bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study of the D + H2 (v = 1) reaction by CARS spectroscopy
Authors: Dreier T. , Wolfrum J. 
Published: January 2005

AbstractThe reactions D + H2 (v = 0, 1) → HD (v = 0, 1) + H have been studiedin a discharge flow reactor by CARS‐spectroscopy. For H2(v = 0) molecules a rate constant of (4, 0 ± 1, 0) 10−16 cm3 s−1 is obtained at 310 K from measured HD (v = 0, 1) product yields. Keeping the degree of vibrational excitation of H2in the microwave discharge in the range of 1% from the increase of the HD (v = 0, 1) CARS signals a rate of k2a, b = (1, 0 ± 0, 4) 10−13cm3 s−1 is derived. The total consumption of H2 (v = 1) in the presence of D atoms gives a rate k2 = (1, 9 ± 0, 2) 10−13 cm3 s−1 at 310 K. The resultsare discussed in regard to previous measurements and theoretical treatments.
State‐to‐state dynamics of the hydrogen exchange reaction
Authors: Valentini James J. , Gerrity Daniel P. 
Published: January 2005

AbstractNascent product quantum state distributions have been measured for reactive, H + D2 → HD + D, and inelastic, H + D2 → D2‡ + H, collisions of H with D2, at collision energies of 0.98 eV, 1.1 eV, and 1.3 eV. These distributions are extracted from coherent anti‐Stokes Raman scattering (CARS) spectra of HD and D2 (recorded under single‐collision conditions) following laser photodissociation of HI to generate translationally hot H atoms in a D2/HI gas mixture. Variation of the photolysis wavelength allows selection of the H atom translational energy. These rotational and vibrational state distributions are compared with those obtained from quasiclassical trajectory calculations on an ab initio potential energy surface. The agreement between the calculated and measured distributions is extremely good. TheHD and D2 product quantum state distributions are well represented by simple linear surprisal functions, with large positive vibrational and rotational surprisal.
Total reaction probabilities for translationally hot (3.7 eV)D atoms reacting with H2 and their astrophysical implications
Authors: Mayne Howard R. , Prasad Sheo S. 
Published: January 2005

AbstractTranslationally hot (3.7 eV center‐of‐mass collision energy) D atoms can be produced by the dissociative recombinationsof DCO+ ions with electrons in interstellar clouds. The reactions of hot D atoms with H2 molecules is an important factor in determining the D to H abundance ratio in the universe from observations of deuterated species in dense interstellar clouds. A simulation of this reaction has been carried out using exact quasiclassical reaction cross sections, together with a series of approximate total collision cross sections. It was found that the total probability of reaction, PR, at 3.7 eV was approximately 0.4. A reaction probability of this magnitude suggeststhat the loss of D atoms by the title reaction be considered in astrochemical modeling of deuterated molecules.
A quasiclassical trajectory study of the collisional dissociation of H2 by H atoms
Authors: Dove John E. , Mandy Margot E. 
Published: January 2005

AbstractThe collision induced dissociation of H2 by H atoms was studied by quasiclassical trajectories using the Liu‐Siegbahn‐Truhlar‐Horowitz potential energy surface. Dissociation cross sections were obtained for five highly internally excited initial states of H2 for translational energies up to 100 kcal mol−1. Rate constants for dissociation out of these states were calculated for temperatures of 1000 to 10,000 K. Initial internal energy strongly enhances the probability of collisional dissociation, vibrational energy being more effective than rotational. The results are compared to those from a similar study of the H2−He system, and are discussed in relation tothe respective potential energy surfaces. The implications for the kineticsof thermal dissociation are also considered.
Rates of addition of tert‐butyl and pivaloyl radicals to acrylonitrile measured by modulated ESR and μSR spectroscopy
Authors: Jent F. , Paul H. , Roduner E. , Heming M. , Fischer H. 
Published: January 2005

AbstractFor the rate constant of addition of tert‐butyl radicals to acrylonitrile at T = 300 K in solution modulated ESR spectroscopy and muon spin rotation yield 106 M−1 s−1 and 2.4 × 106 M−1 s−1. The addition of pivaloyl radical to acrylonitrile proceeds with Arrhenius parameters log A/M−1 s−1 = 7.7 and Ea = 11.5 kJ/ mol. The results are discussed in terms of polar effects in radical addition reactions.
Importance of enolate anions in the high‐pressure kinetics of nitroalkanes and nitroaromatics
Authors: Engelke Ray , Earl William L. , Rohlfing Celeste McMichael 
Published: January 2005

