bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity analysis in chemical kinetics: Recent developments and computational comparisons
Authors: Kramer Mark A. , Rabitz Herschel , Calo Joseph M. , Kee Robert J.
Published: January 2005

The advantages and disadvantages of various methods of parametric sensitivity analysis in chemical kinetic modeling are discussed. Particular attention is given to estimates of computational labor for realistic problems, and quantitative comparisons are made utilizing a 52‐reaction, 11‐species CO oxidation mechanism. The authors′ CHEMSEN/AIM program compares favorably to other techniques in many circumstances, and provides the additional convenience of accepting input information in familiar chemical notation. This paper also reviews recent developments in theory of sensitivity analysis, relevant to chemical kinetic modeling.
Kinetics of thermal decomposition of CuSO4 · 5H2O to CuO
Authors: Gadalla Ahmed M.
Published: January 2005

The effect of particle size, type of crucible, and heating rate on the thermal curves obtained simultaneously for CuSO4 · 5H2O were discussed. The dissociation steps were confirmed. Thermogravimetric techniques for determining the rate‐controlling processes and kinetic parameters were applied for the dehydration steps and the calcination of CuSO4 and CuSO4 · CuO. For the dehydration of the monohydrate one mechanism operates but the activation energy and preexponential factor vary over wide ranges. Differentiating between various mechanisms using the same technique was sometimes difficult giving completely different values for the kinetic parameters. In view of such difficulties the various methods were assessed, the best techniques to treat similar results were recommended and the operating mechanisms and kinetic parameters for the various steps were thus established.
The very‐high‐temperature pyrolysis of ethane: Evidence against high rates for dissociative recombination reactions of methyl radicals
Authors: Kiefer J. H. , Budach K. A.
Published: January 2005

The pyrolysis of 1 and 2% ethane in krypton has been studied in shock waves by the laser‐schlieren technique over 1700–4800 K. For 2400–2800 K an effective zero density gradient is seen following the rapid dissociation of the ethane. Through simulation with various mechanisms it is evident that the high rates for the dissociative recombination reactions of methyl radicals

obtained in recent shock‐tube studies, are incompatible with this observation; these rates must be reduced at least an order of magnitude. On the basis of theory and previous low‐temperature (T) measurements, k = 7.8 × 1011 (‐6562/T) (cm3/mol s) is recommended for the second of these reactions.
Kinetics and mechanism of the shock induced thermal decomposition of n‐propylsilane
Authors: Sawrey B. A. , O'Neal H. E. , Ring M. A. , Coffey D.
Published: January 2005

The kinetics and mechanism of the thermal decomposition of n‐propylsilane have been studied by the single pulse shock tube‐comparative rate technique at pressures around 4700 torr between 1095–1240 K. The primary dissociation processes are 1,1 and 1,2 H2 elimination with ø1,1 ⋍ 0.75 and ø1,2 ⋍ 0.25, respectively. Subsequent decompositions of the primary process product, n‐propylsilylene, to propylene and ethylene is complete even in the presence of excess butadiene. Possible mechanistic paths for these decompositions are discussed and an activation energy range of 30 ± 4 kcal is established for both processes. Induced decomposition via silylene chains accounts for 36–46% of the overall reaction in the uninhibited decomposition of n‐propylsilane. The silylene chains are quenched in excess butadiene, and studies under maximum inhibition give overall decomposition kinetics of, log k(nPrSiD3, s−1) = 15.26–65,300 ± 1950 cal/2.303. Computer modeling results of the overall reaction both in the absence and presence of butadiene are also presented and shown to be in acceptable agreement with the experimental observations.
Kinetics of hydrogen oxidation near the lower explosion limit
Authors: Aleksandrov E. N. , Arutyunov V. S. , Dubrovina I. V. , Kozlov S. N.
Published: January 2005

Kinetics of hydrogen oxidation near the lower explosion limit in the kinetic region of chain termination has been studied. Major effects, causing deviations of the reaction kinetics from calculations by the linear theory of branched chain processes, are shown to be (1) the inhibition of the reacting mixture by the products of interaction of active centers with vacuum grease or with impurities contained in it and (2) the heterogeneous negative interaction of reaction active centers. The kinetics of hydrogen oxidation in this region has been calculated with consideration of the heterogeneous negative chain interaction. A set of parameters has been obtained that make it possible to determine by the shape of the kinetic curves the sign and the value of nonlinear interaction of chains near the lower explosion limit. It has been shown that the experimental data are in good agreement with the calculations, provided the heterogeneous negative chain interaction is taken into consideration and the inhibiting effect of impurities is eliminated. The rate of heterogeneous generation of chains on a quartz surface treated with hydrofluoric or boric acid has been determined.
Kinetic study for addition of the phenylthio radicals to vinylpyridines
Authors: Ito Osamu , Matsuda Minoru
Published: January 2005

The absolute rate constants for reversible addition of the substituted phenylthio radicals to vinylpyridines in solution at 23°C have been determined by flash photolysis method. For each phenylthio radical, the reactivities of vinylpyridines is 3–5 times lower than that of styrene. The relative equilibrium constants estimated with flash photolysis indicate that the stabilities of the adduct carbon‐centered radicals generated from vinylpyridines are similar to that from styrene. The Hammett plots suggest that the difference in the reactivities originates in the polar transition state; the nitrogen atom in 4‐vinylpyridine withdraws the electrons of vinylic double bond.
An investigation of the dark formation of nitrous acid in environmental chambers
Authors: Pitts James N. , Sanhueza Eugenio , Atkinson Roger , Carter William P. L. , Winer Arthur M. , Harris Geoffrey W. , Plum Christopher N.
Published: January 2005

