bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of rate constants as a function of temperature for the reactions W + XYZ = WX + YZ, where W, X, Y, and Z are H or O atoms
Authors: Shaw Robert 
Published: January 2005

AbstractRate constants have been estimated as a function of temperature for seven reactions of the type W + XYZ = WX + YZ, where W, X, Y, and Z are H and O atoms. From transition state theory and estimates of the heat capacities of activation,

where int k is the rate constant per transferable atom for the forward and reverse reactions in the exothermic direction, and where ΔH°≠298 is in kcal/mol. Values of ΔS°≠298 and ΔH°≠298 were obtained from the above equation and previously measured and evaluated rate constants at 298°K. The results are summarized in a table. Rate constants were calculated at temperature from 250 to 2000 K. The estimated rate constants were compared with recommended values. The results for ΔH°≠298 for reactions (15), (16), (17), and (19), in which a stable intermediate may precede the transition state, together with similar results previously found for reactions X + YZ = XY + Z, suggests that many such reactions may have values of ΔH°≠298 that are close to zero. The result for the reaction O + O3 = O2 + O2 is however, an exception to the foregoing perhaps because it is the reaction of a singlet with a triplet.ΔS°≠298 for the same reaction is unexpectedly low.
The triplet state of 4‐nitro‐N, N‐dimethynaphthylamine
Authors: Capellos C. , Lang F. 
Published: January 2005

AbstractNanosecond laser photolytic studies of 4‐nitro‐N,N‐dimethylnaphthylamine (4‐NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500‐510‐nm range. This species is assigned to the lowest triplet excited state of 4‐NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n‐hexane the lifetime 1/k of the triplet state is 9.1 × 10−6 sec, while in acetonitrile 1/k is 2.0 × 10−7 sec. The hydrogen abstraction rate constant kH of the triplet state with tributyl tin hydride (Bu3SnH) in n‐hexane is 1.7 × 107M−1·sec−1, while in the case of isopropyl alcohol as hydrogen donor, kH is 4.0 × 107M−1·sec−1. The activation energy for the hydrogen abstraction by the triplet state from Bu3SnH in deaerated n‐hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n‐π* state which retains its n‐π* character even in polar media.
Absolute rate constants for the reactions of O(3P) atoms with DCl and DBr
Authors: Brown Raymond D. H. , Smith Ian W. M. 
Published: January 2005

AbstractEarlier work on the reactions of O(3P) atoms with HCl and HBr has been extended by measuring rate constants for
equation image
A flow‐tube method was used with chemiluminescent monitoring of the removal of atomic oxygen. Rate constants were measured at temperatures between 340 and 489 K for (2a) and 295 and 419 K for (2b); they can be matched by the Arrhenius expressions:

where the units are cm3 molecule−1 sec−1 and the errors correspond to a single standard deviation. The results of a quasiclassical trajectory study of collisions of O(3P) with HCl (v = 0,1, and 2) and DCl (v= 0,1, and 2) are also reported. These strengthen the conclusion that, although the rates of reactions (1a) and (2a) are selectively enhanced by vibrationally exciting HCl or DCl, molecules with 0 < v ⩽ 2 are mainly removed in collisions with O(3P) atoms by nonreactive relaxation.
The reaction of S(3P) atoms with nitric oxide
Authors: Van Roodselaar A. , Obi K. , Strausz O. P. 
Published: January 2005

AbstractThe flash photolysis–vacuum ultraviolet kinetic absorption spectroscopy technique has been used to measure the absolute rate constant for the reaction of ground state S(3P) atoms withnitric oxide,\documentclass{article}\pagestyle{empty}\begin{document}${\rm S}\left({^{\rm 3} P} \right) + {\rm NO}\mathop {\longrightarrow}\limits^{\rm M} {\rm SNO}\left({{\rm M} = {\rm CO}_2} \right)$\end{document}as a function of nitric oxide concentration and total pressure. The rateconstant was determined to be 1.9±0.1 × 101112/mol2.sec at 298°K, with a high‐pressure limit of 9.3 ± 2.1×109l/mol·sec−1. The observed kinetics are consistent with a termolecular energy transfer mechanism.
Kinetics of the thermal decomposition of bis‐pentafluorine sulfur peroxide in the presence of carbon monoxide
Authors: Czarnowski J. , Schumacher H. J. 
Published: January 2005

