bluuebunny/crossref_metadata_2025 huggingface dataset:
The thermal isomerization of 1,1‐dimethyl‐2‐vinylcyclopropane to cis‐2‐methylhexa‐1,4‐diene via 1,5‐hydrogen migration
Authors: Frey H. M. , Solly R. K.
Published: January 2005

The gas phase isomerization of 1,1‐dimethyl‐2‐vinylcyclopropane to cis‐2‐methylhexa‐1,4‐diene has been studied in a static system. The isomerization is homogeneous and kinetically first order. The rate constants were independent of initial reactant pressure in the range 0.6 to 2 torr and of added nitrogen up to 180 torr. Rate constants determined at 10 temperatures in the range 200 to 254°C fitted the Arrhenius equation
k = 1011.41±0.02 exp (−33,540 ± 47 cal/RT) sec−1

The low A factor and activation energy are consistent with a concerted 1,5‐hydrogen migration via a “tight” cyclic transition complex.
New differential techniques for evaluating rate constants and ratios of rate constants. The behaviors of irreversible first‐and pseudo‐first‐order reactions
Authors: Meites Louis , Meites Thelma
Published: January 2005

A record of the time dependence of the difference between two signals, one proportional to the concentration of a reactant or product in one reaction mixture and the other proportional to the concentration of the same or a corresponding substance in another mixture in which the reaction is initiated at the same time as the first, makes it possible to obtain not only the ratio, but also the individual values, of the rate constants for the two reactions. The effects of the experimental variables on a number of measurable parameters are examined, the errors associated with a number of different ways of evaluating the rate constants and their ratio are discussed, and it is shown how conditions can be selected that should provide values whose precisions compare favorably with those attainable by other techniques.
Reaction of O(1D) with N2O
Authors: Greenberg Raymond I. , Heicklen Julian
Published: January 2005

O(1D), produced from the photolysis of N2O at 2139 Å, reacts with N2O in accord with:

We have used the method of chemical difference to obtain an accurate measure of k2/k3 = 0.59 ± 0.01. Furthermore, the quantum yield of production of O(3P), either on direct photolysis or on deactivation of O(1D) by N2O, is less than 0.02 and probably zero.
A Quantitative study of alkyl radical reactions by kinetic spectroscopy. Part I. Mutual combination of methyl radicals and combination of methyl radicals with nitric oxide
Authors: Basco N. , James D. G. L. , Suart R. D.
Published: January 2005

Combination reactions of the methyl radical have been studied by following the decay of the absorbance of the methyl radical during the course of the reaction by means of kinetic spectroscopy. The limiting values of the second‐order rate constants at high pressure were determined for two reactions at room temperature:

The extinction coefficient of the methyl radical was found to have a maximum value of (1.02 ± 0.06) X 104 1 mole−1 cm−1 at 216.4 nm. Integration of the extinction coefficient over the absorption band of the methyl radical gave an oscillator strength of 1.0 X 10−2.
Reaction of CF3 radicals with group IV tetramethyls
Authors: Bell T. N. , Platt A. E.
Published: January 2005

Arrhenius parameters have been measured for the abstraction of hydrogen from the C Si, Ge, and Sn tetramethyls:

The rate constants correlate with the proton chemical shift, which is related to a polar effect. In all cases except carbon, a hot‐molecule β‐fluorine rearrangement‐elimination reaction occurs following radical combination:

We suggest the occurrence of a radical exchange reaction for the Si, Sn, and Ge systems,

with kexchange (CF3 + Sn(Me)4) ∼ 107 ml m−1 s−1.
Kinetic isotope effects in the reactions of bromine atoms with CH4 and CD4
Authors: Yokota Toshitsugu , Timmons Richard B.
Published: January 2005

The competitive reactions of Br atoms with CH4 and CD4 were studied over the temperature range of 562° to 637°K. Over this temperature interval, the kinetic isotope effect, kH/kD, varied from 3.05 to 2.47 for the reactions

The rate constant ratio kH/kD, expressed in Arrhenius form, was found to equal (1.10 ± 0.05) exp (1030 ± 60/RT). A comparison is presented between the experimental result and the result obtained theoretically from absolute rate theory using the London‐Eyring‐Polanyi‐Sato (LEPS) method of constructing the potential energy surface of the reaction. The agreement between theory and experiment is very poor, and this is believed to arise from the highly unsymmetrical nature of the potential energy surface involved in these reactions. A comparison is also presented between the kH/kD values obtained in the Br + CH4–CD4 experiments and the available data on the corresponding Cl + CH4–CD4 reactions.
A critical review of the kinetics of the dissociation‐recombination reactions of fluorine and chlorine
Authors: Lloyd Alan C.
Published: January 2005

A critical evaluation of the rates of the dissociation and recombination reactions of fluorine and chlorine is given. Data are presented graphically and in tabular form. The effect of various third bodies is discussed. Rate expressions for specified temperature ranges are recommended, while comparison with theoretical values obtained from the Benson and Fueno theory is made where applicable.
Some aspects of theory and experiment in the ethane–methyl radical system
Authors: Waage E. V. , Rabinovitch B. S.
Published: January 2005

A critical examination has been made of some aspects of the thermal decomposition of ethane and the reverse recombination reaction. The experimental Arrhenius A‐factors for ethane are, in general, smaller than those which are calculated from thermodynamic quantities together with the observed rate constants for methyl recombination. Theoretical calculations also illustrate a discrepancy between the experimental work on recombination and decomposition. The experimental shapes of k/kα falloff curves and the pressure region of falloff are compared with the predictions of RRKM theory for various models.
Rotating sector study of the gas phase photolysis of the 1,1,1‐trichloro‐2,2,2‐trifluoroethane–cyclohexane system
Authors: Wampler Fred B. , Kuntz Robert R.
Published: January 2005

