bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of partly diffusion‐controlled reactions. XIV. Effects of reversible energy transfer
Authors: Guillard R. , Andre J. C. , Bouchy M. 
Published: January 2005

AbstractThe general effect of back energy transfer is to reduce the apparent quenching constant which is an important parameter in the interpretation of energy transfer data. However, this interpretation may be erroneous when possible diffusion effects and the existence of nonuniform configurational distributions are not taken into account.
Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K
Authors: Atkinson Roger , Carter William P. L. , Aschmann Sara M. , Winer Arthur M. , Pitts James N. 
Published: January 2005

AbstractRelative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n‐butane of 2.58 × 10−12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2‐methylbutane, 3.97 ± 0.11; 2,2‐dimethylbutane, 2.66 ± 0.08; 2‐methylpentane, 5.68 ± 0.24; 3‐methylpentane, 5.78 ± 0.11; 2,2,3‐trimethylbutane, 4.21 ± 0.08; 2,4‐dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3‐tetramethylbutane, 1.06 ± 0.08; and 2,2,4‐trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2‐dimethylbutane, 2,4‐dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.
Reaction of methyl radicals with haloalkanes
Authors: Sidebottom Howard , Treacy Jack 
Published: January 2005

AbstractThe kinetics of reactions involving halogen atom abstraction from haloalkanes by methyl radicals have been studied in the gas phase. Arrhenius parameters for halogen atom transfer were determined relative to those for methyl radical combination:
equation image

RX
log10A2(L/mol · s)
E2(kcal/mol)

CFCl3
8.3 ± 0.2
10.7 ± 0.4

CF3CCl3
7.9 ± 0.3
9.7 ± 0.6

CF2Cl2
9.1 ± 0.4
11.3 ± 0.7

CF3Cl
8.8 ± 0.5
11.8 ± 1.0

CF3CF2Cl
8.3 ± 0.3
10.9 ± 0.7

CF3Br
8.6 ± 0.2
9.3 ± 0.5

CF3I
8.1 ± 0.1
4.3 ± 0.2

CH3CH2I
8.9 ± 0.3
7.4 ± 0.6

The rate data obtained are used to provide information on the importance of polar effects for halogen abstraction processes.
Deactivation of I(52P1/2) by CF3I, CH3I, C2H5I, and CH4
Authors: Gu Z‐N. , Young A. T. , Houston P. L. 
Published: January 2005

AbstractThe technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time‐resolved detection of the 1.3‐μm emission from I*(2P1/2) has been used to measure the rate constants for deactivation of I* by CH3I, C2H5I, CF3I, and CH4. The recommended values are (2.76± 0.22) × 10−13, (2.85 ± 0.40) × 10−13, (3.5 ± 0.5) × 10−17, and (7.52 ± 0.12) × 10−14, respectively, in units of cm3 molecule−1 S−1.
The heat of formation of the ethyl radical
Authors: Cao J‐R. , Back M. H. 
Published: January 2005

AbstractAn examination of the results of measurements of the forward and reverse rate constants for the reaction

shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol−1. This system therefore provides further support for the recent measurement of this quantity.
Gas/wall collision efficiencies in very low pressure pyrolysis experiments
Authors: Dick Paul G. , Gilbert Robert G. , King Keith D. 
Published: January 2005

AbstractA readily applicable empirical formula is obtained for the collisional efficiency for energy transfer between a highly vibrationally excited reactant and a seasoned (usually quartz) wall, in terms of the molecular weight, potential well depth and dipole moment of the reactant. This expression is used to examine corrections due to nonunit wall collision efficiency in the high‐pressure rate parameters obtained from very low‐pressure pyrolysis experiments. It is found that these corrections are up to ca. ±5 kJ/mol in the high‐pressure activation energy and a factor of ca. 2 in the high‐pressure frequency factor, for molecules with molecular weight less than ca. 100 and where experiments are carried out at temperatures exceeding 1000 K.
The kinetics and mechanism of aqueous cleavage of imide bond in 5, 5‐diethyl barbituric acid (5, 5‐diethyl‐2,4,6‐(1H, 3H) pyrimidinetrione) in a highly alkaline medium
Authors: Khan M. Niyaz , Khan A. Aziz 
Published: January 2005