The formation of nitrous acid (HONO) in the dark from initial concentrations of NO2 of 0.1–20 ppm in air, and the concurrent disappearance of NO2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300‐ and 5800‐L volume (both with surface/volume ratios of 3.4 m−1). In these environmental chambers the initial HONO formation rate was first order in the NO2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo‐first‐order consumption rate of NO2 was (2.8 ± 1.2) × 10−4 min−1 in the 5800‐L Teflon‐coated evacuable chamber and (1.6 ± 0.5) × 10−4 min−1 in a 4300‐L all‐Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO2 reacted in the evacuable chamber and ca.10–30% in the all‐Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NOx− organic‐air mixtures, and of HONO formation in polluted atmospheres, are discussed.
The rate of the reaction of OH with HCl
Authors: Molina M. J. , Molina L. T. , Smith C. A.
Published: January 2005

The absolute rate constant for the OH + HCl reaction has been measured from 240 to 295 K utilizing the techniques of laser/flash photolysis‐resonance fluorescence. The HCl concentrations were monitored continuously by ultraviloet and infrared spectrophotometry. The results can be fit to the following Arrhenius expression:

The rate constant values obtained in this study are 20–30% larger than those recommended previously for modeling of stratospheric chemistry.
VLPR study of the reaction Br + CH3CHO
Authors: Islam Tajmeri S. A. , Marshall Roger M. , Benson Sidney W.
Published: January 2005

The reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k1 = 2.1 × 1012 cm3/mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k‐1 = 1 × 1010 cm3/mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction:

in which step 2 is shown to be rate limiting under VLPR conditions and k2 is estimated at 1012.6 cm3/mol s from recent theoretical models for radical recombination. It is also shown that 0 ⩽ E1 ⩽ 1.4 kcal/mol using theoretical models for calculation of A1 and is probably closer to the lower limit. Reaction −1 is negligible under conditions used.
Kinetics of the redox reactions between ceric sulfate and lactic and atrolactic acids in the medium HClO4‐Na2SO4‐NaClO4
Authors: Calvaruso Giuseppe , Cavasino F. Paolo , Sbriziolo Carmelo
Published: January 2005

The kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4‐Na2SO4‐NaClO4 at 25.0°C and ionic strength 2.0 mol dm−3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression

where kobs indicates the observed pseudo‐first‐order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO] concentrations. Moreover, three equilibria involving cerium(IV) and HSO (or SO) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.
Kinetic study of hydroxylamine‐bromate ion reaction in acid sulfate solution—a competitive consecutive reaction
Authors: Jonnalagadda Sreekantha B.
Published: January 2005

A kinetic study of oxidation of hydroxylamine by bromate ion in acid sulfate solution using spectrophotometric and potentiometric methods is reported. Oxidation of hydroxylamine to nitrate is quantitative and followed competitive, consecutive, and auto catalytics steps characterized by induction periods. In the slow rate limiting step, hydroxylamine on reaction with HOBr (k) forms an intermediate I, which further reacts fast with second molecule of HOBr (k) giving nitrite. Nitrite reacts with HOBr (k) yielding the final product nitrate. Nitric acts as an autocatalyst also and its initial addition decreased the induction periods. In excess of hydrogen ion concentration all the reaction steps follow second‐order kinetics. All the second‐order rate constants are reported and the reaction mechanism is proposed.
Kinetics of the reaction Cl + NO2 + M
Authors: Leu Ming‐Taun
Published: January 2005

The termolecular rate constant for the reaction Cl + NO2 + M has been measured over the temperature range 264 to 417 K and at pressure 1 to 7 torr in a discharge flow system using atomic chlorine resonance fluorescence at 140 nm to monitor the decay of Cl in an excess of NO2. The results are\documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm He}} = 9.4{\rm } \times {\rm }10^{ - 31} \left({\frac{T}{{300}}} \right)^{ - 2.0 \pm 0.05} {\rm cm}^6 {\rm s}^{ - {\rm 1}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm N}2} = (14.8{\rm } \pm {\rm }1.4){\rm } \times {\rm 10}^{ - 31} {\rm cm}^6 {\rm s}^{ - 1}$\end{document} at 296 K where error limits represent one standard deviation. The systematic error of k1 measurements is estimated to be about 15%. Using a static photolysis system coupled with the FTIR spectrophotometer the branching ratio for the formation of the two possible isomers was found to be ClONO(⩾75%) and CINO2(⩽25%) in good agreement with previous measurements.
Optimizing the use of the Kezdy–Mangelsdorf–Swinbourne method for analysis of data following a exp(–kt) + Z
Authors: McKinnon G. H. , Backhouse C. J. , Kalantar A. H.
Published: January 2005

