bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of nitrous acid and nitric oxide in the heterogeneous dark reaction of nitrogen dioxide and water vapor in a smog chamber
Authors: Sakamaki Fumio , Hatakeyama Shiro , Akimoto Hajime
Published: January 2005

The dark reaction of NOx and H2O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO2 and H2O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO2 and H2O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO2 and H218O gave H18ONO exclusively. Taking into consideration the heterogeneous reaction of NO2 and H2O, the upper limit of the rate constant of the third‐order reaction NO + NO2 + H2O → 2HONO was deduced to be (3.0 ± 1.4) × 10−10 ppm−2‐min−1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO2 and H2O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.
Kinetics and mechanism of the reactions of the superoxide ion in solutions. II. The kinetics of protonation of the superoxide ion by water and ethanol
Authors: Afanas′ev I. B. , Kuprianova N. S.
Published: January 2005

The rate constants for the protonation of “free” (that is, solvated) superoxide ions by water and ethanol are equal to 0.5–3.5 ×10−3M−1·s−1 in DMF and AN at 20º. It has been found that the protonation rates for the ion pairs of \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} with the Bu4N+ cation are much slower than those for “free” \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document}. It is suggested that the effects of aprotic solvents on the protonation rates of \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} are mainly due to the fact that the proton donors form solvated complexes of different stability in these solvents.
Methyl thiirane: Kinetic gas‐phase titration of sulfur atoms in SX OY systems
Authors: Martinez Richard I. , Herron John T.
Published: January 2005

The reaction SO + SO →l S + SO2(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C3H6 produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k2 ≃ 3.5 × 10−15 cm3/s at 298 K.
The azoethane‐initiated thermal reaction of isobutene. Heat of formation of the 2‐methyl‐2‐pentyl radical
Authors: Seres L. , Görgényi M. , Farkas J.
Published: January 2005

The azoethane‐sensitized thermal reaction of isobutene has been studied at 526–565 K. The initial concentrations of azoethane and isobutene were in the ranges of 1.40–10.5 × 10−4 and 6.78–26.6 × 10−4 mol/dm3, respectively. From the initial rates of formation of ethane and 2‐methylpentane the heat of formation of the 2‐methyl‐2‐pentyl radical was determined. The result obtained is ±H(2‐methyl‐2‐pentyl) = 0.8 ± 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S0(2‐methyl‐2 pentyl) = 92.8 ± 1.5 cal/mol°K. The results support the high heat of formation of the t‐butyl radical suggested by different authors.
Gas‐phase thermal isomerization of hexachlorocyclopropane
Authors: Cosa Juan José , Hamity Mauricio
Published: January 2005

The gas‐phase thermal isomerization of hexachlorocyclopropane to hexachloropropene at 208–283°C is first order and unaffected by changes in the surface‐to‐volume ratio or by the addition of iodine, tetrachloroethylene, and oxygen. The first‐order rate constants fit the Arrhenius equationThe reaction was interpreted as an unimolecular process taking place with chlorine atom migration. A comparison of the reactivities of several chlorocyclopropanes is made.
Laser‐induced kinetics: Arrhenius parameters for t‐C4H9 + XI → i‐C4H9X + I (X = H,D) and the Heat of Formation of the t‐butyl radical
Authors: Rossi M. J. , Golden D. M.
Published: January 2005

The metathesis reaction of DI with t‐C4H9 generated by 351‐nm photolysis of 2,2′‐azoisopropane was studied in a low‐pressure reactor (VLPϕ Knudsen cell) in the temperature range of 302–411 K. The data obeyed the following Arrhenius relation when combined with recent data by Rossi and Golden gathered by the same technique (t‐C4H9 by thermal decomposition of 2,2′‐azoisobutane): log k2D(M−1s−1) = 9.60 – 1.90/θ, where θ = 2.303RT kcal/mol for 302 K < T > 722 K. The metathesis reaction of HI with t‐C4H9 was studied at 301 K and resulted in k2H(M−1·s−1) = (3.20 ± 0.62) × 108. An analogous Arrhenius relation was calculated for the protiated system if the small primary isotope effect k2H/k2D was assumed to be √2 at 700 K. It was of the following form: log k2H(M−1·s−1) = 9.73 – 1.68/θ.

