bluuebunny/crossref_metadata_2025 huggingface dataset:
Iodine catalyzed pyrolysis of dimethyl sulfide. Heats of formation of CH3SCH2I, the CH3SCH2 radical, and the pibond energy in CH2S
Authors: Shum Lilian G. S. , Benson Sidney W.
Published: January 2005

A kinetic study has been made of the gas phase, I2‐catalyzed decomposition of (CH3)2S at 630–650 K. Some I2 is consumed initially, reaching a steady‐state concentration. The initial major products are CH4 and CH2S together with small amounts of CH3SCH2I, CH3I, HI, and CS2. The initial reaction corresponds to a pseudo‐equilibrium:

accompanied by:

and

which brings (I2) into steady state and a final complex reaction:
equation image

From the initial rate of I2 loss it is possible to obtain Arrhenius parameters for the iodination:
equation image
We measure k1, (644 K) = 150 L/mol s and from both the Arrhenius plot and independent estimates A1 (644 K) = 1011.2 ± 0.3 L/mol s. Thus, E1 = 26.7 ± 1 kcal/mol. From the steady‐state I2 concentration, an assumed mechanism and the known rate parameters for the CH3I/HI system. It is possible to deduce KA (644) = 3.8 × 10−2 with an uncertainty of a factor of 2. Using an estimated ΔS (644) = 4.2 ± 1.0 e.u. we find ΔHA (644) = 7.0 ± 1.1 kcal. With 〈ΔCPA〉644 = 1.2 this becomes: ΔHA(298) = 6.6 ± 1.1 kcal/mol. Then ΔH (CH3SCH2I) = 6.3 ± 1 kcal/mol. Making the assumption that E−1 = 1.0 ± 0.5 kcal/mol we find ΔH (644) = 25.7 ± 0.7 kcal/mol and with 〈ΔCPI〉 = 1.2; ΔH = 25.3 ± 0.8 kcal/mol. This gives ΔH (CH3SĊH2) = 35.6 ± 1.0 kcal/mol and DH (CH3SCH2H) = 96.6 ± 1.0 kcal/mol. This then yields Eπ(CH2S) = 52 ± 3 kcal. From the observed rate of pressure increase in the system and the preceding data k3, is calculated for the step CH3SCH2 → CH3 + CH2S. From an estimated A‐factor E3 is deduced and from the overall thermochemistry values for k−3 and E−3. A detailed mechanism is proposed for the I‐atom catalyzed conversion of CH2S to CS2 + CH4.
The flash photolysis—shock tube technique using atomic resonance absorption for kinetic studies at high temperatures
Authors: Michael J. V. , Sutherland J. W. , Klemm R. B.
Published: January 2005

A flash photolysis‐shock tube technique is described for making kinetic measurements at high temperature. Coupled with sensitive atomic resonance absorption detection, this method allows bimolecular rate constants for atom‐molecule reactions to be measured directly under conditions free from kinetic complications. Experiments were performed in the reflected shock regime, and the temperature and density were calculated using ideal shock wave theory in this initial work. Results for the reaction of atomic hydrogen with ammonia are presented to illustrate the potential of the technique. The values of the Arrhenius rate parameters found in these experiments, 900 K ≤ T ≤ 1850 K, were A = (1.14 ± 0.12) × 10−10 cm3 molecule−1 s−1 and Ea = 13,216 ± 242 cal mol−1. This result gives rate constants that are about five times larger than those from previous studies. Although corrections for nonidealities in the reflected shock region are anticipated and under investigation, the expected changes will be relatively small and thus the large discrepancy noted here will remain.
The rate constants for the reaction of the hydroxyl radical with methyl, n‐propyl, and n‐butyl nitrites
Authors: Baulch Donald L. , Campbell Ian M. , Saunders Sandra M.
Published: January 2005

The kinetics of the reaction of OH radicals with methyl, n‐propyl, and n‐butyl nitrite

have been studied in a discharge flow system under pseudo first‐order conditions. The OH radicals were generated by the reaction of H atoms with NO2 and the concentration of OH; monitored by resonance fluorescence, was followed as a function of time in an excess of each nitrite. Values of k(CH3ONO) = (0.6 ± 0.09) × 109 dm3 mol−1 s−1 k(n – C3H7ONO) = (1.39 ± 0.20) × 109 dm3 mol−1 s−1, and k(n – C4H9ONO) = (2.89 ± 0.43) × 109 dm3 mol−1 s−1 at 295 K were obtained. These results agree with previous relative rate measurements from this laboratory but the value for k (CH3ONO) is a factor of 7 greater than the value obtained by relative rate measurements elsewhere using a different OH source.
Reactivities of cis‐ and trans‐buten‐2‐yl free radicals in presence of D2S. II. Absolute values of rate constants and isotopic effects
Authors: Richard C. , Martin R.
Published: January 2005

Cis‐ and trans‐buten‐2‐yl free radicals are shown to react with butene‐2 cis (Bc) and D2S in the following metathetical steps: magnified image giving rise to butenes‐1 (B1). The initial formations of butene‐1,3 d1 and total butene‐1 in D2SBc mixtures have been studied in the initial pressure range 20–200 torr for Bc, 0–41 torr for D2S and at 717–817 K. The main initiation and termination steps are shown to be: magnified image Assuming a rapid equilibrium between cis‐ and trans‐C4H7⋅, ki ≃ 1015.5 exp(−85.5/RT) s−1 (RT in kcal mol−1) and kt ≃ 1013 mol−1 cm3 s−1, we get: k2c′ = 1.1 k2t′ = 1012.0 exp[(−9.25 ± 2)/RT] mol−1 cm3 s−1 and k2 + 1.5 k2′ ≃ 1012.1 exp[(−15.2 ± 2)/RT] mol−1 cm3 s−1. Isotopic effects relating to processes (2c′) + (2t′) and to (i′) have been evaluated.
Kinetics of interaction of vibrationally excited OH(X2πi)v=9 with simple hydrocarbons at room temperature
Authors: Finlayson‐Pitts B. J. , Toohey D. W. , Ezell M. J.
Published: January 2005