The use of the KMS method for the evaluation of the exponent by the experimentalist requires that a lag or retardation be chosen. The best choice of lag is discussed quantitatively. Its dependence upon the decade range of the data, the relative magnitude of the background, the level and character of the noise, the number and distribution of the data, and the weighted least‐squares method of analysis are all detailed. A table of lags and error factors is given, for various ranges, backgrounds, and kinds of noise. Bias in the extracted rate (k), due to noise and treatment of the data, is also discussed.
Kinetics of nonisothermal calcination of ZnCO3 in air
Authors: Gadalla Ahmed M.
Published: January 2005

Thermal curves obtained simultaneously at constant heating rates were used to study calcination of ZnCO3 in air. Carroll and Manche's technique, Reich's equation, and Kissinger's method gave an average value for the activation energy of 23 kcal/mol. On the other hand, Coats and Redfern's technique showed the activation energy and preexponential factor to vary over wide ranges. They increase to a maximum and decrease again on increasing the temperature. Their values decrease as the heating rate was increased. One‐dimensional diffusion mechanism, obeying parabolic law, may control the entire calcination process.
Reactivity of allylic hydrogen in cyclohexadiene towards OH radicals
Authors: Ohta Tomohiro
Published: January 2005

The yield of benzene in the reaction of 1,4‐ and 1,3‐cyclohexadiene with OH radicals in the presence of oxygen was determined using H2O2 and CH3ONO as OH radical sources. Both in the H2O2 and the CH3ONO systems, the yield of benzene from 1,4‐cyclohexadiene was 15.3% and the yield from 1,3‐cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per CH in cyclohexadiene was determined to be 3.8 × 10−12 cm3 molecule−1 s−1. The branching ratio of the hydrogen abstraction to overall reaction for 1‐butene and 1‐pentene was estimated to be (25–14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts [4].
A shock tube study of the reaction of the hydroxyl radical with propane
Authors: Bott J. F. , Cohen N.
Published: January 2005

The rate coefficient for the reaction of the hydroxyl radical, OH, with propane has been measured at 1220 K in shock tube experiments, and a value of (1.58 ± 0.24) × 1013 cm3/mol s was obtained. This measured value is compared with previous experimental results and a transition‐state theory calculation.
Kinetics of OH reactions with aliphatic thiols
Authors: Wine P. H. , Thompson R. J. , Semmes D. H.
Published: January 2005

The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time‐resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10−11 cm3 molecule−1 s−1, ‐Eact = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10−11 cm3 molecule−1 s−1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.
Principal component analysis of kinetic models
Authors: Vajda S. , Valko P. , Turányi T.
Published: January 2005

An eigenvalue–eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for several species of a reacting system at several time points. The main advantage of this method lies in its ability to reveal those parts of the mechanism which consist of strongly interacting reactions, and to indicate their importance within the mechanism. Results can be used to solve three general kinetic problems. Firstly, an objective condition for constructing a minimal reaction set is presented. Secondly, the uncovered dependencies among the parameters are shown to confirm or deny validity of quasi‐steady‐state assumptions under the considered experimental conditions. Thirdly, taking into account only sensitivities of observed species, the analysis is used to yield error estimates on unknown parameters determined from the experimental observations, and to suggest the parameters that should be kept fixed in the estimation procedure. To illustrate we chose the well‐known hydrogen–bromine reaction and the kinetics of formaldehyde oxidation in the presence of CO.
Homolytic substitution in trialkyltin iodides by photochemically generated iodine atoms. I. Kinetics
Authors: De Ryck P. H. , Verdonck L. , Van Der Kelen G. P.
Published: January 2005

The kinetics of the homolytic substitution of several trialkyltin iodides by iodine atoms are presented. Rate constants have been determined at three different temperatures and the following activation parameters calculated: A, Ea, and ΔS°≠. The observation that the activation energy, ΔG≠, is related to the driving force of the ion‐pair formation, leads to the conclusion that the charge‐transfer model is a valid approach for substitution in the reaction between R3SnI compounds and iodine atoms.
Relative rate constants of the gas‐phase decomposition reactions of the s‐butoxy radical
Authors: Drew Roger M. , Alistair Kerr J. , Olive Jonathan
Published: January 2005

s‐Butoxy radicals have been generated by reacting fluorine with s‐butanol:

Over the temperature range 398.6 to 493.3 K the s‐butoxy radical decomposes by two different pathways to yield acetaldehyde and propionaldehyde, acetaldehyde being the major product:
equation image
The ratio k1/k2 was found to be temperature dependent. An Arrhenius plot of the data (398.6 to 493.3 K) yields the relative Arrhenius parameters, E1 ‐ E2 = −11.2 ± 0.8 kJ mol−1 and (A1/A2) = 0.59 ± 0.14. The ratio of rate constants k1/k2 was shown to be independent of total pressure (80–600 torr) and of the pressure of s‐butanol (2–13 torr). The kinetic results for these s‐butoxy decomposition reactions are discussed in relation to the literature data and in terms of the thermochemistry of the reactions.
Rate constant for the reaction Cl + HO2NO2 → products
Authors: Simonaitis R. , Leu M. T.
Published: January 2005

The total rate constant for the reaction of Cl atoms with HO2NO2 was found to be less than 1.0 × 10−13 cm3 s−1 at 296 K by the discharge flow/resonance fluorescence technique. The reaction was also studied by the discharge flow/mass spectrometric technique. k1a + k1b was measured to be (3.4 ± 1.4) × 10−14 cm3 s−1 at 296 K. The reaction is too slow to be of any importance in stratospheric chemistry.
Kinetics and mechanism of the decomposition of N,N‐dihalopeptides
Authors: Stanbro William D. , Lenkevich Michael J.
Published: January 2005