Preliminary data of Bracey and Walsh indicate that earlier Arrhenius parameters determined for the reverse reaction are somewhat in error. Their value of log k1(M−1·s−1) = 11.5 – 23.8/θ yields 7delta;Hf,3000(t‐butyl) = 9.2 kcal/mol and S3000(t‐butyl) = 74.2 cal/mol7°K when taken in conjuction with this study.
Kinetics of the reaction of OH with pernitric and nitric acids
Authors: Smith C. A. , Molina L. T. , Lamb J. J. , Molina M. J.
Published: January 2005

The absolute rate constants for the reactions of OH + HO2NO2 (1) and OH + HNO3 (2) have been measured with the technique of flash photolysis resonance fluorescence over the temperature ranges of 240–330 K at 760 torr He for reaction (1) and of 240–370 K at 50 and 760 torr He for reaction (2). Reactant concentrations were monitored continuously by ultraviolet and infrared spectrophotometry. The data can be fitted to the following Arrhenius expressions:

These results are in very good agreement with recent studies of reaction (2), and also of reaction (1) at 295 K.
Steric influence in the direction of elimination of gas‐phase pyrolyses of several highly branched secondary acetates
Authors: Arcila Carolina , Pino Maria , Lubinkowski Jacek , Hernandez A Jose Adan , Chuchani Gabriel
Published: January 2005

The rate coefficients for the gas‐phase pyrolyses of a series of structurally related secondary acetates have been measured in a static system over the temperature range of 289.1–359.5°C and the pressure range 50.0–203.0 torr. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3‐hexyl acetate, log k1 (s−) = (12.12 ± 0.33) − (176.1 ± 3.9)kJ/mol/2.203RT; for 5‐methyl‐3‐hexyl acetate, log k1 (s−) = (13.17 ± 0.20) − (186.2 ± 2.3)kJ/mol/2.303RT; and for 5,5‐dimethyl‐3‐hexyl acetate, log k1 (s−) = (12.70 ± 0.19) − (177.4 ± 2.2)kJ/mol/2.303RT. The direction of elimination of these esters has shown from the invariability of olefin distributions at different temperatures and percentages of decomposition that steric hindrance is a determining factor in the eclipsed cis conformation. Moreover, a more detailed analysis indicates that the greater the alkyl–alkyl interaction, the less favored the elimination tends to be. Otherwise, an increase of alkyl–hydrogen interaction caused steric acceleration to be the determining factor.
Electron transfer from α‐aminoalkyl radicals to methyl viologen
Authors: Kim‐Thuan Nguyen , Scaiano J. C.
Published: January 2005

The reactions of tert‐butoxyl radicals with amines, leading to the formation of α‐aminoalkyl radicals, and the reactions of these with the electron acceptor methyl viologen have been examined using laser flash photolysis techniques. For example, the radicals CH3ĊHNEt2 and HOCH2ĊH N(CH2CH2OH)2 react with methyl viologen with rate constants equal to (1.3 ± 0.1) × 109 and (2.1 ± 0.4) × 109M−1 · s−1, respectively, in wet acetonitrile at 300 K.
Product formation in the association reaction of ClO with NO2 investigated by diode laser kinetic spectroscopy
Authors: Cox R. A. , Burrows J. P. , Coker G. B.
Published: January 2005

Diode laser spectroscopy has been employed to monitor the formation of chlorine nitrate (ClONO2) in the association reaction of ClO with NO2. Chlorine nitrate is the only stable end‐product of this reaction at room temperature. Time‐resolved measurements of ClONO2 formation using molecular modulation showed no evidence for any involvement of unstable isomers of ClNO3 in the reaction. These measurements gave a value of k1 = (1.8 ± 0.4) × 10−31 cm6/molecule2 · s for the reaction

at 295 K and an upper limit of 5 ms for the lifetime of any isomeric products at this temperature.
Experimental determination of the energy distribution of activated molecules. Extensive test of hard‐collision approximations
Authors: Becerra R. , Figuera J. M. , Martín M. , Rodríguez J. C.
Published: January 2005

