bluuebunny/crossref_metadata_2025 huggingface dataset:
Quenching of N2(A3Σu+) by O2, O, N, and H
Authors: Dunn O. J. , Young R. A.
Published: January 2005

Metastable N2(A3Σu+), υ = 0, υ = 1, molecules are produced by a pulsed Tesla‐type discharge of a dilute N2/Ar gas mixture. Rate coefficients for quenching these metastable levels by O2, O, N, and H were obtained by time‐resolved emission measurements of the (0, 6) and (1, 5) Vegard–Kaplan bands. In units of cm3/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N2(A3Σu+) are

Within the limits of error these coefficients apply to quenching N2(A3Σu+) υ′ = 1 as well.
Rate constants of elementary reactions in the high temperature system of nitric oxide and hydrogen
Authors: Ando H. , Asaba T.
Published: January 2005

The consumption of nitric oxide in the shock‐heated nitric oxide, hydrogen, and argon system had been studied and modeled as the chain‐branching process containing the reaction H + NO ⇀ N + OH (k3) as a slow‐branching step. Through the computer simulation method the authors clarified the role of the initiation reaction H2 + NO ⇀ HNO + H (k1) in the system and obtained the rate constants of k1 and k3 as k1 = 1013.5±0.15 exp (−55.2 kcal/RT) and k3 = 1013.7±0.15 exp (−48.7 kcal/RT) (cm3/mole·sec), respectively. k1 was one order larger than the value obtained in the flame experiment by Halstead and Jenkins.
The effect of alkyl group substitution on the rate of thermal isomerization of small ring compounds
Authors: Solly Richard K. , Cain Edward N.
Published: January 2005

The thermal isomerization of 1‐chloro‐4‐methylbicyclo[2.2.0]hexane and 1‐chloro‐4‐lthylbicyclo[2.2.0]hexane has been studied in the gas phase and in tetrachloroethylene and o‐dichlorobenzene solvents over the temperature range of 409–512°K. Good first‐order kinetics yield the following Arrhenius equations: log kg/(sec−1) = (13.86 ± 0.03) − (36.90 ± 0.07)/middot; log ka/(sec−1) = (13.55 ± 0.31) − (35.50 ± 0.13)/θ log kb/(sec−1) = (13.55 ± 0.15) − (35.87 ± 0.06)/θ for the 4‐methyl derivative, and log ka/(sec−1) = (13.68 ± 0.29) − (36.19 ± 0.13)/· log kb/(sec−1) = (13.55 ± 0.15) − (35.87 ± 0.06)/θ for the 4‐ethyl derivative. The subscripts g, a, and b refer to the gas phase, tetrachloroethylene, and o‐dichlorobenzene as solvents, respectively, θ = 2.303 RT kcal/mole, and the error limits are least squares deviations. The activation energy is increased by 1.2 ± 0.5 kcal/mole for a methyl group and 1.5 ± 0.5 kcal/mole for an ethyl group with respect to the unsubstituted bridgehead compound. With reference to the reported Arrhenius parameters for all bicyclo[2.2.0]hexane isomerizations, it is shown that this increase in activation energy with alkyl substitution is not due to the steric interaction in the transition complex. It is postulated that the ground‐state reactant bicyclo[2.2.0]hexane molecules are stabilized by alkyl substitution. This ground‐state alkyl stabilization of small ring compounds may also account for an increase in the activation energy on pyrolysis of alkyl substituted cyclopropanes and cyclobutanes.
Kinetics of the heterogeneous electron transfer reaction of triplet pyrene in micelles to Br2− radicals in aqueous solution
Authors: Frank A. J. , Grätzel M. , Henglein A. , Janata E.
Published: January 2005

A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br2− in the surrounding aqueous medium. The reaction 3Pmic + Br
→ P + 2 Br− was followed by optical absorption measurements in the 10−8−10−4–sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 106 sec−1 and 1 × 109M−1 · sec−1.

The fast component is related to the probability of a Br2− radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br2− radical–micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br2− radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented.
An investigation of nonequilibrium kinetic isotope effects in chemically activated vinyl radicals
Authors: Keil D. G. , Lynch K. P. , Cowfer J. A. , Michael J. V.
Published: January 2005

New experimental data have been obtained for H + C2H2, D + C2H2, H + C2D2, and D + C2D2 at room temperature. Two previously described apparatus were used in order to measure the pressure dependence of the reactions. The absolute rate constants are compared to results from other laboratories. The present results and those of Payne and Stief are used to obtain the high‐pressure limiting rate constant at room temperature. When the activation energy from the work of Payne and Stief is considered, it is shown that the A factor for H + C2H2 is too low by a factor of ∼20. If a transmission coefficient is introduced which is constant for all isotopic variations, the pressure dependence can be explained in terms of the randomly energized radicals. RRKM theory is then invoked to explain the observed statistical nonequilibrium kinetic isotope effects.
Kinetics and mechanism of the gas‐phase reaction of O(3P) atoms with acetone
Authors: Lee J. H. , Timmons Richard B.
Published: January 2005

The kinetics of the reaction of O(3P) atoms with acetone were investigated using fast flow methods. The reaction was studied over a temperature range of 298 to 478°K. The specific rate constant obtained was (1.9 ± 0.4) × 1012 exp(—5040 ± 180/1.987 T) cm3/mol·sec. The observation of a sizable primary H/D kinetic isotope effect in comparing rates of CH3COCH3 and CD3COCD3 led to the conclusion that the major reaction channel involves H atom abstraction, namely,