The tripeptide alanylalanylalanine reacts with either HOCl or HOBr to form a N,N‐dihalopeptide. These compounds decompose to the N‐halo‐N′‐(α‐iminoketo)peptides plus halide ion. The rate constants for these reactions in 0.4‐M NaCl were determined to be

where the activation energies are in cal/mol. The N‐halo‐N′‐(α‐iminoketo)‐peptides slowly decompose either by a two‐step hydrolysis reaction to form ammonia, halide ion, and an N‐(α‐acylketo)peptide, or by direct decomposition to a nitrile, an isocyanopeptide, and a halide ion.
The steady‐state oxidation of CO on rhodium(100)
Authors: Daniel W. M. , White J. M.
Published: January 2005

In this article, we present low‐pressure steady‐state results for carbon monoxide oxidation over Rh(100). The results are comparable to those found for other Group VIII transition metals. For a fixed oxygen pressure, the reaction rate is first order in CO pressure until a critical pressure is reached, above which the reaction rate sharply diminishes and the order becomes negative in CO pressure. Coverages of carbon monoxide under steady‐state working conditions have been measured.
Intramolecular catalysis and the rate‐determining step in the alkaline hydrolysis of ethyl salicylate
Authors: Khan M. Niyaz , Gambo S. K.
Published: January 2005

The alkaline hydrolysis of ethyl salicylate has been studied at 35°C within the [ŌH] range of 0.001–2.00 M. The observed hydroxide ion concentration dependence of rate has been explained by proposing the occurrence of two parallel kinetic steps shown as in the rate law: rate = k1[H2O] [ES] + k2[ŌH] [ES] where ES− represents ionized ethyl salicylate. The value of k1, is ca. 106 times larger than the expected value of rate constant for uncatalyzed aqueous cleavage of ethyl‐p‐hydroxybenzoate. This rate advantage is attributed to intramolecular general base catalysis. The analysis of observed activation parameters indicates that ca. 106 times rate enhancement is entirely due to favorable entropy change. The Brønsted‐type plots show an extremely low sensitivity of rate constants k1 and k2 with respective Brønsted coefficient of β = −0.03 ± 0.01 and β = −0.01 ± 0.05, on the basicity of leaving groups of salicylate esters (alkoxide and phenoxide ions). The low values of these Brønsted coefficients indicate essentially little or an insignificant amount of bond cleavage between carbonyl carbon and leaving group in the rate‐determining step in both the k1 and k2 steps. The rate constants obtained at different ethanol concentration follow Grunwald‐Winstein mY equation with m = 0.14 ± 0.01.
Complex dynamical behavior in a new chemical oscillator: The chlorite–thiourea reaction in a CSTR
Authors: Alamgir Mohamed , Epstein Irving R.
Published: January 2005

The reaction between chlorite ion and thiourea has been studied both in a closed (batch) system and in a flow reactor (CSTR). The principal stoichiometry is given by

In batch, the reaction displays an induction period, whose length is proportional to [CS(NH2)2]/[ClO] [H+], followed by the rapid buildup and disappearance of a ClO2 intermediate. At [ClO]/[CS(NH2)2] ratios between 2.5 and 3.5, a second peak in the ClO2 absorbance is observed. In the CSTR, this iodine‐free system displays simple and complex periodic oscillation, bistability, aperiodic oscillation, and birhythmicity.
Reactions of alkoxy radicals with O2. III. i‐C4H9O radicals
Authors: Zabarnick Steven , Heicklen Julian
Published: January 2005

i‐C4H9ONO was photolyzed with 366‐nm radiation at −8, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of i‐C3H7CHO, Φ{i‐C3H7CHO}, was measured as a function of reaction of reaction conditions. The primary photochemical act is
equation image
and it proceeds with a quantum yield ϕ1 = 0.24 ± 0.02 independent of temperature. The i‐C4H9O radicals can react with NO by two routes
equation image
The i‐C4H9O radical can decompose via
equation image
or react with O2 via
equation image
Values of k4/k2 ≃ k4b/k2 were determined to be (2.8 ± 0.6) × 1014, (1.7 ± 0.2) × 1015, and (3.5 ± 1.3) × 1015 molec/cm3 at 23 55, and 88°C, respectively, at 150‐torr total pressure of N2. Values of k6/k2 were determined from −8 to 120°C. They fit the Arrhenius expression:

For k2 ≃ 4.4 × 1011 cm3/s, k6 becomes (3.2 ± 2.0) × 10−13 exp{−(836 ± 159)/T} cm3/s. The reaction scheme also provides k4b/k6 = 3.59 × 1018 and 5.17 × 1018 molec/cm3 at 55 and 88°C, respectively, and k8b/k8 = 0.66 ± 0.12 independent of temperature, where
equation image
An FTIR spectroscopic study of the reactions Br + CH3CHO → HBr + CH3CO and CH3C(O)OO + NO2 ⇌ CH3C(O)OONO2 (PAN)
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P.
Published: January 2005