The rate constant for the combination of 1,1‐dichloro‐2,2,2‐trifluoroethyl radicals in the gas phase has been measured by applying the rotating sector technique to the 1,1,1‐trichloro‐2,2,2‐trifluoroethane–cyclohexane photochemical system. The combination rate constant, k5, was found to be 6.6 × 1012 cc mole−1 sec−1. Arrhenius parameters for the reaction, magnified image are given by the expression log k4 = 11.81 – (9700/2.3RT).
Study of the pyrolysis of H2O2 in the presence of H2and CO by use of UV absorption of HO2
Authors: Kijewski H. , Troe J.
Published: January 2005

In dissociation experiments of H2O2 under shock wave conditions, the spectra of H2O2 and HO2 have been observed in the UV at 2200 ≤ 2800 Å. By the use of these spectra the H2O2 decomposition in the presence of H2 and CO at 870 ≤ T ≤ 1000°K has been analyzed. It was found that in this temperature range, in contrast to low temperature behavior, reactions of H atoms with H2O2 and with HO2 are equally important. The rate of the reaction H + H2O2 ← HO2 + H2 was estimated in comparison with the rate of the reaction between H and HO2. Good agreement between calculated and measured concentration profiles of HO2 and H2O2 was obtained.
Abstraction of hydrogen by methylene
Authors: McNesby J. R. , Kelly R. V.
Published: January 2005

The photolysis of CD2CO at 313 nm in the presence of neopentane was carried out over the temperature range 576–706 K. Analysis of the products and isotopic analysis of the methanes demonstrate abstraction of H from neopentane and D from CD2CO by methylene. The relative kinetics of abstraction of H and D have been measured over the temperature range, and the absolute value for the collision yield of the abstraction of H from neopentane by CD2 at 653 K has been been estimated to be about 1.5 × 1011 mole−1 cm3 sec−1, a value 103 times larger than the corresponding reaction of CH3.
The reactions of O(1D) with ozone and nitrous oxide
Authors: Goldman Charles S. , Greenberg Raymond I. , Heicklen Julian
Published: January 2005

Ozone was photolyzed at room temperature in the presence of N2O at 2537 Å and 2288 Å to produce O(1D) atoms. These atoms can react with either O3or N2O viamagnified imageFrom the quantum yield of N2, the relative rate constantsk6a/k6andk2/k6could be obtained, wherek6+k6a+k6b. The former rate constant ratio was found to be 0.37 ± 0.03 at 2537 Å and 0.33 ± 0.03 at 2288 Å, in good agreement with an earlier report from our laboratory. The ratiok2/k6was found to be 2.6 at 2537 Å, but 4.1 at 2288 Å. The difference in the two numbers, if real, may reflect differences in reactivity due to different amounts of excess translational energy in the O(1D) atom at the two wavelengths.
Gas and liquid phase kinetics of the unimolecular isomerization of 1‐chloro‐4‐bromobicyclo[2.2.0]hexane: The radical stabilization energy of an α‐bromine atom
Authors: Cain Edward N. , Solly Richard K.
Published: January 2005

The kinetics of the gas phase isomerization of 1‐chloro‐4‐bromobicyclo[2.2.0]hexane to 2‐chloro‐5‐bromohexa‐1,5‐diene have been measured in a static system over the temperature range of 135–215°C, with a variation in the total pressure from 0.6 to 400 torr. For these conditions the rate constants are well represented by the Arrhenius equation:where θ = 2.303RTkcal/mole. Transition state estimates for the biradical mechanism for the isomerization of bicyclo[2.2.0]hexanes are shown to be in good agreement with these Arrhenius parameters. By comparison of the activation energy with that for the isomerization of bicyclo[2.2.0]hexane and 1,4‐dichlorobicyclo[2.2.0]hexane, the radical stabilization energy of an α‐bromine atom is shown to be 1.0 ± 1.8 kcal/mole. Rates are also reported in the liquid phase at temperatures of 155°C and 175°C with diphenyl ether, nitrobenzene, and dimethylsulfoxide as solvents. The observed rate constants are all faster (by a factor of 1.1–1.7) than those measured in the gas phase and display no correlation between rate and solvent polarity.
The SO2‐sensitized phosphorescence of biacetyl vapor in photolyses at 2650 and 2875 Å. The intersystem crossing ratio in sulfur dioxide
Authors: Horowitz Abraham , Calvert Jack G.
Published: January 2005

Quantum yields of the triplet sulfur dioxide (3SO2)‐sensitized phosphoresence (Φsens) in biacetyl (Ac2) have been determined in experiments over a wide range of pressures of SO2 and Ac2. Excited singlet sulfur dioxide (1SO2) was generated using 2650‐Å and 28757hyphen;Å light. The values of Φsens were dependent on the [SO2]/[Ac2] ratio, as anticpated theoretically. However, in runs at a fixed [SO2]/[Ac2] ratio, the measured Φsens values were dependent on the total pressure. This theoretically unexpected effect is probably largely the result of biacetyl triplet diffusion with deactivation at the cell wall. Treatment of the quantum yield data in terms of the complete mechanism gave new estimates of the following rate functions: 1SO2 + SO2 → (2SO2) (1), 1SO2 + SO2 → 3SO2 + SO2 (2), k2/(k1 + k2) = 0.082 ± 0.003 (2650 Å), 0.095 ± 0.005 (2875 Å) 3SO2 + Ac2 → SO2 + 3Ac2 (9a), 3SO2 + Ac2 → SO2 + Ac2 (9b), k9a + k9b = (8.4 ± 2.1) × 1010 (2650 Å), (8.1 ± 3.0) × 1010 l./mole‐sec (2875 Å) 3SO2 → SO2 + hvp (6), k6 = (7.3 ± 1.3) × 101 sec−1.
A flash photolysis–resonance fluorescence kinetics study of ground‐state sulfur atoms: I. Absolute rate parameters for reaction of S(3P) with O2(3Σ).
Authors: Davis D. D. , Klemm R. B. , Pilling M.
Published: January 2005