Relative rate constants for the removal of vibrationally excited OH in the ninth vibrational level of its ground electronic state [designated hereafter by OH† (9)] by interaction with a series of simple hydrocarbons at room temperature are reported. The reaction of hydrogen atoms with ozone was used to generate OH†(9) in a fast flow discharge system at 1.1 ± 0.1 torr total pressure. The decrease in the (9 → 3 band) Meinel band chemiluminescent emission intensity at 626 nm was followed as a function of the concentration of added organic or of a reference deactivator (O2), respectively, at a fixed reaction time; these data gave relative rate constants, k/k, for the removal of OH†(9) by the organic. The relative rate constants determined in this study are as follows: C2H6, 2.7 ± 0.2; C3H8, 4.4 ± 0.4; n–C4H10, 7.5 ± 0.6; iso–C4H10, 7.3 ± 0.8; n–C5H12, 10.4 ± 0.7; C2H4, 22.9 ± 1.8; C3H6, 43.4 ± 1.4; cis–2–C4H8, 47.7 ± 3.1; C6H6, 29 ± 7. (Errors are two standard deviations of the weighted mean of experiments in two flow tubes with different wall coatings and carrier gases.) The implications of the trends in these rate constants for the relative contributions of energy transfer and reaction to the net removal of OH† (9) are discussed.
The pyrolysis of dimethyl sulfide, kinetics and mechanism
Authors: Shum Lilian G. S. , Benson Sidney W.
Published: January 2005

The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system at 681–723 K by monitoring total pressure‐time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths:
equation image
with a slow, minor, secondary reaction:
equation image

In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by

with θ = 2.303 RT in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data:

which agrees well with the experimental one over the range studied. The reaction is initiated by Me2S → Me + MeS⋅ and propagated by metathetical radical attack on Me2S. C2H4 is formed by an isomerization reaction which may in part be due to a hot radical:
equation image
Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.
Kinetics of oxidation of some α‐amino acids L(−) arginine, L(−) histidine, L(+) ornithine, L(−) tryptophan, L(−) threonine by sodium N‐chloro‐4 methyl benzene sulphonamide (chloramine‐T) in alkaline medium
Authors: Gupta K. C. , Gupta Kumkum
Published: January 2005

Kinetic studies of oxidation of L(−) arginine, L(+) ornithine, L(−) histidine, L(−) tryptophan, L(−) threonine have been carried out in alkaline medium. The reaction showed an inverse fractional order in OH− and first‐order dependence on both amino acid and chloroamine‐T concentration. The effect of varying ionic strength (KCl) on the rate of oxidation is negligible. A general mechanism for the oxidation has been suggested by considering interaction between anionic species of amino acid and p‐toluene‐sulphochloramide. The effect of solvent and temperature have been also discussed. The fractional order obtained in OH− is due to the fact that a fraction of overall reaction proceeds via an alternative OH− independent path. The combined rate law in accordance to observed kinetics is derived as

The rate constants predicted by the derived rate law as the concentration of OH− ions change, are in excellent agreement with the observed rate constants, thus further justifying these rate laws and hence the proposed mechanistic schemes.
Kinetic study for the reactions of OH radicals with dimethylsulfide, diethylsulfide, tetrahydrothiophene, and thiophene
Authors: Martin D. , Jourdain J. L. , LeBras G.
Published: January 2005

The reactions of OH radicals with dimethylsulfide (DMS) diethylsulfide (DES), tetrahydrothiophene (THT), and thiophene have been studied at room temperature for DES and THT, at 273, 293, and 318 K for DMS, and at 293 and 318 K for thiophene by the discharge flow EPR technique in a halocarbon wax coated reactor. The following rate constants were obtained at room temperature.
equation image
For the reaction OH + DMS (1), a very low temperature dependence was noticed.

Some additional results concerning the mass spectrometric analysis of the products are also reported.
Kinetic study of the reaction of OH with HCl from 240–1055 K
Authors: Ravishankara A. R. , Wine P. H. , Wells J. R. , Thompson R. L.
Published: January 2005

Absolute rate coefficients for the reaction of OH with HCl (k1) have been measured as a function of temperature over the range 240–1055 K. OH was produced by flash photolysis of H2O at λ > 165 nm, 266 nm laser photolysis of O3/H2O mixtures, or 266 nm laser photolysis of H2O2. OH was monitored by time‐resolved resonance fluorescenceor pulsed laser–induced fluorescence. In many experiments the HCl concentration was measured in situ in the slow flow reactor by UV photometry. Over the temperature range 240–363 K the following Arrhenius expression is an adequate representation of the data: k1 = (2.4 ± 0.2) × 10−12 exp[−(327 ± 28)/T]cm3 molecule−1 s−1. Over the wider temperature range 240–1055 K, the temperature dependence of k1 deviates from the Arrhenius form, but is adequately described by the expression k1 = 4.5 × 10−17 T1.65 exp(112/T) cm3 molecule−1 s−1. The error in a calculated rate coefficient at any temperature is 20%.
The accuracy of equation approximating the integral of the Arrhenius equation to perform the kinetic analysis of solid state reactions
Authors: Criado J. M. , Ortega A.
Published: January 2005

The accuracies of the approximation of the temperature integral of the Arrhenius law proposed by Coats and Redfern(CR), Doyle(D), Gyulai and Greenhow(GG), and MacCallum and Tanner(McT) have been tested. It has been demonstrated that these methods (only with the exception of the MacCallum and Tanner procedure) generally lead to accurate enough values of the activation energy of solid state reactions.