Based on an FTIR‐product study of the photolysis of mixtures containing Br2CH3CHO and Br2CH3CHOHCHO in 700 torr of N2, the rate constant for the reaction Br + CH3CHO → HBr + CH3CO was determined to be 3.7 × 10−12 cm3 molecule−1 s−1. In addition, the selective photochemical generation of Br at λ > 400 nm in mixtures containing Br2CH3CHO14NO2 (or 15NO2)O2 was shown to serve as a quantitative preparation method for the corresponding nitrogen‐isotope labeled CH3C(O)OONO2 (PAN). From the dark‐decay rates of 15N‐labeled PAN in large excess 14NO2, the rate constant for the unimolecular reaction CH3C(O)OO15NO2 → CH3C(O)OO + 15NO2 was measured to be 3.3 (±0.2) × 10−4 s−1 at 297 ± 0.5 K.
Oxidation of naphthalene and phenanthrene by pyridinium fluorochromate (PFC)—a kinetic and mechanistic study
Authors: Bhattacharjee Bharati , Bhattacharjee Manabendra N. , Bhattacharjee Mitra , Bhattacharjee Apurba K.
Published: January 2005

The kinetics of the oxidation of naphthalene and phenanthrene by pyridinium fluorochromate, C5H5NHCrO3F, PFC, has been studied. The main product of the oxidation is the corresponding quinone. While each oxidation, studied in aqueous acetic acid (80–95%, v/v) medium, is first order with respect to the oxidant, the rate is almost independent of the substrate concentration. The reactions are catalyzed by acid, the acid‐catalyzed reactions being very fast, which precluded determination of their order in acid medium. The kinetic isotope effect, kH/kD is 5.50 at 303 K for naphthalene. The reaction does not induce polymerization of acrylonitrile. The effects of temperature and solvent compositions were studied and activation parameters evaluated. Probable mechanisms are discussed.
Spectra and reactions of acetyl and acetylperoxy radicals
Authors: Basco Norman , Parmar Sucha S.
Published: January 2005

The ultraviolet absorption spectra of the acetyl and acetylperoxy radicals have been characterized in the range 195–280 nm. The acetyl radical was generated by the flash photolysis of Cl2 in the presence of CH3CHO and was converted to the acetylperoxy radical in the presence of excess O2. The extinction coefficient of the acetylperoxy radical was measured to be 2300 L/mol cm at the maximum at 207 nm and the rate constant for the reaction

was evaluated to be k5 = (4.8 ± 0.8) × 109 L/mol s.
Relative rates of nucleophilic reactions of benzyl carbocation formed in photolysis of benzyl chloride and benzyl acetate in aqueous solution
Authors: Jaarinen Soili , Niiranen Jukka , Koskikallio Jouko
Published: January 2005

Benzyl chloride and benzyl acetate were photolyzed in 30% methanol–water mixtures (V/V) at 0°C. The photolysis produces benzyl carbocations that react with nucleophiles. The reaction products were analyzed by gas chromatography or liquid chromatography. From the amounts of products the relative values of rate constants of reactions of benzyl carbocation with nucleophiles N and water k(N)/k(H2O) were calculated. Benzyl carbocation reacts with I−, Br−, Cl−, and Ac− ions with approximately diffusion‐controlled rate. A value of 2.4 × 107 dm3 mol−1 s−1 for the rate constant k(H2O) and a lifetime of 0.7 ns were estimated for benzyl carbocation in the aqueous solution.
Rate constants for the reaction OH + CO as functions of temperature and water concentration
Authors: Beno Mary F. , Jonah Charles D. , Mulac William A.
Published: January 2005

Rate constants for the reaction OH + CO have been measured as functions of temperature (340–1220 K) and water concentration in the presence of 1 atm of argon. Results at zero water concentration yield the expression, log kƒ (cm3 molecule−1 S−1) = −12.96 + 4.7 × 10−4 T, for the reaction rate constant as a function of temperature. These results are in very good agreement with previous direct measurements and in reasonable agreement with flame and shock tube measurements. Explanations are offered for the involvement of the water molecule in the present experiments and earlier measurements from this laboratory throughout the entire temperature range. Results are consistent with previous results showing little, if any, pressure effect of Ar on the reaction up to 1 atm of Ar.
Tables of rate constants extracted from chemical kinetics and photochemical data for use in stratospheric modeling. Evaluation number 7
Authors: Demore W. B. , Margitan J. J. , Molina M. J. , Watson R. T. , Golden D. M. , Hampson R. F. , Kurylo M. J. , Howard C. J. , Ravishankara A. R.
Published: January 2005

These tables of evaluated rate constants for use in stratospheric modeling have been taken from the most recent report of the NASA Panel that has been periodically producing such reviews. They are reproduced here to make a broader community aware of their existence. This article should NOT be cited, nor should these rate constants be used without consulting the full report. All citations should be to that original report (JPL Publ. 85‐37), which contains extensive documentation and discussion of the rationale of the evaluation. Copies may be obtained by requesting JPL Publ. 85‐37 from Documentation Services, 111‐116B, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109.
Kinetics of Ce(IV) oxidation of α‐keto acids in sulfuric‐perchloric acid media
Authors: Saraç A. Sezai
Published: January 2005