The flash photolysis–resonance fluorescence technique has been used to measure the reaction of ground‐state sulfur atoms with molecular oxygen as a function of both temperature and total pressure. The most suitable source of S(3P) for this study was found to be COS in the presence of CO2, as a diluent gas and with the photolysis flash filtered so as to remove all radiation of wavelengths below 1650 Å. Under these conditions, it was found that over the temperature range of 252–423°K the rate data could be fit to a simple Arrhenius‐type equation of the form

Units are cm3 molec−1 s−1. The small A‐factor for this reaction, the lack of any pressure dependence, and the direct observation of the production of O(3P) with increasing reaction time suggest that the S(3P) atom attacks the O2(3Σ) molecule end‐on forming SOO which rapidly falls apart to form SO (3Σ) and O(3P).
Rate constants for radical recombination. III. The trifluoromethyl radical
Authors: Hiatt R. , Benson S. W.
Published: January 2005

Products of the radical reactions arising from t‐Bu2O2, CF3I, and CH3I at 146°C in the vapor phase have been measured over a 33‐fold range of CH3I/CH3I ratios and shown to be governed by the rapidly established equilibrium

Together with K estimated by thermochemical methods, the results yield, for the rate of recombination for CF3· radicals, kr = 109.7 ± 0.5 M−1 sec−1.
Rates of reaction of atomic oxygen with C2H3F, C2H3Cl, C2H3Br, 1,1‐C2H2F2, and 1,2‐C2H2F2
Authors: Huie Robert E. , Herron John T. , Davis Douglas D.
Published: January 2005

Rate constants for the reactions of atomic oxygen (O3P) with C2H3F, C2H3Cl, C2H3Br, 1,1‐C2H2F2, and 1,2‐C2H2F2 have been measured at 307°K using a discharge‐flow system coupled to a mass spectrometer. The rate constants for these reactions are (in units of 1011 cm3 mole−1 s−1) 2.63 ± 0.38, 5.22 ± 0.24, 4.90 ± 0.34, 2.19 ± 0.18, and 2.70 ± 0.34, respectively. For some of these reactions, the product carbonyl halides were identified.
Table of the Kassel integral
Authors: Emanuel George
Published: January 2005

An e×tensive table is given of the Kassel integral

that occurs in the Rice‐Ramsperger‐Kassel theory of unimolecular gas reactions.
Arrhenius parameters for the reactions CH3. + C4H10 → CH4 + C4H9. and C2H5. + C4H10 → C2H6 + C4H9.
Authors: Pacey P. D. , Purnell J. H.
Published: January 2005

Study of n‐butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions

and of the Arrhenius parameters of the reactions

Established data for k1/k2 allow estimation of k1 for 951°K and this, with recent thermochemical data, yields the result log k−1 (l.mole s−1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k3k4 (l.2mole−2s−2) is found to be associated with the Arrhenius parameters log (A3A4) = 21.90 ± 0.6 and (E3 + E4) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A4 = 10.5 ± 0.4 (l.mole−1s−1) and E4 = 20.1 ± 1.7 kcal/mole, hence log A3 = 11.4 ± 0.8 (l.mole−1s−1) and E3 = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical–alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.
The dissociation of 3‐chloro‐1‐butene and the resonance energy of the chloro‐allyl radical
Authors: Trenwith A. B.
Published: January 2005

Methane is a primary product of pyrolysis of 3‐chloro‐l‐butene at temperatures in the range 776–835°K, and from its rate of formation values have been obtained for the limiting high‐pressure rate constant of the reaction
equation image
These may be represented by the expression log [(k1)∞/sec−1] = (16.7 ± 0.3) − (71.5 ± 1.5)/θ, where θ = 2.303RT kcal/mole. Assuming a zero activation energy for the reverse reaction and that over the experimental temperature range the rates at which a methyl radical adds on to chlorobutene are comparable to those at which it abstracts hydrogen, the activation energy for the dissociation reaction leads to a value of 83.2 ± 1.9 ckal/mole for D(HCHClCH:CH2) at 298°K. Taking D(HCHClCH2CH 3) = 95.2 ± 1.0 kcal/mole a value of 12.0 ± 2.1 kcal/mole is obtained for the resonance energy of the chloroallyl radical. This value in conjunction with resonance energies obtained in earlier work indicates that substitution of a hydrogen atom on the carbon atom adjacent to the double bond in the allyl radical leads to no significant variation in the allylic resonance energy.
High‐pressure photoionization mass spectrometry. Effect of internal energy and density on the ion–molecule reactions occurring in methyl, dimethyl, and trimethylamine
Authors: Hellner L. , Sieck L. W.
Published: January 2005