The rather low Arrhenius preexponential factor obtained in this reaction is compared and contrasted with those reported for other reactions of O(3P) with low molecular weight compounds.
The very low‐pressure pyrolysis of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether and the enthalpy of formation of the phenoxy radical
Authors: Colussi A. J. , Zabel F. , Benson S. W.
Published: January 2005

A value of the enthalpy of formation of the phenoxy radical in the gas phase, ΔH°,298K (ϕO·, g) = 11.4 ± 2.0 kcal/mol, has been obtained from the kinetic study of the unimolecular decompositions of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether

Trivial names for ethoxy benzene, 2‐propenoxy (allyloxy) benzene, and α‐methoxytoluene, respectively

at very low pressures. Bond fission, producing phenoxy or benzyl radicals, respectively, is the only mode of decomposition in each case. The present value leads to a bond dissociation energy BDE(ϕO—H) = 86.5 ± 2 kcal/mol,

1 kcal = 4.18674 kJ (absolute)

in good agreement with recent estimates made on the basis of competitive oxidation steps in the liquid phase. A comparison with bond dissociation energies of aliphatic alcohols, BDE(RO—H) = 104 kcal/mol, reveals that the stabilization energy of the phenoxy radical (17.5 kcal/mol) is considerably greater than the one observed for the isoelectronic benzyl radical (13.2 kcal/mol). Decomposition of phenoxy radicals into cyclopentadienyl radicals and CO has been observed at temperatures above 1000°K, and a mechanism for this reaction is proposed.
Kinetics of the Fe3+ ion–H2O2 reaction: Steady‐state and terminal‐state analysis
Authors: Kremer Mordechai L. , Stein Gabriel
Published: January 2005

Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H2O2 by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe3+ and H2O2 becomes stabilized.
Kinetics of gas‐phase addition reactions of methyl radicals. I. Addition to ethylene, acetylene, and benzene
Authors: Holt Pauline M. , Kerr J. Alistair
Published: January 2005

The reactions have been studied by a mass‐balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived:

Temperature

E
log A
range

Reaction
(kcal/mol)
(1./mol·sec)
(°K)

ĊH3 + C2H4 → Ċ3H7
7.3 ± 1.0
8.32 ± 0.5
350 – 500

ĊH3 + C2H2 → Ċ3H5
7.7 ± 1.5
8.79 ± 0.8
379 – 487

ĊH3 + C6H6 → C7H9
7.6 ± 1.0
8.79 ± 0.5
372 – 484

The results for methyl addition to ethylene are based on previous determinations by other techniques as well as the present studies. The results for methyl addition to acetylene and benzene are derived solely from the present experiments and are calculated relative to a rate constant of log k2(l./mol·sec) = 7.42 ‐ (7.1/θ) for the reference reaction (2), ·H3 + (CH3)3CH → CH4 + ·4H9.
Kinetics and mechanism of the reaction H + CH3ONO
Authors: Moortgat G. K. , ŠSlemr F. , Warneck P.
Published: January 2005

The reaction of hydrogen atoms with methyl nitrite was studied in a fast‐flow system using photoionization mass spectrometry and excess atomic hydrogen. The associated bimolecular rate coefficient can be expressed by

in the temperature range of 223‐398°K. NO, CH3OH, CH4, C2H6, CH2O, and H2O are the main products; OH and CH3 radicals were detectable intermediates. The mechanism was deduced from the observed product yields using normal and deuterated reactants. The primary reaction steps were identified as
equation image
followed by a rapid unimolecular decomposition of CH2ONO into CH2O and NO. Since the extent of reaction channel (1b) could not be determined independently, only extreme limits could be obtained for the individual contributions of the two channels of reaction (3) which follows the generation of CH3O radicals:
equation image
The most probable values, k3a/k3 = 0.31 ± 0.30 and k3b/k3 = 0.69 ± 0.30, support the previous results on this reaction, although the range of uncertainties is much greater here.
The very low‐pressure pyrolysis of phenyl methyl sulfide and benzyl methyl sulfide. The enthalpy of formation of the methylthio and phenylthio radicals
Authors: Colussi A. J. , Benson S. W.
Published: January 2005

The kinetics and mechanisms of the unimolecular decompositions of phenyl methyl sulfide (PhSCH3) and benzyl methyl sulfide (PhCH2SCH3) have been studied at very low pressures (VLPP). Both reactions essentially proceed by simple carbon‐sulfur bond fission into the stabilized phenylthio (PhS·) and benzyl (PhCH2·) radicals, respectively. The bond dissociation energies BDE(PhS‐CH3) = 67.5 ± 2.0 kcal/mol and BDE(PhCH2‐SCH3) = 59.4 ± 2 kcal/mol, and the enthalpies of formation of the phenylthio and methylthio radicals ΔH° ,298K(PhS·, g) = 56.8 ± 2.0 kcal/mol and ΔH°f, 298K(CH3S·, g) = 34.2 ± 2.0 kcal/mol have been derived from the kinetic data, and the results are compared with earlier work on the same systems. The present values reveal that the stabilization energy of the phenylthio radical (9.6 kcal/mol) is considerably smaller than that observed for the related benzyl (13.2 kcal/mol) and phenoxy (17.5 kcal/mol) radicals.
Primary processes in the 147‐nm photolysis of 1,1‐dichloroethane
Authors: Salomon D. , Kirk A. W. , Tschuikow‐Roux E.
Published: January 2005