AbstractThe kinetic study of alkaline hydrolysis of 5, 5‐diethyl barbituric acid has been carried out at various [OH] and different temperatures ranging from 85–95°C. The reaction follows an irreversible first‐order consecutive reaction path of the type \documentclass{article}\pagestyle{empty}\begin{document}${\rm A}\buildrel{{k1{\rm obs}}}\over\longrightarrow{\rm B}\buildrel{{k2{\rm obs}}}\over\longrightarrow$\end{document} X under pseudo‐first‐order kinetic conditions. A, B, and X represent for 5, 5‐diethyl barbituric acid, diethyl malonuric acid, and ammonia, respectively. The pH‐rate profiles obtained at three different temperatures reveal distinct phases which are attributed to a change in rate‐determining step with change in [OH]. On the basis of the observed data, a possible mechanism has been discussed.
Gas phase reactions of CF3, C2F5, and n‐C3F7 with carbon tetrachloride
Authors: de Vöhringer C. M. , Staricco E. H. 
Published: January 2005

AbstractThe reactions of some perfluoroalkyl radicals with carbon tetrachloride have been studied using the photolysis of the corresponding perfluoroalkyl iodide as the free radical source. The Arrhenius parameters, based on the value of 2.3 × 1013 cm3 mol−1 s−1 for the self‐combination rate constant of all radicals are:

Reaction
log(A/cm3 mol−1 s−1)
E/kcal mol−1

CF3 + CCl4
12.8
11.3

C2F5 + CCl4
12.8
11.6

n‐C3F7 + CCl4
12.9
12.0
Termolecular reactions of alkali metal atoms with O2 and OH
Authors: Patrick Roger , Golden David M. 
Published: January 2005

AbstractCalculations of low‐pressure limit, third‐order rate constants are presented for the association reactions A + O2 + N2 and A + OH + N2 (A = Li, Na, K) over the temperature range 200–2000 K and a comparison is made with the available experimental data.
Mechanism of the chain process forming H2 in the photooxidation of formaldehyde
Authors: Veyret Bernard , Roussel Pascal , Lesclaux Robert 
Published: January 2005

AbstractA mechanism for the formation in a chain of H2, CO, and HCOOH in the photooxidation of formaldehyde is proposed. This mechanism is initiated by the addition of HO2 to formaldehyde. Hydrogen atoms are produced by the thermal dissociation of the HOCH2O radical: HOCH2O → H + HCOOH; ΔH = + 3.2 kcal/mol [5]. Photolysis of CH2OO2NO mixtures and product analysis were carried out in conjunction with kinetic simulation yielding an estimate for the activation energy of the dissociation reaction : E5 = 14.9 ± 1.0 kcal/mol. Previous observations of this chain process are considered in view of this mechanism.
The kinetics and the mechanism of the thermal reaction between sulfurtetrafluoride (SF4) and trifluoromethylhypofluorite (CF3OF)
Authors: Gonzalez Alicia C. , Schumacher H. J. 
Published: January 2005

AbstractThe kinetics of the thermal reaction between SF4, and CF3OF has been studied between 142°C and 185°C. The reaction was found to be homogeneous and the only products formed are equimolecular amounts of SF6 and CF3O2CF3 and smaller amounts of CF3OSF5. The reaction mechanism was not affected by the total pressure, the oxygen pressure, or by the buildup of products. The experimental data can be explained by the following mechanism:
equation image
The rate constants can be expressed as
The kinetic study of thermal dehydration stages of SrCl2 · 2H2O and its deuterium analog
Authors: Tanaka Haruhiko , Shimada Satoshi , Negita Hisao 
Published: January 2005

AbstractThe kinetic deuterium isotope effect in the thermal dehydration stages of powdered SrCl2 · 2H2O was examined by means of both isothermal and dynamic gravimetries. These dehydration processes proved to be controlled by a random nucleation and its subsequent growth mechanism. No significant kinetic isotope effect was seen in these dehydration stages. It seems that there exists a kinetic compensation effect between the hydrate and its deuterium analog, if any isotopic differences in activation energy and frequency factor could exist.
Hydrogen abstraction from substituted aromatic compounds
Authors: Lissi E. A. , Collados J. , Olea A. 
Published: January 2005

