bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical rate constant calculations for O(3P) with saturated hydrocarbons
Authors: Michael J. V. , Keil D. G. , Klemm R. B.
Published: January 2005

Theoretical rate constants have been calculated for O(3P) with five saturated hydrocarbons, CH4, C2H6, C3H8, iso‐C4H10, and neo‐C5H12. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(3P) + CH4 is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO‐ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.
Kinetic and mechanistic studies of oxidation of alanine and phenylalanine by sodium N‐chlorobenzene sulfonamide (chloramine‐B) in hydrochloric acid medium
Authors: Mahadevappa D. S. , Ahmed M. Sayeed , Gowda N. M. Made , Gowda B. Thimme
Published: January 2005

The kinetics of oxidation of alanine and phenylalanine by sodium N‐chlorobenzene sulfonamide (CAB) has been investigated at 30°C in two ranges of acid concentrations. The reactions follow identical kinetics for both amino acids. At low acid concentration (0.03–0.10M), simultaneous catalysis by H+ and Cl− ions is noted. The rate shows a first‐order dependence on [CAB], but is independent of [substrate]. A variation of the ionic strength or the dielectric constant of the medium or the presence of the added reaction product benzene sulfonamide (BSA) has no pronounced effect on the rate.

At [HCl] > 0.2M, the rate is independent of [H+], but shows a first‐order dependence on [CAB] and a fractional‐order dependence on [amino acid]. The addition of BSA or Cl− ions, or a change in the ionic strength of the medium has no influence on the rate. Upon decreasing the dielectric constant of the medium, the rate increased, indicating positive ion–dipole interaction in the rate‐determining step. The reaction was studied at different temperatures, and activation parameters have been computed. Rate laws in agreement with experimental results have been derived. Suitable mechanisms to account for the observed kinetics are proposed. The rate constants obtained from the derived rate laws as [H+], [Cl−], and [substrate] vary are in excellent agreement with the observed rate constants, thus justifying the proposed rate laws and hence the suggested mechanistic schemes.
Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium
Authors: Sahu R. , Neogi G. , Acharya S. , Panda R. K.
Published: January 2005

The kinetics of electron transfer from hexacyanoferrate(II) to tris(dimethylglyoximato)‐nickelate(IV), Ni(dmg)32−, to produce Fe(CN)63− and Ni(dmgH)2, follows a pseudo‐first‐order disappearance in the Ni(IV). The pseudo‐first‐order rate constants kobs are linearly dependent on [Fe(CN)64−]0 in a fiftyfold range of 2 × 10−4−1 × 10−2M, and the average values of kobs/[Fe(CN)64−]0 range from 194M−1·s−1 at pH = 5.20 to 0.2M−1·s−1 at pH = 9.07 in aqueous medium at 35°C and μ = 0.57M. Results are interpreted in terms of a probable mechanism involving rate‐determining outer sphere one‐electron transfer steps from the reductant and one‐protonated reductant species to the unprotonated and one‐protonated Ni(IV) species present in solution. The more electrophilic one‐protonated reductant species apparently reacts several orders of magnitude faster than the unprotonated one.
Kinetic and mechanistic studies on the oxidation of nitrite by peroxomonophosphoric acid
Authors: Panigrahi Ganesh Prasad , Nayak Ramanando
Published: January 2005

The kinetics of oxidation of nitrite to nitrate by peroxomonophosphoric acid in aqueous acid medium have been studied. The observed monotonic fall in rate with increasing pH of the medium has been rationalized on the basis of proton‐dissociation equilibria of the substrate as well as the oxidant species. It is found that only HNO2 reacts with the different PMPA species.
Disproportionation reactions between alkyl and fluoroalkyl radicals. II. Fluoro‐ and trifluoromethyl with ethyl radicals
Authors: Pritchard G. O. , Nilsson W. B. , Marchant P. E. , Case L. C. , Parmer J. F. , Youngs R. F.
Published: January 2005

Cross‐disproportionation/combination ratios for CFH2 and CF3 with C2H5 radicals have been determined to be Δ = 0.032 ± 0.012 and δ = 0.098 ± 0.020, respectively, over the temperature range 25–75°C. For the pathway that yields CFH and C2H6, δ = 0.020 ± 0.005 at 25°C.
Pseudo‐phase ion‐exchange model for micellar catalysis in the acid hydrolysis of vinyl ethers
Authors: Velázquez Maria Mercedes , García‐Mateos Inmaculada , Herraez Miguel A. , Rodriguez Licesio J.
Published: January 2005

The rate of the perchloric acid hydrolysis of aqueous ethyl and butyl vinyl ethers at 25.0°C, in the presence of micellar aggregates [anionic, sodium dodecyl sulfate (SDS); cationic, cetyl trymethyl ammonium bromide (CTAB); and nonionic, polyoxyethylen23dodecanol, (Brij 35)], has been studied. Negligible effects were observed in the cases of cationic and nonionic micelles. Anionic micelles produce an enhancement in the reaction velocity, and the rate constants go through maxima with increasing SDS concentration. These maxima disappear in the presence of excess sodium perchlorate. All these facts are interpreted quantitatively by means of the pseudo‐phase ion‐exchange model.
Kinetic characteristics of chloride‐assisted oxidative dealkylation of alkylcobalamins
Authors: Fanchiang Yueh‐Tai
Published: January 2005

