethanol reactive groups, which are part of the conjugated pi-system of the dyes and are able to give acylation reactions with phosphonate substrates followed by a rapid intramolecular N-alkylation. The nerve-agent mimic-triggered cyclization reaction transforms a dimethylamino group into a quaternary ammonium, inducing a change of the electronic properties of the delocalized systems that results in a hypsochromic shift of the absorption band of the dyes. Similar reactivity studies are also carried out with other "non-toxic" organophosphorus compounds, but no changes in the UV/Vis spectra were observed. The emission behaviour of the reagents in acetonitrile and water-acetonitrile 3:1 v/v mixtures is also studied in the presence of nerve-agent simulants and other organophosphorous derivatives. The reactivity between 1-9 and DCP, DCNP, or DFP in buffered water-acetonitrile 3:1 v/v solutions under pseudo first-order kinetic conditions, using an excess of the corresponding simulant, are studied in order to determine the rate constants (k) and the half-life times (t(1/2)=ln2/k) for the reaction. The detection limits in water/acetonitrile 3:1 v/v are also determined for 1-9 and DCP, DCNP, and DFP. Finally, the chromogenic detection of nerve agent simulants both in solution and in gas phase are tested using silica gel containing adsorbed compounds 1, 2, 3, 4, or 5 with fine results. PMID:20512798

  3. The Effect of Particle Size on Hydrolysis Reaction Rates and Rheological Properties in Cellulosic Slurries

    NASA Astrophysics Data System (ADS)

    Dasari, Rajesh K.; Berson, R. Eric

    The effect of varying initial particle sizes on enzymatic hydrolysis rates and rheological properties of sawdust slurries is investigated. Slurries with four particle size ranges (33 μm < x ≤ 75 μm, 150 μm < x ≤ 180 μm 295 μm < x ≤ 425 μm, and 590 μm < x ≤ 850 μm) were subjected to enzymatic hydrolysis using an enzyme dosage of filter paper units per gram of cellulose at 50°C and 250 rpm in shaker flasks. At lower initial particle sizes, higher enzymatic reaction rates and conversions of cellulose to glucose were observed. After 72 h 50 and 55% more glucose was produced from the smallest size particles than the largest size ones, for initial solids concentration of 10 and 13% (w/w), respectively. The effect of initial particle size on viscosity over a range of shear was also investigated. For equivalent initial solids concentration, smaller particle sizes result in lower viscosities such that at a concentration of 10% (w/w), the viscosity decreased from 3000 cP for 150 μm < x ≤ 180 μm particle size slurries to 61.4 cP for 33 μm < x ≤ 75 μm particle size slurries. Results indicate particle size reduction may provide a means for reducing the long residence time required for the enzymatic hydrolysis step in the conversion of biomass to ethanol. Furthermore, the corresponding reduction in viscosity may allow for higher solids loading and reduced reactor sizes during large-scale processing.

  4. Predicting reaction rate constants of ozone with organic compounds from radical structures

    NASA Astrophysics Data System (ADS)

    Yu, Xinliang; Yi, Bing; Wang, Xueye; Chen, Jianfang

    2012-05-01

    The reaction rate constants of ozone with organic compounds in the atmosphere were predicted by a quantitative structure-activity relationship (QSAR) model. Density functional theory (DFT) calculations, for the first time, were carried out on the radicals from organic compounds, at the UB3LYP level of theory with 6-31G(d) basis set. A set of quantum chemical descriptors calculated from the radicals, the energy of the highest occupied molecular orbital of beta spin states (EβHOMO), the molecular average polarizability (α), and the total energy (ET), were used to build the general QSAR model for aliphatic compounds, applying the genetic algorithm (GA) technique and support vector machine (SVM) regression. The root mean square errors (RMSE) are 0.680 for the training set (68 compounds), 0.777 for the validation set (36 compounds) and 0.709 for the test set (35 compounds). Investigated results indicate that the SVM model given here has good predictivity for aliphatic compounds.