The room temperature photolysis of 1,1‐dichloroethane at 147 nm in the pressure range of 1.34‐196.2 torr is characterized almost entirely by the molecular elimination of HCl, Cl2, and small quantities of H2. Acetylene is also produced. While it is possible that the C2H2 arises, in part, from the decomposition of vibrationally excited ground states of C2H3Cl and/or C2H4, in this particlar case serious consideration has to be given to alternative explanations where the products of the primary processes are formed in electronically excited states. The ±, elimination of molecular chlorine is not inconsistent with an increased degree of ClCl interaction predicted for a «Rydberg «state of 1,1‐C2H4Cl2. Varying small yields of CH4 are observed in the presence and absence of NO. The effect of large pressures of CF4 on the quantum yields of the major products is extremely small. The extinction coefficient for 1,1‐C2H4Cl2 at 147 nm and 296°K is 246 ± 29 cm−1 ± atm−1.
Kinetics of the gas‐phase elimination of isopropyl α‐halo acetates and the taft correlation
Authors: Chuchani Gabriel , Hernandez Jose A. , Yepez Magdalia , Alonso Miguel E.
Published: January 2005

The gas‐phase pyrolysis of three secondary acetates in the temperature range of 290‐350°C and the pressure range of 40‐236 mm Hg reveals a homogeneous first‐order law and unimolecular elimination. The rate constants are given by the following Arrhenius equations: isopropyl fluoroacetate:

isopropyl chloroacetate:

isopropyl iodoacetate:

The differences in rates I > Br > Cl > F apparently question previous assumptions where the pyrolyses of esters follow the same sequence as acid strength. The experimental data give a good correlation with σ* values, where ρ* = ‐1.85 at 330°C. Some kind of discrete bond polarization at the CαO bond of the acetate in the cyclic transition state seems to be involved in this type of reactions.
Estimation of rate constants as a function of temperature for the reactions W + XYZ = WX + YZ, where W, X, Y, and Z are H or O atoms
Authors: Shaw Robert
Published: January 2005

Rate constants have been estimated as a function of temperature for seven reactions of the type W + XYZ = WX + YZ, where W, X, Y, and Z are H and O atoms. From transition state theory and estimates of the heat capacities of activation,

where int k is the rate constant per transferable atom for the forward and reverse reactions in the exothermic direction, and where ΔH°≠298 is in kcal/mol. Values of ΔS°≠298 and ΔH°≠298 were obtained from the above equation and previously measured and evaluated rate constants at 298°K. The results are summarized in a table. Rate constants were calculated at temperature from 250 to 2000 K. The estimated rate constants were compared with recommended values. The results for ΔH°≠298 for reactions (15), (16), (17), and (19), in which a stable intermediate may precede the transition state, together with similar results previously found for reactions X + YZ = XY + Z, suggests that many such reactions may have values of ΔH°≠298 that are close to zero. The result for the reaction O + O3 = O2 + O2 is however, an exception to the foregoing perhaps because it is the reaction of a singlet with a triplet.ΔS°≠298 for the same reaction is unexpectedly low.
The triplet state of 4‐nitro‐N, N‐dimethynaphthylamine
Authors: Capellos C. , Lang F.
Published: January 2005

Nanosecond laser photolytic studies of 4‐nitro‐N,N‐dimethylnaphthylamine (4‐NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500‐510‐nm range. This species is assigned to the lowest triplet excited state of 4‐NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n‐hexane the lifetime 1/k of the triplet state is 9.1 × 10−6 sec, while in acetonitrile 1/k is 2.0 × 10−7 sec. The hydrogen abstraction rate constant kH of the triplet state with tributyl tin hydride (Bu3SnH) in n‐hexane is 1.7 × 107M−1·sec−1, while in the case of isopropyl alcohol as hydrogen donor, kH is 4.0 × 107M−1·sec−1. The activation energy for the hydrogen abstraction by the triplet state from Bu3SnH in deaerated n‐hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n‐π* state which retains its n‐π* character even in polar media.
Absolute rate constants for the reactions of O(3P) atoms with DCl and DBr
Authors: Brown Raymond D. H. , Smith Ian W. M.
Published: January 2005

Earlier work on the reactions of O(3P) atoms with HCl and HBr has been extended by measuring rate constants for
equation image

A flow‐tube method was used with chemiluminescent monitoring of the removal of atomic oxygen. Rate constants were measured at temperatures between 340 and 489 K for (2a) and 295 and 419 K for (2b); they can be matched by the Arrhenius expressions:

where the units are cm3 molecule−1 sec−1 and the errors correspond to a single standard deviation. The results of a quasiclassical trajectory study of collisions of O(3P) with HCl (v = 0,1, and 2) and DCl (v= 0,1, and 2) are also reported. These strengthen the conclusion that, although the rates of reactions (1a) and (2a) are selectively enhanced by vibrationally exciting HCl or DCl, molecules with 0 < v ⩽ 2 are mainly removed in collisions with O(3P) atoms by nonreactive relaxation.
The reaction of S(3P) atoms with nitric oxide
Authors: Van Roodselaar A. , Obi K. , Strausz O. P.
Published: January 2005

The flash photolysis–vacuum ultraviolet kinetic absorption spectroscopy technique has been used to measure the absolute rate constant for the reaction of ground state S(3P) atoms withnitric oxide,\documentclass{article}\pagestyle{empty}\begin{document}${\rm S}\left({^{\rm 3} P} \right) + {\rm NO}\mathop {\longrightarrow}\limits^{\rm M} {\rm SNO}\left({{\rm M} = {\rm CO}_2} \right)$\end{document}as a function of nitric oxide concentration and total pressure. The rateconstant was determined to be 1.9±0.1 × 101112/mol2.sec at 298°K, with a high‐pressure limit of 9.3 ± 2.1×109l/mol·sec−1. The observed kinetics are consistent with a termolecular energy transfer mechanism.
Kinetics of the thermal decomposition of bis‐pentafluorine sulfur peroxide in the presence of carbon monoxide
Authors: Czarnowski J. , Schumacher H. J.
Published: January 2005

