bluuebunny/crossref_metadata_2025_split huggingface dataset:
The reactions of methyl radicals with atomic and molecular oxygen
Authors: Washida N. , Bayes Kyle D. 
Published: January 2005

AbstractThe reaction of methyl radicals with atomic and molecular oxygen was studied with a photoionization mass spectrometer. The methyl radicals were generated by reacting oxygen atoms with ethylene in a fast‐flow tube reactor. The rate constant for the reaction of methyl radicals with oxygen atoms was (1.0 ± 0.2) × 10−10 cm3/molec · sec with no significant variation with temperature over the range of 259–341°K. The reaction of methyl radicals with molecular oxygen involves both a two‐body reaction, having a rate constant \documentclass{article}\pagestyle{empty}\begin{document}$\begin{array}{*{20}c} {k_{{\rm 3a}} = (10^{- 12.54 \pm 0.35})\exp [(- 940 \pm 250)T^{- 1}]} & {{\rm cm}^{\rm 3} /{\rm molec} \cdot {\rm sec}} \end{array}$\end{document}
and a three‐body recombination having a negative temperature dependence. The methyl peroxy radical could be observed at its steady‐state concentration. The rate constants determined at low pressures are compatible with the values determined at higher pressures by flash photolysis. Formaldehyde appears to be a major product of the two‐body reaction of CH3 with O2, and also of the reaction of CH3O2 with oxygen atoms.
The gas‐phase reaction of O3 with H2CO
Authors: Braslavsky S. , Heicklen Julian 
Published: January 2005

AbstractExplosions occur when O3 and H2CO are mixed in a fresh vessel, even in the presence of several hundred torr of N2 or O2. However, in an aged vessel the reaction is well behaved. The reaction between O3 and H2CO was studied at room temperature in an aged vessel in the presence of about 400 torr of either N2 or O2. The initial rate of O3 decay in the presence of N2 is about 103 times faster than in the presence of O2, and very small amounts of O2 quickly reduce the initial rate of O3 decay in the N2 case. A chain mechanism is postulated to account for the results in which chain initiation can occur both by thermal decomposition of O3, followed by reaction of O(3P) with H2CO to produce HO and HCO, as well as by

equation image

which may occur both homogeneously and heterogeneously. The rate coefficient k1 ≃ 2.1 × 10−24 cm3/molec · sec represents an upper limit (to within a factor of 2 uncertainty) to the direct gas‐phase reaction between O3 and H2CO.
The photochemistry of hexafluoroacetylacetone in the vapour phase. Occurrence of a novel HF elimination reaction
Authors: Bassett John E. , Whittle Eric 
Published: January 2005

AbstractPhotolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2‐difluoro‐2,3‐dihydro‐5‐trifluoromethylfuran‐3‐one: magnified imageThe HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF2 radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, magnified image
The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both ϕ1 and ϕ5 depend on pressure and the ratio ϕ1/ϕ5 increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio ϕ1/ϕ5 increases as the vibrational energy of electronically excited HFAA increases.
Photoelimination of HF by hexafluoroacetylacetone: A tandem laser study
Authors: Pimentel George C. , G.‐Tablas F. M. , Hartmann Josef , Whittle Eric 
Published: January 2005

AbstractTandem chemical laser techniques have been used to detect HF formed through photoelimination from 1,1,1,5,5,5‐hexafluoroacetylacetone, HFAA. Information about the HF vibrational population ratios is deduced: N2/N1 < 0.37 and N1/N0 < 0.45. This work supports the deduction by Bassett and Whittle that photodecomposition of the enol form of HFAA results mainly in HF elimination and ring closure to a dihydrofuranone, a new type of reaction.
The photolysis of SO2 at 3130 Å in the presence of cis‐ and trans‐2‐pentene
Authors: Wampler Fred B. 
Published: January 2005