AbstractThe thermal decomposition of F5SOOSF5, P, in the presence of CO has been investigated between 130.1° and 161.9°C at total pressures between 50 and 600 torr. The reaction is homogeneous, and the only final products formed are CO2 and S2F10. The rate of reaction is proportional to the pressure of P. The partial pressures of CO and O2 and the total pressure have no influence on the course of reaction:

The results are explained by the following mechanism:
equation image
Kinetics of fluorescence decay of SO2 excited in the 2662–3273 Å region
Authors: Su Fu , Bottenheim Jan W. , Sidebottom Howard W. , Calvert Jack G. , Damon Edward K. 
Published: January 2005

AbstractThe kinetics of fluorescence decay of SO2 excited in the 2975–3273 Å region was studied using a powerful, frequency doubled, tunable dye laser system. The existence of two emitting species, first observed by Brus and McDonald, was confirmed. The collision‐free lifetimes of the long‐lived (L) species ranged from 100 to 300 μsec and the short‐lived (S) species from 17 to 43 μsec over the wavelength range employed. The magnitude of the bimolecular quenching rate constant for the L state was a function of the excitation energy; the data show that about 1 kcal/mol of internal energy is lost per collision of the SO2(L) species excited in the range of 2998–3107 Å. Studies of the relative initial fluorescence intensity of the S to that of the L state (IS°/IL°) were made in experiments which extended to 0.11 mtorr. The pressure dependence of the IS°/IL° ratio for experiments at 3107, 3211, and 3225 Åproved that the S and L states do not decay independently. Either efficient bimolecular S → L conversion occurs or bimolecular S ⇄ L interconversion of both states is important. These data coupled with spectroscopic studies of Hamada and Merer and Shaw and coworkers favor the designation of the S and L states as SO2(1A2) and SO2(1B1), respectively. However, if the assignment is correct, then the band origin of the 1B1 state must be at a somewhat longer wavelength, λ> 3273 Å than tentative spectroscopic assignments suggest. Bimolecular quenching rate constants for the L and S components with various atmospheric gases were determined in 3130‐ and 2662‐Å studies.
Stopped‐flow study of the gas‐phase reaction of ozone with organic sulfides: Dimethyl sulfide
Authors: Martinez Richard I. , Herron John T. 
Published: January 2005

AbstractThe autoinhibiting reaction of ozone with dimethyl sulfide (DMS), has been studied at 296°K and 1.1 kPa (8 torr) as a function of the concentrations of both reactants. The major products of the reaction are H2CO, H2O, CO, and SO2. The specific rate of primary attack of O3 on DMS is immeasurably slow. It is suggested that the rapid overall rate observed for this reaction is due to a chain reaction initiated by the very slow primary reaction. It is concluded that reaction (1) cannot be important under atmospheric conditions and that the major loss process for DMS in the atmosphere is probably reaction with photochemically generated free radicals.
Dynamics of a conformational change in aqueous 18‐crown‐6 by an ultrasonic absorption method
Authors: Liesegang Gerard W. , Farrow Michael M. , Rodriguez Licesio J. , Burnham Roger K. , Eyring Edward M. , Purdie Neil 
Published: January 2005

AbstractA temperature dependence study of the ultrasonic amplitudes, velocities, and relaxation times for a presumed conformational transition of noncomplexed aqueous 18‐crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) is discussed. At all temperatures a single relaxation was observed within a 15–255‐MHz frequency range. The equilibrium constant for the presumed conformational transition \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CR}_1 \mathop \rightleftarrows\limits^{K_{12} } {\rm CR}_2 $\end{document} was determined to be K21 = (2 ± 2) × 10−2. The activation parameters are ΔH21≠ = 10.2 ± 1.0 kcal/mol, ΔS21≠ = 7.7 ± 0.2 cal/(mol·deg), ΔH12≠ = 7.4 ± 1.0 kcal/mol, and ΔS12≠ = 7.7 ± 0.2 cal/(mol·deg), while the thermodynamic enthalpy and entropy were found to be −2.6 ± 1.0 kcal/mol and 0 ± 0.2 cal/(mol·deg), respectively. The rate constants at 25.0°C for the presumed conformational transition are k21 = (1.0 ± 0.3) × 107 sec−1 and k12 = (6.2 ± 0.2) × 108 sec−1.
Evidence for strongly temperature‐dependent A factors in alkane decomposition and high heats of formation for alkyl radicals
Authors: Tsang Wing 
Published: January 2005