AbstractThe reactivity of tert‐butoxy radicals with methyl substituted aromatic compounds is almost exclusively determined by the aromatic moiety and almost independent of the methyl group position. The hydrogen abstraction from the carbon α to the aromatic ring is hardly sensitive to the produced radical stabilization. This lack of dependence can be explained in terms of the large exothermicity of the process.
The electronic effects of substituents at the acyl carbon in the gas‐phase elimination kinetics of tert‐butyl α‐substituted acetates
Authors: Reikonnen Nadejda , Martin Ignacio , Chuchani Gabriel , Lubinkowski Jacek 
Published: January 2005

AbstractThe gas‐phase eliminations of several tert‐butyl esters, in a static system and in vessels seasoned with allyl bromide, have been studied in the temperature range of 171.5–280.1°C and the pressure range of 23–98 torr. The rate coefficients for the homogeneous unimolecular elimination of these esters are given by the following Arrhenius equations: for tert‐butyl pivalate, log k1(s−1) = (13.44 ± 0.30) − (169.1 ± 3.1) kJ · mol−1 (2.303RT)−1; for tert‐butyl trichloroacetate, log k1(s−1) = (12.41 ± 0.08) − (141.1 ± 0.7) kJ · mol−1 (2.303RT)−1; and for tert‐butyl cyanoacetate log k1(s−1) = (11.31 ± 0.44) − (137.8 ± 4.1) kJ · mol−1 (2.303RT)−1. The data of this work together with those reported in the literature yield a good linear relationship when plotting log k/k0 vs. σ* values (ρ* = 0.635, correlation coefficient r = 0.972, and intercept = 0.048 at 250°C). The positive ρ* value suggests that the movement of negative charge to the acyl carbon in the transition state is rate determining. The present results along with previous investigations ratify the generalization that electron‐withdrawing substituents at the acyl side of ethyl, isopropyl, and tert‐butyl esters enhance the elimination rates, while electron‐releasing groups tend to reduce them. The negative nature of the acyl carbon and the polarity in the transition state increases slightly from primary to tertiary esters.
Thermal decomposition of ethane in shock waves
Authors: Hidaka Yoshiakai , Shiba Shoichi , Takuma Hirokazu , Suga Masao 
Published: January 2005

AbstractThe thermal decomposition of ethane was studied behind reflected shock waves over the temperature range 1200–1700 K and over the pressure range 1.7−2.5 atm, by both tracing the time variation of absorption at 3.39 μm and analyzing the concentration of the reacted gas mixtures. The mechanism to interpret well not only the earlier stage of C2H6 decomposition, but also the later stage was determined. The rate constant of reactions, C2H6 → CH3 + CH3, C2H6 + C2H3 → C2H5 + C2H4, C2H5 → C2H4 + H were calculated. The rate constants of the other reactions were also discussed.
Effects of ring strain on gas‐phase rate constants. 3. NO3 radical reactions with cycloalkenes
Authors: Atkinson Roger , Aschmann Sara M. , Long William D. , Winer Arthur M. 
Published: January 2005

AbstractRate constants for the gas‐phase reactions of NO3 radicals with a series of cycloalkenes have been determined at 298 ± 2 K, using a relative rate technique. Using an equilibrium constant for the NO2 + NO3 ⇄ N2O5 reactions of 3.4 × 10−11 cm3 molecule−1, the following rate constants (in units of 10−13 cm3 molecule−1 s−1) were obtained: cyclopentene, 4.52 ± 0.52; cycloheptene, 4.71 ± 0.56; bicyclo[2.2.1]‐2‐heptene, 2.41 ± 0.28; bicyclo[2.2.2]‐2‐octene, 1.41 ± 0.17; bicyclo[2.2.1]‐2,5‐heptadiene, 9.92 ± 1.13; and 1,3,5‐cycloheptatriene, 12.6 ± 2.9. When combined with previous literature rate constants for cyclohexene and 1,4‐cyclohexadiene, these data show that the rate constants for the nonconjugated cycloalkenes studied depend to a first approximation on the number of double bonds and the degree and configuration of substitution per double bond. No obvious effects of ring strain energy on these NO3 radical addition rate constants were observed. Our previous a priori predictive techniques for the alkenes and cycloalkenes can now be extended to strained cycloalkenes.
Studies on the rate of isotopic oxygen exchange between [Re(py)4O2]+ and solvent water
Authors: Kashani Fred F. , Murmann R. Kent 
Published: January 2005