The rates of oxidation of four α‐keto acids, glyoxylic, pyruvic, phenylglyoxylic, and 2‐oxobutyric acids by Cerium(IV) in H2SO4HaHSO4 and H2SO4HClO4 solutions, have been studied spectrophotometrically. The rate data suggest that CeSO is the most reactive of the Cerium(IV)‐sulfate complexes present in the H2SO4NaHSO4 and H2SO4HClO4 systems. The oxidation reaction is proposed to be a one‐electron process with the rate‐determining step being the decomposition of a α‐ketoacid‐Cerium(IV) complex to a free radical and carbon dioxide through a transition state.
A reevaluation of low temperature experimental rate data for the reactions of O atoms with methane, ethane, and neopentane
Authors: Cohen N.
Published: January 2005

The experimental data for the reactions of oxygen atoms with methane, ethane, and neopentane at temperatures below ca. 600 K have been reexamined. In the case of CH4 and C2H6 reactions, detailed computer models have been assembled to test the assumptions regarding stoichiometries that were made in the original studies in order to derive elementary rate coefficients from the experimentally observed reaction rates. It was found in both cases that the measurements are especially sensitive to secondary reactions not taken into account and impurities in the reagent alkane. Because the original reports did not include sufficient experimental details, it is not now possible to correct their results quantitatively. However, it appears, qualitatively, that the values for the O + CH4 and O + C2H6 rate coefficients were overestimated by factors of approximately 2 to 3 in the 250–400 K temperature range, with the error increasing as T decreases. Although the experimental results for the O + neopentane reaction are not as sensitive to the same kinds of complications, a comparison of the low‐temperature measurements with those for the O + ethane reaction suggests that the previously recommended rate coefficients, based on the data of Herron and Huie, are probably also too high by a factor of 2 to 3.
Stopped‐flow investigations of the reaction kinetics of carbon dioxide with some primary and secondary alkanolamines in aqueous solutions
Authors: Barth D. , Tondre C. , Delpuech J. ‐J.
Published: January 2005

The reaction kinetics of carbon dioxide with four alkanolamines of industrial importance (MEA, DGA, DEA, and DIPA) have been investigated with the aid of the stopped‐flow technique, allowing the determination of rate constants for carbamates formation. The constants obtained for MEA at 20°C and 25°C are in good agreement with recent literature data. The kinetic behavior of DGA was found to be almost identical to that of MEA.

The rate constants obtained for DIPA at 25°C (54 M−1 s−1) is half as large as that for DEA (110 M−1 s−1). The former one is satisfactorily compared with the recent values proposed by Blauwhoff et al. Activation energies have also been obtained for DEA (23.2 kJ mol−1) and for DIPA (58.7 kJ mol−1) and their mechanistic implications are discussed in relation with the relevanceof a rate‐determining proton transfer step in the process of carbamate formation.
Kinetics and mechanism of the pyrolysis of 1‐Chloro‐1, 1‐difluoroethane in the presence of chlorine
Authors: Huybrechts G. , Hubin Y.
Published: January 2005

The first stage thermal reactions of CF2CICH3 in the presence of chlorine have been studied between 554 and 614 K. These are
equation image
and

Rate equations derived from a radical mechanism are shown to fit the experimental results. Values of Arrhenius parameters for the decomposition of the CF2ClCH2. radical and its reactions with Cl2 and Cl are given.
Rate constants of O2(1Δg)
Authors: Raja Nalini , Arora P. K. , Chatha J. P. S.
Published: January 2005

The rate constants of O2(1Δg) with aliphatic alcohols, terpenes, unsaturated hydrocarbons, chlorinated hydrocarbons, oxygen, and diamines have been studied in thepresence of NO2. The rate constants for oxygen, 1,2‐ethane diamine, and 1,2‐propane diamine are (9.9 ± 0.4) × 102, (8.7 ± 0.7) × 104, and (1.4 ± 0.3) × 104 1/mol/s, respectively. The rate constants for all other compounds are less than the oxygen rate constant.
Molecular beam scattering studies of the reaction D + H2 (v = 0) and D + H2 (v = 1) → HD + H
Authors: Goetting R. , Toennies J. P. , Vodegel M.
Published: January 2005

The reaction D + H2 → HD + H has been investigated in two molecular beam scattering experiments. Angular and time‐of‐flight distributions have been measured for the initial vibrational ground state (v = 0) at a most probable collision energy of Ecm = 1.5 eV and for the first vibrational excited state (v = 1) at Ecm = 0.28 eV with the same apparatus. Results for the ground‐state experiment are compared with quasiclassical trajectory calculations(QCT) on the LSTH‐hypersurface transformed into the laboratory system and averaged over the apparatus distributions. The agreement isquite satisfactory. At this high collision energy the HD products are no longer scattered in a backward direction but in a wide angular region concentrated about θ = 90° in the center‐of‐mass system. The absolute reactive cross section has been determined and the agreement with the theoretical value from QCT calculations is within the experimental error. The high sensitivity of the experiment to different properties of the doubly differential cross section has also been demonstrated. A preliminary evaluation of the experiment with initial vibrational excitation (v = 1) shows that the HD‐product molecules are preferably backward scattered and the change of internal energy is small supporting the concept of a reaction which is adiabatic with respect to the internal degrees of freedom.
A coupled states calculation of accurate quantum rate constants for H + H2
Authors: Colton Mitchell C. , Schatz George C.
Published: January 2005