The accuracy of these methods increases in the sequence: CC > D ≃ GG ≫ McT.
Hydrogen abstraction by hydrocarbon radicals. I. Interactions between 1‐phenyl ethyl radicals and 1‐phenyl ethanol as well as benzyl alcohol
Authors: Gedra Á. , Lukács J. , Vidóczy T. , Sümegi L. , Gál D.
Published: January 2005

Hydrogen abstraction by 1‐phenylethyl radicals (ṘH) from phenylmethyl‐carbinol (HROH) and benzyl alcohol (H2R′OH) has been studied in the liquid phase at 120°C. 1‐Phenylethyl radicals have been generated by thermal decomposition of azo‐bis‐1‐phenyl ethane and the formation of ethylbenzene (RH2), acetophenone (RO), and 2,3‐di‐phenyl butane (R2H2) has been monitored during the reaction.

In order to optimize the experimental conditions, a mechanism has been assumed for the various pathways of the disappearance of ṘH and by using estimated rate parameters a presimulation was performed.

The relative rate constants obtained are:

and

where kH refers to the hydrogen abstraction while kt is the combination rate coefficient of the radicals ṘH.
Gas phase reaction of heptafluoroisopropyl radicals with carbon tetrachloride
Authors: de Vöhringer Cecilia M. , Staricco Eduardo H.
Published: January 2005

The reaction
magnified image
was investigated in the gas phase over the range 80–225°C using the photolysis of heptafluoroisopropyl iodide as the source of radicals. The rate constant, based on the value of 1013.36 cm3 mol−1 s−1 for the recombination of i‐C3F7 radicals, is given by

where θ = 2.303 RT/cal mol−1. Arrhenius parameters for chlorine abstraction from CCl4 by CF3, C2F5, n‐C3F7, and some hydrogenated radicals are compared.
Kinetics and mechanism of oxidation of aliphatic aldehydes by peroxomonosulphate
Authors: Renganathan Rajalingam , Maruthamuthu Pichai
Published: January 2005

The kinetics of the oxidation of aliphatic aldehydes, formaldehyde, acetaldehyde, propionaldehyde, n‐butyraldehyde, and trichloroacetaldehyde by Peroxomonosulphate (PMS) was carried out in aqueous perchloric acid medium (0.1–1 M H+) at constant ionic strength of 1.2 M in the temperature range 10°–60°C. The reactions of all the aldehydes were found to obey a total second‐order kinetics, first order each with respect to [Peroxomonosulphate] and [aldehyde]. Acetaldehyde, propionaldehyde, and n‐butyraldehyde exhibited acid catalysis with the concurrent occurrence of acid‐independent reaction path conforming to the rate law

Formaldehyde was found to undergo oxidation only by acid‐dependent path (kb = 0) and trichloroacetaldehyde exhibited only the acid‐independent reaction path (ka = 0). The products of oxidation were found to be the respective carboxylic acids in each case. The stoichiometry of the reaction, [Peroxomonosulphate]:[Aldehyde] = 1:1, indicated the absence of carbonyl‐assisted decomposition and self‐decomposition of peroxomonosulphate. The kinetic and thermodynamic parameters evaluated pointed to the mechanism of a fast nucleophilic attack of the oxidant on the aldehyde followed by slow acid catalyzed and/or uncatalyzed decomposition of the intermediate to product. A sharp comparison is made with the corresponding reactions of the similar peroxides, S2O and H2PO.
Opacity analysis of the H3 system: Modified rotating‐rod versus Frozen‐Orientation models
Authors: Agmon Noam
Published: January 2005

The Rotating‐Rod Model is modified to make the adjustable α parameter which appears in the treatment energy dependent. Its predictions for opacity and excitation functions compare well with quasi‐classical H3 trajectory results, for translational and vibrationalenergy variations and isotopic mass effects. The Frozen‐Orientation Model in its present form is incapable of such an agreement for mass combinations other than H + D2. It is suggested that the decreaseof α with energy can be interpreted as a transition from adiabatic tosudden behavior, where alignment is only on the average, and much energy isdeposited in the bending modes. This is supported by a correlation between α and the average final rotation.
Isotope effect on the location of variational transition states: The hydrogen exchange reaction
Authors: Morcillo Luis Bañares , Ureña Angel Gonzalez , Menzinger Michael
Published: January 2005

The microcanonical variational transition states of the isotopic reactions H + T2 and T + H2 are shown to migrate with increasing energy in opposite directions away from the classical barrier, i.e., into the reactant and product valleys, respectively. The energy dependence of this isotopic shift is examined and excitation functions are reported, both for collinear and near‐collinear reactions.
A comparative study of the PK(II) and LSTH potential energy surfaces for the H3 system
Authors: Pollak Eli
Published: January 2005

Recent dynamical computations on the LSTH and PK(II) potential energy surfaces are analyzed in terms of different properties of the surfaces. Differences in the bend level structure of resonances are found tobe due to the weaker vibrational force constant at the saddle point of the LSTH surface. The importance of including van der Waals wells in the potential energy surface is demonstrated by analysis of quantal resonances in thecollinear Mu + D2 reaction.
Rate constants for one‐electron oxidation by methylperoxyl radicals in aqueous solutions
Authors: HUIE Robert E. , NETA P.
Published: January 2005

Rate constants for one‐electron oxidation by the methylperoxyl radicals (CH3O2, HOCH2O2, −O2CCH2O2, and CCI3O2) in aqueous solutions have been measured by pulse radiolysis and found to be in the range of 3 × 105 to 6 × 108 M−1 s−1 for compounds with redox potentials between 0.6 and 0.1 V. Substitution on the methylperoxyl radical with OH or CO2− has only a minor effect on the rate of oxidation but substitution with three chlorines increases the rate constants by two orders of magnitude. The redox potential of the CH3O2 radical is estimated to be 0.6–0.7 V.
Oxidation of benzyl alcohols by nitrous and nitric acids in strong sulfuric acid media
Authors: Ross David S. , Gu Chee‐Liang , Hum Georgina P. , Malhotra Ripudaman
Published: January 2005

We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol−1. A Hammett plot of logk2 vs. σ+ is linear with a ρ value of −1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.
Kinetics of the oxidation of nitric oxide by chlorine and oxygen in nonaqueous media
Authors: Nottingham Winston C. , Sutter John R.
Published: January 2005

The kinetics of the reaction between nitric oxide and chlorine have been investigated in both carbon tetrachloride and glacial acetic acid. The nitric oxide‐oxygen reaction has been investigated in carbon tetrachloride.