The recent experiments on the chloride‐assisted dealkylation of alkylcobalamins by a variety of oxidants (IrCl, AuCl, Fe(H2O)5Cl2+, and PtCl), which are scattered in several previous publications, and their general kinetic characteristics are summarized. The kinetic studies are also extended to include the dealkylations of (methylaquo)−3,5,6‐trimethylbenzimidazolylcobamide and protonated base‐off ethylcobalamin by IrCl (1.0M Cl−) and by Fe(III) ions at 0.1M Cl−, and the demethylation of (methylaquo)−3,5,6‐trimethylbenzimidazolylcobamide by AuCl (1.0M Cl−). This extension is in an effort to substantiate the general mechanism which has been previously proposed for these oxidative dealkylations. The general kinetic characteristics are described in terms of a preassociation of the reactants, followed by a rate‐determining electron‐transfer process to yield the R‐B radical, which then undergoes further reactions to produce the products observed. The overall reactions are discussed within the framework of chlorine‐bridging inner sphere electron‐transfer reactions.
Kinetics of tetrachloroethylene photochlorination
Authors: Ledakowicz S. , Nowicki L. , Perkowski J.
Published: January 2005

Photochlorination of tetrachloroethylene has been studied in a homogeneous liquid system. Kinetic parameters such as reaction orders for chlorine, tetracholoroethylene and light intensity, preexponential factor, and activation energy were evaluated from experimental data. The following kinetic equation was obtained by parameter estimation following the Marquardt procedure:
Kinetics of recombination, dismutation, and disproportionation reactions involving neutral ketyl radicals and radical anions
Authors: Koroli L. L. , Kuzmin V. A. , Khudyakov I. V.
Published: January 2005

The kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH⋅),
equation image
the dismutation of benzophenone radical anions,
equation image
the disproportionation between BPH⋅ and stable nitroxyl radicals, (magnified image), magnified image and the electron transfer magnified image have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n‐hexane is controlled by diffusion with 2k1 ≃ kdiff. In aliphatic alcohols and toluene, which form solvation complexes with BPH⋅, reaction (1) is diffusion‐enhanced and activation‐controlled, respectively, with 2k1 < kdiff. In a viscous solvent such as 1‐propanol–glycerol mixture (100 ≲ η ≲ 450 cP) reaction (1) is diffusion‐controlled. Reaction (2) in alkaline 1‐propanol and alkaline 1‐propanol–glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water–glycerol and 1‐propanol–glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k3 (k4) are 2–6 times as small as the corresponding kdiff values due to the low steric factor of the reactions (therefore called pseudodiffusion‐controlled reactions). The theoretical estimates of k3 (k4) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.
Liquid‐phase autooxidation of retinyl polyenes
Authors: Finkelshtein E. I. , Rubchinskaya Yu. M. , Kozlov E. I.
Published: January 2005

The autooxidation of retinyl acetate and methyl retinoate was investigated in chlorobenzene at 45°C. The rates of thermal initiation in the retinyl acetate solutions were measured, and a value was determined of the rate constant for the reaction of oxygen with retinyl acetate (RH + O2→ R· + HO2·):kio= (1.3 ± 0.2) × 10−5L/mol · s. The number of moles of oxygen absorbed per mole of polyene depends on the substrate concentration. A kinetic scheme for the methyl retinoate autooxidation was proposed which takes into account the isomerization of primary peroxy radicals, and the rate constants for different elementary reactions were estimated. The partial rate constant for “allylic” hydrogen abstraction from retinyl acetate was estimated to be ≥ 1.65 × 103L/mol · s. A probable propagation sequence was proposed for the autooxidation of retinyl acetate.
Kinetics of rich ammonia flames
Authors: Dean Anthony M. , Chou Mau‐Song , Stern David
Published: January 2005

We report laser absorption measurements of NH3 decay within the flame front region of rich, atmospheric pressure ammonia flames. These data are combined with earlier OH, NH, and NH2 measurements to obtain new estimates for the oscillator strength of NH2. This value, fi = 6.4 × 10−5 for the PQ1,7 line in the (0,9,0) ← (0,0.0) vibrational band of the A2A1 ← X2B1 transition, suggests ΔH(NH) ≅ 87 kcal/mol. The ammonia profiles were also combined with previous data on NO, NH, NH2, and OH to provide an extensive database at fuel equivalence ratios (ø) of 1.28, 1.50, and 1.81 for comparison to our kinetic model predictions. This modeling used a one‐dimensional flame code which explicitly accounts for the diffusional component in our flame experiments. Modeling results using a conventional mechanism predicted concentration profiles which deviated markedly from our observations. It was possible to obtain much more satisfactory fits by postulating reactions between various NHi (i = 1, 2) species to form N—N bonds. The N2Hj (j = 1–3) species could then lose H atoms via dissociation to ultimately form N2. Inclusion of these reactions in the mechanism allowed us to predict concentration—distance profiles for five different species at three different equivalence ratios that are in good agreement with experiment. The most important component of this mechanism is the recognition that the NHi + NHi reactions dominate the kinetics in rich flames. A most satisfying aspect of these calculations is that the key rate constants in the NHi + NHi sequence were estimated using simple RRK theory.
High temperature study of the reactions of O and OH with NH3
Authors: Salimian S. , Hanson R. K. , Kruger C. H.
Published: January 2005

Mixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750–2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration—time histories. The early‐time NH3 and OH concentration profiles were sensitive to the rate constants of the reactionsmagnified imageleading to the following best‐fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(−4470/T) and k3 = 1013.91±0.2 exp(‐4230/T) cm3 mol−1 s−1. The results of this study combined with previous low‐temperature data suggest a significant non‐Arrhenius behavior for both k2 and k3.
Kinetics of OH reactions with furan, thiophene, and tetrahydrothiophene
Authors: Wine P. H. , Thompson R. J.
Published: January 2005

The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254–425 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule−1 S−1): k1 = (1.33 ± 0.29) × 10−11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10−12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10−11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.
Rate constants for the reactions of OH radicals with alkyl substituted olefins
Authors: Ohta Tomohiro
Published: January 2005

Relative rate constants for the reactions of hydroxyl radicals with a series of alkyl substituted olefins were measured by competitive reactions between pairs of olefins at 298 ± 2 K and 1 atmospheric pressure. Hydroxyl radicals were produced by the photolysis of H2O2 with 254‐nm irradiation. The obtained rate constants were (× 10−11 cm3 molecule−1 s−1): 2.53 ± 0.06, propylene; 5.49 ± 0.17, cis‐2‐butene; 5.47 ± 0.1, isobutene; 6.46 ± 0.13, 2‐methyl‐1‐butene; 6.37 ± 0.16, cis‐2‐pentene; 6.23 ± 0.1, 2‐methyl‐1‐pentene; 8.76 ± 0.14, 2‐methyl‐2‐pentene; 6.24 ± 0.08, trans‐4‐methyl‐2‐pentene; 10.3 ± 0.1, 2,3‐dimethyl‐2‐butene; 9.94 ± 0.1, 2,3‐dimethyl‐2‐pentene; 5.59 ± 0.07, trans‐4,4‐dimethyl‐2‐pentene. A trend in alkyl substituent effect on the rate constant was found, which is useful to predict kOH on the basis of the number of alkyl substituents on the double bond.
Kinetics of the gas‐phase reactions of NO3 radicals with a series of aromatics at 296 ± 2 K
Authors: Atkinson Roger , Carter William P. L. , Plum Christopher N. , Winer Arthur M. , Pitts James N.
Published: January 2005

Rate constants have been determined at 296 ± 2 K for the gas phase reaction of NO3 radicals with a series of aromatics using a relative rate technique. The rate constants obtained (in cm3 molecule−1 s−1 units) were: benzene, <2.3 × 10−17; toluene, (1.8 ± 1.0) × 10−17; oxylene, (1.1 ± 0.5) × 10−16; mxylene, (7.1 ± 3.4) × 10−17; pxylene, (1.4 ± 0.6) × 10−16; 1,2,3‐trimethylbenzene, (5,6 ± 2.6) × 10−16; 1,2,4‐trimethylbenzene (5.4 ‐ 2.5) × 10−16; 1,3,5‐trimethylbenzene, (2.4 ± 1.1) × 10−16; phenol, (2.1 ± 0.5) × 10−12; methoxybenzene, (5.0 ± 2.8) × 10−17; o‐cresol, (1.20 ± 0.34) × 10−11; m‐cresol, (9.2 ± 2.4) × 10−12; p‐cresol, (1.27 ± 0.36) × 10−11; and benzaldehyde, (1.13 ± 0.25) × 10−15. These kinetic data, together with, in the case of phenol, product data, suggest that these reactions proceed via H‐atom abstraction from the substituent groups. The magnitude of the rate constants for the hydroxy‐substituted aromatics indicates that the nighttime reaction of NO3 radicals with these aromatics can be an important loss process for both NO3 radicals and these organics, as well as being a possible source of nitric acid, a key component of acid deposition.
The high temperature oxidation of the methyl side chain of toluene
Authors: Brezinsky K. , Litzinger T. A. , Glassman I.
Published: January 2005

From the results of order of magnitude analyses, it is concluded that during the oxidation of toluene, radical‐atom and radical‐radical reactions (1) and (3) play an unusually important and approximately equal role in the formation of benzaldehyde, an intermediate that leads eventually to the complete removal of the side chain.
equation image
An additional radical‐radical system, reaction (2), is shown to be the most likely source of benzyl alcohol observed during toluene oxidation.
equation image
Kinetic studies of a catalyzed metalloporphyrin formation
Authors: Adeyemo Adegboye O. , Krishnamurthy M.
Published: January 2005

Kinetics of the incorporation of mercury(II) ion in tetra (p‐trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO3) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 103 M−1 s−1 and 7 ± 2 × 106 M−1 s−1, respectively. Kinetics of zinc(II) incorporation in tetra(p‐trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady‐state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.
Rate constants for the reaction of OH radicals with a series of alkenes and dialkenes at 295 ± 1 K
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate technique, rate constants for the gas phase reactions of the OH radical withn‐butane,n‐hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1‐butene, 1.19 ± 0.06; 1‐pentene, 1.19 ± 0.05; 1‐hexene, 1.40 ± 0.04; 1‐heptene, 1.51 ± 0.06; 3‐methyl‐1‐butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09;cis‐2‐butene, 2.13 ± 0.05;trans‐2‐butene, 2.43 ± 0.05; 2‐methyl‐2‐butene, 3.30 ± 0.13; 2,3‐dimethyl‐2‐butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3‐butadiene, 2.53 ± 0.08; 2‐methyl‐1,3‐butadiene, 3.81 ± 0.15;n‐butane, 0.101 ± 0.012; andn‐hexane, 0.198 ± 0.017. From a least‐squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10−11cm3molecule−1s−1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self‐consistent data set for the reactions of OH radicals with a large number of organics at room temperature.
Rate constant for the OH + CO reaction: Pressure dependence and the effect of oxygen
Authors: Demore W. B.
Published: January 2005