AbstractThe photolysis of SO2 at 3130 Å, FWHM = 165 Å, and 22°C has been investigated in the presence of cis‐ and trans‐2‐pentene. Quantum yields for the SO2 photosensitized isomerization of one isomer to the other have been made for a variation in the [SO2]/[C5H10] ratio of 3.41–366 for cis‐2‐C5H10 and of 1.28–367 for trans‐2‐C5H10. A kinetic analysis of each of these systems permitted new estimates to be made for the SO2 collisionally induced intersystem crossing ratio at 3130 Å from SO2(1B1) to SO2(3B1). The estimates of k1a/(k1a + k1b) obtained are 0.12 ± 0.01 and 0.12 ± 0.02 (two different kinetic analyses in the cis‐2‐C5H10 study) and 0.20 ± 0.05 and 0.20 ± 0.04 (two different kinetic analyses in the trans‐2‐C5H10 study). Collisionally induced intersystem crossing ratios of k2a/(k2a + k2b) = 0.51 ± 0.10 and k3a/(k3a + k3b) = 0.62 ± 0.12 were obtained for cis‐ and trans‐2‐pentene, respectively. Quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis‐ and trans‐2‐C5H10 were estimated as (1.00 ± 0.29) × 1011 l./mole·sec and (0.857 ± 0.160) × 1011 l./mole/sec, respectively. Prolonged irradiations, extrapolated to infinite irradiation times, for mixtures initially containing SO2 and pure isomer, either the cis or trans, yielded a photostationary composition of [trans‐2‐pentene]/[cis‐2‐pentene] = 2.1 ± 0.1.
Kinetics of the reaction of atomic hydrogen with methyl hydroperoxide
Authors: Šslemr F. , Warneck P. 
Published: January 2005

AbstractThe reaction H + CH3OOH was investigated under conditions of excess atomic hydrogen concentration using a flow reactor attached to a photoionization mass spectrometer. The rate coefficient of the reaction was determined as

The three important reaction channels were found to be
equation image
with the individual contributions determined as indicated. The product methoxy and methylperoxy radicals react mainly with atomic hydrogen under the employed experimental conditions according to
equation image
where the estimates for the percentage contributions of the various channels were derived from the measured product yields.
The Very low‐pressure pyrolysis of 2‐phenylethylamine. The enthalpy of formation of the aminomethyl radical
Authors: Colussi A. J. , Benson S. W. 
Published: January 2005

AbstractThe thermal unimolecular decomposition of 2‐phenylethylamine (PhCH2CH2NH2) into benzyl and aminomethyl radicals has been studied under very‐low‐pressure conditions, and the enthalpy of formation of the aminomethyl radicals, ΔH°f, 298K (H2NCH2·) = 37.0 ± 2.0 kcal/mol, has been derived from the kinetic data. This result leads to a value for the C—H bond dissociation energy in methylamine, BDE(H2NCH2—H) = 94.6 ± 2.0 kcal/mol, which is about 3.4 kcal/mol lower than in C2H6 (98 kcal/mol), indicating a sizable stabilization in α‐aminoalkyl radicals.
Application of Forst's method to the calculation of thermal unimolecular reaction rates and isotope effects in the falloff region
Authors: Dill Bernd , Heydtmann Horst 
Published: January 2005

AbstractA method proposed in 1972 by W. Forst is used to calculate the experimentally accessible pressure dependence of thermal unimolecular rate constants. The specification of an activated complex always employed in RRKM calculations is avoided. This allows for a more consistent comparison between the results obtained by the application to various unimolecular processes. In order to bring experimental and calculated curves into agreement, fourcenter eliminations of hydrogen halides from alkyl halides require the formal introduction of a collision efficiency factor λ ≃ 0.2, and for the concerted ring opening of 1,1‐dichlorocyclopropane λ ≃ 0.4 must be assumed. The isotope effects for the decomposition of CD3CD2Cl and CH3CD2Cl have been studied, and the pressure dependence of kH/kD is reported. Studying the biradical ring opening of oxetan, cyclobutane, and cyclopropane, the falloff curves and isotope effects are predicted within the experimental uncertainty by the use of λ ≃ 1.0. This different behavior of concerted and biradical reactions against falloff calculations can hardly be attributed to experimental uncertainties in the Arrhenius parameters and/or the collision frequency alone.
Kinetics of the gas‐phase thermal decomposition of 1,1,2‐trifluoro‐2‐trifluoromethylcyclopropane
Authors: Quero E. D. , Ferrero J. C. , Staricco E. H. 
Published: January 2005

AbstractThe kinetics of the gas‐phase thermal decomposition of 1,1,2‐trifluoro‐2‐trifluoromethyl‐cyclopropane to 2,3,3,3‐tetrafluoropropene and CF2was studied in the temperature range of 539–604°K and with a total pressure of 17 to 300 torr of a 1:20 mixture of reactant and perfluoroethylene. Some runs were also made with the reactant only, with initial pressures of 0.2 to 20 torr. The reaction is first order, homogeneous, and the rate constants fit the following Arrhenius relationship:.
The thermal and initiated thermal decomposition of biacetyl‐d6
Authors: Schliebs R. , Knoll H. , Scherzer K. 
Published: January 2005