AbstractThe rate of oxygen exchange between trans‐[Re(py)4O2]+ and solvent water in pypyH+ buffer solution follows simple first‐order kinetics and both oxygens are equivalent. The half‐life for isotopic oxygen exchange is about 12 h at a pH of 5.0, 25°C, and [py] = 0.10 M. The observed rate constant for exchange increases with acidity, in the pH range 4 to 6, decreases with [py], and is nearly independent of ionic strength. A small but significant increase of kobs occurs with increasing complex concentration. The rate of exchange follows the rate equation kobs/2 = k0 + k1/[py] with k0 = 1.4 × 10−5(2) s−1 and k1 = 4.7 × 10−7(1) M, s−1 at 25°C. The activation parameters for the reaction at pH = 7.15 (predominately the k0 term) are: ΔH* = +137.(1) kJ/M and ΔS* = +126.(1) J/MK. The pH effect and complex concentration effect are discussed in mechanistic terms. These results are compared to those found for [Re(en)2O2]+ and [Re(CN)4O2]3−.
“Complex” versus “free radical” mechanism for the catalytic decomposition of H2O2 by ferric ions
Authors: Kremer Mordechai L. 
Published: January 2005

AbstractKinetic and spectrophotometric measurements made during the Fe3+ ion catalyzed decomposition of H2O2 have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k3/KM = 4.94 M−1 min−1, k4 = 193 M−1 min−1, εI/KM = 52.3 M−2 cm−1, εII = 25.7 M−1 cm−1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O2 evolved in the reaction using [H2O2] ∼ 10−2 M has been calculated and found to be nearly stoichiometric. O2 evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O2 and the “free radical mechanism” predicting exactly stoichiometricamounts of O2. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H2O2 both with Fe2+ and Fe3+ ions, as well as other reactions assumed to proceed via free radicals.
Rate constants of reactions of chlorine atoms with aliphatic hydrocarbons and halogen derivatives in the liquid phase
Authors: Sergeev G. B. , Smirnov V. V. , Porodenko E. V. , Pukhovsky A. V. 
Published: January 2005

AbstractThe kinetics of liquid phase chlorination of methane in a difluorodichloromethane medium has been studied in a temperature interval of 293–150 K. The value of activation energy found for the hydrogen abstraction stage by a chlorine atom (E1) equals 14.2 ± 2.5 kJ/mol, with the processes of chlorine atoms recombination and the cage effect being taken into account. The method of competitive reactions has been employed to assess the constants of reaction of chlorine atoms (k1) with ethane, propane, hexane, ethylene, allyl bromide, allyl chloride, ethyl chloride, and cyclohexane in nonpolar solvents, viz. difluorodichloromethane and 1,2‐dibromotetrafluoroethane. The values (k1) obtained in the liquid phaseare two to four orders lower than those in the gas phase, while the activation energy is 2–6 kJ/mol higher.
The influence of the effective potential on the strong collision limiting low–pressure rate coefficients
Authors: Cobos Carlos J. 
Published: January 2005

AbstractThe influence of the effective potential energy curves on the calculation of the strong collision limiting low‐pressure rate coefficients of thermal dissociation‐recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero‐point barriers, as originallyproposed by Troe, was performed. A comparison between calculations realizedwith an exactly fitted looseness parameter, α, and with a standard value of α = 1.0 Å−1, indicates that the use of this last value is satisfactorily justified in the evaluation of thestrong collision limiting low‐pressure rate coefficients. A study interms of restrictive relationships between the looseness and Morse parameters and ab initio, radial potentials (for CH4, CH3O2, and HO2) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long‐range potentials are also briefly discussed.
Drug‐binding to biological macromolecules. A kinetic study of the system chlorodiazepoxide (librium) and bovine serum albumin
Authors: Nissani Edna , Perlmutter‐Hayman Berta 
Published: January 2005

AbstractThe Kinetics of the binding of librium to bovine serum albumin were investigated at an ionic strength of 0.15 M, in the pH‐range between 5.5 and 10.5, using the temperature‐jump method. Two relaxation times were observed. The first, rapid one is assigned to the equilibrium between reactants and complex, whereas the second, slower relaxation time measures a conformational change of this complex. Both relaxation times are independent of pH up to about 8.0 when they increase sharply to a new plateau at a pH of about 9.3. A possible parallelism between this behavior and the N ⇌ B transition of albumin is discussed. The overall equilibrium constant K, as well as the equilibrium constant between the two conformers, K2, were estimated from our kinetic results. Whereas the change of K with changing pH was within the experimental error, the equilibrium between the two conformers of the complex is somewhat shifted by an increase of the pH. At all values of pH, however, they are present in comparable concentrations. The value of K was also measured spectrophotometrically. The results of the two methods showed reasonable agreement. The relaxation times were affected very little by a change in temperature between 12 and 25°C from which it is concluded that the isomerization has a high negative value of ΔS‡.
Infrared laser‐induced decomposition of 2,2‐dimethyloxetane
Authors: Holbrook K. A. , Shaw C. J. , Oldershaw G. A. , Dyer P. E. 
Published: January 2005