The appearance of product, NOCl or NO2, was monitored spectrophotometrically at a wavelength of 475 nm for NOCl and 343 nm for NO2. These measurements were performed using an Amino‐Morrow stopped‐flow apparatus equipped with a Beckman D U monochromator.

The data for both the NOCl2 and NOO2 systems could be fitted to the third‐order integrated equation and the calculated rate constants were 2.75 × 103 M−2 s−1 and 2.79 × 106 M2 s−1, respectively, at 25.1°C.

There was a noted increase in rate constants on changing the solvent from carbon tetrachloride to acetic acid.

The likelihood of a termolecular encounter is inherent in the mechanism, however, no real evidence to substantiate either a direct termolecular or a series of two bimolecular steps has been obtained, although a −7 kcal for ΔH0 would support the latter.
Rate constant of OH + OCS reaction over the temperature range 255–483 K
Authors: Cheng Bing‐Ming , Lee Yuan‐Pern
Published: January 2005

The rate constant of the reaction between OH and OCS in helium over the temperature range 255–483 K has been determined using the discharge flow‐resonance fluorescence technique. The OCS has been carefully purified to avoid interference from H2S and CO impurities. An FTIR with a multireflection cell was used to determine the impurity concentrations and the purified sample was found to contain less than 0.005% of H2S. At 300 K, the rate constant was determined to be (2.0 ±0.40.8) × 10−15 cm3 molecule−1 s−1. Although the rate constants showed slight positive deviation at lower temperatures, thev can be satisfactorily fitted by the Arrhenius equation, k = 1.13 × 10−13 exp(−1200/T) cm3 molecule−1 s−1. No pressure dependence was observed at all temperatures, nor was O2 enhancement observed under our experimental conditions.
Rates and mechanisms of oxidation of ZnTPP by CCI3O2 radicals in various solvents
Authors: Alfassi Z. B. , Harriman A. , Mosseri S. , Neta P.
Published: January 2005

Trichloromethylperoxyl radicals were produced by pulse radiolysis of air saturated solutions containing CCl4. The rate constants for the reaction of CCl3O2 radicals with zinc tetraphenylporphyrin (ZnTPP) were determined in various solvents. They were found to vary between 3 × 107 and 3 × 109 M−1 s−1. The changes in rate constants result from complexation of ZnTPP with the different solvents, but did not correspond to changes in redox potential of ZnTPP. The rate constants were found to depend on the strength of the axial complexation, indicating an inner sphere mechanism whereby the radical binds to the metal prior to electron transfer.
The reaction of acetylperoxy radicals with NO2
Authors: Basco Norman , Parmar Sucha S.
Published: January 2005

Acetylperoxy radicals were produced by the flash photolysis of chlorine in the presence of acetaldehyde and oxygen. By adding various concentrations of nitrogen dioxide, the rate constant for the reaction producing PAN
equation image
was measured to be k4 (153 Torr) = (2.29 ± 0.05) × 109 L/mol s.

The effect of pressure has been studied over the range 76–612 Torr and the data fitted to a fall‐off curve with k = 1.85 × 1013 L2/mol2 s. and k = 3.67 × 109 L/mol s. With a calculated value of the dissociation constant, k = 268 L/mol s and of the equilibrium constant, K4 = 1.04 × 1012 L/mol, the expected strong collision value for k is 2.79 × 1014 L2/mol2 s.

The ultraviolet absorption spectrum of PAN has been characterized in the range 205–260 nm.
A study of the reaction NO3 + NO2 + M → N2O5 + M(M = N2, O2)
Authors: Wallington Timothy J. , Atkinson Roger , Winer Arthur M. , Pitts James N.
Published: January 2005

The gas‐phase reaction of the NO3 radical with NO2 was investigated, using a flash photolysis‐visible absorption technique, over the total pressure range 25–400 Torr of nitrogen or oxygen diluent at 298 ± 2 K. The absolute rate constants determined (in units of 10−13 cm3 molecule−1 s−1) at 25, 100, and 400 Torr total pressure were, respectively, (4.0 ± 0.5), (7.0 ± 0.7), and (10 ± 2) for M = N2 and (4.5 ± 0.5), (8.0 ± 0.4), and (8.8 ± 2.0) for M = O2. These data show that the third‐body efficiencies of N2 and O2 are identical, within the error limits, and that previous evaluations for M = N2 are applicable to the atmosphere. In addition, upper limits were determined for the rate constants of the reactions of the NO3 radical with methanol, ethanol, and propan‐2‐ol of ⩽6 × 10−16, ⩽9 × 10−16, and ⩽2.3 × 10−15 cm3 molecule−1 s−1, respectively, at 298 ± 2 K.
Absolute rate constants for hydrogen abstraction from hydrocarbons by the trichloromethylperoxyl radical
Authors: Mosseri S. , Alfassi Z. B. , Neta P.
Published: January 2005