The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200–730 torr. All experiments were at room temperature. The method involved laser‐induced fluorescence to measure steady‐state OH concentrations in the 184.9 nm photolysis of H2O‐CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10%. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.
Rates of OH radical reactions. XII. The reactions of OH with cC3H6, cC5H10, and cC7H14. Correlation of hydroxyl rate constants with bond dissociation energies
Authors: Jolly Gurvinder S. , Paraskevopoulos George , Singleton Donald L.
Published: January 2005

Absolute rate constants for H‐atom abstraction by OH radicals from cyclopropane, cyclopentane, and cycloheptane have been determined in the gas phase at 298 K. Hydroxyl radicals were generated by flash photolysis of H2O vapor in the vacuum UV, and monitored by time‐resolved resonance absorption at 308.2 nm [OH(A2Σ+→X2Π)]. The rate constants in units of cm3 mol−1 s−1 at the 95% confidence limits were as follows: k(cC3H6) = (3.74 ± 0.83) × 1010, k(cC5H10) = (3.12 ± 0.23) × 1012, k(cC7H14) = (7.88 ± 1.38) × 1012. A linear correlation was found to exist between the logarithm of the rate constant per CH bond and the corresponding bond dissociation energy for several classes of organic compounds with equivalent CH bonds. The correlation favors a value of D(cC3H5–H) = (101 ± 2) kcal mol−1.
Reactivities of cis‐ and trans‐buten‐2‐yl free radicals in presence of D2S. I. Relative values of rate constants
Authors: Richard C. , Martin R.
Published: January 2005

Cis‐ and trans‐buten‐2‐yl free radicals are shown to react with D2S in metathetical steps: magnified image Relative formation rates of monodeuteriated butenes in D2S – 2 – C4H8 mixtures were measured at low extent of reaction in the experimental range: 20–200 torr 2 – C4H8, 0–41‐torr D2S and 717–817 K. In these pressure and temperature ranges, the fractional rate constant values kc/kc′/kt/kt′ remain practically constant and equal to: 0.36/0.17/0.32/0.15. It is concluded from these data that cis‐buten‐2‐yl free radicals are a little more reactive than their trans‐isomers and that the mesomeric form CH3CH:CHCH2 is about twice as reactive as CH3ĊHCH:CH2.
Determination of the energy distribution in unimolecular reactions under soft collision conditions
Authors: Figuera Juan M. , Menéndez Vicente , Rodríguez Juan C.
Published: January 2005

The effective energy distribution of activated molecules at the time of reaction under soft collision conditions ƒ′(E, ω) is pressure dependent and therefore difficult to recover from unimolecular decomposition data obtained at different pressures. We show in this work that the part of this function restricted to the condition that the collision frequency ω has to be equal to the microscopic rate constant k(E) at the energy given ƒ″[E,ω = k(E)] is a reasonable approximation to the input energy distribution ƒ(E) for quite soft collisions. This function is not pressure dependent and then recoverable at least in principle and as a matter of fact is not conceptually far from the function that the already reported deconvolution methods based in physical approximations attempt to recover. The deconvolution methods have been checked under soft collision conditions. We have found that the input energy distribution is recovered with reasonable accuracy for energies transferred by collision 〈ΔE〉 above 5 kcal mol−1, conditions common in polyatomic systems.
Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films
Authors: Amorebieta V. T. , Colussi A. J.
Published: January 2005

The decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low‐pressure flow reactor between 850–1280 K. Whereas CH3Cl is thoroughly stable, molecular chlorine readily dissociates by a first‐order process with an activation energy about a half of its bond energy. The decompositions of CH2Cl2 and CCl4 over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.
N2O5 photolysis products investigated by fluorescence and optoacoustic techniques
Authors: Barker J. R. , Brouwer L. , Patrick R. , Rossi M. J. , Trevor P. L. , Golden D. M.
Published: January 2005

Pulsed laser photolysis of N2O5 near 290 nm coupled with fluorescence detection (calibrated by NO2 photolysis) showed that the O(3P) quantum yield is ≤0.1. A pulsed laser optoacoustic technique in a flow tube (ca. 6 torr of N2) was tested by photolysis of NO2 and then applied to N2O5. Nitric oxide was added to react with NO3 free radical and the resulting increase in the optoacoustic signal confirmed the presence of NO3 free radicals. Based on the relative optoacoustic signals observed for NO2 and N2O5, the quantum yield for NO3 production is 0.8 ± 0.2.
Mechanism of the silane decomposition. I. Silane loss kinetics and rate inhibition by hydrogen. II. Modeling of the silane decomposition (all stages of reaction)
Authors: White R. T. , Espino‐Rios R. L. , Rogers D. S. , Ring M. A. , O'Neal H. E.
Published: January 2005

Part I: Kinetic data for the static system silane pyrolysis (from 640–703 K, 60–400 torr) are presented. For conversion from 3–30%, first‐order kinetics are obtained, with silane loss rates equal to half the hydrogen formation rates. At conversions greater than 40%, rate inhibition attributable to the back reaction of hydrogen with silylene occurs. Overall reaction rates are not surface sensitive, but disilane and trisilane yield maxima under some conditions are. A nonchain mechanism capable of describing quantitatively all stages of the silane pyrolysis is proposed. Post 1.0% initiation is both homogeneous (gas phase) and heterogeneous (on the walls), and reaction intermediates are silylenes and disilenes. Free radicals are not involved at any stage of the reaction. Rate data at high conversions and with added hydrogen provide kinetics for the addition of silylene to hydrogen [reaction (−1)1] relative to its addition to silane [reaction (2)]: k−1,/k2 = 10−0.65 × e−3200 cal/RT. With E2 = 1300 cal, this gives a high pressure activation energy for silylene insertion into hydrogen of E−1 = 8200 cal.