The thermal decomposition of F5SOOSF5, P, in the presence of CO has been investigated between 130.1° and 161.9°C at total pressures between 50 and 600 torr. The reaction is homogeneous, and the only final products formed are CO2 and S2F10. The rate of reaction is proportional to the pressure of P. The partial pressures of CO and O2 and the total pressure have no influence on the course of reaction:

The results are explained by the following mechanism:
equation image
Kinetics of fluorescence decay of SO2 excited in the 2662–3273 Å region
Authors: Su Fu , Bottenheim Jan W. , Sidebottom Howard W. , Calvert Jack G. , Damon Edward K.
Published: January 2005

The kinetics of fluorescence decay of SO2 excited in the 2975–3273 Å region was studied using a powerful, frequency doubled, tunable dye laser system. The existence of two emitting species, first observed by Brus and McDonald, was confirmed. The collision‐free lifetimes of the long‐lived (L) species ranged from 100 to 300 μsec and the short‐lived (S) species from 17 to 43 μsec over the wavelength range employed. The magnitude of the bimolecular quenching rate constant for the L state was a function of the excitation energy; the data show that about 1 kcal/mol of internal energy is lost per collision of the SO2(L) species excited in the range of 2998–3107 Å. Studies of the relative initial fluorescence intensity of the S to that of the L state (IS°/IL°) were made in experiments which extended to 0.11 mtorr. The pressure dependence of the IS°/IL° ratio for experiments at 3107, 3211, and 3225 Åproved that the S and L states do not decay independently. Either efficient bimolecular S → L conversion occurs or bimolecular S ⇄ L interconversion of both states is important. These data coupled with spectroscopic studies of Hamada and Merer and Shaw and coworkers favor the designation of the S and L states as SO2(1A2) and SO2(1B1), respectively. However, if the assignment is correct, then the band origin of the 1B1 state must be at a somewhat longer wavelength, λ> 3273 Å than tentative spectroscopic assignments suggest. Bimolecular quenching rate constants for the L and S components with various atmospheric gases were determined in 3130‐ and 2662‐Å studies.
Stopped‐flow study of the gas‐phase reaction of ozone with organic sulfides: Dimethyl sulfide
Authors: Martinez Richard I. , Herron John T.
Published: January 2005

The autoinhibiting reaction of ozone with dimethyl sulfide (DMS), has been studied at 296°K and 1.1 kPa (8 torr) as a function of the concentrations of both reactants. The major products of the reaction are H2CO, H2O, CO, and SO2. The specific rate of primary attack of O3 on DMS is immeasurably slow. It is suggested that the rapid overall rate observed for this reaction is due to a chain reaction initiated by the very slow primary reaction. It is concluded that reaction (1) cannot be important under atmospheric conditions and that the major loss process for DMS in the atmosphere is probably reaction with photochemically generated free radicals.
Dynamics of a conformational change in aqueous 18‐crown‐6 by an ultrasonic absorption method
Authors: Liesegang Gerard W. , Farrow Michael M. , Rodriguez Licesio J. , Burnham Roger K. , Eyring Edward M. , Purdie Neil
Published: January 2005

A temperature dependence study of the ultrasonic amplitudes, velocities, and relaxation times for a presumed conformational transition of noncomplexed aqueous 18‐crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) is discussed. At all temperatures a single relaxation was observed within a 15–255‐MHz frequency range. The equilibrium constant for the presumed conformational transition \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CR}_1 \mathop \rightleftarrows\limits^{K_{12} } {\rm CR}_2 $\end{document} was determined to be K21 = (2 ± 2) × 10−2. The activation parameters are ΔH21≠ = 10.2 ± 1.0 kcal/mol, ΔS21≠ = 7.7 ± 0.2 cal/(mol·deg), ΔH12≠ = 7.4 ± 1.0 kcal/mol, and ΔS12≠ = 7.7 ± 0.2 cal/(mol·deg), while the thermodynamic enthalpy and entropy were found to be −2.6 ± 1.0 kcal/mol and 0 ± 0.2 cal/(mol·deg), respectively. The rate constants at 25.0°C for the presumed conformational transition are k21 = (1.0 ± 0.3) × 107 sec−1 and k12 = (6.2 ± 0.2) × 108 sec−1.
Evidence for strongly temperature‐dependent A factors in alkane decomposition and high heats of formation for alkyl radicals
Authors: Tsang Wing
Published: January 2005

The experimental data on alkane decomposition from shock‐tube and radical buffer studies and radical combination from very‐low‐pressure pyrolysis and modulation spectroscopy are shown to be consistent. They lead to experimental A factors which decrease by factors of 10–2000 from 300° to 1100°K. Heats of formation for ethyl, isopropyl, and t‐butyl radicals have been found to be 10, 10 and 20 kJ higher than currently accepted numbers from metathesis reactions.
Kinetics and mechanism of oxidation of aliphatic ketoximes by thallium(III) acetate—part I
Authors: Balakrishnan T. , Santappa M.
Published: January 2005

The oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20–40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H+], ionic strength, temperature, etc. The reactions were found to be totally second order–first order with respect to each reactant. The second‐order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one‐electron oxidation to the iminoxy radical followed by an another one‐electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.
Competition between multiphoton fluorescence and multiphoton ionization in NO
Authors: Jackson W. M. , Lin C. S.
Published: January 2005