The approximations developed to determine the energy distribution function of molecules activated above energy decomposition threshold, from experimental data, have been tested. The approach involved the theoretical (RRKM) calculations of “pseudoexperimental” data for a variety of activated energy distributions. (Single or double Gaussian representations were used in all cases.) Subsequently the algorithms mentioned were applied in order to recuperate the original (i.e., input) energy distributions from these pseudoexperimental data. The results obtained provide strong evidence in favor of the validity of the algorithms and illustrate the necessary requirements for their applications. A trend toward lower accuracy as the energy distributions move to higher energies has been observed. Evidence of the influence of the distribution width is also reported. The origins of the approximation errors have been studied, and ways for further improvement are suggested.
High‐temperature kinetics of thermal decomposition of acetic acid and its products
Authors: Mackie J. C. , Doolan K. R.
Published: January 2005

Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300–1950 K in a single‐pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall‐off behavior has been taken into account and limiting high‐pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.
Kinetics of the competitive chlorinations of some perfluoroalkyl iodides determination of the bond dissociation energies D(CD3‐I), D,(C2F5‐I), and D,(i,‐C3F7‐I)
Authors: Ahonkhai Samuel I. , Whittle Eric
Published: January 2005

The reactions

(R = CF3, C2F5, and i,‐C3F7) have been studied competitively in the gas phase over the range of 27–231°C. The following Arrhenius parameters were obtained:

log A,(cm3/mol · s)
E,(kJ/mol)

R = CF3
13.99 ± 0.21
17.1 ± 2.0

R = C2F5
13.97 ± 0.20
11.5 ± 2.0

R = i,‐C3F7
14.18 ± 0.20
10.2 ± 2.0

The above data lead to bond dissociation energies D(R‐I) which are compared with previous published results. The following values are recommended: D,(CF3‐I) = 224, D,(C2F5‐I) = 219, and D,(i,‐C3F7‐I) = 215 kJ/mol.
Hydrogen/deuterium abstraction by chlorine atoms from gaseous ethyl chlorides. Secondary kinetic isotope effects in the system CH3CH2Cl, CH3CHDCl, CH3CD2Cl
Authors: Niedzielski J. , Tschuikow‐Roux E. , Yano T.
Published: January 2005

The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground‐state chlorine atoms has been investigated over the temperature range of 8–94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:magnified imageThe temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:

and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.
Thermal decomposition of azoisopropane. II. Secondary decomposition processes
Authors: Péter A. , Ács G. , Huhn P.
Published: January 2005

The thermal decomposition of azoisopropane (AIP) was studied in the presence of various quantities of propylene in the temperature and pressure intervals 498–553 K and 3.33–5.33 kPa. The inhibition functions relating to formation of the products were determined; these proved a good basis for interpretation of the formation of the secondary decompositon products of AIP. The experimental data support the conception that the βμ radical—radical reaction
equation image
occurs. The product of this is not stable; its decomposition is one of the sources of the secondary products. The ratio of the rate constants was determined for the following reactions:magnified image
Efficient production of electronically excited BiF(AO+) via collisions with NF(a1Δ)
Authors: Herbelin John M. , Klingberg Robert A.
Published: January 2005

An efficient process for converting the energy stored in electronically excited NF(a1Δ) into blue‐green BiF (AX) band emissions has been discovered. Bismuth atoms are converted to BiF and then repeatedly pumped to the (AO+) state in two steps via collisions with NF(a1Δ). A model has been formulated that predicts BiF emission intensities that are in excellent agreement with the observed values. Some of the rate coefficients required for this model are estimated by means of charge‐transfer theories. The cyclic nature of this system, along with its other basic properties, suggests that it has a strong potential to be an efficient blue‐green laser system.
Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L. , Winer Arthur M. , Pitts James N.
Published: January 2005