AbstractThe experimental data on alkane decomposition from shock‐tube and radical buffer studies and radical combination from very‐low‐pressure pyrolysis and modulation spectroscopy are shown to be consistent. They lead to experimental A factors which decrease by factors of 10–2000 from 300° to 1100°K. Heats of formation for ethyl, isopropyl, and t‐butyl radicals have been found to be 10, 10 and 20 kJ higher than currently accepted numbers from metathesis reactions.
Kinetics and mechanism of oxidation of aliphatic ketoximes by thallium(III) acetate—part I
Authors: Balakrishnan T. , Santappa M. 
Published: January 2005

AbstractThe oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20–40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H+], ionic strength, temperature, etc. The reactions were found to be totally second order–first order with respect to each reactant. The second‐order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one‐electron oxidation to the iminoxy radical followed by an another one‐electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.
Competition between multiphoton fluorescence and multiphoton ionization in NO
Authors: Jackson W. M. , Lin C. S. 
Published: January 2005

AbstractA nitrogen laser pumped tunable dye laser has been used to observe the three‐photon ionization of NO through a two‐photon resonance with the C2II state. Fluorescence is also observed from this state. The wavelength dependence of both signals have been measured. A reaction mechanism is postulated, which includes the initial two‐photon excitation of the C2II state as the rate‐limiting step. This mechanism predicts the observed second‐order intensity dependence of the ionization signal and shows that the simple rate equation treatment is valid in this system.
Kinetics and mechanism of oxidation of diethyl ketone by N‐bromosuccinimide
Authors: Singh Kameshwar , Tiwari J. N. , Mushran S. P. 
Published: January 2005

AbstractOxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by using N‐bromosuccinimide (NBS) as oxidant in the temperature range of 25°‐50°C. It has been found that the order with respect to NBS is zero while with respect to diethyl ketone and [H+], it is unity. Succinimide, sodium perchlorate, and mercuric acetate have an insignificant effect on the reaction rate, while the dielectric effect was negative. A solvent isotope effect (k0D2O/k0H2O = 1.6–1.8) at 35°C has been observed. On the basis of the available evidences a suitable mechanism consistent with the experimental results has been proposed in which it is suggested that the mechanistic route for NBS oxidation in an acidic medium is through the enol form of the ketone. The magnitude of the solvent effect also supports the mechanism. Various activation parameters have been calculated, and the 1,2‐dicarbonyl compound has been identified as the end product of the reaction.
Thermal stability of cyclohexane and 1‐hexene
Authors: Tsang Wing 
Published: January 2005

AbstractThe mechanism and initial rates of decomposition of cyclohexane and 1‐hexene have been determined from single‐pulse shock‐tube experiments. The main initial processes involve isomerization of cyclohexane to 1‐hexene, followed by decomposition of 1‐hexene. From comparative rate experiments the following rate expressions have been derived:

The 1‐hexene bond‐braking reaction leads to an allylic resonance energy of 42.7 kJ and a heat of formation of allyl radicals of 176.6 kJ (300°K). There appear to be general relations relating the rate expressions for the decomposition of alkynes, alkanes, and alkenes. Studies on the induced decomposition of cyclohexane have also been carried out.
Computer modeling of smog chamber data: Progress in validation of a detailed mechanism for the photooxidation of propene and n‐butane in photochemical smog
Authors: Carter William P. L. , Lloyd Alan C. , Sprung Jeremy L. , Pitts James N. 
Published: January 2005

