bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular momentum conservation in unimolecular and recombination reactions
Authors: Smith Sean C. , Gilbert Robert G.
Published: January 2005

It is shown that the master equation describing fall‐off effects in unimolecular and recombination reactions, with angular momentum (J) conservation taken into account, can be solved exactly if the assumption is made that the probability of collisional energy transfer in J is independent of initial state; this assumption is shown to be physically acceptable (from general conservation considerations and from trajectory calculations) for typical neutral radical recombination and decomposition reactions. This leads to a J‐averaged master equation which can be readily solved by standard means. Illustrative computations using this treatment are presented.
Kinetics of the gas‐phase thermal elimination of (β‐bromo ethyl)‐pyrazole
Authors: Perez Jorge Daniel , Phagouapé Leonardo Miguel
Published: January 2005

Pyrazole elimination and vinyl bromide were found as products in the Flash Vacuum Pyrolysis of (β‐Bromo ethyl)‐pyrazole. To obtain kinetic parameters (Ea) we carried out competitive reactions using (β‐chloro ethyl)‐pyrazole as an internal standard. A thermochemical study to calculate Δ(ΔH) for this reaction was carried out.
Production and decomposition of highly excited 2‐butyl radicals by the addition of hot hydrogen atoms to but‐2‐ene. Cross section for the addition reaction
Authors: Al‐Niami Kisma , Holbrook Kenneth A. , Oldershaw Geoffrey A.
Published: January 2005

Highly excited 2‐butyl radicals have been generated by addition of hot hydrogen atoms to but‐2‐ene. Atoms of initial energy 130 kJ mol−1 and 161 kJ mol−1 were produced by photolysis of H2S. Rates of decomposition of the highly excited 2‐butyl radicals were monitored by analysis of stabilization and decomposition products, and the extent of energy‐loss of the hydrogen atoms in nonreactive collisions assessed by measuring the effect of added xenon on product yields. A model involving the cross‐section for the addition reaction, energy transfer in nonreactive collisions between hydrogen atoms and but‐2‐ene, RRKM rate constants for decomposition of excited 2‐butyl radicals, and collisional energy transfer from the radicals, has been used to calculate product yields for comparison with experimental values. It is concluded that the cross‐section for addition of hydrogen atoms of energy about 130 kJ mol−1 to but‐2‐ene is 0.055 ± 0.028 nm2. This value is compatible with the A factor for the thermal addition reaction.
Angular momentum conservation in multichannel unimolecular reactions
Authors: Smith Sean C. , Gilbert Robert G.
Published: January 2005

A recently developed solution of the master equation for unimolecular and recombination reactions is extended to give new means for incorporating angular momentum (J) conservation in the fall‐off regime for multichannel reactions. The calculated pressure dependence of a typical multichannel unimolecular dissociation reaction (thermal dissociation of 1‐iodopropane) shows that if one of the channels has a transition state with a moment of inertia (I†) significantly different from that of the parent molecule (I) (e.g., a “simple‐fission” type), neglect of angular momentum conservation causes the predicted branching ratio to be grossly in error at lower pressures. Specifically, if I† > I the rate coefficient is underestimated whereas if I† < I the rate coefficient is overestimated.
The mechanism of the reversible reaction: 2C2H2 ⇌ vinyl acetylene and the pyrolysis of butadiene
Authors: Benson Sidney W.
Published: January 2005

It is shown that kinetic data on the polymerization of acetylene to vinyl acetylene and benzene can be reconciled with the formation of a 1,4 biradical which can isomerize by a 1‐3, H‐atom shift to the molecular product. Since the biradicals have a negligibly small life‐time in the system the overall process appears to be a concerted bimolecular reaction. The labile isomer CH2  C: which had been suggested as being the reactive intermediate, is argued on energy considerations not to be a plausible intermediate.

Data on the reverse pyrolysis of vinyl acetylene to acetylene are consistent with the model. Extending the model to butadiene explains the observed molecular nature of its decomposition to ethylene and acetylene.