In this article we present the results of converged quantum reactivescattering calculations of thermal rate constants for H + H2 using the Liu‐Siegbahn‐Truhlar‐Horowitz (LSTH) potential energy surface. These calculations are based on the coupled states (CS) approximation wherein rotational states having different body fixed angular momentum projection quantum numbers are decoupled. By comparision with accurate coupled channel results on the Porter‐Karplus No. 2 (PK2) potential surface, we estimate that the maximumerror in thermal rate constants arising from both this approximation and from other numerical approximations in the calculation is less than 25%. We also show that the sum over projection quantum numbers Ω associated with the CS calculation may be approximated quite accurately in terms of the Ω = 0 rate constants by assuming that the |Ω| > 0 rate constants differ from Ω = 0 by a shift in activation energy, which reflects the vibrationally adiabatic bending energy associated with each Ω.

Comparison of the LSTH rate constants with experiment indicates average errors of 16% and 24% relative to the two modern measurementsof the rate constants for H + H2. These errors are reduced to 18% and 9% if the CS rate constants are multiplied by exp(0.0065 eV/kT). The expected error (based on recent quantum structure calculations) associated with the 0.425 eV barrier of theLSTH potential surface is 0.0065 eV. Overall, the agreement of either the LSTH or modified LSTH rate constants with experiment is within the 32% maximum disagreement between the two experimental measurements at all butthe lowest temperature that has been studied.

Comparison of our CS rate constants with the results from simpler theories is considered using both the LSTH and PK2 potential surfaces. The best overall agreement is with transition state theories that use accurate dynamical methods to calculate tunnelling factors. These include reduced dimensionality quantum dynamics methods and variational transition state theory using either the Marcus‐Coltrin or least action ground‐state tunnelling paths. Comparison with the results of quasiclassical trajectory calculations indicates substantial errors at low temperatures.
Dynamical stereochemistry of the hydrogen exchange reaction: A computational study
Authors: Schechter I. , Levine R. D.
Published: January 2005

The barrier for the hydrogen exchange reaction increases with the bend angle of H3. The implications for the dynamics of the reaction are explored on two levels. The static one uses the concept of a relaxed potential. This provides for a convenient, yet realistic representation. Itallows for the response of the molecule to the approaching atom. Among features made very evident by the relaxed potential is the possibility that hotH atoms can react by insertion. It also shows the widening of the cone of acceptance upon reagent vibrational excitation. On the dynamical level, classical trajectory computations are used to illustrate the dependence of the reactivity on the angle of attack and on the translational and vibrational excitation of the reagents. Detailed product distributions are generally not sensitive to the attack angle. An exception is the HD/H2 branching ratio in H + HD reactive collisions.
Semiclassical variational transition state calculations for the reactions of H and D with thermal and vibrationally excited H2
Authors: Garrett Bruce C. , Truhlar Donald G. , Varandas A. J. C. , Blais Normand C.
Published: January 2005

We present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol−1 barrier and a carefully fitted long‐range attraction. The low‐temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol−1, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited‐state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants.
Kinetics of the reactions of halogenated methyl radicals (CF3, CF2Cl, CFCl2, and CCl3) with molecular chlorine
Authors: Timonen Raimo S. , Russell John J. , Gutman David
Published: January 2005

The kinetics of four gas‐phase reactions involving halogenated methyl radicals (R  CF3, CF2Cl, CFCI2, and CCI3) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real‐time experiments as a function of Cl2 concentration to obtain the rate constants of these R + Cl2 reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF3 and CCl3 with Cl2 and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl2 reactions compared to that of the CH3 + Cl2 reaction are attributed in part to the different polarities of the transition states formed.
Room temperature rate constants for the reaction of OH with selected chlorinated and oxygenated hydrocarbons
Authors: Edney E. O. , Kleindienst T. E. , Corse E. W.
Published: January 2005

A study was conducted to measure the hydroxyl radical rate constants using a relative rate procedure in which the photolysis of methyl nitrite was the source of OH. During the course of this study, the OH rate constant was measured for a number of chlorinated solvents for which measurements have not previously been reported or for which there are few reliable measurements.

Room temperature OH rate constants are presented for six chlorinated hydrocarbons (allyl chloride, benzyl chloride, chlorobenzene, epichlorohydrin, trichloroethylene, and vinylidene chloride) and four oxygenated hydrocarbons (acrolein, methacrolein, methyl ethyl ketone, and propylene oxide). Also included are OH rate constants for alkanes (ethane, propane, isobutane, and cyclohexane), alkenes (trans−2‐butene and isoprene), and aromatic hydrocarbons (benzene, toluene, o−, m−, and p‐xylene). Rate constants for compounds not previously reported include vinylidene chloride (1.49 ± 0.21 × 10−11 cm3 molecule−1 s−1) and benzyl chloride (2.96 ± 0.15 × 10−12 cm3 molecule−1 s−1). The analysis for chlorinated hydrocarbons included a correction for possible chlorine atom reactions.
The mechanism and rate parameters for the pyrolysis of n‐hexane in the range 723–823 K
Authors: Imbert Freddy E. , Marshall Roger M.
Published: January 2005

The pyrolysis of n‐hexane has been investigated in the ranges 723–823 K and 10–100 Torr at up to 3% decomposition. The reaction is homogeneous and free from the self‐inhibition by olefin products observed for several other alkanes. The products of the reaction are hydrogen, methane, ethane, ethene, propene, but‐1‐ene, and pent‐1‐ene, with smaller amounts of propane. It is shown that the results are in quantitative agreement with a conventional Rice‐Herzfeld chain mechanism terminated by the combination and disproportionation of ethyl radicals, but with the mechanism extended so as to include the unimolecular isomerizations via a six‐membered cyclic transition state between 1‐hexyl and 2‐hexyl (1‐methylpentyl) radicals.