  5. Change of Electroweak Nuclear Reaction Rates by CP- and Isospin Symmetry Breaking - A Model Calculation

    NASA Astrophysics Data System (ADS)

    Stumpf, Harald

    2006-09-01

    Based on the assumption that electroweak bosons, leptons and quarks possess a substructure of elementary fermionic constituents, in previous papers the effect of CP-symmetry breaking on the effective dynamics of these particles was calculated. Motivated by the phenomenological procedure in this paper, isospin symmetry breaking will be added and the physical consequences of these calculations will be discussed. The dynamical law of the fermionic constituents is given by a relativistically invariant nonlinear spinor field equation with local interaction, canonical quantization, selfregularization and probability interpretation. The corresponding effective dynamics is derived by algebraic weak mapping theorems. In contrast to the commonly applied modifications of the quark mass matrices, CP-symmetry breaking is introduced into this algebraic formalism by an inequivalent vacuum with respect to the CP-invariant case, represented by a modified spinor field propagator. This leads to an extension of the standard model as effective theory which contains besides the "electric" electroweak bosons additional "magnetic" electroweak bosons and corresponding interactions. If furthermore the isospin invariance of the propagator is broken too, it will be demonstrated in detail that in combination with CP-symmetry breaking this induces a considerable modification of electroweak nuclear reaction rates.

  6. Proteolysis inside the membrane is a rate-governed reaction not driven by substrate affinity

    PubMed Central

    Dickey, Seth W.; Baker, Rosanna P.; Cho, Sangwoo; Urban, Siniša

    2013-01-01

    SUMMARY Enzymatic cleavage of transmembrane anchors to release proteins from the membrane controls diverse signaling pathways and is implicated in over a dozen diseases. How catalysis works within the viscous, water-excluding, two-dimensional membrane is unknown. We developed an inducible reconstitution system to interrogate rhomboid proteolysis quantitatively within the membrane in real time. Remarkably, rhomboid proteases displayed no physiological affinity for substrates (Kd ~190 μM, or 0.1 mol%). Instead, ~10,000-fold differences in proteolytic efficiency with substrate mutants and diverse rhomboid proteases were reflected in kcat values alone. Analysis of gate-open mutant and solvent isotope effects revealed that substrate gating, not hydrolysis, is rate limiting. Ultimately a single proteolytic event within the membrane normally takes minutes. Rhomboid intramembrane proteolysis is thus a slow, kinetically controlled reaction not driven by transmembrane protein-protein affinity. These properties are unlike those of other studied proteases or membrane proteins but strikingly reminiscent of one subset of DNA-repair enzymes, raising important mechanistic and drug-design implications. PMID:24315097

  7. The rates of S(N)2 reactions and their relation to molecular and solvent properties.

    PubMed

    Arnaut, Luis G; Formosinho, Sebastião J

    2007-01-01

    The energy barriers of symmetrical methyl exchanges in the gas phase have been calculated with the reaction path of the intersecting/interacting-state model (ISM). Reactive bond lengths increase down a column of the Periodic Table and compensate for the decrease in the force constants, which explains the near constancy of the intrinsic barriers in the following series of nucleophiles: F(-) approximately Cl(-) approximately Br(-) approximately I(-). This compensation is absent along the rows of the Periodic Table and the trend in the reactivity is dominated by the increase in the electrophilicity index of the nucleophile in the series Crate constants in solution to be calculated with remarkable simplicity and accuracy. The relationship between the S(N)2 and electron-transfer mechanisms is clarified and it is shown that smaller solvent static effects should be expected for electron transfer in the absence of a thermodynamic driving force. PMID:17616960

  8. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption.