Absolute rate constants have been measured for the reactions of trichloromethylperoxyl radicals with cyclohexane, cyclohexene, and hexamethylbenzene. The CCl3O2 radicals were produced by pulse radiolysis of air‐saturated CCl4 solutions containing various amounts of the hydrocarbons. The rate constants were determined by competition with the one‐electron oxidation of metalloporphyrins, using the rate of formation of the metalloporphyrin radical cation absorption to monitor the reaction by kinetic spectrophotometry. The rate constants for hydrogen abstraction from cyclohexane, cyclohexene, and hexamethylbenzene were found to be 1 × 103, 1.0 × 105, and 7.5 × 104 M−1 s−1, respectively.
Collisional energy transfer in highly vibrationally excited molecules: A very low‐pressure pyrolysis study of acetyl chloride
Authors: Lim Kieran F. , Gilbert Robert G. , Brown Trevor C. , King Keith D.
Published: January 2005

The average downward energy transfer (〈Δ Edown〉) is obtained for highly vibrationally excited acetyl chloride with Ne and C2H4 bath gases at ca. 870 K. Data are obtained by the technique of very low‐pressure pyrolysis (VLPP). Fitting these data by solution of the appropriate reaction‐diffusion integrodifferential master equation yields the gas/gas collisional energy transfer parameters: 〈Δ Edown〉 values are 220 ± 10 cm−1 (Ne bath gas) and 330 ± 20 cm−1 (C2H4).

These energy transfer quantities are much less than those predicted by statistical theories, or those observed for similar sized molecules such as CH3CH2Cl. These results are explained by the qualitative predictions of the biased random walk model wherein the fundamental mechanism of energy transfer is the multiple interactions between the bath gas and the individual atoms of the reactant molecule, during the course of the collision event. The charge distribution of acetyl chloride decreases the number of such interactions, thereby reducing the amount of energy transferred per collision.
A modeling study of the oxidation of propionaldehyde in the negative temperature coefficient regime
Authors: Kaiser E. W.
Published: January 2005

A chemical kinetic reaction mechanism has been developed which describes the oxidation of propanal within the temperature range 400–700 K. This mechanism has been tested against data obtained by four experimental groups over a wide range of initial conditions. The induction period and the absolute rate of propanal consumption are predicted to within a factor of 2 for initial densities of oxygen and propanal ranging over factors of 400. The existence and location of the negative temperature coefficient in the consumption of propanal are also simulated properly. The yields of all major and most minor products are predicted to within a factor of 2 for the wide variety of initial conditions tested. Sensitivity analyses were carried out at 553 and 713 K to identify the reactions primarily responsible for controlling the rate of propanal consumption and the distribution of products.
Kinetic study of the reaction of IO with CH3SCH3
Authors: Martin D. , Jourdain J. L. , Laverdet G. , Le Bras G.
Published: January 2005

The reaction IO + CH3SCH3 → products (3) was studied at room temperature and near 1 Torr pressure of He, using the discharge flow mass spectrometric technique. The rate constant was found to be k3 = (1.5 ± 0.5) × 10−11 cm3 molecule−1 s−1. CH3S(O)CH3 was detected as a product suggesting the following channel: IO + CH3SCH3 → CH3S(O)CH3 + I. The rate constant of the reaction IO + IO → products (1) was also measured: k1 = (3 ± 0.5) × 10−11 at 298 K and 1 Torr pressure. The atmospheric implication of reaction (3) is discussed. The results indicate that this reaction could be a potential important sink of CH3SCH3 in marine atmosphere.
Self‐inhibition or the lack of it in the pyrolyses of neopentane and n‐hexane
Authors: Marshall Roger M.
Published: January 2005

Published data show that in its early stages (up to 3% decomposition), the pyrolysis of n‐hexane in the ranges 723–823 K and 10–100 Torr is not inhibited by the olefin products, in contrast with neopentane pyrolysis which is very strongly inhibited in similar conditions. Detailed consideration of the chain mechanisms for the two pyrolyses shows that the reactivity of the chain terminating radical towards hydrogen abstraction from an allylic CH bond in product olefin is the factor which determines whether or not observable self‐inhibition occurs. Thus, n‐hexane pyrolysis, whose chain decomposition is terminated by recombination and disproportionation of ethyl, is not significantly self‐inhibited, whereas that of neopentane which is terminated by recombination of methyl is very strongly inhibited because methyl is 14× more reactive than ethyl. The implications for other alkanes are briefly discussed.
Kinetics and mechanism of the thermal reactions of endo‐ and exo‐5‐cyanobicyclo[2.2.2]oct‐2‐ene and methyl‐substituted derivatives in the gas phase
Authors: Van Mele B. , Huybrechts G.
Published: January 2005

The thermal reactions of endo‐ and exo‐5‐cyanobicyclo‐[2.2.2]oct‐2‐ene and their trans‐ and cis‐6‐methyl‐substituted derivatives have been investigated in the gas phase between 518 and 630 K. Each product decomposes by two parallel first‐order retro‐Diels‐Alder reactions, a main one with formation of cyclohexa‐1,3‐diene and a minor one with elimination of ethene. Slight isomerizations are also observed. The kinetic results can be explained in terms of a biradical mechanism. The rate‐determining step is shown to depend on the amount of resonance energy in the biradical. Heats of formation and entropies of the bicyclo[2.2.2]oct‐2‐enes studied are estimated.
Large inefficiencies of unweighted least‐squares treatment of logarithmically transformed A exp(–kt) data
Authors: Kalantar A. H.
Published: January 2005

The standard deviations (σ) of the parameters of a single exponential function can vary strongly with the range of the data, the character of the underlying error structure and also with the inclusion or omission of the appropriate relative weights. These effects are studied quantitatively, for least squares analysis of uniformly spaced, ln‐linearized simulated data. The parameters, k and A, extracted are less precise when weighting is omitted, increasingly so as the range of the data increases, particularly for the case of equal amplitude errors for each A exp(–kti) datum. The results, expressed as efficiencies (σ2[using weights]/σ2[omitting weights]), show < 1% efficiency in some cases. This is tantamount to ignoring > 99% of the data and treating the remainder with proper relative weighting.
Disproportionation reactions between alkyl and fluoroalkyl radicals. IV. Pentafluoroethyl and ethyl radicals
Authors: Pritchard G. O. , Kennedy V. H. , Heldoorn G. M. , Piasecki M. L. , Johnson K. A. , Golan D. R.
Published: January 2005