Part II: An analysis is made of each rate constant of the silane mechanism and the modeling results are compared with experimental results. Agreement is excellent. It is concluded that the dominant sink reaction for silylene intermediates is 1,2—H2 elimination from disilane (followed by Si2H4 polymerization and wall deposition). The model is in accord with slow isomerization between disilene and silylsilylene and near exclusive 1,2—H2 elimination from Si2H6. It is also concluded that disilene is about 10 kcal/mol more stable than silylsilylene and that the activation energy for isomerization of silylsilylene to disilene is greater than 26 kcal/mol.
Rate constants for the reactions of conjugated olefins with NO2 in the gas phase
Authors: Ohta Tomohiro , Nagura Hiroaki , Suzuki Shin
Published: January 2005

Gas‐phase rate constants for the reaction of NO2 with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono‐olefins by factors of 103–104. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies: k1,3‐cyclohexadiene = 5.8 × 10−14 exp[−(6.1 ± 1.6)/RT] cm3 molecule−1 s−1; kcis‐2‐butene = 4.68 × 10−14 exp(−11.2/RT) cm3 molecule−1 s−1 [2]. A linear free energy relationship between the reactions of OH and NO2 with conjugated diolefins was observed.
The use of transition‐state theory to extrapolate rate coefficients for reactions of O atoms with alkanes
Authors: Cohen N. , Westberg K. R.
Published: January 2005

Conventional transition‐state theory is used for extrapolating rate coefficients for reactions of O atoms with alkanes to temperatures above the range of experimental data. Expressions are developed for estimating structural properties of the activated complex necessary for calculating enthalpies and entropies of activation. Particular attention is given to the problem of the effect of the O atom adduct on the internal rotations in the activated complex. Differences between primary, secondary, and tertiary attack are discussed, and the validity of representing the activated complexes of all O + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Experimental data for reactions of O atoms with 15 different alkanes (CH4, C2H6, C3H8, C4H10, C5H12, C6H14, C7H16, C8H18, i–C4H10, (CH3)4C, (CH3)2CHCH(CH3)2, (CH3)3CC(CH3)3, c–C5H10, c–C6H12, c–C7H14) are reviewed.

The following approximate expressions for ΔS‡(298) and E(298), the entropy and energy of activation, respectively, are consistent with the experimental data and with the calculations:
magnified image
where nC = number of carbon atoms in the alkane and nH = the number of “equivalent” H atoms. Using the conventional transition state theory expression, k(298) = 1015.06 exp(ΔS‡/R) exp(–E(298)/298R) L mol−1s−1, one then obtains:

These expressions agree with experimental values within a factor approximately 2 for alkanes larger than C3H8.
The thermodynamic state of the hot gas behind reflected shock waves: Implication to chemical kinetics
Authors: Michael J. V. , Sutherland J. W.
Published: January 2005

Procedures are discussed to correct for nonideality in a shock tube used in the reflected mode in conjunction with flash photolysis and atomic resonance absorption to measure chemical kinetics of atoms at high temperatures. Experimentally, pressure time profiles for the incident and reflectedshock regions are made close to the location of the observation windows through which absorbance is measured. The corresponding temperatures are calculated from the adiabatic equation of state. Justification for this procedure is provided by extending Mirels' boundary layer theory to take intoaccount interaction of the reflected wave with the flowing gas in the free stream and in the boundary layer. These theoretical methods are described for calculating the thermodynamic and hydrodynamic states behind the reflected wave from initial values of pressure and temperature and the measured velocity of the incident wave. The implication of these results to kinetic measurements at high temperature is discussed.
An Ab initio determination of the rate constant for H2 + CN → H + HCN
Authors: Wagner Albert F. , Bair Raymond A.
Published: January 2005

The reactants, products, and saddle point for the reaction H2 + CN → H + HCN have been studied by ab initio calculations. The computed structures, frequencies, and energetics are compared directly to available measurements and, indirectly, to experimental rateconstants. The theoretical rate constants used in the comparison are calculated with conventional transition state theory. By reduction of the computed reaction barrier to 4.1 kcal mol,−1 good agreement with experimental rate constants is obtained over a 3250‐K temperature range. This computed rate constant is well represented by the form 4.9 × 10−18 T2.45 e−1, 126/T over the temperature range of 250 K–3500 K. Substantial reaction rate curvature is found due to low‐frequency bending modes at the saddle point. The results for this reaction are compared to other abstraction reactions involving H atom transfer to identify correlations between reaction exothermicity and both abstraction barriers and reaction rate curvature.
The high temperature pyrolysis of ethylbenzene
Authors: Pamidimukkala K. M. , Kern R. D.
Published: January 2005