The ion–molecule reactions of CH3NH2+, (CH3)2NH+, and (CH3)3N+ with the respective amines have been investigated at thermal kinetic energies in a high‐pressure photoionization mass spectrometer at several wavelengths (energies) in the vacuum ultraviolet. The absolute rate coefficient for proton transfer from (CH3)3N+ to (CH3)3N decreases from 8.2 × 10−10 cm3/molecule · sec at 147.0 nm (8.4 eV) to 4.9 × 10−10 cm3/molecule. sec at 106.7‐104.8 nm (11.7 eV). In dimethylamine, the rate coefficient decreases from 11.6 × 10−10 cm3/molecular. sec at 8 4 eV to 10.2 × 10−10 cm3/molecule osec at 11.7 eV, while no significant effect of energy was detected in methylamine. The reactions of several fragment ions are also reported. Experiments were also carried out at pressures up to 0.5 torr in order to investigate the further solvation of CH3NH2+, (CH3)2NH2+, and (CH3)3NH+. It was found that the maximum proton solvation numbers in methyl‐, dimethyl‐, and trimethyl‐amine are 4, 3, and 2, respectively, under these conditions.
The pyrolysis of hexachloroethane
Authors: White Merle L. , Kuntz Robert R.
Published: January 2005

The thermal decomposition of hexachloroethane in the presence of chlorine has been studied over the temperature range 340‐400°C and a pressure range of 0.5°2.5 atm. The rate of the unimolecular CC bond spliting reaction can be described by the Arrhenius equation

Comparison of these rate data with thermodynamic data suggests a combination rate for CCl3 radicals which is consistent with earlier measurements.
The gas‐phase thermal unimolecular elimination of 1,1‐dimethylketene from 7,7‐dimethylbicyclo[3.2.0]hept‐2‐en‐6‐one
Authors: Egger Kurt W.
Published: January 2005

The gas‐phase thermal decomposition of 7,7‐dimethylbicyclo[3.2.0]hept‐2‐en‐6‐one (DBH) to yield cyclopentadiene and 1,1‐dimethylketene as primary products was studied in the temperature range of 470‐550 °K using a static reaction system. First‐order rate constants for the depletion of DBH based on the internal standard technique and gaschromatographic analyses were independent of the initial starting pressure (7‐68 torr) and of the conversion, ranging between 5% and 89%. (Throughout this paper, 1 torr = (101.325/760) kNm−2, and 1 cal = 4.184J). The reaction is essentially homogeneous, as the nature of the reaction vessel surface (Teflon or glass) had no effect on the observed rate constants which fit the Arrhenius relationship

where θ = 2.303 RT. These activation parameters, when compared with those for similar reactions involving the molecules bicyclo[3.2.0]hept‐2‐en‐6‐one, bicyclo[3.2.0]heptan6‐one, and cyclobutanone, demonstrate a very small effect of the alkyl substituents bonded to the carbon atom adjacent to the carbonyl carbon. Accepting the previously discussed concerted and pronounced polar nature of the mechanism for these retro‐ketene addition reactions, the present data suggest that considerable changes in charge densities between the ground and transition state are only occurring on the two opposite centers of the molecule, with the negative charge residing essentially on the oxygen atom and the positive charge on the opposing bridgehead carbon atom. It then appears that the charge separation in the transition state is more appropriately described as being pseudo‐zwitterionic rather than quadrupolar in nature.
High temperature decomposition of ethane
Authors: Burcat Alexander , Skinner Gordon B. , Crossley Robert W. , Scheller Karl
Published: January 2005

Measurements of the rate of formation of methane in the thermal decomposition of ethane in dilute mixtures with argon were made by the shock tube technique. Derived values of the rate constant of the dissociation reaction are compared with earlier data of the same type and with recent shock tube data on the combination of methyl radicals. An RRKM calculation correlating all the data is described, from which an Arrhenius equation for the range 1000–1500°K, log k∞ = 16.9 − 89,500/2.3RT, is obtained.
Kinetics of the thermal decomposition of CF3CHCL2 in a single‐pulse shock tube
Authors: Sekhar M. V. C. , Millward G. E. , Tschuikow‐Roux E.
Published: January 2005

The pyrolysis of 2,2‐dichloro‐1,1,1‐trifluoroethane was studied over the temperature range of 1120–1260°K at total reflected shock pressures from ∼2800 to 3100 torr. Below 1260°K, the decomposition leads to three reaction products which were identified as CF2CFCl, CF2CFH, and CF3CCl3. The results are interpreted in terms of a parallel CCl bond rupture process which becomes competitive with the molecular HCI elimination. The rate constant for the α,α‐elimination process

has been deduced to be

It was also possible to obtain the overall rate constant for the formation of CF2CFH, which is given by

Some evidence for hydrogen fluoride elimination was found at temperatures above 1260°K. However, at these higher temperatures CC bond scission also occurs and the kinetics of the system become untractable.
Rates of recombination of free radicals. V. The tert‐butyl radical
Authors: Hiatt R. , Benson S. W.
Published: January 2005

Analysis of the products from a vapor‐phase mixture of EtI and t‐BuI, in which free radicals were generated thermally, has yielded a rate constant for the recombination of 2t‐Bu⋅ of 105.4 M−1 sec−1 at 100°C. The close agreement between this and other recent estimations from vapor‐phase work is noted, as is the disparity between these values and those on the order of 109 M−1 sec−1 obtained in solution.
Rotating sector study of the gas phase photochlorination of 2,2‐dichloro‐1,1,1‐trifluoroethane
Authors: Cullison R. F. , Pogue R. C. , White M. L.
Published: January 2005