A new determination of the disproportionation/combination ratio for C2F5 and C2H5 radicals gives a value of Δ(C2F5, C2H5) = 0.24 ± 0.02, independent of temperature. The cross‐combination ratio for the two radicals was found to increase with temperature and the significance of this is discussed in evaluating Δ.
The photochemistry of methyl cyclobutyl ketone. Part 2. Temperature dependence and the acetyl radical decomposition
Authors: Baldwin Philip J. , Canosa‐Mas Carlos E. , Frey H. Monty , Walsh Robin
Published: January 2005

Following earlier room‐temperature studies, gaseous mixtures of methyl cyclobutyl ketone (MCK) diluted in argon have been photolyzed at temperatures up to 205°C. Experiments have been carried out at a variety of pressures (up to ca. 2 atm) at wavelengths of 313 nm (steady state conditions) and 308 nm (pulsed photolysis). The results are consistent with a mechanism dominated by radical‐radical reactions involving acetyl, methyl, and cyclobutyl radicals. Acetyl radical processes predominate at lower temperatures while methyl radical reactions are more important at high temperatures.

The results are interpreted via kinetic modelling of a mechanism in which a key role is played by the acetyl radical decomposition reaction

Values for k3 have been obtained and its temperature and pressure dependence are fitted by RRKM theory and a weak‐collisional activation model to yield

This high‐pressure limiting Arrhenius equation is consistent with other studies in the same temperature range, but is difficult to reconcile with higher temperature investigations.
The gas phase reactions of hydroxyl radicals with a series of aliphatic alcohols over the temperature range 240–440 K
Authors: Wallington Timothy J. , Kurylo Michael J.
Published: January 2005

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of aliphatic alcohols using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for methanol (k1), ethanol (k2), and 2‐propanol (k3) were used to derive the Arrhenius expressions

and

At 296 K, the measured rate constants (in units of 10−13 cm3 molecule−1 s−1) were: k1 = (8.61 ± 0.47), k2 = (33.3 ± 2.3), and k3 = (58.1 ± 3.4). Room temperature rate constants for the OH reactions with several other aliphatic alcohols were also measured. These were (in the above units): 1‐propanol, (53.4 ± 2.9); 1‐butanol, (83.1 ± 6.3) and 1‐pentanol, (108 ± 11). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.
Measurement of absolute rate data for the reaction of ground state atomic silicon, Si(33PJ), with halogenated olefinic and aromatic compounds by time‐resolved atomic resonance absorption spectroscopy
Authors: Basu Subhash C. , Husain David
Published: January 2005

We present a kinetic study of the reaction of ground state silicon atoms with halogenated unsaturated organic compounds (R). Si(33PJ) was generated by the repetitive pulsed irradiation of SiCl4 in the presence of excess helium buffer gas and the reactant R in a slow flow system, kinetically equivalent to a static system. The ground state atom was monitored by time‐resolved atomic resonance absorption spectroscopy at λ = 252 nm [Si(43PJ) ← Si(33PJ)] on time scales by which the optically metastable tates,Si(31D2) and Si(31S0) had relaxed to the 3P state, using signal averaging methods. Computerized fitting of the resulting atomic decay traces in the presence of the various reactants, R, yielded the following new body of absolute second‐order rate constants (kR, T = 300 K, errors = 2sigma;):

R
kR/cm3 molecule−1 s−1

C2F4
1.6 ± 0.2 × 10−10

C2Cl4
9.9 ± 1.7 × 10−10

CH2CF2
4.0 ± 0.6 × 10−10

CHClCCl2
7.0 ± 1.1 × 10−10

CF3CHCH2
4.6 ± 0.5 × 10−10

C6H6
4.4 ± 1.0 times; 10−10

C6F6
4.4 ± 0.6 × 10−10

C6HF5
4.6 ± 1.3 × 10−10

C6H2F4
3.9 ± 0.8 × 10−10

C6F5—CF3
5.1 ± 0.6 × 10−10

These data are compared, where appropriate, with analogous data for unsaturated hydrocarbon organic compounds. They are also discussed within the general context of nuclear recoil measurements involving 31Si.
A study of product ratios in the direct (313 nm) and Hg‐sensitized (254 nm) photodecomposition of 2‐methylcyclohexanone in the gas phase
Authors: Pritchard G. O. , Badcock C. C. , Follmer D. W.
Published: January 2005

The photolysis of 2‐methylcyclohexanone has been studied in the gas phase at 313 nm, mainly at 100°C, over a range of pressures. The Hg(63P1) photosensitized decomposition has also been investigated at 100°C. Under conditions of high excitation and/or little collisional quenching the major products are carbon monoxide and the hydrocarbons: 1‐hexene, trans‐and cis‐2‐hexene and methylcyclopentane, with minor aldehyde formation. The various product ratios are presented in tabular form. At lower excitation energies, and with increased collisional deactivation, trans‐ and cis‐5‐heptenal become important products, and the trans/cis aldehyde ratio is seen to be slightly pressure dependent when all the systems are compared. Similarly, there is a small pressure dependence for the Σ hexenes/methylcyclopentane ratio. From experiments at 250°C the temperature dependence of this ratio was established, and for thermalized hexane‐1,5‐diyl an activation energy difference (Ed − Ec) = −1.3 kcal mol−1 has been determined for the disproportionation and combination of the biradical. The mechanism for the photolysis is discussed in terms of triplet state photochemistry and biradical intermediates as developed, in particular, by Frey and coworkers, this Journal, 16, 1337 (1984).
The kinetics and mechanism of the decomposition of N‐chloroleucine
Authors: Antelo Juan M. , Arce Florencio , Franco Julia , Rodriguez Pilar , Varela Angel
Published: January 2005