The thermal decomposition of ethylbenzene has been investigated behind reflected shock waves over the temperature and pressure ranges of 1350–2080 K and 0.25–0.5 atm using a 1.6% C8H10  Ne mixture. Major products of the pyrolysis are C7H8, C7H7, C6H6, C4H2, C2H4, C2H2, and CH4; C8H8 appears throughout the temperature range as a minor product. Comparison of the product profiles obtained by time‐of‐flight mass spectrometry and the results of model calculations strongly supports the initiation step of β CC bond homolysis for C8H10 dissociation. A 51 kinetic step reaction mechanism with 24 species was formulated to model the temperature and time dependence of the major products observed in our experiments.
Characterization of solid solutions composed of oxides of Cu, Zn, and Cr for methanol synthesis
Authors: Gadalla A. M. , Haddad A.
Published: January 2005

Solid solutions of Cu2O alone and Cu2O with ZnO or Cr2O3 in ZnO · Cr2O3 as well as solid solutions of ZnO in Cu2O · Cr2O3 have activities and selectivities for methanol synthesis comparable to solid solutions of Cu2O in ZnO. Addition of a secondary phase to these solid solutions limits the grain growth and produces higher surface areas.
The kinetics and mechanism of alkaline hydrolysis of N‐substituted phthalimides
Authors: Khan M. Niyaz
Published: January 2005

The aqueous cleavage of N‐(2‐bromoethyl)phthalimide (NBEPH), N‐(3‐bromopropyl)phthalimide (NBPPH), and N‐carbethoxyphthalimide (NCPH) have been studied within the [ŌH] range of 5 × 10−4 M to 2 × 10−3 M, pH range of 8.82 to 10.62 and 8.06 to 8.66, respectively. The observed pseudo‐first‐order rate constants, kobs, reveal a linear relationship with [ŌH] with essentially zero intercept. The alkaline hydrolysis of N‐(hydroxymethyl)phthalimide (NHMPH) has been studied within the [ŌH] range of 5.64 × 10−6 M to 2.0 M. The [OH]‐rate profile reveals that both ionized and nonionized NHMPH are reactive toward ŌH. The second‐order rate constant, kOH, for the reaction of ŌH with non‐ionized NHMPH is ca. 104 times larger than that with ionized NHMPH. The values of kOH obtained for NBEPH, NBPPH, NCPH, and nonionized NHMPH show a reasonable linear relationship with Taft substituent constants, and the slope (ρ*) of the plot is 1.01 ± 0.10. The low value of ρ* of 1.01 is attributed to nucleophilic attack as the rate‐limiting. The kOH value for ionized NHMPH reveals nearly 103‐fold negative deviation from the linear Taft plot.
Kinetics of cerium(IV) oxidation of macrocyclic complexes of chromium(III) and fate of chromium(IV) intermediates
Authors: Nair Balachandran Unni , Ramasami T. , Ramaswamy D.
Published: January 2005

Kinetics and mechanism of the cerium(IV) oxidation of Cr(III) complexes of a series of macrocyclic (or pseudomacrocyclic) ligands with [14]‐membered intraligand ring‐sizes have now been investigated at I = 1.0 M (LiClO4) Temp. 30°C. The complexes of the formulation Cr(macrocycle)(X)(H2O) where X = CHCl2 and H2O, n = 0 or 1 undergo oxidation to Cr(VI) with the formation of chromium(IV) intermediates. The observed kinetic parameters for the Ce(IV) oxidation of Cr(III) macrocyclic complexes have been discussed in terms of changes brought about by the macrocyclic ligands on the Cr(III)—Cr(IV) redox potentials and in specific rates for Cr(IV)—Cr(V) conversion. On the basis of this study, it has been suggested that the trapping of Cr(IV) is easier when a macrocyclic ligand having a symmetrical intra‐ligand ring size and unsaturation in the cyclic structure is coordinated equatorially. Cyclic voltammetric studies indicate the formation of Cr(IV) transient in the case of electrochemical oxidation of trans‐Cr(Me4[14]tetraene)(H2O).
Micellar catalysis by perfluorooctanoic acid
Authors: Berndt D. C. , Ayoub M. E. , Akhavan‐Tafti M. H.
Published: January 2005

Rates of acidic hydrolysis of hexano‐, octano‐, and decanohydroxamic acids and of 4‐bromophenylaceto‐ and phenylacetohydroxamic acids have been determined in aqueous perfluorooctanoic acid—a reactive counterion surfactant system. Typical micellar catalysis was observed for the hydrolyses of the n‐alkyl hydroxamic acids but not for the arylacetohydroxamic acids. The Arrhenius activation energy for hydrolysis of octano‐hydroxamic acid is smaller above the cmc of the surfactant than it is below the cmc.
Kinetics of methylchlorosilane formation on Zn‐promoted Cu3Si
Authors: Agarwala J. P. , Falconer John L.
Published: January 2005