AbstractWe review and systematize experimental evidence concerning the extreme high‐pressure kinetics of condensed phase nitroalkanes and nitroaromatics. This systematization suggests that enolate aci anions of the nitroalkanes and enolate aci‐quinone anions of the nitroaromatics are important in the initial high‐pressure kinetics of such systems. Kinetic data from experiments which observed the effect of: (1) small amounts of chemical additives, (2) substitution for protons, (3) difference in chemical isomer, (4) exposure to ultra‐violet light, and (5) application of very high pressure can all be rationalized within the framework of our hypothesis. We suggest a static high‐pressure ultra‐violet absorption spectroscopy experiment on nitromethane that would test the proposed hypothesis.
A comparison of various methods for calculating unimolecular reaction rate constants
Authors: Weston Ralph E. 
Published: January 2005

AbstractA test of the Kassel quantum expressions for unimolecular rate constants and densities of vibrational states is described. Rate constants are calculated for nine reactions previously used in such tests, over a wide range of temperatures and pressures. The Kassel expression using the geometric mean of the molecular vibration frequencies is generally found to give better results than that using the arithmetic mean.
The O + NH3reaction: A review
Authors: Cohen N. 
Published: January 2005

AbstractExperimental data for the reaction of O atoms with NH3have been reviewed with particular attention to the possible effects of secondary reactions on the deduced rate coefficient. A reaction mechanism was assembled and computer calculations carried out to simulate several sets of experiments. The sensitivity of the calculations to uncertainties in the various rate coefficients was assessed. Transition‐state theory calculations were carried out on the rate coefficientk1for the O + NH3→ OH + NH2reaction. These studies suggest that the reaction stoichiometry is dependent on temperature, initial reagent ratios, and extent of reaction; that available data are not sufficient to determine whether the initial step is H‐atom abstraction (producing OH and NH2radicals) or O‐atom addition (producing an NH3O* complex): and that the low temperature values ofk1(T⩽ 400 K) are not consistent with values deduced at higher temperatures if the reaction proceeds by H‐atom abstraction. Taking all the evidence into account, it is recommended that the expression 1.1 × 103T2.1exp(−2620/T) L mol−1s−1be used fork1until more definitive experimental measurements are made at low temperatures.
The mechanism of thermal eliminations part XXIII: [1] The thermal decomposition of pyruvic acid
Authors: Taylor Roger 
Published: January 2005

AbstractThe thermal decomposition of pyruvic acid into carbon dioxide and acetaldehyde is a unimolecular first‐order reaction and takes place according to the rate equation, logk = 13.53–41,250/4.575 K. These parameters contrast markedly with those recently reported, viz. logk = 7.19–27,700/4.575 K and confirm that the latter, which gave an unacceptably low value for the frequency factor, are anomalous. The lower reactivity of pyruvic acid compared to oxalic acid is interpreted in terms of normal electronic effects.
Data on the thermochemistry of azoalkanes
Authors: Ács G. , Péter A. 
Published: January 2005

AbstractThe rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetrical azoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔHƒ (CH3N2) = 51.5 ± 1.8 kcal mol−1, ΔHƒ (C2H5N2) = 44.8 ± 2.5 kcal mol−1, ΔHƒ (2−C3H7N2) = 37.9 ± 2.2 kcal mol−1, [NA‐(C)] = 27.6 ± 3.7 kcal mol−1, [NA‐(ṄA) (C)] = 61.2 ± 3.1 kcal mol−1.
The effect of methanol on the self reaction of HO2 radicals
Authors: Andersson B. Y. , Cox R. A. , Jenkin M. E. 
Published: January 2005

AbstractThe rate constant for the HO2 self reaction has been determined as a function of methanol vapor concentration at 278 K and 299 K. A molecular modulation technique was used in which HO2 radicals were photochemically produced in flowing gas mixtures comprised of Cl2, CH3OH, N2 and O2 with HO2 monitored in the UV at 220 nm. A positive linear dependence of the second order rate constant on methanol concentration was found and this effect increased with decreasing temperature. The rate constant for the HO2 self reaction can be described by

in nitrogen at atmospheric pressure and in the methanol concentration range 1 · 1016 to 3 · 1017 molecules cm−3.
Thermal isomerization of azulene to naphthalene in shock waves
Authors: Brouwer L. , Troe J. 
Published: January 2005