A nitrogen laser pumped tunable dye laser has been used to observe the three‐photon ionization of NO through a two‐photon resonance with the C2II state. Fluorescence is also observed from this state. The wavelength dependence of both signals have been measured. A reaction mechanism is postulated, which includes the initial two‐photon excitation of the C2II state as the rate‐limiting step. This mechanism predicts the observed second‐order intensity dependence of the ionization signal and shows that the simple rate equation treatment is valid in this system.
Kinetics and mechanism of oxidation of diethyl ketone by N‐bromosuccinimide
Authors: Singh Kameshwar , Tiwari J. N. , Mushran S. P.
Published: January 2005

Oxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by using N‐bromosuccinimide (NBS) as oxidant in the temperature range of 25°‐50°C. It has been found that the order with respect to NBS is zero while with respect to diethyl ketone and [H+], it is unity. Succinimide, sodium perchlorate, and mercuric acetate have an insignificant effect on the reaction rate, while the dielectric effect was negative. A solvent isotope effect (k0D2O/k0H2O = 1.6–1.8) at 35°C has been observed. On the basis of the available evidences a suitable mechanism consistent with the experimental results has been proposed in which it is suggested that the mechanistic route for NBS oxidation in an acidic medium is through the enol form of the ketone. The magnitude of the solvent effect also supports the mechanism. Various activation parameters have been calculated, and the 1,2‐dicarbonyl compound has been identified as the end product of the reaction.
Thermal stability of cyclohexane and 1‐hexene
Authors: Tsang Wing
Published: January 2005

The mechanism and initial rates of decomposition of cyclohexane and 1‐hexene have been determined from single‐pulse shock‐tube experiments. The main initial processes involve isomerization of cyclohexane to 1‐hexene, followed by decomposition of 1‐hexene. From comparative rate experiments the following rate expressions have been derived:

The 1‐hexene bond‐braking reaction leads to an allylic resonance energy of 42.7 kJ and a heat of formation of allyl radicals of 176.6 kJ (300°K). There appear to be general relations relating the rate expressions for the decomposition of alkynes, alkanes, and alkenes. Studies on the induced decomposition of cyclohexane have also been carried out.
Computer modeling of smog chamber data: Progress in validation of a detailed mechanism for the photooxidation of propene and n‐butane in photochemical smog
Authors: Carter William P. L. , Lloyd Alan C. , Sprung Jeremy L. , Pitts James N.
Published: January 2005

A detailed mechanism is presented for reactions occurring during irradiation of part‐per‐million concentrations of propene and/or n‐butane and oxides of nitrogen in air. Data from an extensive series of well‐characterized smog chamber experiments carried out in our 5800‐liter evacuable chamber–solar simulator facility designed for providing data suitable for quantitative model validation were used to elucidate several unknown or uncertain kinetic parameters and details of the reaction mechanism.

The mechanism was then tested against the data base from the smog chamber runs. In general, most calculated concentration–time profiles agreed with experiments to within the experimental uncertainties. Fits were usually attained to within ∼±20% or better for ozone, NO, propene, and n‐butane, to within ∼±30% or better for NO2, PAN, methyl ethyl ketone, 2‐butyl nitrate, butyraldehyde, and (in runs not containing propene) methyl nitrate, to within ⋐±50% or better for the minor products 1‐butyl nitrate and propene oxide, and to within a factor of 2 for methyl nitrate in propene‐containing runs. Propionaldehyde was consistently underpredicted in all runs; it is probably a chamber contaminant. For formaldehyde and acetaldehyde, the major products in both systems, fits to within ⋐±20% were often obtained, yet for a number of experiments, significantly greater discrepancies were observed, probably as a result of experimental and/or analytical problems.

The good fits to experimental data were attained only after adjusting several rate constants or rate constant ratios related to uncertainties concerning chamber effects or the chemical mechanism. The largest uncertainty concerns the necessity to include in the mechanism a significant rate of radical input from unknown sources in the smog chamber. Other areas where fundamental kinetic and mechanistic data are most needed before a predictive, detailed propene + n‐butane‐NOx‐air smog model can be completely validated concern other chamber effects, the O3 + propene mechanism, decomposition rates of substituted alkoxy radicals, primary quantum yields for radical production as a function of wavelength for aldehyde and ketone photolyses, and the mechanisms and rates of reactions of peroxy radicals with NO and NO2.
The 5‐hexenyl cyclization
Authors: Schmid Peter , Griller David , Ingold Keith U.
Published: January 2005

The cyclization of the 5‐hexenyl radical to form the cyclopentylmethyl radical has been reexamined by kinetic EPR spectroscopy at temperatures between 183 and 232°K in cyclopropane solvent. The rate constant, kc for this important radical rearrangement can be represented by

where Θ = 2.3RT kcal/mol.
Rate constants for the combination of trichloromethyl radicals and the electron‐transfer reaction between hydroxymethyl radicals and carbon tetrachloride in solution
Authors: Paul H.
Published: January 2005

The rate constant for the bimolecular combination of trichloromethyl radicals in methanol is determined as a function of temperature by steady‐state kinetics and electron‐spin resonance with modulated radical initiation. The rate constant is in accord with the Smoluchowski equation and indicates a diffusion‐controlled radical termination. The temperature dependence of the rate constant for the electron‐transfer reaction between hydroxymethyl radicals and carbon tetrachloride in methanol is determined, and is found to disagree with predictions of the Marcus theory. This disagreement is tentatively ascribed to the structure of the transition state.
The question of the applicable time regime for the steady‐state approximation in the simulation of complex mechanisms
Authors: Edelson D.
Published: January 2005

A mechanism proposed by Pilling and Noyes for ignition in carbon monoxide containing traces of water has been modeled using a complete numerical integration, and results have been compared with the steady state treatment (QSSA) of the previous authors. The numerical results were found to be in close agreement. However, the complete solution also yields the time required for the steady state to be reached, and it is shown that this is too large for the results of the QSSA to be considered applicable to this problem. This is substantiated by a further calculation in which temperature is introduced as an additional variable, and it is shown that thermal runaway is reached without any of the intermediate radicals which propagate the reaction chain ever going into a steady state.