AbstractThe unimolecular decomposition of 2,2 dimethyloxetance to give either isobutence and formaldehyde or ethene and acetone induced by a pulsed CO2 laser has been investigated. Absorption characteristics and fractional decomposition have been studied as a function of laser fluence, irradiation frequency, reactant pressure, and added inert bath gas. Both absorption cross section and fractional decomposition are approximately independent of pressure of 2,2‐dimethyloxetane below 50 times; 10−3 torr and increase with pressure at higher pressures of 2,2‐dimethyloxetane. At pressures sufficiently low that collisions are negligible during the laser pulse, added inert gases reduce the amount of decomposition. Calculations of the fractional decomposition have been carried out based on RRKM theory and assuming either a Boltzmann or a Poisson intermolecular energy distribution. Master equation calculations of both absorption and decomposition for 10R20 irradiation have also been performed. Agreement between observed and calculated results for 10R20 irradiation could be obtained only by assuming that most, but not all, of the molecules in the irradiated volume absorb the laser radiation. Differences between the absorptions of the 10R20 and 9P20 lines and in the resulting extents of decomposition indicate that the fraction of irradiated molecules which absorbs 9P20 radiation is smaller than the fraction which absorbs 10R20 radiation.
The kinetics and the mechanism of the thermal gas‐phase reaction between bis(trifluoromethyl)trioxide, CF3O3CF3 and 1,1‐dichlorodifluoroethylene, CF2CCI2
Authors: Czarnowski J. 
Published: January 2005

AbstractThe thermal addition of CF3O3CF3(T) to CF2CCl2(E) has been investigated between 49.6 and 69.5°C. The initial pressure of CF3O3CF3 was varied between 7 and 240 torr and that of CF2CCl2 between 4 and 600 torr. Four products of formula CF3O(E)j OOCF3, where j = 1 → 4 are formed. The sum of the products Σ CF3O(E)jOOCF3 is equal to the amount of trioxide decomposed.The reaction is homogeneous. Its rate is not affected by the total pressure and the presence of inert gas. It is a free radical telomerization with four basic steps: thermal decomposition of CF3O3CF3 into CF3O. and CF3O2., chain initiation by addition of CF3O. to olefin incorporated in, and telomeric radicals termination.The consumption of alkene is well represented by the equation:

where (d[E]/d[T]) =

is the mean chain length of telomerization.

varies from 1.45 at 1.5 torr of E to 3.3 at 400 torr of E. Above this pressure E has no influence on

.The estimated value of the constant for the addition of telomeric radicals to alkene is:
On the errors of Arrhenius parameters and estimated rate constant values
Authors: Héberger Károly , Kemény Sándor , Vidóczy Tamás 
Published: January 2005

AbstractA detailed statistical study is presented, based on simulated experimental data, on the estimation of activation parameters using the Arrhenius equation: k = A exp(B/T). The close correlation of the two parameters is shown, which requires the computation of the covariance matrix for the representation of uncertainties. This matrix facilitates the correct estimation of the confidence interval for interpolated (or extrapolated) values of rate coefficients. It is proposed that the full correlation matrix should be published in any article dealing with the determination of Arrhenius parameters.The importance of correct weighting is emphasized. Nonlinear fitting to the Arrhenius equation can be carried out without weighting only in case the (absolute) error of rate coefficient is independent of the temperature. Simulated experiments show that noncorrect weighting shifts the average values of fitted parameters and increases the variance of the parameters as well.With respect to the modified Arrhenius equation: k = A · Tn exp(B/T), statistical analysis shows that the physically meaningful estimation of all three parameters is impossible. Nonlinear fitting of three parameters is suggested for interpolation (and extrapolation) of rate coefficients, whereas in case of activation parameter estimation, the fixing of “n” on the basis of theoretical considerations is advised followed by the estimation of the remaining two parameters.