    PubMed

    Strmcnik, Dusan; Uchimura, Masanobu; Wang, Chao; Subbaraman, Ram; Danilovic, Nemanja; van der Vliet, Dennis; Paulikas, Arvydas P; Stamenkovic, Vojislav R; Markovic, Nenad M

    2013-04-01

    The development of hydrogen-based energy sources as viable alternatives to fossil-fuel technologies has revolutionized clean energy production using fuel cells. However, to date, the slow rate of the hydrogen oxidation reaction (HOR) in alkaline environments has hindered advances in alkaline fuel cell systems. Here, we address this by studying the trends in the activity of the HOR in alkaline environments. We demonstrate that it can be enhanced more than fivefold compared to state-of-the-art platinum catalysts. The maximum activity is found for materials (Ir and Pt₀.₁Ru₀.₉) with an optimal balance between the active sites that are required for the adsorption/dissociation of H₂ and for the adsorption of hydroxyl species (OHad). We propose that the more oxophilic sites on Ir (defects) and PtRu material (Ru atoms) electrodes facilitate the adsorption of OHad species. Those then react with the hydrogen intermediates (Had) that are adsorbed on more noble surface sites. PMID:23511418

  9. Astrophysical Reaction Rate for the Neutron-Generator Reaction {sup 13}C({alpha},n){sup 16}O in Asymptotic Giant Branch Stars

    SciTech Connect

    Johnson, E. D.; Rogachev, G. V.; Baby, L. T.; Cluff, W. T.; Crisp, A. M.; Diffenderfer, E.; Green, B. W.; Hinners, T.; Hoffman, C. R.; Kemper, K. W.; Momotyuk, O.; Peplowski, P.; Pipidis, A.; Reynolds, R.; Roeder, B. T.; Mukhamedzhanov, A. M.; Goldberg, V. Z.; Brown, S.

    2006-11-10

    The reaction {sup 13}C({alpha},n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2{sup +} 6.356 MeV subthreshold resonance in {sup 17}O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The {alpha}-particle ANC for the subthreshold state has been measured using the sub-Coulomb {alpha}-transfer reaction ({sup 6}Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.

  10. Asn-150 of Murine Erythroid 5-Aminolevulinate Synthase Modulates the Catalytic Balance between the Rates of the Reversible Reaction.

    PubMed

    Stojanovski, Bosko M; Ferreira, Gloria C

    2015-12-25

    5-Aminolevulinate synthase (ALAS) catalyzes the first step in mammalian heme biosynthesis, the pyridoxal 5'-phosphate (PLP)-dependent and reversible reaction between glycine and succinyl-CoA to generate CoA, CO2, and 5-aminolevulinate (ALA). Apart from coordinating the positioning of succinyl-CoA, Rhodobacter capsulatus ALAS Asn-85 has a proposed role in regulating the opening of an active site channel. Here, we constructed a library of murine erythroid ALAS variants with substitutions at the position occupied by the analogous bacterial asparagine, screened for ALAS function, and characterized the catalytic properties of the N150H and N150F variants. Quinonoid intermediate formation occurred with a significantly reduced rate for either the N150H- or N150F-catalyzed condensation of glycine with succinyl-CoA during a single turnover. The introduced mutations caused modifications in the ALAS active site such that the resulting variants tipped the balance between the forward- and reverse-catalyzed reactions. Although wild-type ALAS catalyzes the conversion of ALA into the quinonoid intermediate at a rate 6.3-fold slower than the formation of the same quinonoid intermediate from glycine and succinyl-CoA, the N150F variant catalyzes the forward reaction at a mere 1.2-fold faster rate than that of the reverse reaction, and the N150H variant reverses the rate values with a 1.7-fold faster rate for the reverse reaction than that for the forward reaction. We conclude that the evolutionary selection of Asn-150 was significant for optimizing the forward enzymatic reaction at the expense of the reverse, thus ensuring that ALA is predominantly available for heme biosynthesis. PMID:26511319

  11. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Astrophysics Data System (ADS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-04-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

  12. Gas-phase chemistry of benzyl alcohol: Reaction rate constants and products with OH radical and ozone

    NASA Astrophysics Data System (ADS)

    Harrison, Joel C.; Wells, J. R.

    A bimolecular rate constant, kOH+Benzyl alcohol, of (28 ± 7) × 10 -12 cm 3 molecule -1 s -1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with benzyl alcohol, at (297 ± 3) K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, kO3+Benzyl alcohol, of approximately 6 × 10 -19 cm 3 molecule -1 s -1 was determined by monitoring the decrease in benzyl alcohol concentration over time in an excess of ozone (O 3). To more clearly define part of benzyl alcohol's indoor environment degradation mechanism, the products of the benzyl alcohol + OH were also investigated. The derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N, O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to positively identify benzaldehyde, glyoxal and 4-oxopentanal as benzyl alcohol/OH reaction products. The elucidation of other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible benzyl alcohol/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms.