AbstractThe thermal isomerization of azulene was studied in shock waves over the range 1300–1900 K. Monitoring azulene and naphthalene light absorptions in the UV, a complete conversion azulene → naphthalene was observed. After correction for some falloff effects, a limiting high pressure rate constant kx = 1012.93 exp(−263 kJ mol−1/RT) s−1 was derived. Based on this kx, specific rate constants k(E) for photoexcitation experiments were constructed.
High temperature collisional energy transfer in highly vibrationally excited molecules. III: Isotope effects in tert‐butyl bromide systems
Authors: Brown Trevor C. , King Keith D. , Gilbert Robert G. 
Published: January 2005

AbstractChanges in the magnitude of 〈ΔEdown〉, the average downward collisional energy transferred between a highly vibrationally excited reactant molecule and an inert bath gas, upon perdeuteration of the substrate are reported for tert‐butyl bromide dilute in Ar, Kr, N2, and CO2. The technique of pressure‐dependent very low‐pressure pyrolysis (VLPP) was used to obtain the absolute values of 〈ΔEdown〉, which are for C4H9Br, 230 (Ar), 285 (Kr), 270 (N2), and 365 (CO2) while for C4D9Br, 200 (Ar), 250 (Kr), 220 (N2), and 335 (CO2), all in cm−1 at ca. 720 K. The estimated uncertainties in these values are ca. ± 10%. These observed 〈ΔEdown〉, values and trends found with results from this series of isotope studies, are compared with current theoretical models. Extrapolated high‐pressure temperature‐dependent rate coefficients (s−1) for the thermal decomposition of reactant are 1013.8±0.3 exp(−175 ± 8 kJ mol−1/RT) for C4H9Br and 1014.3±0.3 exp(−183 ± 8 kJ mol−1/RT) for C4D9Br. These results are in accord with other studies and the expected isotope effect.
Kinetic study of the recombination reaction OD + NO2 + M → DNO3 + M
Authors: Bossard Alain R. , Singleton Donald L. , Paraskevopoulos George 
Published: January 2005

AbstractRate constants for the recombination reaction OD + NO2 + M → DNO3 + M have been determined in the falloff region (5–500 torr) and at 297 ± 2 K, in the presence of He, N2, and SF6 as third bodies, by using a pulsed laser photolysis‐resonance absorption technique. Values of k0, kx and the falloff parameter Fc have been estimated. Our rate constants were, within the experimental uncertainty, the same as those reported for the reaction of OH radicals with NO2.
Kinetics and mechanism of the alkali metal ions promoted electron transfer between 12‐tungstocobaltate(III) and citric acid
Authors: Saha Swapan K. , Ghosh Manik C. , Banerjee Pradyot 
Published: January 2005

AbstractThe kinetics of the interactions of the Keggin type heteropolyanion [CoW12O40]5−, with all the molecular and anionic forms of citric acid have been investigated spectrophotometrically in the pH range 0.60–5.45 at 60°C. With the exception of the molecular form of the acid (H3L), all the other species (H2L−, HL2−, and L3−) undergo oxidation through an alkali metal ion catalyzed path in addition to the uncatalyzed one. The catalytic power increases with increasing size of the alkali metal ion. The contributions of each path have been evaluated from the kinetic data with the help of the measured dissociation constant values of citric acid. A plausible mechanism involving the formation of a bridged outer‐sphere complex of the reacting species with the alkali cation, has been suggested. The observed limiting dependence of kobs on [citrate] at high concentrations owing to an equilibrium between the reactants preceeding the electron transfer step supports the proposed mechanism. The pH‐rate profile gives an excellent fit with the evaluated kinetic parameters.
Kinetics and thermochemistry of the methyl radical: Study of the CH3 + HCl reaction
Authors: Russell John J. , Seetula Jorma A. , Senkan Selim M. , Gutman David 
Published: January 2005

AbstractThe kinetics of the reaction between CH3 and HCl was studied in a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature (296–495 K) and were fitted to an Arrhenius expression: k1 = 5.0(±0.7) × 10−13 exp{−1.4(±0.3) kcal mol−1/RT} cm3 molecule−1 s−1. This information was combined with known kinetic parameters of the reverse reaction to obtain Second Law determinations of the methyl radical heat of formation {34.7(±0.6) kcal mol−1} and entropy {46(±2) cal mol−1 K−1} at 298 K. Using the known entropy of CH3, a more accurate Third Law determination of the CH3 heat of formation at this temperature was also obtained {34.8(±0.3) kcal mol−1}. The values of k1 obtained in this study are between those reported in prior investigations. The results were also used to test the accuracy of the thermochemical information which can be obtained from kinetic studies of R + HX (X = Cl, Br, I) reactions of the type described here.
A kinetic study of the air oxidation of pyrogallol and purpurogallin
Authors: Abrash Henry I. , Shih Dorcas , Elias Woodrow , Malekmehr Farshad 
Published: January 2005