This study provides an example of the failure of QSSA to provide an adequate solution to a chemical kinetic problem for reasons which have not been previously discussed in the literature. For problems of more than a very few variables there is no practical way short of numerical integration to estimate the time regime during which the steady state applies. Practitioners of QSSA are thus advised of yet another precaution in assesing the credibility of their results.
Kinetics and mechanism of oxidation of sugars by quinquevalent vanadium in binary mixture solvents of DMSO–water and acetic acid–water in H2SO4 medium
Authors: Pati Subas C. , Panda Markandeswar
Published: January 2005

The kinetics of oxidation of aldosugars and ketosugar by quinquevalent vanadium in binary mixtures of DMSO–water and acetic acid–water in sulfuric acid medium have been studied. The reaction is first order in both oxidant and substrate. The effect of acidity on the reaction kinetics has been determined. The effect of acidity shows a clear difference. The ketose has a unit dependence, whereas aldoses have a 0.5 dependence in H0. The role of solvent in these reactions has also been studied, and the effect of temperature on these reactions has been determined. A suitable mechanism has been postulated taking all the observed facts into consideration.
The gas‐phase decomposition of alkoxy radicals
Authors: Batt L.
Published: January 2005

It is shown that it is possible to obtain good data for the rate constant for the decomposition of alkoxy radicals [RO] by using nitric oxide as a radical trap. Two experimental systems have been used.

The first system involves the use of dialkyl peroxides [(RO)2] as thermal sources of alkoxy radicals. The peroxide concentration was ∼10−4M, nitric oxide ∼2 × 10−4M, and the extent of reaction was ∼10%. The total pressure was altered using carbon tetrafluoride as an inert gas. The mechanism is
equation image
Hence R2/R3 = k2[NO]/k3. Our previous studies show that k2 lies in the range 1010.3±0.2M−1·sec−1.

The second system employs alkyl nitrites [RONO] as a thermal source of alkoxy radicals. The experimental conditions are very similar, except that we chose to use an atmosphere of nitric oxide for initial experiments. If anything nitric oxide appears to be superior to carbon tetrafluoride as an energy transfer agent. The mechanism is
equation image
Hence R3 = k1'k3[RONO]/(k3 + k2 + k6 [NO]).

Results are given for R = t‐Am, s‐Bu, t‐Bu, i‐Pr, Et, and Me. In addition the first unequivocal evidence is given for the pressure dependence of k3 when R = t‐Bu. The implications for atmospheric chemistry and combustion are also discussed.
A quantitative study of alkyl radical reactions by kinetic spectroscopy III. Absorption spectrum and rate constants of mutual interaction for the ethyl radical
Authors: Adachi Hiroyuki , Basco N. , James D. G. L.
Published: January 2005

Intrinsic spectral and kinetic parameters have been measured for the ethyl radical, which was formed in the gas phase by the flash photolysis of azoethane. Absolute values of the extinction coefficient ϵ(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of the ethyl radical. The absorption spectrum is broad, structureless, and comparatively weak; ϵ(247) = 4.8 × 102 l/mol·cm at the maximum, and the oscillator strength is (9.1 ± 0.5) × 10−3. This is in good qualitative agreement with a spectrum obtained independently using the technique of molecular modulation spectrometry.

The biomolecular reactions of mutual interaction were the only significant reactions of the ethyl radical in this system; kinetic analysis of the second‐order decline of the absorbance during the dark period yielded a value of k/ϵ(λ) for each experiment. The rate constant for mutual interaction was evaluated from the product of corresponding measurements of k/ϵ(λ) and ϵ(λ) individual values are independent of the wavelength of measurement, and the mean value is k = (1.40 ± 0.27) × 1010 l/mol·sec. The rate constant for mutual combination was derived with the aid of product analysis as k2 = (1.24 ± 0.23) × 1010 l/mol·sec; it stands in close agreement with the set of “high” values obtained by direct measurement using a variety of methods.
Weak collision effects: Non‐steady‐state thermal unimolecular reactions
Authors: Malins R. J. , Tardy D. C.
Published: January 2005

Bench‐mark calculations for non‐steady‐state thermal systems are presented. Although the equations and calculations were modeled for the isomerization of cyclopropane in the single‐pulse shock tube, the results are qualitatively and semiquantitatively correct for any experimental technique in which a finite time is required to energize the reactant to the reaction temperature. A useful parameter in describing this nonequilibrium behavior is the induction time τ95; the log of τ95 is linearly related to the collision frequency ω. For the model cyclopropane system a steady state is reached in ∼1 msec when ω ≈ 108 sec−1 and T ≈ 1500 K.
Neighboring olefinic double‐bond participation in gas phase pyrolysis of some alkenyl chlorides
Authors: Chuchani Gabriel , Hernandeza. Jose A. , Martin Ignacio
Published: January 2005