  13. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Technical Reports Server (NTRS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

  14. An Analogy Using Pennies and Dimes to Explain Chemical Kinetics Concepts

    ERIC Educational Resources Information Center

    Cortes-Figueroa, Jose E.; Perez, Wanda I.; Lopez, Jose R.; Moore-Russo, Deborah A.

    2011-01-01

    In this article, the authors present an analogy that uses coins and graphical analysis to teach kinetics concepts and resolve pseudo-first-order rate constants related to transition-metal complexes ligand-solvent exchange reactions. They describe an activity that is directed to upper-division undergraduate and graduate students. The activity…

  15. An Analogy Using Pennies and Dimes to Explain Chemical Kinetics Concepts

    ERIC Educational Resources Information Center

    Cortes-Figueroa, Jose E.; Perez, Wanda I.; Lopez, Jose R.; Moore-Russo, Deborah A.

    2011-01-01

    In this article, the authors present an analogy that uses coins and graphical analysis to teach kinetics concepts and resolve pseudo-first-order rate constants related to transition-metal complexes ligand-solvent exchange reactions. They describe an activity that is directed to upper-division undergraduate and graduate students. The activity

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

    PubMed Central

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

    2011-01-01

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

  17. Shell Model Based Reaction Rates for rp-PROCESS Nuclei in the Mass Range A=44-63

    NASA Astrophysics Data System (ADS)

    Fisker, J. L.; Barnard, V.; Görres, J.; Langanke, K.; Martínez-Pinedo, G.; Wiescher, M. C.

    2001-11-01

    We have used large-scale shell-model diagonalization calculations to determine the level spectra, proton spectroscopic factors, and electromagnetic transition probabilities for proton rich nuclei in the mass range A=44-63. Based on these results and the available experimental data, we calculated the resonances for proton capture reactions on neutron deficient nuclei in this mass range. We also calculated the direct capture processes on these nuclei in the framework of a Woods-Saxon potential model. Taking into account both resonant and direct contributions, we determined the ground-state proton capture reaction rates for these nuclei under hot hydrogen burning conditions for temperatures between 108 and 1010 K. The calculated compound-nucleus level properties and the reaction rates are presented here; the rates are also available in computer-readable format from the authors.

  18. Timescales and rates for peridotite-groundwater reactions in the Samail Ophiolite, Sultanate of Oman

    NASA Astrophysics Data System (ADS)

    Paukert, A. N.; Matter, J.; Stute, M.; Kelemen, P. B.

    2014-12-01

    The peridotite section of the Samail Ophiolite, Sultanate of Oman is a site of ongoing low temperature serpentinization and carbonation. We present geochemical data for waters collected from boreholes in the peridotite to help describe subsurface water-rock reactions and rates. We constrained groundwater age using 3H-3He dating, He accumulation, dissolved noble gas thermometry, and stable isotopes (δ2H, δ18O). Dissolved gas samples were collected from boreholes and used to estimate ongoing serpentinization rates. Boreholes in peridotite contain two water types: Type I Mg2+-HCO3- water and Type II Ca2+-OH- water. All of our groundwater dating techniques suggest boreholes with Type I water contain modern recharge. Type I boreholes have 3H-3He dates of 0-40 years, 3He/4He ratios similar to the atmosphere, and low levels of He accumulation. Noble gas thermometry shows recharge temperatures of 32oC, the modern mean annual ground temperature. Stable isotopes in Type I waters fall between the northern and southern local meteoric water lines, similar to other modern northern Oman groundwaters (Weyhenmeyer et al., Wat. Resour. Res., 2002). In contrast, Type II hyperalkaline groundwaters from boreholes in peridotite appear to be significantly older. Waters have pre-bomb 3H levels, and significant He accumulation from sources such as crustal production from radioactive decay or mantle He. Noble gas temperatures range from 30oC to 25oC, with the cooler samples potentially having recharged during a glacial period. Stable isotopes for Type II waters plot either between the northern and southern meteoric water lines or are enriched in δ18O. The enrichment may be due to evaporation or a change in the source of local water vapor during glacial periods. Dissolved gases from boreholes with Type I water are primarily N2, while gases from boreholes with Type II water include millimolar concentrations of H2, CH4, or both. These dissolved gases suggest the Type II boreholes are in or near areas of active low temperature serpentinization. Serpentinization rates calculated from dissolved gas concentrations and groundwater flow vary from 4x10-8 to 2x10-6 volume fraction peridotite serpentinized per year.