AbstractPyrogallol (1,2.3‐benzentriol, 1) reacts with dioxygen in weakly alkaline solutions to form purpurogallin (2,3,4,6‐tetrahydroxy‐5H‐benzocycloheptene‐5‐one, 2) which then reacts to form purpurogalloquinone (3) which then decays to a product absorbing at 440 nm. The formation of 3 requires 1.5 mol O2 per mol 1, and 1.0 mol per mol 2. No O2 is consumed during the decay of 3, and this reaction, being insensitive to O2 concentrations and the presence of both superoxide dismutase (SOD) and catalase, does not appear to be an oxidation. The first‐order rate of decay of 3 decreases with increasing pH. 1 and 3 react at pH 9.0 with a second‐order rate constant of ca. 100 M−1 s−1. SOD inhibits the oxidation of 1 and 2. Slight and variable apparent inhibition of the oxidation of 2 and 3 by SOD may be due to trace impurities in 2, but not contamination by 1. The peak concentration of 3 is attained more rapidly during the oxidation of 1 than during the oxidation of 2. A kinetic scheme based on parallel oxidation of 1 by dioxygen and superoxide, and it which the semiquinone of 1 oxidizes 2, is partially successful in simulating the observed kinetic behavior.
Thermal decomposition of propyne and allene in shock waves
Authors: Hidaka Yoshiaki , Nakamura Takuji , Miyauchi Aya , Shiraishi Toshihiko , Kawano Hiroyuki 
Published: January 2005

AbstractPropyne (p‐C3H4) or allene (a‐C3H4) mixtures, highly diluted with Ar, were heated to the temperature range 1200–1570 K at pressures of 1.7–2.6 atm behind reflected shock waves. The thermal decompositions of propyne and allene were studied by both measuring the profiles of the IR emission at 3.48 μm or 5.18 μm and analyzing the concentrations of reacted gas mixtures. The mechanism and the rate constant expressions were discussed from both the profiles and the concentrations of reactant and products obtained. The rate constant expressions for reactions, (1) p‐C3H4 → a‐C3H4, (−1) a‐C3H4 → p‐C3H4, and (5) p‐C3H4 + H → CH3 + C2H2 were evaluated.
Unusual selectivities of radical reactions. Experimental studies on alkyl versus phenoxyl reaction systems
Authors: Rüegge Daniel , Fischer Hanns 
Published: January 2005

AbstractRadical reactions involving two or more intermediates and many mutual reaction channels may lead to the specific formation of one cross‐reaction product if one species is rather persistent and if transient and persistent species are produced with equal rates. A previous kinetic analysis of the phenomenon revealed that the concentrations of the intermediates and the selectivities of product formation depend critically on the relative initiation rates. The present experimental ESR studies on systems involving simultaneously generated phenoxyl radicals as persistent and alkyl radicals as transient species confirm the predicted behavior. They also lead to absolute rate constants for reactions of alkyl with phenoxyl radicals and for hydrogen atom transfer from phenols to alkyl radicals.
The production of chlorine atoms from the reaction of OH with chlorinated hydrocarbons
Authors: Kleindienst Tadeusz E. , Shepson Paul B. , Nero Chris M. , Bufalini Joseph J. 
Published: January 2005

AbstractMeasurements from previous studies have shown that when hydroxyl radicals react with various chlorinated hydrocarbons under atmospheric conditions, free chlorine atoms can be produced. In one such study (Edney et al., [3]) from an analysis of the rate equations under a strict set of assumptions, Cl‐atom yields could be inferred. Since the approach was indirect, a more direct method for obtaining these yields has been developed. The technique described in this study involves scavenging Cl atoms produced by the reaction (using ethylene or propylene as the scavenger) and then measuring the yield of the stable chlorinated product generated. Cl‐atom yields were determined for allyl chloride, vinyl chloride, vinylidene chloride, trichloroethylene, and benzyl chloride. The experiments were performed by irradiating mixtures of CH3ONO/NO/chlorinated hydrocarbon/alkene in air in 150‐L Teflon chambers. The yields for the reaction of Cl atoms with the alkenes generating the stable products were determined in seperate experiments. Yields for the formation of Cl atoms upon reaction with hydroxyl radicals are as follows (with 1 σ deviation): allyl chloride: 0.37 ± 0.10, vinyl chloride: 0.04 ± 0.01, vinylidene chloride: 0.23 ± 0.09, trichloroethylene: 0.63 ± 0.34, and benzyl chloride: 0.08 ± 0.03.
Predicting the preexponential temperature dependence of bimolecular metathesis reaction rate coefficients using transition state theory
Authors: Cohen N. 
Published: January 2005