The kinetics of the direct synthesis reaction (Si + 2CH3Cl → (CH3)2SiCl2) were measured on a Cu3Si alloy containing 1.2 atom % Zn. Reaction was carried out in a differential reactor (520–595 K, 1 atm) attached to an ultrahigh vacuum (UHV) system. Auger spectroscopy was used to characterize the surface before and after reaction. Zinc does not significantly change the overall rate of reaction, but it changes selectivity to dimethyldichlorosilane (the desired product), surface composition, activation energies, and induction times. The rate of silicon diffusion to the surface is not limiting in the presence of zinc. Zinc is found to be a promoter for improved selectivity only in low concentrations, and only a fraction of the surface appears to be active for reaction. The kinetics appear relatively insensitive to the surface composition or the form of surface carbon. A Cu3Si surface with Zn is shown to be a good model catalyst for the direct synthesis reaction.
Photoenhancement of the nitrous acid formation in the surface reaction of nitrogen dioxide and water vapor: Extra radical source in smog chamber experiments
Authors: Akimoto Hajime , Takagi Hiroo , Sakamaki Fumio
Published: January 2005

The surface reaction of NO2 and H2O vapor to emit HONO into the gas phase was studied in the evacuable and bakeable photochemical chamber under the irradiation of UV‐visible light (≳ 290 nm). Kinetic analysis of the NO, NO2, and HONO with the aid of computer modeling strongly suggested that the formation of HONO by the surface reaction is photoenhanced. When a linear regression was assumed, the photoenhancement factor defined by {(k′21/k21) − 1} was expressed as (6.8 ± 2.5)k1 under our experimental conditions, where k1 is the primary photolysis rate of NO2, and k21, k′21 are the second‐order‐equivalent rate constants of the HONO formation reaction in dark and under irradiation, respectively. The discussion was made that this photocatalitic enhancement of HONO formation would explain the nature of the extra OH radical flux in the smog chamber experiments, which has been discussed as “unknown radical source” and has still been unexplained by the surface dark reaction of NO2 and H2O to emit HONO.
The kinetics of oxiranes addition to bis/2‐hydroxyalkyl/disulfides and bis/2‐hydroxyalkyl/sulfides in the presence of N,N‐dimethylcyclohexylamine
Authors: Wilk Kazimiera A. , Sokołowski Adam , Burczyk Bogdan , Chlebicki Jan
Published: January 2005

Rate constants for the reaction of oxiranes with bis/2‐hydroxyalkyl/disulfides, bis/2‐Hydroxyalkyl/sulfides, and 1,6‐Hexanediol in the presence of N,N‐dimethylcyclohexylamine were studied at the temperature range of 50–90°C. A mechanism of these reactions has been proposed and its kinetic equation has been presented.
The kinetics and mechanisms of the gas phase elimination of 4‐(methylthio)‐1‐butyl acetate and 1‐chloro‐4‐(methylthio)‐butane
Authors: Chuchani Gabriel , Martin Ignacio , Dominguez Rosa M.
Published: January 2005

The gas phase elimination of 4‐(methylthio)‐1‐butyl acetate and 1‐chloro‐4‐(methylthio)‐butane has been investigated in a seasoned, static reaction vessel over the temperature range of 310–410°C and the pressure range of 46–193 Torr. The presence of the inhibitors propene, cyclohexene, and/or toluene had no effect on the rates. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for 4‐(methylthio)‐1‐butyl acetate, log k1(s−1) = (12.32 ± 0.29) − (192.1 ± 3.6) kJ/mol/2.303RT; for 1‐chloro‐4‐(methylthio)‐butane, log k1(s−1) = (12.23 ± 0.59) − (175.7 ± 6.8) kJ/mol/2.303RT. The CH3S substituent in 1‐chloro‐4‐(methylthio)‐butane has been found to participate in the elimination reaction, where tetrahydrothiophene and methyl chloride formation may result from an intimate ion‐pair type of mechanism. The yield of a cyclic product in gas phase reactions provides additional evidence of an intimate ion pair mechanism through neighboring group participation in gas phase elimination of special types of organic halides.
A structure‐activity relationship for the estimation of rate constants for the gas‐phase reactions of OH radicals with organic compounds
Authors: Atkinson Roger
Published: January 2005

A previous technique for the calculation of rate constants for the gas‐phase reactions of the OH radical with organic compounds has been updated and extended to include sulfur‐ and nitrogen‐containing compounds. The overall OH radical reaction rate constants are separated into individual processes involving (a) H‐atom abstraction from CH and OH bonds in saturated organics, (b) OH radical addition to >CC< and CC unsaturated bonds, (c) OH radical addition to aromatic rings, and (d) OH radical interaction with NH2, >NH, >N, SH, and S groups. During its development, this estimation technique has been tested against the available database, and only for 18 out of a total of ca. 300 organic compounds do the calculated and experimental room temperature rate constants disagree by more than a factor of 2. This suggests that this technique has utility in estimating OH radical reaction rate constants at room temperature and atmospheric pressure of air, and hence atmospheric lifetimes due to OH radical reaction, for organic compounds for which experimental data are not available. In addition, OH radical reaction rate constants can be estimated over the temperature range ca. 250–1000 K for those organic compounds which react via H‐atom abstraction from CH and OH bonds, and over the temperature range ca. 250–500 K for compounds containing >CC< bond systems.
Kinetics of the gas‐phase reactions of Cl atoms with chloroethenes at 298 ± 2 K and atmospheric pressure
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate technique, rate constants have been determined for the gas‐phase reactions of Cl atoms with the cholorethenes and ethane at 298 ± 2 K and 735 torr total pressure of air. Using a rate constant of 1.97 × 10−10 cm3 molecule−1 s−1 for the reaction of Cl atoms with n‐butane, the following rate constants (in units of 10−11 cm3 molecule−1 s−1) were obtained: vinyl chloride, 12.7 ± 0.2; 1,1‐dichloroethene, 14.0 ± 0.2; cis‐1,2‐dichloroethene, 9.65 ± 0.10; trans‐1,2‐dichloroethene, 9.58 ± 0.18; trichloroethene, 8.08 ± 0.10; tetrachloroethene, 4.13 ± 0.23; and ethane, 6.17 ± 0.08 (where the indicated error limits do not include the uncertainties in the rate constant for n‐butane). A small amount of cis‐trans isomerization was observed for the reactions involving the cis‐ and trans‐1,2‐dichloroethenes. These data are compared and discussed with the available literature data.
The kinetics and mechanism of the pyrolysis elimination of methyl 4‐bromocrotonate
Authors: Chuchani Gabriel , Martin Ignacio
Published: January 2005