AbstractA detailed mechanism is presented for reactions occurring during irradiation of part‐per‐million concentrations of propene and/or n‐butane and oxides of nitrogen in air. Data from an extensive series of well‐characterized smog chamber experiments carried out in our 5800‐liter evacuable chamber–solar simulator facility designed for providing data suitable for quantitative model validation were used to elucidate several unknown or uncertain kinetic parameters and details of the reaction mechanism.The mechanism was then tested against the data base from the smog chamber runs. In general, most calculated concentration–time profiles agreed with experiments to within the experimental uncertainties. Fits were usually attained to within ∼±20% or better for ozone, NO, propene, and n‐butane, to within ∼±30% or better for NO2, PAN, methyl ethyl ketone, 2‐butyl nitrate, butyraldehyde, and (in runs not containing propene) methyl nitrate, to within ⋐±50% or better for the minor products 1‐butyl nitrate and propene oxide, and to within a factor of 2 for methyl nitrate in propene‐containing runs. Propionaldehyde was consistently underpredicted in all runs; it is probably a chamber contaminant. For formaldehyde and acetaldehyde, the major products in both systems, fits to within ⋐±20% were often obtained, yet for a number of experiments, significantly greater discrepancies were observed, probably as a result of experimental and/or analytical problems.The good fits to experimental data were attained only after adjusting several rate constants or rate constant ratios related to uncertainties concerning chamber effects or the chemical mechanism. The largest uncertainty concerns the necessity to include in the mechanism a significant rate of radical input from unknown sources in the smog chamber. Other areas where fundamental kinetic and mechanistic data are most needed before a predictive, detailed propene + n‐butane‐NOx‐air smog model can be completely validated concern other chamber effects, the O3 + propene mechanism, decomposition rates of substituted alkoxy radicals, primary quantum yields for radical production as a function of wavelength for aldehyde and ketone photolyses, and the mechanisms and rates of reactions of peroxy radicals with NO and NO2.
The 5‐hexenyl cyclization
Authors: Schmid Peter , Griller David , Ingold Keith U. 
Published: January 2005

AbstractThe cyclization of the 5‐hexenyl radical to form the cyclopentylmethyl radical has been reexamined by kinetic EPR spectroscopy at temperatures between 183 and 232°K in cyclopropane solvent. The rate constant, kc for this important radical rearrangement can be represented by

where Θ = 2.3RT kcal/mol.
Rate constants for the combination of trichloromethyl radicals and the electron‐transfer reaction between hydroxymethyl radicals and carbon tetrachloride in solution
Authors: Paul H. 
Published: January 2005

AbstractThe rate constant for the bimolecular combination of trichloromethyl radicals in methanol is determined as a function of temperature by steady‐state kinetics and electron‐spin resonance with modulated radical initiation. The rate constant is in accord with the Smoluchowski equation and indicates a diffusion‐controlled radical termination. The temperature dependence of the rate constant for the electron‐transfer reaction between hydroxymethyl radicals and carbon tetrachloride in methanol is determined, and is found to disagree with predictions of the Marcus theory. This disagreement is tentatively ascribed to the structure of the transition state.
The question of the applicable time regime for the steady‐state approximation in the simulation of complex mechanisms
Authors: Edelson D. 
Published: January 2005

AbstractA mechanism proposed by Pilling and Noyes for ignition in carbon monoxide containing traces of water has been modeled using a complete numerical integration, and results have been compared with the steady state treatment (QSSA) of the previous authors. The numerical results were found to be in close agreement. However, the complete solution also yields the time required for the steady state to be reached, and it is shown that this is too large for the results of the QSSA to be considered applicable to this problem. This is substantiated by a further calculation in which temperature is introduced as an additional variable, and it is shown that thermal runaway is reached without any of the intermediate radicals which propagate the reaction chain ever going into a steady state.This study provides an example of the failure of QSSA to provide an adequate solution to a chemical kinetic problem for reasons which have not been previously discussed in the literature. For problems of more than a very few variables there is no practical way short of numerical integration to estimate the time regime during which the steady state applies. Practitioners of QSSA are thus advised of yet another precaution in assesing the credibility of their results.
Kinetics and mechanism of oxidation of sugars by quinquevalent vanadium in binary mixture solvents of DMSO–water and acetic acid–water in H2SO4 medium
Authors: Pati Subas C. , Panda Markandeswar 
Published: January 2005