AbstractThe thermochemical kinetics formulation of conventional transition state theory for bimolecular reactions allows for a separate contribution from each degree of freedom (translation, rotation, vibration, etc.) in the activated complex to the entropy and heat capacity of activation, and thus to the preexponential terms in the Arrhenius rate expression, k = ATn exp(−B/T). The number of vibrations and (possibly hindred) internal rotations varies depending on the nature of the reaction: atom + diatom, diatom + linear polyatom, etc. The temperature exponent n can be evaluated explicitly for each type of reaction if the harmonic oscillator‐rigid free rotor approximation is valid for the reagents and activated complex and if the contribution from tunneling is small. Various reaction types are examined successively, and n is evaluated for each case. The possible contributions of other factors (vibrational anharmonicity, hindered internal rotation, tunneling, “looseness” of activated complex) to the value of n are also considered.
A relative rate study of the reaction of bromine atoms with a variety of organic compounds at 295 K
Authors: Wallington Timothy J. , Skewes Loretta M. , Siegl Walter O. , Japar Steven M. 
Published: January 2005

AbstractThe relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i‐butane or acetaldehyde or both. Using rate constants of 1.74 × 10−15 and 3.5 × 10−12 cm3 molecule−1 s−1 for the reaction of Br with i−butane and acetaldehyde respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: 2, 3−dimethylbutane, (6.40 ± 0.77) × 10−15; cyclopentane, (1.16 ± 0.18) × 10−15, ethene, (≤2.3 × 10−13); propene, (3.85 ± 0.41) × 10−12; trans‐2‐butene, (9.50 ± 0.76) × 10−12, acetylene, (5.15 ± 0.19) × 10−15; and propionaldehyde, (9.73 ± 0.91) × 10−12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals.
A product study of the gas‐phase reaction of methyl vinyl ketone with the OH radical in the presence of NOx
Authors: Tuazon Ernesto C. , Atkinson Roger 
Published: January 2005

AbstractThe gas‐phase reaction of methyl vinyl ketone with the OH radical, in the presence of NOx, was investigated at 298 ± 2 K and atmospheric pressure of air. Glycolaldehyde and methylglyoxal were observed to be the major products, with a combined yield of 0.89 ± 0.16. The sum of the yields of the two other main products, formaldehyde and peroxyacetyl nitrate, were found to be essentially unity. The product yield data for glycolaldehyde and methylglyoxal indicate that OH radical addition to the terminal carbon atom of the >CC< bond accounts for 72 ± 21% of the overall reaction, with the remaining 28 ± 9% proceeding via addition to the inner carbon atom of the double bond.
Incubation in cyclohexene decomposition at high temperatures
Authors: Shi Jichun , Barker John R. 
Published: January 2005

AbstractA detailed master equation simulation has been carried out for the thermal unimolecular decomposition of C6H10 in a shock tube. At the highest temperatures studied experimentally [J. H. Kiefer and J. N. Shah, J. Phys. Chem., 91, 3024 (1987)], the average thermal vibrational energy is greater than the reaction threshold and therefore 〈ΔE〉 (up and down steps) is positive for molecules at that energy, rather than negative; the converse is true at lower temperatures. The calculated incubation time, in which the decomposition rate constant rises to 1/e of its steady state value, is found to be only weakly dependent on temperature (at constant pressure) between 1500 K and 2000 K and to depend almost exclusively on 〈ΔE〉d (down steps, only), and not on collision probability model. Simulations of the experimental data show the magnitude of 〈ΔE〉d depends weakly on assumed collision probability model, but is nearly independent of temperature. The second moment 〈ΔE〉½ is found to be independent of both temperature and transition probability model. The experimental data are not very sensitive to the possible energy‐dependence of 〈ΔE〉d for a wide range of assumptions. It is concluded that the observed experimental “delay times” probably can be identified with the incubation time; further experiments are desirable to test this possibility and obtain more direct measures of the incubation time.