AbstractThe thermal and methyl radical initiated decomposition of biacetyl‐d6 were investigated at conversions 5% over the temperature range of 387‐412°C and 251–292°C, respectively. The deuterated sample contained 10.5% biacetyl‐d5. The reaction products were analyzed by mass spectrometry.The following data could be determined from product ratios:
equation image
where E is in kcal/molWith reasonable assumptions and literature data Arrhenius parameters for elementary steps were derived and discussed in particular with respect to isotopic effects in H/D‐abstraction reactions.
Comment on the evaluation of the arrhenius parameters by the least squares method
Authors: Cvetanovic R. J. , Singleton D. L. 
Published: January 2005

AbstractArrhenius parameters are frequently evaluated incorrectly by applying the least squares method to the logarithmic form of the Arrhenius equation without simultaneously transforming the statistical weights as required for the change of variable from k to ln k. This has been mentioned briefly in an earlier paper. In the present communication the correct procedures are discussed and illustrated by several examples of evaluations. In particular, Arrhenius parameters calculated by the Taylor series expansion of the exponential form of the Arrhenius equation are compared with those calculated from the logarithmic form, using an exact and two approximate transformations of the statistical weights. The comparisons indicate thatthe preferred procedure for obtaining Arrhenius parameters is either the Taylor series method or the logarithmic method with proper transformation of the experimentally determined statistical weights of the rate constants ki. The common approximation of assuming equal statistical weights of ln ki when the logarithmic form of the Arrhenius expression is used is shown not to be always appropriate, and reasons forthis are given.
Pyrolytic production of Se (3P) from carbon diselenide. I. Equilibrium
Authors: Marquart J. R. , Belford R. L. , Fraenkel H. A. 
Published: January 2005

AbstractThermodynamic characteristics of the dissociation of carbon diselenide are examined. Results of a shock‐tube study of CSe2 pyrolysis are combined with previously unreported photoionization spectroscopy data on CSe2 and with a critical examination of the available literature on Se(g), Se2(g), CSe(g), CSe2(g), and CSe2(t). Based on the best currently available information, recommendations are made for the values of enthalpies, entropies, heat capacities, and derived functions. In particular, the most likely value for ΔH0 (CSe2(g) → CSe(g) + Se(g, 3P)) is +83 kcal/mol, and for Kp at 2000°K it is 0.018 atm.
Photolysis of 1,1,1‐difluorochloroethane (Freon 142) at 147 nm
Authors: Ichimura T. , Kirk A. W. , Tschuikow‐Roux E. 
Published: January 2005

Abstract1,1,1‐Difluorochloroethane (Freon 142) was photolyzed at 147 nm in the pressure range of 3.6–20.6 torr. The effects of added NO, H2S, and CF4 were investigated. The extinction coefficient at 147 nm and 296°K was determined to be 64 ± 8 atm−1 · cm−1.The molecule photodecomposes largely by α,β elimination of HCl to give 1,1‐difluoroethylene (Φ = 0.74 ± 0.06). There is no observable elimination of HF, but there is strong evidence for the elimination of the elements of FCl though the relative importance of this process is minor, as are contributions from carboncarbon and carbonhalogen bond fission.The 1,1‐difluoroethylene formed is undoubtedly vibratonally excited and is the source of a pressure‐dependent small yield of fluoroacetylene. Over the pressure range studied there is no evidence that the major primary process itself is affected by changes in total pressure as is the case in the 147‐nm photolysis of ethyl chloride.
The reaction of ozone with thiophene in the gas phase
Authors: Kaduk Bruce A. , Toby Sidney 
Published: January 2005