The overall rate constant of initiation is estimated to be given by

The rate constant for the reaction
equation image
is given by

which when combined with published data gives an Arrhenius plot curved upwards at low values of 1/T as has been observed for several other hydrogen abstraction reactions of methyl and of ethyl. Estimates are made of rate constants and ratios of rate constants for several reactions of the free radicals involved in the reaction. It is suggested that the minor product propane arises mainly from a hydrogen abstraction by 1‐propyl from hexane with a contribution from a minor termination process involving ethyl and methyl.
A critical review of the chemical kinetics of SF4, SF5, and S2F10 in the gas phase
Authors: Herron John T.
Published: January 2005

The gas phase chemical kinetics of SF4, SF5, and S2F10 are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF6. Specific reaction systems treated are SF4 + F2, SF5 + SF5, and the pyrolysis of S2F10. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given.
Bimolecular QRRK analysis of methyl radical reactions
Authors: Dean A. M. , Westmoreland P. R.
Published: January 2005

Reactions which proceed through energized adducts, including radical recombinations, insertions, and addition to unsaturates, frequently exhibit unusual kinetic behavior. The branching ratios among various product channels are often complex functions of both temperature and pressure. Four such reactions involving methyl radicals are analyzed by combining chemical activation distribution functions with QRRK methods to predict rate constants for each channel. These include three oxidation paths, CH3 + O, CH3 + O2, CH3 + OH, and the addition reaction CH3 + C2H2. These predictions are compared to experiments wherever possible; generally, the agreement is quite satisfactory. Analysis of the energetics of the various reaction channels, using parameters which are readily available, provides a convenient framework for prediction. Suggested rate constants for the various channels for the four reactions are given at three pressures, 20, 760, and 7600 Torr, for the temperature range 300–2500 K. The approach used here can easily be applied to other reactions.
Kinetics of the reactions of the hydroxyl radical with dimethyl ether and diethyl ether
Authors: Tully Frank P. , Droege August T.
Published: January 2005

Absolute rate coefficients for the reactions of the hydroxyl radical with dimethyl ether (k1) and diethyl ether (k2) were measured over the temperature range 295–442 K. The rate coefficient data, in the units cm3 molecule−1 s−1, were fitted to the Arrhenius equations k1 (T) = (1.04 ± 0.10) × 10−11 exp[−(739 ± 67 cal mol−1)/RT] and k2(T) = (9.13 ± 0.35) × 10−12 exp[+(228 ± 27 kcal mol−1)/RT], respectively, in which the stated error limits are 2σ values. Our results are compared with those of previous studies of hydrogen‐atom abstraction from saturated hydrocarbons by OH. Correlations between measured reaction‐rate coefficients and CH bond‐dissociation energies are discussed.
Kinetics of the gas‐phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and α,β‐unsaturated aldehydes
Authors: Atkinson Roger , Aschmann Sara M. , Goodman Mark A.
Published: January 2005

Rate constants for the gas‐phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and α,β‐unsaturated aldehydes have been determined at 298 ± 2 K using a relative rate technique. Using rate constants for the reactions of NO3 radicals with ethene and propene of (1.1 ± 0.5) × 10−16 cm3 molecule−1 s−1 and (7.5 ± 1.6) × 10−15 cm3 molecule−1 s−1, respectively, the following rate constants (in units of 10−16 cm3 molecule−1 s−1) were obtained: acetylene, ≤0.23; propyne, 0.94 ± 0.44; vinyl chloride, 2.3 ± 1.1; 1,1‐dichloroethene, 6.6 ± 3.1; cis‐1,2‐dichloroethene, 0.75 ± 0.35; trans‐1,2‐dichloroethene, 0.57 ± 0.27; trichloroethene, 1.5 ± 0.7; tetrachloroethene, <0.4; allyl chloride, 2.9 ± 1.3; acrolein, 5.9 ± 2.8; and crotonaldehyde, 41 ± 9. The atmospheric implications of these data are discussed.
Kinetics, mechanism, and stereochemistry of Diels‐Alder reactions of CN‐substituted ethenes with cyclohexa‐1, 3‐diene in the gas phase
Authors: Van Mele B. , Huybrechts G.
Published: January 2005

The kinetics of the Diels‐Alder additions of CH2 = CHCN, CH2 = C(CH3) CN, and cis‐ and trans‐CH3CH = CHCN to cyclohexa‐1, 3‐diene have been studied in the gas phase. The stereochemistry of these reactions is discussed. In terms of a biradical mechanism, a minimum value of 4.1 ± 0.8 kcal mol−1 for the stabilizing effect of a CN group vis‐à‐vis a methyl group is shown to fit the experimental activation energies.