The rate constant for the combination of 2,2‐dichloro‐1,1,1‐trifluoroethyl radicals has been measured by applying the rotating sector technique to the gas phase photochlorination of 2,2‐dichloro‐1,1,1‐trifluoroethane at 315°K. The observed value is 6.89 × 1012 cc/mole.sec. This value is in excellent agreement with measurements by Wampler and Kuntz which yielded a temperature‐independent value of 6.6 × 1012 cc/mole.sec. The measurement by Wampler and Kuntz was determined from the photochemical system (CF3CCl3 + C‐C6H12 + hν). The Arrhenius parameters for the reaction CF3CCl2· + Cl2 → CF3CCl3 + Cl were found to be given by the expression log k3 = 12.10 − 5830/2.3RT (units in mole, cc, and sec). This is a relatively high activation energy for a chlorination reaction and makes the reaction ever slower than the chlorination of chloroform.
Further studies on the dissociation of HBr behind shock waves
Authors: Cohen N. , Giedt R. R. , Jacobs T. A.
Published: January 2005

Previously reported shock tube studies of the dissociation of HBr in the temperature range of 2100–4200°K have been extended to lower temperatures (1450–2300°K) in pure HBr. The course of reaction was followed by monitoring the radiative recombination emission in the visible spectrum from Br atoms. The results imply that, in the lower range of temperatures, the activation energy of dissociation, E in the expression AT−2e−E/RT, can be approximated by the HBr bond energy (88 kcal/mole). It was also found that, in this temperature range, the rate of HBr dissociation is sensitive to the Br2 dissociation rate and the HBr + Br exchange rate. When these rates were adjusted to bring computed reaction profiles into agreement with experimental ones, it was found that the higher‐temperature data could also be fitted reasonably well with an HBr dissociation activation energy of 88 kcal/mole, contrary to the conclusions of our previous work, which favored an activation energy of 50 kcal/mole. The “best value” for k1Ar, the rate coefficient for HBr dissociation in the presence of Ar as chaperone, appears to be 1021.78 ± 0.3 T−2 10−88/θ cc/mole sec, where θ = 2.3 RT/1000; that for k1HBr, is 1022.66T−210−88/θ. A detailed review is given of the rate coefficients for the other pertinent reactions in the H2–Br2 system, viz., Br2 dissociation and reactions of HBr with H and Br.
Formation of association ions in the photoionization of alkyl halides
Authors: Sieck L. W. , Gorden R.
Published: January 2005

The methyl and ethyl chlorides and bromides, as well as methyl iodide, were photoionized in the vacuum ultraviolet at 300 K in a mass spectrometer over the pressure range 0.5 to approximately 100 millitorr. Under these conditions, stabilized parent ion dimers are found in CH3Br, CH3I, and C2H5Br, but not in the chlorides. Lower limits for the dissociative lifetimes of the ion–molecule collision complexes were estimated and are as follows: (CH3Br)2+, 1.6 μs; (CH3I)2+, 1.9 μs; and (C2H5Br)2+, 5.4 μs. An increase in photon energy (internal energy content of the reactant ion) decreases the dissociative lifetime of the collision complex in CH3I.
A method for computer analysis of kinetics of competing first‐ and second‐order reactions
Authors: Gorman Donald S. , Connolly John S.
Published: January 2005

Competing first‐ and second‐order reactions of transient molecular species (e.g., triplet states and free radicals) are a common occurrence in kinetic studies such as flash photolysis and pulse radiolysis. We have developed a method for analyzing the decay kinetics of any species (Y) whose disappearance is described by −dY/dt = k1Y + k2Y2. The computer program (written in time‐sharing BASIC) employs an iterative technique to obtain the least‐squares estimates of the three parameters in the integrated rate equation.
The methyl radical combination rate constant as determined by kinetic spectroscopy
Authors: Bass Arnold M. , Laufer Allan H.
Published: January 2005

The rate constant for the reaction

has been determined by means of vacuum ultraviolet flash photolysis and time‐resolved kinetic spectroscopic observations of the 1504‐Å absorption band of CH3. The measurements made using three different sources of methyl radicals (azomethane, dimethylmercury, and ketene‐hydrogen) were in accord and yielded a value for the rate constant of k1 = (9.53 ± 1.17) × 10−11 cc molec−1 sec−1. A detailed error analysis is presented. The f‐value for the 1504‐Å band of CH3 is determined to be (2.5 ± 0.7) × 10−2.
A computational modeling study of the low‐temperature pyrolysis of n‐alkanes; mechanisms of propane, n‐butane, and n‐pentane pyrolyses
Authors: Allara D. L. , Edelson D.
Published: January 2005

The mechanisms of the pyrolyses of the n‐alkanes C3H8, n‐C4H10, and n‐C5H12 at temperatures between 390 and 560°C have been studied by the construction and evaluation of sets of several hundred reactions. Rate parameter values were assigned using literature data and calculated estimates. Time‐dependent numerical solutions were computed for the experimental conditions of several rate and product studies reported in the literature. The comparisons of these a priori computations with experiment show excellent agreement for propane and agreement for butane and pentane within the estimated error limits of the assigned rate parameters. These results demonstrate that the general “state of knowledge” of the mechanism of alkane pyrolysis, namely, the reactions and their rate parameters, is such that reasonable a priori predictions of experimental results can be made. Discussions of the major stepwise processes in the pyrolyses are presented, and the importance of allyl radicals in termination is demonstrated.
Disproportionation‐combination ratios in thermalized cyclic radical systems. Rate of isomerization of pent‐2‐en‐5‐yl radical
Authors: Stein S. E. , Rabinovitch B. S.
Published: January 2005