The pyrolysis of methyl 4‐bromocrotonate in the temperature range 300–340°C and pressure range 74–170 torr has been shown to be homogeneous, unimolecular, and to follow a first‐order rate law. The reaction was carried out in a static system, seasoned with allyl bromide, and in the presence of the radical chain exhibitor toluene. The rate coefficients are represented by the Arrhenius expression: log k1(s−1) = (13.30 ± 0.66) − (185.2 ± 7.5) kJ mol−1 (2.303RT)−1. The carbomethoxy group appears to provide anchimeric assistance in the process of dehydrobromination and lactone products formation. The partial rates for the parallel reaction have been estimated, reported, and discussed. The pyrolysis elimination is explained in terms of an intimate ion pair‐type of mechanism.
Reactions of N2(A3Σ)
Authors: Golde Michael F.
Published: January 2005

N2(A3Σ), the lowest electronically excited state of N2, has a long and distinguished history due to its role in nitrogen discharges and the nitrogen afterglow. Recently, the production of N2(A) via photolysis and chemiluminescent reactions has been newly explored, and new facets of its reactivity have been uncovered. N2(A) is unusual, in that its deactivation probability in collision with small molecules spans many orders of magnitude, and is frequently strongly dependent on the vibrational content of N2(A). This behavior and the observed product channels can be understood in terms of a simple model for the energy transfer process. Brief comparison with reactions of related species is made.
Measurement of absolute rate data for the reaction of atomic potassium, K(42S½), with CH3F, C2H5F, C6H5F, CH3Br, C2H5Br, HCl and HBr by time‐resolved atomic resonance absorption spectroscopy at λ = 404 nm (K(52PJ) ← K(42S½))
Authors: Husain D. , Lee Y. H.
Published: January 2005

We present a kinetic study of atomic potassium in its electronic ground state, K(42S½), generated in the “single‐shot mode” by pulsed irradiation at elevated temperatures and monitored by time‐resolved atomic resonance absorption spectroscopy using the Rydberg doublet at λ = 404 nm (K[52PJ]←K[42S½]). Profiles for the decay of atomic potassium in the presence of various halogenated reactants were recorded at different temperatures, yielding the following Arrhenius parameters (kR = A exp(−E/RT), errors 1σ):

R
A/10−10 cm3 molecule−1s−1
E/kJ mol−1
Temp. Range

CH3F
1.93+1.1−0.7
59±3.3
822–922 K

C2H5F
1.40+2.5−0.9
62±6.6
694–807 K

C6H5F
2.0+1.6−0.9
41±3.9
705–812 K

CH3Br
1.7+0.3−0.2
15.9±1.2
798–903 K

HCl
5.6+3.5−2.1
34.7±3.5
828–902 K

HBr
1.9+0.3−0.3
34±1.2
836–925 K

A limited body of data is reported for k(K + C2H5Br) = 3.6 × 10−11 cm3 molecule−1 s−1 for the temperature range 704–733 K. These results for atomic potassium constitute a new body of absolute rate data which are compared with some previous results for reactions of atomic potassium with other reactants, and for reactions of atomic sodium, also determined by time‐resolved atomic resonance absorption spectroscopy. The data for HCl and HBr are finally compared with early estimates reported using diffusion flames.
Kinetics of the gas‐phase reactions of the OH radical with (C2H5)3PO and (CH3O)2P(S)Cl at 296 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Goodman Mark A. , Winer Arthur M.
Published: January 2005

The kinetics of the gas‐phase reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl and of the reactions of NO3 radicals and O3 with (CH3O)2P(S)Cl have been studied at room temperature. Using a relative rate technique, the rate constants determined for the reactions of the OH radical with (C2H5O)3PO and (CH3O)2P(S)Cl at 296 ± 2 K and 740 torr total pressure of air were (5.53 ± 0.35) × 10−11 and (5.96 ± 0.38) × 10−11 cm3 molecule−1 s−1, respectively. Upper limits to the rate constants for the NO3 radical and O3 reactions with (CH3O)2P(S)Cl of <3 × 10−14 cm3 molecule−1 s−1 and <2 × 10−19 cm3 molecule−1 s−1, respectively, were obtained. These data are compared and discussed with previous literature data for organophosphorus compounds.
The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5
Authors: Kondo Osamu , Marshall Roger M. , Benson Sidney W.
Published: January 2005

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k1. The reaction scheme is

where k2 ≫ k1 and k−1 [HBr] is negligibly small under our conditions.

Arrhenius parameters for k1 were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts.

where θ = 2.303 RT (kcal mol−1).

The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (2P1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.