At 298 K the rate constant for the decomposition of N‐chloroleucine has the constant value 3.20 × 10−4 s−1 over the range pH 5–12, increases with increasing acidity at pH < 5, and increases with pH at pH > 12. A mechanism is put forward which explains these results.
The thermochemistry of polyoxides and polyoxy radicals
Authors: Francisco J. S. , Williams I. H.
Published: January 2005

A new estimate is derived for the group additivity contribution ΔH[O—(O)2] = 55 ± 6 kJ mol−1, based upon recent experimental data, which enables heats of formation and bond dissociation energies to be estimated for species ROnR and RO(R = H, CH3, and CF3). Semi‐empirical MNDO calculated heats of formation, for these species, provide independent support for the new thermochemical estimates. The results are also consistent with other theoretical and experimental evidence.
Thermal decomposition of 1,2 butadiene
Authors: Kern R. D. , Singh H. J. , Wu C. H.
Published: January 2005

The thermal decomposition of 1,2 butadiene has been studied behind reflected shock waves over the temperature and total pressure ranges of 1300–2000 K and 0.20–0.55 atm using mixtures of 3% and 4.3% 1,2 butadiene in Ne. The major products of the pyrolysis are C2H2, C4H2, C2H4, CH4 and C6H6. Toluene was observed as a minor product in a narrow temperature range of 1500–1700 K. In order to model successfully the product profiles which were obtained by time‐of‐flight mass spectrometry, it was necessary to include the isomerization reaction of 1,2 to 1,3 butadiene. A reaction mechanism consisting of 74 reaction steps and 28 species was formulated to model the time and temperature dependence of major products obtained during the course of decomposition. The importance of C3H3 in the formation of benzene is demonstrated.
ESR equilibrium measurements of the OH bond energy in α‐tocopherol
Authors: Coronel M. E. J. , Colussi A. J.
Published: January 2005

ESR equilibrium measurements in radical buffer systems yield a value of 76.0 kcal/mol for the OH bond energy in α‐tocopherol.
The high temperature pyrolysis of 1,3‐butadiene II: Pulsed laser flash absorption rate constants, and consideration of possible molecular dissociation pathways
Authors: Kiefer J. H. , Mitchell K. I. , Wei H. C.
Published: January 2005

Rate constants for the unimolecular dissociation of 1,3‐butadiene have been measured with the pulsed laser flash absorption technique, following butadiene disappearance at 222 nm. The results are in excellent agreement with previous laser‐schlieren measurements interpreted with a ΔH°298 = 100 kcal/mol heat of dissociation. A new RRKM calculation agreeing with both sets of rate constants gives log k∞(s−1) = 17.03 ± 0.3 – 94(kcal/mol)/RT. These data and product measurements using ARAS, single‐pulse product analysis, and time‐of‐flight mass spectrometry, in shock tubes, all provide independent evidence against any major participation by molecular reactions in the dissociation. The only dissociation channel, or combination of channels, consistent with all the measurements is C‐C scission to two vinyl radicals. However, the extremely slow rate of H‐atom formation seen in ARAS experiments then requires an unacceptably low rate of vinyl dissociation.
The UV absorption spectra and kinetics of the self reactions of CH2ClO2 and CH2FO2 radicals in the gas phase
Authors: Dagaut Philippe , Wallington Timothy J. , Kurylo Michael J.
Published: January 2005

The ultraviolet absorption spectra of chloromethylperoxy and fluoromethylperoxy radicals, CH2ClO2 and CH2FO2, and the kinetics of their respective self reactions have been studied in the gas phase using a flash photolysis technique. The absorption spectra for both radicals were quantified over the wavelength range 210 and 290 nm. The measured absorption cross‐sections

were used to derive the observed self‐reaction rate constants (for reactions 1 and 2) over the temperature range 228–380 K, defined as –d[CH2XO2]/dt = 2k[CH2XO2]2, where X represents Cl or F.
magnified image
The rate constants at 298 K were found to be independent of pressure over the range 25–400 torr N2 with values of k1(298 K) = (3.78 ± 0.45) × 10−12 and k2(298 K) = (3.07 ± 0.65) × 10−12 in units of cm3 molecule−1 s−1. The kinetic data over the complete temperature range are represented by the Arrhenius expressions:

where the error limits represent 2σ from linear least squares analysis. These results are discussed with respect to previous measurements of the absorption spectra and reactions of alkylperoxy radicals.
Use of a simplex technique and contour diagrams for the determination of the reaction rate constants between glutathione and thiram in the presence of NADPH
Authors: Elskens Marc , Penninckx Michel J. , Vandeloise Robert , Donckt Emile Vander
Published: January 2005

The Modified Simplex Method (MSM) coupled with contour diagrams is used to determine the rate constants of a kinetic scheme involving three sequential second order processes.

Reaction between glutathione and the dithiocarbamate fungicide tetramethylthiuram disulfide produces the oxidized form of glutathione which is then reduced in the presence of NADPH. The concentration of the reducing agent is monitored as a function of time. In the absence of simplifying assumption a closed form solution of the rate equations does not exist. Computed curves of NADPH concentration versus time were generated using the software SIMULCIN.