Disproportionation–combination rate ratios have been measured for a number of pairs of thermalized radicals (298°K) generated by thermalization of chemically activated cycloalkyl radicals, their ring‐opened products, and ethyl radicals. These ratios are reported and briefly discussed. The rate of isomerization of the chemically activated pent‐2‐en‐5‐yl radical via H‐atom transfer to the allylic pent‐1‐en‐3‐yl radical is also given.
Kinetics and mechanism of the hydrogenation of cyclohexene
Authors: Hendrikse J. L. , Kaspersma J. H. , Coenen J. W. E.
Published: January 2005

The rate of hydrogenation of cyclohexene, catalyzed by CoH3(PPh3)3, has been measured under various conditions and, based on these data, a mechanism has been postulated. For the individual steps of the mechanism enthalpy and entropy differences have been determined. The interpretation of these parameters gives evidence for a more detailed mechanism, in which solvent molecules play an important part as “stand‐in” for ligands, dissociated from the catalyst species.
Very‐low‐pressure pyrolysis of nitroso‐ and pentafluoronitrosobenzene CNO bond dissociation energies
Authors: Choo Kwang Yul , Golden David M. , Benson Sidney W.
Published: January 2005

The high‐pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very‐low‐pressure pyrolysis (VLPP) technique.

Bond dissociation energies of DH0(C6H5NO) = 51.5 ± 1 kcal/mole and DH0 (C6F5NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log kr(M−1·sec−1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δHf0(C6H5NO), δHf0(C6F5NO), and δHf0(C6F5) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH0(C6F5–X), were obtained from the reported values of δHf0(C6F5X) and our estimated δHf0(C6F5) [X = H, CH3, NO, Cl, F, CF3, I, and OH].
Shock initiated ignition in COSO2Ar mixtures
Authors: Lifshitz A. , Frenklach M. , Schechner P. , Carroll H. F.
Published: January 2005

The ignition of COS + O2 mixtures diluted in argon was studied behind reflected shocks in a single‐pulse shock tube over the temperature range of 1100–1700°K. Ignition delay times and the distribution of reaction products before and after ignition were determined experimentally. From a total of 63 tests run at varying initial conditions, the following correlation for the induction times was derived:

where β1 = +0.30, β2 = 1.12, and E = 16.9 kcal/mole. Using a reaction scheme of 14 steps, the following values were obtained by a computer modeling of the induction times: β1 = +0.22, β2 = 1.55, and E = 17.3 kcal/mole. The calculations showed that the reaction COS + S → CO + S2 caused the inhibiting effect of the COS. The reaction COS → O ± CO2 + S has a very strong accelerating effect, whereas the parallel channel COS + O → CO + SO shows the opposite effect. It was also shown that the reaction O + S2 → SO + O is very slow and does not contribute to the overall oxidation reaction. It is suggested that the rate constant given to the four‐center reaction COS + SO → CO2 + S2, that is, 1011 cm3/mole · sec at 300°K is incorrect. This constant is not much higher than 108 cm3/mole · sec at 1300°K.
Kinetics of the pyrolyses of endo‐ and exo‐5‐methylbicyclo (2.2.2) oct‐2‐ene in the gas phase
Authors: Huybrechts G. , Ngoy G.
Published: January 2005

The pyrolyses of endo‐ and exo‐5‐methylbicyclo (2.2.2) oct‐2‐ene (endo‐ and exo‐MBO) have been studied between 608 and 679°K at pressures between 7 and 37 torr. These reactions correspond to parallel first‐order eliminations of propene and ethylene:
equation image
The rate constants (in sec−1) for endo‐MBO are given by

and those for exo‐MBO by

Reaction mechanisms involving diradicals are shown to be compatible with the experimental results. The heats of formation and the entropies of endo and exo‐MBO are estimated.
Very low‐pressure pyrolysis (VLPP) of alkyl cyanides. II. n‐propyl cyanide and isobutyl cyanide. The heat of formation and stabilization energy of the cyanomethyl radical
Authors: King Keith D. , Goddard Richard D.
Published: January 2005

The very low‐pressure pyrolysis (VLPP) technique has been used to study the pyrolysis of n‐propyl cyanide over the temperature range of 1090–1250°K. Decomposition proceeds via two pathways, C2C3 bond fission and C3C4 bond fission, with the former accounting for >90% of the overall decomposition. Application of unimolecular reaction rate theory shows that the experimental unimolecular rate constants for C2C3 fission are consistent with the high‐pressure Arrhenius parameters given by

where θ=2.303RT kcal/mole. The activation energy leads to DH2980[C2H5CH2CN]=76.9±1.7 kcal/mole and ΔH(ĊH2CN, g)=58.5±2.2 kcal/mole. The stabilization energy of the cyanomethyl radical has been found to be 5.1±2.6 kcal/mole, which is the same as the value for the α‐cyanoethyl radical. This result suggests that DH[CH2(CN)H] ∼ 93 kcal/mole, which is considerably higher than previously reported. The value obtained for ΔHƒ0(ĊH2CN) should be usable for prediction of the activation energy for C2C3 fission in primary alkyl cyanides, and this has been confirmed by a study of the VLPP of isobutyl cyanide over the temperature range of 1011–1123°K. The decomposition reactions parallel those for n‐propyl cyanide, and the experimental data for C2C3 fission are compatible with the Arrhenius expression

A significant finding of this work is that HCN elimination from either compound is practically nonexistent under the experimental conditions. Decomposition of the radical, CH3CHCH2CN, generated by C3C4 fission in isobutyl cyanide, yields vinyl cyanide and not the expected product, crotonitrile. This may be explained by a radical isomerization involving either a 1,2‐CN shift or a 1,2‐H shift.
Kinetics of the molybdate catalyzed oxidation of iodide by hydrogen peroxide
Authors: Smith R. H. , Kilford J.
Published: January 2005

The kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped‐flow method. The results are interpreted in terms of the mechanism
equation image

and the implied rate law

where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k4 = (3.3 ± 1) × 102 1./mole · s, K1 = (1.2 ± 0.6) × 104 1./mole, K2 = (1.3 ± 0.7) × 103 1./mole, and K3 = (4 ± 3) × 102 1./mole at 298°K.
The kinetics of the gas‐phase reaction between ozone and alkenes
Authors: Toby Erina S. , Toby Sidney , O'Neal H. Edward
Published: January 2005

The rate law − d[O3]/ dt = k1[A][O3] + k3[A][O3]2/ (k4 + k5[O2]) has been found to obtain for the reaction of ozone with allene and with 1,2‐butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone–ethylene reaction, and we find that as [O3]0 increases, the (O2 formed)/(O3 used) ratio approaches 1.5. Values of k1, k3/k5 for ethylene are compared with those for allene, 1,3‐butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O3 with ethylene, and the thermochemistry of the chain sequence is examined in detail.
Mechanism of isotope exchange reaction between methane and deuterium
Authors: Gardiner W. C. , Herrmann J. M. , Mallard W. G. , Owen J. H.
Published: January 2005

The rate of CH4 disappearance in a shock‐heated CH4:D2:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm−1 He‐Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH4 pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH4.

Additional simulations for the experimental conditions of previous single‐pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH4.
Radiation‐induced dechlorination of carbon tetrachloride in cyclohexane Solutions. The kinetics of liquid‐phase reactions of trichloromethyl radicals
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A.
Published: January 2005

The kinetics of the gamma‐radiation induced free‐radical chain reaction in solutions of carbon tetrachloride in cyclohexane (RH) has been investigated in the temperature range of 303–383°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated cyclohexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated:

equation image

The following rate expression was obtained:

The error limits are the standard deviation from the least mean square Arrhenius plots. Effects of phase on the kinetics of reactions (3) and (4) are considered.
Gas‐phase ozonolysis of cis‐ and trans‐dichloroethylene
Authors: Blume Cary W. , Hisatsune I. C. , Heicklen Julian
Published: January 2005

Dichloroethylene (DCE), either cis or trans, was reacted with O3 at 23°C in both N2 and O2 buffered mixtures. Both reactant consumption and product formation were monitored by infrared spectroscopy and, in some cases, O3 consumption was monitored by ultraviolet absorption. For thoroughly dried mixtures, the initial products were only HCClO and O2, but geometrical isomerization also occurred. The stoichiometry of the overall reaction always was

equation image

The HCClO was unstable and disappeared slowly in a first‐order reaction which was, at least in part, heterogeneous. The products were CO and HCl so that the stoichiometric reaction was

equation image

The rate law was complex. The rate was always faster in N2 than in O2. In the N2 buffered reaction, inhibition occurred as the reaction progressed and O2 was produced. From the reactant and product decay curves, the following rate behavior was established:

equation image

where high and low concentrations are relative terms for the initial pressure ranges covered ([DCE]0 = 0.21−78.4 torr, [O3]0 = 0.30−6.76 torr). The rate coefficients k2, k3, and k4 were larger for the trans‐DCE than the cis‐DCE, and for each isomer they were larger in N2 than in O2 buffered reactions.

The ozonolysis can be explained in terms of the mechanism

equation image

equation image

where R2 is DCE, RO is HCClO, and RO2 is HCClO2. Rate ceofficients are computed.

The isomerization is first order in [O3] and approximately first order in [DCE] for the limited kinetic data we were able to obtain. The isomerization does not appear to be explained by the reverse reactions of reactions (6), (7), and (9). Presumably isomerization occurs through some other route.
Radiation‐induced dechlorination of carbon tetrachloride. II. The kinetics of liquid‐phase reactions of trichloromethyl radicals in n‐hexane solutions
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A.
Published: January 2005

The kinetics of the gamma‐radiation induced free‐radical chain reaction in solutions of carbon tetrachloride in n‐hexane (RH) was investigated in the temperature range of 297.5–373°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated hexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated:

equation image

The following rate expression was obtained:

where θ = 2.303 RT in kcal/mole. The error limits are the standard deviation from the least mean square Arrhenius plots. It is concluded that reaction (4) is diffusion controlled in the liquid phase, and that the activation energies in the gas and liquid phases of reaction (3) are equal.
Molecular beam study of F2+I2
Authors: Coggiola M. J. , Valentini James J. , Lee Y. T.
Published: January 2005

Crossed molecular beam techniques have been used to study the endoergic reaction between F2 and I2. Above a threshold energy of 4 kcal/mole the observed products are I2F and F. At higher energies IF is also produced. Angular and velocity distributions indicate that the IF does not result from a four‐center exchange reaction.
Radiolytic decomposition of methanesulfonyl chloride in liquid cyclohexane. A kinetic determination of the bond dissociation energies D(ME‐SO2) and D(c‐C6H11‐SO2)
Authors: Horowitz Abraham
Published: January 2005

The gamma radiation induced decomposition of MeSO2Cl in cyclohexane (RH) was studied between 60 and 150°C. Throughout this temperature range the reaction proceeds by a free radical chain mechanism. Its propagation is described by the following reactions:
equation image