4‐Chloro‐1‐butene, 5‐chloro‐1‐pentene, and 6‐chloro‐1‐hexene have been shown to decompose, in a static system, mainly to hydrogen chloride and the corresponding alkadienes. In packed and unpacked clean Pyrex vessels the reactions were significantly heterogeneous. However, in a vessel seasoned with allyl bromide these reactions were homogeneous, unimolecular, and follow a first‐order law. The working temperature range was 389.6–480.0°C and with a pressure range of 53–221 Torr. The rate constants for the homogeneous reactions were expressed by the following Arrhenius equations: 4‐chloro‐1‐butene: logk(sec−1) = (13.79 ± 0.17) – (223.8 ± 2.1)kJ/mole/2.303RT; 5‐chloro‐1‐pentene: logk(sec−1) = (14.25 ± 1.20) – (238.4 ± 12.7)kJ/mole/2.303RT; and 6‐chloro‐1‐hexene: logk(sec−1) = (12.38 ± 0.22) – (209.6 ± 2.9)kJ/mole/2.303RT. The olefinic double bond has been found to participate in the rate of dehydrohalogenation of 4‐chloro‐1‐butene. The insulation of the CH2CH in chlorobutene by one or two methylene chains to the reaction center does not indicate neighboring group participation. The three‐membered conformation is the most favored structure for anchimeric assistance of the double bond in gas phase pyrolysis of alkenyl chlorides. The heterolytic nature of these eliminations is also supported by the present work.
The kinetics and the mechanism of the oxidation of carbon monoxide in the presence of hydrogen
Authors: Arustamyan A. M. , Shakhnazaryan I. K. , Philipossyan A. G. , Nalbandyan A. B.
Published: January 2005

The kinetics of the slow oxidation of CO in the presence of H2 have been studied above the second explosion limit for the mixture 2CO + O2 + X% H2 at the temperature range of 530–570°C, pressures from 300 to 530 torr, and hydrogen contents of 1.1, 2.8, and 5.7%. The second explosion limit has been experimentally determined for the mixture of 2CO + O2 containing 1.0, 3.0, and 5.7% H2. On the basis of the oxidation scheme of CO in the presence of H2, which includes the accepted mechanism of oxidation of hydrogen supplemented by the reactions in which CO takes part, the second explosion limit and the profiles of the slow reaction are calculated by computer methods. The agreement found between experimental and calculated values allows one to conclude that the scheme under consideration rather completely described the slow reaction above the second limit and the occurrence of the second explosion limit in the mixture CO–O2–H2. The rate constant for the reaction HO2 + CO → OH + CO2 was calculated from the experimental data and was found to agree with previous determinations.
Oxidation of cyanogen. II. The mechanism of the oxidation
Authors: Lifshitz Assa , Frenklach Michael
Published: January 2005

A detailed investigation of the mechanism of cyanogen oxidation is presented. Recent induction time measurements of ignition in cyanogen–oxygen–argon mixtures behind reflected shocks are computer modeled to obtain an agreement between the experimental and calculated values. A 15‐step reaction scheme is suggested to reproduce the parameters E and βi in the experimental parametric relation: τ = 10αexp(E/RT)IICiβi. An explanation is offered to the very strong dependence of the induction time on the cyanogen concentration and the very weak dependence on the oxygen concentration. The sensitivity spectrum shows that the induction time is highly dependent on the O + C2N2 → NCO + CN and NCO + M → N + CO + M reactions (shortened) and the O + NCO → CO + NO and N + NCO → N2 + CO reactions (increased).
The thermal decompositions of carbamates. IV. The ethyl Nmethylcarbamate system
Authors: Daly N. J. , Ziolkowski F.
Published: January 2005

Ethyl Nmethylcarbamate decomposes thermally over the temperature range of 600–650 K by competing first‐order reactions, one forming methylamine, carbon dioxide, and ethylene, the other forming methyl isocyanate and ethanol. The first‐order rate constants are described in S1 units by the equations
equation image
where R = 1.986 cal/deg mol. The appareance of symdimethylurea among the products raised the possibility of gas‐phase transesterifications. These were ruled out by the study of the reactions of sym‐dimethylurea at 604 K which showed its behavior to be well explained by the rapid decomposition in the gas phase
equation image
which is reversed in the condensation stage in the analysis.
Study of the ethane oxidation reaction by the kinetic tracer method
Authors: Moshkina R. I. , Polyak S. S. , Sokolova N. A. , Masterovoi I. F. , Nalbandyan A. B.
Published: January 2005

The kinetics of ethane oxidation was studied at 320, 340, 353 and 380°C, mixture composition 2 C2H6 + 1 O2, and total pressure 609 torr. It was found that at 320°C CH2O and CH3CHO were branching agents. A series of experiments was conducted on 2C2H6 + O2 oxidation in the presence of 0.7% 14C‐labeled ethylene. The ethylene oxide was found to form only from C2H4, formaldehyde formed from C2H4 and C2H6; and CH3CHO, C2H5OH, and CH3OH formed only from ethane. The formation rates of C2H4, C2H4O, and CH2O were calculated by the kinetic tracer method. At 320°C the fraction of oxygen‐containing products formed from C2H4 was 16–18%, and at 353 and 380°C it was 30–40%.
Carbon kinetic isotope effect in the oxidation of methane by hydroxyl
Authors: Rust Fleet , Stevens C. M.
Published: January 2005

The carbon kinetic isotope effect in the reaction of CH4 with OH has an experimentally measured value of 1.003. The measurement was performed using a static system in which the source of OH was the gas‐phase photolysis of H2O2 with ultraviolet light produced by a high‐pressure mercury arc lamp. Implications for the tropospheric cycle of CH4 are considered briefly.
Thermal decomposition of ammonia in shock waves
Authors: Yumura M. , Asaba T. , Matsumoto Y. , Matsui H.
Published: January 2005