The yields of C5 and C6 alkyl nitrates from neopentane, 2‐methylbutane, 2‐methylpentane, 3‐methylpentane, and cyclohexane have been measured in irradiated CH3ONONO‐alkane‐air mixtures at 298 ± 2 K and 735‐torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3‐nitro‐2‐methylbutane, 2‐nitro‐2‐methylpentane, 2‐nitro‐3‐methylpentane, and cyclohexyl nitrate, relative to that for n‐butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n‐butane of 2.58 × 10−12 cm3 molecule−1 s−1, these OH radical rate constants are (in units of 10−12 cm3 molecule−1 s−1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3‐nitro‐2‐methylbutane, 1.75 ± 0.06; 2‐nitro‐2‐methylpentane, 1.75 ± 0.22; and 2‐nitro‐3‐methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO2 radicals reacting with NO to form RONO2) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3‐nitro‐2‐methylbutane, 0.109 ± 0.003; 2‐nitro‐2methylbutane, 0.0533 ± 0.0022; 2‐nitro‐2‐methylpentane, 0.0350 ± 0.0096; 3‐ + 4‐nitro‐2‐methylpentane, 0.165 ± 0.016; and 2‐nitro‐3‐methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n‐alkanes.
The formation of C3H3 (propynyl) radicals in the reaction of CH2(1A1) with acetylene
Authors: Canosa‐Mas Carlos E. , Ellis Mark , Frey H. Monty , Walsh Robin
Published: January 2005

Results obtained from the photolysis of ketene with acetylene strongly support the formation of C3H3 radicals in the title reaction. Stationary state studies are interpreted in terms of the reaction

with a rate constant (109.8 s−1) which is compared to RRKM predictions. In pulsed laser induced decomposition experiments, recombination products involving C3H3 have been detected (some for the first time) and their formation modeled using step (3) with the same rate constant.
The kinetics of the addition of alkyl radicals to carbonyl groups. I. The kinetics of the gas phase decomposition reactions of the trifluoro‐t‐butoxy radical
Authors: Kerr J. Alistair , Wright J. Paul
Published: January 2005

Trifluoro‐t‐butoxy radicals have been generated by reacting fluorine with 2‐trifluoromethyl propan‐2‐ol:

Over the temperature range 361‐600 K the trifluoro‐t‐butoxy radical decomposes exclusively by loss of the CF3 group [reaction (−2)] rather than by loss of CH3 group [reaction (−1)]:
equation image
The limits of detectability of the product CF3COCH3, by gas‐chromatographic analysis, place a lower limit on the ratio k−2/k−1 of ca. 75. The implications of these results in relation to the reverse radical addition reactions to the carbonyl group are discussed along with the thermochemistry of the reactions.
UV absorption study of the dissociation of SO2 and SO in shock waves
Authors: Plach H. J. , Troe J.
Published: January 2005

The thermal decomposition of SO2 and of the primary dissociation product SO have been studied in shock waves by the uv absorption technique. The controversy about SO2 dissociation data from uv absorption signals was resolved and attributed to the extensive overlap of SO2 and SO uv absorption spectra. The derived rate coefficients are k1/[Ar] = 1015.6 exp(‐420 kJmol−1/RT) cm3mol−1 s−1 (temperature range 3000–5000 K) for SO2 dissociation, and k3/[Ar] = 1014.6 exp(‐448 kJmol−1/RT) cm3 mol−1 s−1 (temperature range 4000–6000 K) for SO dissociation. Anomalously high values of the apparent collision efficiencies βc in SO2 dissociation are attributed to marked contributions from excited electronic states.
High temperature determination of the rate coefficient for the reaction H2O + CN → HCN + OH
Authors: Szekely Attila , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

The rate coefficient, k, of the reaction

has been determined in the temperature range 2460–2840 K using a shock tube technique. C2N2H2OAr mixtures were heated behind incident shock waves and the CN and OH concentration time histories were monitored simultaneously using broad‐band absorption near 388 nm (CN) and narrow‐line laser absorption at 306.67 nm (OH). The rate coefficient expression providing the best fit to the data was

with uncertainty limits of about ±45% in the temperature range 2460–2840 K. The rate coefficient of the reverse reaction was calculated using detailed balancing, and its extrapolation to lower temperatures was compared with previously published results.
Decomposition of di‐tert‐butyl nitroxide in aqueous solutions
Authors: Cáceres T. , Urzúa C. , Lissi E. A.
Published: January 2005