The rate constant values are optimized by the MSM procedure to obtain the best agreement between calculated and experimental data. The significance, validity limits of the estimated rate constants and the relevance of these in vitro data to previous in vivo studies are discussed.
Gas phase reaction of Cl atoms with a series of oxygenated organic species at 295 K
Authors: Wallington Timothy J. , Skewes Loretta M. , Siegl Walter O. , Wu Ching‐Hsong , Japar Steven M.
Published: January 2005

The relative rate technique has been used to determine the rate constants for the reaction of chlorine atoms with a series of oxygenated organic species. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The decay rates of the organic species were measured relative to that of ethane or n‐butane. Using rate constants of 5.7 × 10−11 cm3 molecule−1 s−1, and 2.25 × 10−10 cm3 molecule−1 s−1 for the reaction of Cl with ethane and n‐butane respectively the following rate constants were derived, in units of 10−11 cm3 molecule−1 s−1: propane, (16.0 ± 0.4);i‐butane, (15.1 ± 0.9) n‐pentane, (31.0 ± 1.6); n‐hexane, (34.5 ± 2.3); cyclohexane, (36.1 ± 1.5); methanol, (4.57 ± 0.40); ethanol, (8.45 ± 0.91); n‐propanol, (14.4 ± 1.2); t‐butylalcohol, (3.26 ± 0.19); acetaldehyde, (8.45 ± 0.79); propionaldehyde, (11.3 ± 0.9); dimethylether, (20.5 ± 0.8); diethylether, (35.6 ± 2.8); and methyl‐t‐butylether, (16.6 ± 1.2). Quoted errors represent 2σ, and do not include any errors due to uncertainties in the rate constants used to place our relative measurements on an absolute basis. The results are discussed with respect to the mechanisms of these reactions and to previous literature data.
Kinetics and mechanism for the reactions of H atoms with CH3SH and C2H5SH
Authors: Martin D. , Jourdain J. L. , Le Bras G.
Published: January 2005

A kinetic study of the reactions of H atoms with CH3SH and C2H5SH has been carried out at 298 K by the discharge flow technique with EPR and mass spectrometric analysis of the species. The pressure was 1 torr. It was found: k1 = (2.20 ± 0.20) × 10−12 for the reaction H + CH3SH (1) and k2 = (2.40 ± 0.16) × 10−12 for the reaction H + C2H5SH (2). Units are cm3 molecule−1 s−1. A mass spectrometric analysis of the reaction products and a computer simulation of the reacting systems have shown that reaction (1) proceeds through two mechanisms leading to the formation of CH3S + H2 (1a) and CH3 + H2S (1b).
Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system, and the quenching of O2(1Σg+) by atomic hydrogen
Authors: Michelangeli Diane V. , Choo Kuang‐Yul , Leu Ming‐Taun
Published: January 2005

The generation of metastable O2(1Σg+) and O2(1Δg) in the H + O2 system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O2(1Σg+) and O2(1Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO2(2A′000) → HO2(2A″000), HO2(2A′001) → HO2(2A″000), and H O2(2A″200) → HO2(2A″000) emissions were detected in the H + O2 system. The rate constants for the quenching of O2(1Σg+) by H and H2 were determined to be (5.1 ± 1.4) × 10−13 and (7.1 ± 0.1) × 10−13 cm3 s−1, respectively. An upper limit for the branching ratio to produce O2(1Σg+) by the H + HO2 reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.
Rate constants for abstraction of hydrogen from ethylene by methyl and ethyl radicals relative to abstraction from propane and isobutane
Authors: Ahonkhai S. I. , Lin X‐H. , Back M. H.
Published: January 2005

A method is described for the measurement of relative rate constants for abstraction of hydrogen from ethylene at temperatures in the region of 750 K. The method is based on the effect of the addition of small quantities of propane and isobutane on the rates of formation of products in the thermal chain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions,
equation image
measurements of the ratio of the rates of formation of methane and ethane in the presence and absence of the additive gave the following results:

Values for k2 and k3 obtained from these ratios are compared with previous measurements.
Effect of solvent on the reactions of coordination complexes part VII: Kinetics of solvolysis of cis‐(bromo) (imidazole) bis‐(ethylenediamine)cobalt (III) and cis‐(bromo) (N‐methyl imidazole)bis‐(ethylenediamine) cobalt(III) in methanol‐water media
Authors: Dash Anadi C. , Dash Neelamadhab
Published: January 2005

The kinetics of the solvolytic aquation of cis‐(Bromo) (imidazole) bis(ethylenediamine) cobalt (III) and cis‐(Bromo) (N‐methylimidazole) bis(ethylenediamine) cobalt(III) have been investigated in aqueous methanol media with methanol content 0–80% by weight and at temperatures 40–55°C. The pseudo‐first order rate constant decreases with increasing methanol content. Plots of log k vs. D (where Ds is the bulk‐dielectric constant of the solvent mixture) and log k vs. the Grunwald‐Winstein Y‐solvent parameter are nonlinear, the curvature of the plots is relatively more significant for the imidazole complex. The plots of log k vs. molfraction of methanol (XMeOH) for both the substrates also deviate from linearity, the deviation being less and less marked, particularly for the N‐methyl imidazole complex, as the temperature is increased. Hence preferential solvation phenomenon appears to be less significant when the N‐H proton of imidazole is replaced by ‐CH3 group. The plots of calculated values of the transfer free energy of the dissociative transition state, cis‐{[(en)2Co(B)]3+}* (B = imidazole, N‐methylimidazole), relative to that of the initial state, cis‐[Co(en)2(B)Br]2+, for the transfer of the ions from water to the mixed solvent, against XMeOH exhibit maxima at XMeOH = 0.06, 0.27, and 0.12, 0.36 and minima at XMeOH = 0.12 and 0.19 for cis‐[(en)2Co(imH)Br]2+ and its N‐methylimidazole analogue respectively which are in keeping with the solvent structural changes around the initial state and transition state of these substrates as the solvent composition is varied.

Plots of activation enthalpy and entropy against molfraction of the solvent mixtures exhibit maxima and minima. This type of variations of the activation parameters, ΔH≠ and ΔS≠, with XMeOH speaks of the enthalpy and entropy changes associated with the solvent‐shell reorganization of the complex ions both in the initial and in the transition states which contribute appreciably to the overall activation enthalpy and entropy of the aquation reaction.