AbstractThe reaction between ozone and thiophene was studied from 30 to 125°C over a pressure range of 0.005‐0.3 torr ozone and 0.1‐1 torr thiophene. The most abundant product was O2 with smaller amounts of CO2 and SO2. The mass balance was 100% for oxygen and approached 100% for sulfur at the higher values of [O3]0. The carbon balance, however, was only 25% and no H‐containing products were found, suggesting that the missing product is a hydrocarbon which may be a polymer. The rate law found was ‐d[O3]/dt = k1[Th] [O3] + k2 [Th] [O3]2 where log k1(M−1 · sec−1) = 7.8 ± 0.5 ‐ (8400 ± 700)/2.3RT, and log k2(M−2 · sec−1) = 12.4 ± 0.4 ‐ (4700 ± 400)/2.3RT. Added O2 had no effect on k1 but reduced k2 to a limiting value. It is thus not possible to measure the primary rate constant in this system by measuring the overall rate in the presence of oxygen, and this restriction may also apply to other ozone systems. A mechanism is postulated involving two chain sequences, one of which is inhibited by added O2. A comparison with other ozone systems is made, and the chain lengths are far greater for ozone + thiophene than other systems, under the conditions employed. Possible intermediates in the mechanism are discussed.
Modeling study of two‐step photodissociation method of isotope enrichment
Authors: Hwang W. C. , Kamada R. F. , Badcock C. C. 
Published: January 2005

AbstractA general comprehensive model of the two‐step photodissociation method of isotope enrichment for diatomic reactants was constructed. The model includes kinetic and absorption processes, isotopic species, and temperature. Criteria to measure different aspects of enrichment were established.The results show that, in general, isotopic mixing by kinetic processes can be controlled. The relative importance of intensities of excitation sources for the two steps depends on the degree of saturation of the first‐step absorption transition.For the specific system modeled, i.e., the dissociation of HBr followed by scavenging with NO, the model predicts that detection of bromine enrichment is possible. The important processes and their influence on enrichment were identified, and optimization of experimental parameters was modeled.
Thermal stability of primary amines
Authors: Tsang Wing 
Published: January 2005

AbstractTertiary‐amyl amine has been decomposed in single‐pulse shock‐tube experiments. Rate expressions for several of the important primary steps are

This leads to D(CH3H) – D(NH2H) = −10.5 kJ and D[(CH3)3CH] – D[(CH3)2NH2CH] = + 6 kJ.The present and earlier comparative rate single‐pulse shock‐tube data when combined with high‐pressure hydrazine decomposition results‐(after correcting for fall off effects through RRKM calculations) gives

where kr(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then

Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated:
Electrocyclic versus homolytic decompositions of peroxides: Solvent and phase effects
Authors: Hiatt R. , Rahimi P. M. 
Published: January 2005

AbstractThe thermal decomposition of isopropyl peroxide in solvents is shownto be a competition between unimolecular homolysis (kr) and an electrocyclic reaction yielding H2plus acetone (kH). The value ofkHincreases markedly with increasing solvent polarity: PhCH3<i‐PrOH < MeOH < H2O. LogkHcorrelates linearly withEt(orZ). The effect onkris similar but less pronounced. Logkr's for bothi‐Pr2O2andt‐Bu2O2are shown to correlate with the molar solubility parameter δ. The negligible contribution of the electrocyclic reaction to thermal decompositions of peroxides in the vapor phase is thus not due to peculiar behavior of that reaction, which clearly has a polartransition state. It is argued that the transition state for unimolecular homolysis has no polar character despite the apparent sensitivity of homolysis rates to solvent polarity.
Radiationless transitions between excited singlet states of biacetyl
Authors: Richard C. , Bouchy M. , Andre J. C. , Niclause M. 
Published: January 2005

AbstractEmission processes from lower excited states S1 (fluorescence) and T1 (phosphorescence) have been studied in the gas and liquid phases when biacetyl is excited into the second singlet state S2. (In agreement with Kasha's rule no fluorescence is observed from the S2 state.)In the liquid phase, when biacetyl is excited into the singlet states S1 and S2, no difference is observed between these emission processes. This phenomenon certainly results from an efficient nonradiative transition between the second excited singlet state S2 and the first excited state S1 with practically no excess vibrational energy. The quantum yield of this transition is almost unity and does not depend on the nature of the solvent.In the gas phase no emission processes are observed when biacetyl is excited into the S2 state at low pressure (less than 10 mm Hg). High pressure of inert gas is necessary in order to observe these processes. As for excitation into the S1 state with vibrational energy, loss of vibrational energy through collisions occurs from the S2 state. The quantum yield of the S2 → S1 transition by excitation at 290 nm is estimated around 0.5–0.6 at 6 atm of inert gas (ethane, ethylene, or carbon dioxide).
The mechanism of the vapor‐phase chlorination of benzene derivatives
Authors: Dorrepaal Wim , Louw Robert 
Published: January 2005