Di‐tert‐butyl nitroxide (DTBN) decomposes in aqueous solutions producing 2‐methyl‐2‐nitroso propane (MNP) and tert‐butanol. The process is acid catalyzed, it is of second order in DTBN, and takes place with a rate constant of (1.0 ± 0.1) M−2 s−1. The reaction is also catalyzed by the anionic surfactant sodium dodecyl sulfate and by Fe(II) and Fe(III) ions. The catalysis by Fe(III) involves a very fast reduction of Fe(III) ions with concomitant formation of 2‐methyl‐2‐nitroso propane. The reaction catalyzed by Fe(II) also produces 2‐methyl‐2‐nitroso propane with a formation rate given by: d[MNP]/dt = (0.25 ± 0.10) [Fe(II)] [DTBN]. This reaction rate is nearly pH independent.
An outdoor smog chamber and modeling study of toluene–NOx photooxidation
Authors: Leone Joseph A. , Flagan Richard C. , Grosjean Daniel , Seinfeld John H.
Published: January 2005

An experimental investigation of the gas‐phase photooxidation of toluene–NOx–air mixtures at part‐per‐million concentrations has been carried out in a 65‐m3, outdoor smog chamber to assess our understanding of the atmospheric chemistry of toluene. In addition, six CONOx–air irradiations were conducted to characterize the chamber with regard to any wall radical sources. Measured parameters in the toluene–NOx experiments included O3, NO, NO2, HNO3, peroxyacetyl nitrate (PAN), CO, toluene, benzaldehyde, o‐cresol, m‐nitrotoluene, peroxybenzoyl nitrate (PBZN), temperature, relative humidity, aerosol size distributions, and particulate organic carbon. Predictions of the reaction mechanism of Leone and Seinfeld [7] are found to be in good agreement with the data under a variety of initial conditions. Additional simulations are used to investigate various mechanistic pathways in areas where our understanding of toluene chemistry is still incomplete.
Kinetics of the reactions of hydroxyl radical with aliphatic aldehydes
Authors: Semmes D. H. , Ravishankara A. R. , Gump‐Perkins C. A. , Wine P. H.
Published: January 2005

Rate coefficients for OH reactions with the 2–5 carbon aliphatic aldehydes have been measured under pseudo first‐order conditions in OH. OH was generated by flash photolysis of H2O at wavelengths greater than 165 nm and its concentration monitored using time‐resolved resonance fluorescence spectroscopy. Two reactions were studied only at 298 K while five reactions were studied over the temperature range 250–425 K; negative activation energies were observed for all five reactions. Aldehyde reactivity toward OH is nearly independent of the identity of the hydrocarbon side chain. Our results are compared with those obtained in previous studies of OH‐aldehyde reaction kinetics and their mechanistic implications are discussed.
Model study of synchronization and other phenomena in light perturbation of the Briggs–Rauscher reaction
Authors: Kumpinsky Enio , Epstein Irving R. , De Kepper Patrick
Published: January 2005

Calculations are performed to model several phenomena observed when a photosensitive oscillating chemical reaction, the Briggs–Rauscher (BR) reaction, is subject to irradiation in a continuous‐flow stirred‐tank reactor. The BR mechanism proposed earlier by De Kepper and Epstein is supplemented by additional steps involving the photogeneration and subsequent reaction of iodine atoms. The calculations show qualitative agreement with the following experimentally observed phenomena: (a) change in the period and amplitude of oscillation as a function of the intensity of constant illumination, (b) synchronization between periodically varying illumination and the period of chemical oscillation, (c) phase shifts induced by single light pulses, and (d) dark steady states which are excitable by single light pulses and become oscillatory at appropriate levels of constant illumination.
The reactions of alkoxy radicals with O2. II. n‐C3H7O radicals
Authors: Zabarnick Steven , Heicklen Julian
Published: January 2005

n‐C3H7ONO was photolyzed with 366 nm radiation at −26, −3, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yields of C2H5CHO, C2H5ONO, and CH3CHO were measured as a function of reaction conditions. The primary photochemical act is
equation image
and it proceeds with a quantum yield ϕ1 = 0.38 ± 0.04 independent of temperature. The n‐C3H7O radicals can react with NO by two routes
equation image
The n‐C3H7O radical can decompose via
equation image
or react with O2 via
equation image
Values of k4/k2 ≃ k4b/k2 were determined to be (2.0 ± 0.2) × 1014, (3.1 ± 0.6) × 1014, and (1.4 ± 0.1) × 1015 molec/cm3 at 55, 88, and 120°C, respectively, at 150‐torr total pressure of N2. Values of k6/k2 were determined from −26 to 88°C. They fit the Arrhenius expression:

For k2 ≃ 4.4 × 10−11 cm3/s, k6 becomes (2.9 ± 1.7) × 10−13 exp{−(879 ± 117)/T} cm3/s. The reaction scheme also provides k4b/k6 = 1.58 × 1018 molec/cm3 at 120°C and k8a/k8 = 0.56 ± 0.24 independent of temperature, where
equation image
Temperature coefficients for reactions of OH radicals with alkanes between 300 and 1000 K
Authors: Walker R. W.
Published: January 2005

Recently, Atkinson et al. have developed a more sophisticated approach than simple additivity to determine group rate constants at room temperature for reactions of OH radicals with alkanes. In this article, use is made of reliable experimental data at room temperature and at 753 K to determine temperature coefficients for these reactions. Evidence based on experiment is cited in support of the expression k = AT1e−E/RT as a suitable quantitative expression for the variation of k with temperature between 300 and 1000 K for OH attack at any particular specific group in an alkane. Values are given for A and E for a number of groups found in both linear and branched alkanes. With highly branched alkanes, steric effects may limit the use of even the more sophisticated additivity approach used here. Use of the group values permits the calculation of both the overall rate constant for OH + alkane, the agreement with the limited amount of experimental data available being very good, and the proportions of each species of alkyl radical formed in the overall attack. Such information is vital to quantitative modeling of combustion processes currently being carried out extensively. The values given in the article are recommended for use over the temperature range 300–1000 K.
Bovine serum albumin and alizarin yellow G — a model system for positive cooperative binding to macromolecules
Authors: Nissani E. , Perlmutter‐Hayman B.
Published: January 2005

The kinetics of the binding of alizarin yellow G to six nonequivalent binding sites on bovine serum albumin were investigated, using the stopped flow and T‐jump techniques. The first step in the reaction sequence is very fast, and is followed by a slower step which is suggested to be an internal rearrangement of the collision complex formed in the first step. This temporal sequence shows that the strong cooperativity between the first and second binding sites is not due to the existence of different conformations in equilibrium in free albumin, but rather to a ligand‐induced change. Next, an additional, still slower transformation is observed. From the fact that this transformation is not rate‐determining for the formation of higher complexes we conclude that it corresponds to a branch reaction. The higher complexes are again formed with very high rate constants. The first complex has a high negative value of both ΔH and ΔS° of formation. For the second and higher complexes, the heat of formation is much lower, and the standard entropy of formation is positive. The formation of these complexes is thus largely entropy‐driven. The difference between the thermodynamic parameters of the first and subsequent ligands is in accordance with the assumption that only the binding of the first ligand entails significant structural changes.
The OH(v = 9) + O3 reaction pathway
Authors: Slanger T. G. , Huestis D. L.
Published: January 2005

The oxygen‐hydrogen system, including the reactive species H, O, H2, O2, O3, OH, and HO2, is very complex, and contains numerous reactions whose kinetics and branches have been insufficiently explored. In the present study we use computer modeling to simulate observations made in a 300‐K ozone‐hydrogen mixture, in which a critical H2 pressure leads to rapid ozone decomposition, and generation of high concentrations of atomic oxygen. Initiation of the reaction chain involves heterogeneous O and/or H atom production, and the chain branching step is the reaction OH(v) + O3 → OH + O + O2, which is shown to be the predominant pathway for these reactants. The critical H2 pressure (ca. 3 torr) sets important constraints upon the system kinetics.
Separation of polar and steric effects on absolute rate constants and arrhenius parameters for the reaction of tert‐butyl radicals with alkenes
Authors: Münger K. , Fischer H.
Published: January 2005