AbstractThe kinetics of oxidation of aldosugars and ketosugar by quinquevalent vanadium in binary mixtures of DMSO–water and acetic acid–water in sulfuric acid medium have been studied. The reaction is first order in both oxidant and substrate. The effect of acidity on the reaction kinetics has been determined. The effect of acidity shows a clear difference. The ketose has a unit dependence, whereas aldoses have a 0.5 dependence in H0. The role of solvent in these reactions has also been studied, and the effect of temperature on these reactions has been determined. A suitable mechanism has been postulated taking all the observed facts into consideration.
The gas‐phase decomposition of alkoxy radicals
Authors: Batt L. 
Published: January 2005

AbstractIt is shown that it is possible to obtain good data for the rate constant for the decomposition of alkoxy radicals [RO] by using nitric oxide as a radical trap. Two experimental systems have been used.The first system involves the use of dialkyl peroxides [(RO)2] as thermal sources of alkoxy radicals. The peroxide concentration was ∼10−4M, nitric oxide ∼2 × 10−4M, and the extent of reaction was ∼10%. The total pressure was altered using carbon tetrafluoride as an inert gas. The mechanism is
equation image
Hence R2/R3 = k2[NO]/k3. Our previous studies show that k2 lies in the range 1010.3±0.2M−1·sec−1.The second system employs alkyl nitrites [RONO] as a thermal source of alkoxy radicals. The experimental conditions are very similar, except that we chose to use an atmosphere of nitric oxide for initial experiments. If anything nitric oxide appears to be superior to carbon tetrafluoride as an energy transfer agent. The mechanism is
equation image
Hence R3 = k1'k3[RONO]/(k3 + k2 + k6 [NO]).Results are given for R = t‐Am, s‐Bu, t‐Bu, i‐Pr, Et, and Me. In addition the first unequivocal evidence is given for the pressure dependence of k3 when R = t‐Bu. The implications for atmospheric chemistry and combustion are also discussed.
A quantitative study of alkyl radical reactions by kinetic spectroscopy III. Absorption spectrum and rate constants of mutual interaction for the ethyl radical
Authors: Adachi Hiroyuki , Basco N. , James D. G. L. 
Published: January 2005

AbstractIntrinsic spectral and kinetic parameters have been measured for the ethyl radical, which was formed in the gas phase by the flash photolysis of azoethane. Absolute values of the extinction coefficient ϵ(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of the ethyl radical. The absorption spectrum is broad, structureless, and comparatively weak; ϵ(247) = 4.8 × 102 l/mol·cm at the maximum, and the oscillator strength is (9.1 ± 0.5) × 10−3. This is in good qualitative agreement with a spectrum obtained independently using the technique of molecular modulation spectrometry.The biomolecular reactions of mutual interaction were the only significant reactions of the ethyl radical in this system; kinetic analysis of the second‐order decline of the absorbance during the dark period yielded a value of k/ϵ(λ) for each experiment. The rate constant for mutual interaction was evaluated from the product of corresponding measurements of k/ϵ(λ) and ϵ(λ) individual values are independent of the wavelength of measurement, and the mean value is k = (1.40 ± 0.27) × 1010 l/mol·sec. The rate constant for mutual combination was derived with the aid of product analysis as k2 = (1.24 ± 0.23) × 1010 l/mol·sec; it stands in close agreement with the set of “high” values obtained by direct measurement using a variety of methods.
Weak collision effects: Non‐steady‐state thermal unimolecular reactions
Authors: Malins R. J. , Tardy D. C. 
Published: January 2005

AbstractBench‐mark calculations for non‐steady‐state thermal systems are presented. Although the equations and calculations were modeled for the isomerization of cyclopropane in the single‐pulse shock tube, the results are qualitatively and semiquantitatively correct for any experimental technique in which a finite time is required to energize the reactant to the reaction temperature. A useful parameter in describing this nonequilibrium behavior is the induction time τ95; the log of τ95 is linearly related to the collision frequency ω. For the model cyclopropane system a steady state is reached in ∼1 msec when ω ≈ 108 sec−1 and T ≈ 1500 K.