AbstractThe title reaction, displaying peculiar characteristics as to relative rates and isomer distributions, has been studied in detail. Prior to this study, different mechanisms had been advanced by several groups. Kinetic features (isomer patterns, relative and absolute rates, reaction orders, influences of additives, H/D isotope effects) strongly point to a free‐radical (chain) process, in which (1) is a crucial step. This abstraction reaction, endothermal by about 6 kcal/mol, apparently proceeds via a transition state closely resembling the free aryl radical. Relative rates and isomer distributions therefore reflect differences in stabilization energies, or in DH°(Ar – H). With high arene–Cl2 intake ratios or, more pronounced, with CCl4 as the reagent, aryl radicals also lead to biaryl, where arene successfully competes with the halogenating agent. This interpretation is quantitatively supported by our observation that “added,˝” recognizable aryl radicals yield the same chlorination–arylation product ratio, and by the results of competitive chlorination of benzene and chloroform over a temperature range of 200°C, where the latter study substantiates the value DH0(C6H5 – H) ≈ 109 kcal/mol.
Application of RRKM theory to the reactions OH + NO2+ N2→ HONO2+ N2(1) and ClO + NO2+ N2→ ClONO2+ N2(2); a modified gorin model transition state
Authors: Smith G. P. , Golden D. M. 
Published: January 2005

AbstractRate constants as a function of both temperature and pressure were calculated for the title reactions using RRKM theory in conjunction with a modified Gorin transition state. The modification introduces a hindrance parameter which accounts for repulsive interactions between the rotating fragments. At the highest stratospheric pressures (∼50 torr) and at stratospheric temperature (∼220°K), the extent of “falloff” from first‐order [N2] dependence is ∼70% for reaction (1) and ∼35% for reaction (2).
The Kinetics of alkyl radical reactions with aliphatic alcohol glasses as studied by electron spin resonance
Authors: Stepanov A. A. , Tkatchenko V. A. , Bol'Shakov B. V. , Tolkatchev V. A. 
Published: January 2005

AbstractMethyl radical reactions with matrix molecules in glasses C2H5OH, (CH2OH)2, n‐ and i‐C3H7OH, n‐ and i‐C4H9OH, n‐ and i‐C5H11OH, C2D5OH, and i‐C3D7OD, and the reactions of Ċ2H5, Ċ3H7, Ċ4H9, Ċ5H11 with methanol glasses have been studied. Alkyl radicals were produced by photolysis of diphenylamine–alkylhalide–alcohol mixtures using ultraviolet light. In all cases the alkyl radical decay follows the law c = c0 exp(‐k √t). The √t law should not be associated with alkyl radical diffusion in a matrix. A method of processing the kinetics of those reactions in which one paramagnetic species changes into another with the total concentration being constant and the electron spin resonance spectra of both species overlapping, is described.
The kinetics of the reactions of methyl radicals with Br2, Cl2, and BrCl
Authors: Evans Brian S. , Whittle Eric 
Published: January 2005

AbstractA general competitive method is described for the study of the kinetics of the reactions of radicals with halogens and interhalogen compounds in the gas phase. The method is applied to the reactions
equation image
over the temperature range of 48°–199°C. It is found that

where Θ=2.303RT J/mol. Also

There is no correlation between differences in activation energies and differences in enthalpy changes for these reactions, but polar effects may be important in reactions (7) and (8).
Reaction of H with C2N2 at pressures near 1 torr
Authors: Phillips L. F. 
Published: January 2005

AbstractThe rate of disappearance of C2N2 in the presence of a large excess of H atoms has been measured in a discharge‐flow system at pressures near 1 torr and temperatures in the range of 282–338 K. Under these conditions the reaction has a small negative temperature coefficient. A transition from second‐order to third‐order kinetics with decreasing pressure occurs at pressures near 1 torr. The results are discussed in terms of the mechanism
equation image
where k7 = (1.5 ± 0.2) × 10–15 cm3/molec1·sec is found for the forward rate of reaction (7). The results also give k7k8/k−7 = 3.7 × 10−31 cm6/molec2·sec and k7k9/k−7 = 3.0 × 10−32 cm6/molec2·sec, the first being probably an upper limit and the second probably a lower limit; hence k8/k9 = 12 is found as an upper limit.