The thermal decomposition of ammonia was studied by means of the shock‐tube and vacuum ultraviolet absorption spectroscopy monitoring the concentration of atomic hydrogen. The rate constants of both the initiation reaction
equation image
and the consecutive reaction
equation image
were determined directly as

and

respectively.
Kinetics and mechanism of the autoxidation of pentaerythrityl tetraheptanoate at 180–220°C
Authors: Hamilton Edwin J. , Korcek Stefan , Mahoney Lee R. , Zinbo Mikio
Published: January 2005

A kinetic and mechanistic study of the autoxidation of liquid pentaerythrityl tetraheptanoate (PETH) at 180–220°C has been carried out utilizing a stirred‐flow reactor. The results are consistent with the occurrence of a chain reaction scheme similar to that proposed for n‐hexadecane autoxidation, namely, the formation of monohydroperoxides by the intermolecular abstraction reaction (3), the formation of α,γ‐ and α,δ‐dihydroperoxides and α,γ‐ and α,δ‐hydroperoxyketones by intramolecular peroxy radical abstraction reactions (4) and (4*), the bimolecular termination of peroxy radicals, reaction (6), and the rapid conversion of α,γ‐hydroperoxyketones to the corresponding cleavage acids and methyl ketones, reaction (7). Comparisons of various rate parameters for the n‐hexadecane and PETH systems reveal that the values of k7 and (k3/H atom)/(2 k6)1/2 are within experimental uncertainties identical for the two systems at 180°C. The proposed reaction scheme includes the concurrent formation of hydroxy radicals and hydroperoxyketone species. The results of kinetic analysis and the experimentally observed isomer distributions of primary and secondary monohydroperoxide products at high and low oxygen pressures suggest that ≈60% of the hydrogen abstractions from PETH at high oxygen pressures occur by hydroxy radicals.
Rate constants for self‐ and cross terminations of transient radicals in solution by effect modulated electron spin resonance spectroscopy
Authors: Paul H. , Segaud C.
Published: January 2005

It is shown how electron spin resonance spectroscopy with modulated radical initiation can be used to analyze by purely spectroscopic means the second‐order termination kinetics of systems containing two different kinds of radicals. The technique is applied to species generated by photoreduction of acetone in tetraethoxy silane. The bimolecular self‐ and cross reactions of\documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm O)}_{\rm 3} {\rm SiO\dot CHCH}_{\rm 3} (\dot R_1 )\,and\,(CH_3 )_2 \dot COH(\dot R_2 )$\end{document}are found to be encounter‐controlled processes. For the cross termination the often used relationk12= (4k1k2)1/2is verified experimentally.
Rate data for O + OCS → SO + CO and SO + O3 → SO2 + O2 by a new time‐resolved technique
Authors: Robertshaw John S. , Smith Ian W. M.
Published: January 2005

Pulsed laser photolysis of O3 in a large excess of N2 has been used to generate O(3P) atoms in the presence of OCS. By observing chemiluminescence from the small fraction of electronically excited SO2 formed in the reaction of SO with O3, rate constants of (1.7 ± 0.2) × 10−14 and (8.7 ± 1.6) × 10−14 cm3/molecule sec have been determined at 296 ± 4 K for the reactions
equation image
and
equation image

In addition, it has been shown that any reaction between SO and OCS has a rate constant 10−14 cm3/molecule sec.
Kinetics and mechanism of the bromination of aromatic compounds by N‐bromosuccinimide in solution
Authors: Sivakamasundari S. , Ganesan R.
Published: January 2005

The kinetics of bromination of several aromatic compounds (anilides, anisoles, and phenols) was investigated in 80% aqueous acetic acid (v/v) in the temperature range 20–50°C using N‐bromosuccinimide (NBS) as the reagent. The reaction was found to be first order in the aromatic substrate (ArH), and zero order in NBS, the overall order being 1. Stoichiometry of the reaction was 1:1. An increase in solvent polarity increased the reaction rate, and chloride ions were found to be specific catalysts for the reaction. Arrhenius activation energy remained almost constant for all the substrates. A probable mechanism explaining all these observed facts was proposed. The mechanism involved an attack by Br+ or more probably by a solvated Br+ ion on the aromatic substrate.
Photooxidation of 1,3‐butadiene containing systems: Rate constant determination for the reaction of acrolein with ⋅OH radicals
Authors: Maldotti Andrea , Chiorboli Claudio , Bignozzi Carlo A. , Bartocci Carlo , Carassiti Vittorio
Published: January 2005

The photooxidation of the 1,3‐butadiene–NO–air system at 298 ± 2 K was investigated in an environmental chamber under simulated atmospheric conditions. The irradiation gave rise to the formation of acrolein in a 55% yield, based on 1,3‐butadiene initial concentration for all the experimental runs.

The rate of formation of acrolein was the same as that of 1,3‐butadiene consumption, indicating that acrolein is the major product of the 1,3‐butadiene oxidation in air.

The dependence of acrolein concentration on irradiation time showed thata secondary process, identified as an oxidation of acrolein by ⋅OH radicals, was occurring during the photochemical runs. The rate constant of this secondary process was determined by measuring the relative rates of disappearance of acrolein and n‐butane during the irradiation of acrolein‐n‐butane‐NO‐air mixtures. The so obtained relative rate constant value was placed on an absolute basis using a reported rate constant for the n‐butane + ⋅OH reaction; a value of (1.6 ± 0.2) × 1010 M−1 sec−1 was obtained.