The kinetic analysis of the results of the experiments with added SO2, which were carried out in the temperature range of 80 to 150°C, gives 14.94 ± 0.92 and 11.91 ± 0.82 kcal/mole for D(Me‐SO2) and D(c‐C6H11‐SO2), respectively. These bond dissociation energies are considerably lower than the gas‐phase values, and the possible cause of this difference is discussed. Present results also seem to indicate that D(MeSO2‐H) does not exceed 95 kcal/mole. Competitive experiments with added tetrachloroethylene result in

where θ = 2.303RT in kcal/mole.
Charge transfer reactions in alkane and cycloalkane systems. Estimated ionization potentials
Authors: Lias S. G. , Ausloos P. , Horvath Z.
Published: January 2005

Rate constants of change transfer reactions kCT, involving C3C9 alkanes and cycloalkanes, have been determined in an ion cyclotron resonance mass spectrometer. The rate constants are significantly lower than the corresponding rate constants for collision when the reaction is less than about 0.5 eV exothermic for linear alkane ions, or less than about 0.2 eV exothermic for cycloalkane ions. In this region of low reaction efficiency, the efficiency of reaction with linear or branched alkanes seems to depend primarily on reaction exothermicity. (The efficiencies of reaction of a given ion with cyclic alkanes also depend on ΔHrn, but are higher than for reactions with other compounds). Although the lowered reaction efficiencies probably result, at least in part, from unfavorable Franck–Condon factors in the energy range near the ionization onset, quantitative correlations between reaction efficiency and estimated relative Franck–Condon factors were not observed. When the enthalpy of reaction is small (less than about −0.15 eV), it is seen that the reverse charge transfer can also occur, and equilibrium is established under the conditions of these experiments. From the observed equilibrium constants, values for the standard free energy change are derived, and assuming that ΔS is small for electron transfer equilibria, values of ΔHrn are estimated. In the case of the equilibria involving cyclohexane ion, these values of ΔHrn lead to estimates of the ionization potentials of methylcyclopentane, 3‐methylpentane, n‐octane, 2,2‐dimethylbutane, and 2,3‐dimethylbutane, which are lower than the ionization potentials of cyclohexane, that is, <9.88 eV, although all these compounds had previously been reported to have ionization potentials above 10.03 eV. That the ionization potentials are indeed lower than 10.03 eV is confirmed by determining the quantum yields of ionization with 10.03‐eV photons.

It is pointed out that the conclusions reached here apparently also apply to the charge transfer reactions of alkane ions in the liquid phase.
The gas‐phase kinetics of the reaction of 1,1‐difluoroiodoethane with hydrogen iodide: The C–I bond dissociation energy in 1,1‐difluoroiodoethane
Authors: Pickard J. M. , Rodgers A. S.
Published: January 2005

The kinetics of gas‐phase reaction of CH3CF2I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism:
equation image

A least squares treatment of the data gave

where θ = 2.303 RT kcal/mole. The observed activation energy E1 was combined with E2 = 0 ± 1 kcal/mole to yield

The result, combined with data for several CI bond dissociation energies, leads us to conclude that the C(sp3)I bond is relatively insensitive to F for H substitution and that the C(sp2)–I bond has considerable double‐bond character.
The flash photolysis of azomethane. Minor products from the photolysis of methyl radicals and a rate constant for CH3 + NO
Authors: Pilling M. J. , Robertson James A. , Rogers Graham J.
Published: January 2005

The flash photolysis of azomethane in a quartz reaction vessel produces mainly ethane (>75%) plus smaller quantities of methane, ethylene, and acetylene. The minor products are interpreted quantitatively in terms of methyl radical photolysis at 216 nm to give CH2 and H. This interpretation is substantiated by the dependence of the minor products on flash intensity. The reduction of the ethane yield on adding NO is employed to obtain a rate constant for CH3 + NO as a function of total pressure, based on a value for methyl radical recombination of 4.2 × 10−11 cm3/molec · sec. An RRKM analysis is used to extrapolate the data to give a limiting high‐pressure rate constant for CH3 + NO of (1.2 ± 0.1) × 10−11 cm3/molec · sec at 298°K.
Photochemistry of the SO2, 2‐pentene system at 3660 Å
Authors: Wampler Fred B.
Published: January 2005

The photolysis of SO2 in the presence of cis‐ and trans‐2‐pentene has been investigated at 3660 Å and 22°C. Quantum yield measurements of the SO2 photosensitized conversion of one isomer into the other are consistent with a mechanism in which the only participating excited electronic state of SO2 is the SO2(3B1) state. Quantum yield measurements were made for a variation in PSO2/Pisomer reactant ratios of 4.01–283 and 57.5–351 for the cis and trans isomers, respectively. The data are consistent with a mechanism in which a (SO2‐olefin)3 collision intermediate is the precursor to the photosensitized isomeric products. The intermediate undergoes unimolecular decay to yield the cis and trans isomers with probabilities of 0.26 ± 0.05 and 0.69 ± 0.04, respectively. Estimates of the quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis‐ and trans‐2‐pentene are (0.633 ± 0.125) × 1011 l./mole/sec and (1.00 ± 0.27) × 1011 l./mole/sec, respectively. An experimentally determined photostationary composition, [trans‐2‐pentene]/[cis‐2‐pentene] = 2.3 ± 0.1 was in fair agreement with that of 1.7 ± 0.7 as predicted from kinetic data derived in this study.
The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2
Authors: Barker John R. , Benson Sidney W. , Golden David M.
Published: January 2005

The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391–432°K:

The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec−1) = (15.7 ± 0.5) ‐ (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M−1· sec−1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined:

When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396–442°K:

A review of literature data produced k7a = 109.8±0.5M−1·sec−1, giving log k12(M−1·sec−1) = (8.5 ± 1.5) ‐ (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.