Absolute rate constants and their temperature dependencies were measured for the reaction of tert‐butyl radicals with 24 substituted ethenes and several other compounds in 2‐propanol solution by time‐resolved electron spin resonance. At 300 K the rate constants cover the range from 60 M−1 s−1 (1,2‐dimethylene) over 16,500 M−1 s−1 (vinyl‐chloride) to 460,000 M−1 s−1 (2‐vinylpyridine). For the mono‐ and 1,1‐disubstituted ethenes log k300 increases and the activation energy decreases with increasing electron affinity of the olefins. The frequency factors are in the range log A/M−1 s−1 = 7.5 ± 1.0 as typical for addition reactions, with minor exceptions. Electron affinity (polar) and steric effects on reactivity are separated for the addition of tert‐butyl to chloro‐ and methyl‐substituted ethylenes. A comparison with rate data for methyl, ethyl, 2‐propyl, and other radicals indicates both polar and steric effects on radical substitution.
Termolecular reaction of nitrogen monoxide and oxygen: A still unsolved problem
Authors: Olbregts J.
Published: January 2005

The oxidation of nitrogen monoxide has been studied extensively between 226 and 758 K at pressures of NO and O2 ranging from about 0.2 to 30 torr. It has been shown that (i) the reaction is properly first order against oxygen and second order against nitrogen monoxide, as well under initial conditions as during the course of the reaction; (ii) the termolecular rate constant, k, first decreases with increasing temperature and reaches a minimum value at 600 K; (iii) the transition state theory is unable to describe this behavior correctly, (iv) under the present experimental conditions k can be represented either by

or by

The latter equation is compatabile with a multiple‐step mechanism.
Thermal decomposition of methane: Autocatalysis
Authors: Roscoe John M. , Thompson Marla J.
Published: January 2005

The origin of autocatalysis in the pyrolysis of methane has been investigated by kinetic modeling. A mechanism is presented that provides good agreement with experimental data at 1038 K and 433 torr into the autocatalytic region. The main causes of autocatalysis are secondary initiation by hydrocarbon products larger than C2H6 and chain radical methylation sequences.
Excimer laser perturbations of methane flames: High temperature reactions of OH and CH
Authors: Chou Mau‐Song , Dean Anthony M.
Published: January 2005

An ArF excimer laser was used to perturb radical concentrations and a tunable dye laser was used to follow the rise and subsequent decay of OH and CH in rich (ϕ = 1.6–1.8) atmospheric pressure methane flames. The excimer beam is only slightly focussed to minimize temperature excursions and the influence of diffusion and convection on the decay rates. The observed OH decay is consistent with that predicted using a detailed kinetic mechanism. The observed CH decay is much faster than predicted. The effects of equivalence ratio and height above burner suggests that a major CH decay channel involving an intermediate with higher concentration in rich flames is not properly treated in the mechanism.
Variational sensitivity analysis of a photochemical smog mechanism
Authors: Gautier Olivier , Carr Robert W. , Seigneur Christian
Published: January 2005

The variational method of sensitivity analysis is applied to a recent chemical kinetic mechanism for photochemical smog. It is demonstrated that the variational method is capable of readily handling a large mechanism. The analysis can be applied to a single chemical species or to an arbitrarily large group of species contained in an objective function. Examples of the use of different objective functions are given. The variational method provides temporally distributed sensitivity coefficients. Therefore, the results are presented as a time‐dependent ranking of reactions in orderof decreasing importance with respect to the objective function species. This ranking permits the time‐dependent relative influence of each reaction to be readily determined by inspection. Particular attention is paid to reactions governing daytime O3 formation and nighttime NO3 and HONO formation.
Reaction of CF3 radicals with C2H6
Authors: Arican Haluk , Arthur Neville L.
Published: January 2005

The hydrogen transfer reaction between C2H6 and CF3 radicals, generated by the photolysis of CF3I, has been studied in the temperature range 298–617 K. The rate constant, based on the value of 1013.36 cm3 mol−1 s−1 for the recombination of CF3 radicals, is given by

where k2 is in cm3 mol−1 s−1 and E is in J mol−1. These results are compared with those previously reported, and the following best value for k2 is recommended:
Experimental study of the D + H2 (v = 1) reaction by CARS spectroscopy
Authors: Dreier T. , Wolfrum J.
Published: January 2005

The 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

Nascent 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

Translationally 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

The 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

For 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

We 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

A 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

Experimental 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

The 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

The 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

The 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

The 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

Changes 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

Rate 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

The 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

The 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.