  19. An effective rate equation approach to reaction kinetics in small volumes: theory and application to biochemical reactions in nonequilibrium steady-state conditions.

    PubMed

    Grima, R

    2010-07-21

    Chemical master equations provide a mathematical description of stochastic reaction kinetics in well-mixed conditions. They are a valid description over length scales that are larger than the reactive mean free path and thus describe kinetics in compartments of mesoscopic and macroscopic dimensions. The trajectories of the stochastic chemical processes described by the master equation can be ensemble-averaged to obtain the average number density of chemical species, i.e., the true concentration, at any spatial scale of interest. For macroscopic volumes, the true concentration is very well approximated by the solution of the corresponding deterministic and macroscopic rate equations, i.e., the macroscopic concentration. However, this equivalence breaks down for mesoscopic volumes. These deviations are particularly significant for open systems and cannot be calculated via the Fokker-Planck or linear-noise approximations of the master equation. We utilize the system-size expansion including terms of the order of Omega(-1/2) to derive a set of differential equations whose solution approximates the true concentration as given by the master equation. These equations are valid in any open or closed chemical reaction network and at both the mesoscopic and macroscopic scales. In the limit of large volumes, the effective mesoscopic rate equations become precisely equal to the conventional macroscopic rate equations. We compare the three formalisms of effective mesoscopic rate equations, conventional rate equations, and chemical master equations by applying them to several biochemical reaction systems (homodimeric and heterodimeric protein-protein interactions, series of sequential enzyme reactions, and positive feedback loops) in nonequilibrium steady-state conditions. In all cases, we find that the effective mesoscopic rate equations can predict very well the true concentration of a chemical species. This provides a useful method by which one can quickly determine the regions of parameter space in which there are maximum differences between the solutions of the master equation and the corresponding rate equations. We show that these differences depend sensitively on the Fano factors and on the inherent structure and topology of the chemical network. The theory of effective mesoscopic rate equations generalizes the conventional rate equations of physical chemistry to describe kinetics in systems of mesoscopic size such as biological cells. PMID:20649359

  20. Determination of the astrophysical 12N(p,γ)13O reaction rate from the 2H(12N,13O)n reaction and its astrophysical implications

    NASA Astrophysics Data System (ADS)

    Guo, B.; Su, J.; Li, Z. H.; Wang, Y. B.; Yan, S. Q.; Li, Y. J.; Shu, N. C.; Han, Y. L.; Bai, X. X.; Chen, Y. S.; Liu, W. P.; Yamaguchi, H.; Binh, D. N.; Hashimoto, T.; Hayakawa, S.; Kahl, D.; Kubono, S.; He, J. J.; Hu, J.; Xu, S. W.; Iwasa, N.; Kume, N.; Li, Z. H.

    2013-01-01

    The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The 12N(p,γ)13O reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3α process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the 2H(12N, 13O)n proton transfer reaction at Ec.m.=8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of 13Og.s. → 12N+p was extracted to be 3.92±1.47 fm-1 from the measured angular distribution and utilized to compute the direct component in the 12N(p,γ)13O reaction. The direct astrophysical S factor at zero energy was then found to be 0.39±0.15 keV b. By considering the direct capture into the ground state of 13O, the resonant capture via the first excited state of 13O and their interference, we determined the total astrophysical S factors and rates of the 12N(p,γ)13O reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that 12N(p,γ)13O will only compete successfully with the β+ decay of 12N at higher (˜2 orders of magnitude) densities than initially predicted.