Reactions of other oligomers of acetylene are discussed.
Kinetics and mechanism of osmium (VIII) and ruthenium(III) catalyzed oxidation of aliphatic amines by chloramine‐T in alkaline and perchloric acid media
Authors: Gupta Sushma , Ali Vazid , Upadhyay Santosh K.
Published: January 2005

The kinetics of oxidation of aliphatic amines viz., ethylamine, n‐butylamine, isopropylamine (primary amines), diethylamine (secondary amine), and triethylamine (tertiary amine) by chloramine‐T have been studied in NaOH medium catalyzed by osmium (VIII) and in perchloric acid medium with ruthenium(III) as catalyst. The order of reaction in [Chloramine‐T] is always found to be unity. A zero order dependence of rate with respect to each [OH−] and [Amine] has been observed during the osmium(VIII) catalyzed oxidation of diethylamine and triethylamine while a retarding effect of [OH−] or [Amine] on the rate of oxidation is observed in case of osmium(VIII) catalyzed oxidation of primary aliphatic amines. The ruthenium(III) catalyzed oxidation of amines follow almost similar kinetics. The order of reactions in [Amine] or [Acid] decreases from unity at higher amine or acid concentrations.

The rate of oxidation is proportional to {k′ and k″ [Ruthenium(III)] or [Osmium(VIII)]} where k′ and k″ (having different values in case of ruthenium(III) and osmium(VIII)) are the rate constants for uncatalyzed and catalyzed path respectively. The suitable mechanism consisting with the kinetic data is proposed in each case and discussed.
Hydrogen transfer from 9,10‐dihydrophenanthrene to anthracene
Authors: Billmers R. , Brown R. L. , Stein S. E.
Published: January 2005

Kinetic studies of the transfer of hydrogen from 9,10‐dihydrophenanthrene to anthracene were done at 350°C in the liquid phase. Principal products were phenanthrene and 9,10‐dihydroanthracene. Autocatalysis occurred at low extents of reaction, where H‐transfer from 9,10‐dihydroanthracene to anthracene caused an increase in free radical concentrations. At higher extents of reaction, 9,10‐dihydroanthracene inhibited rates by diverting intermediate 9‐hydrophenanthryl radicals back to reactants. A quantitative kinetic model based on literature rate and thermodynamic data fits the observations well. A key net reaction is the transfer of an H‐atom from a radical (9‐hydrophenanthryl) to a molecule (anthracene). It is shown that this process does not involve a free H‐atom intermediate. The derived rate constant for this exothermic process (7.5 × 103 M−1 s−1) is considerably greater than that for the related, but thermoneutral H‐transfer between anthracene moieties (120 M−1 s−1).
Kinetics and mechanism of indigo carmine‐acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion
Authors: Muthakia G. K. , Jonnalagadda S. B.
Published: January 2005

A kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′‐dioxobi‐indolin‐2,2′‐ylidene‐5,5′‐disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H+ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H+and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant‐oxidant ratio. In both uncatalyzed and catalyzed reactions isatin‐5‐monosulphonic acid (2,3‐dioxoindoline‐5‐sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested.

Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H+] 2.25M, [iodate] 1.00 × 10−3Mand [IC] 5.0 × 10−5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.
Decomposition of the t‐butoxy radical: II. Studies over the temperature range 303—393 K
Authors: Batt L. , Hisham M. W. M. , Mackay M.
Published: January 2005

The near U‐V photolysis of t‐butyl nitrite has been studied over the temperature range 303–393 K. Under these conditions t‐butyl nitrite was shown to be a very clean photochemical source of t‐butoxy radicals. This allows a study of the decomposition of the t‐butoxy radical to be made over this temperature range (3).
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Extrapolation of the rate constants k3 to high pressure and combination with our previous thermal data give the results:
The gas phase pyrolysis of phenol
Authors: Lovell A. B. , Brezinsky K. , Glassman I.
Published: January 2005

Phenol pyrolysis has been studied in a turbulent flow reactor by analyzing concentration‐time profiles of three major decomposition products: carbon monoxide, cyclopentadiene, and benzene. Experimental conditions were P = 1 atm, T = 1064 − 1162 K, and initial phenol concentrations of 500−2016 ppm. The major experimental observations were that the decomposition product profiles were nearly linear as a function of time and that the overall rate of carbon monoxide production was greater than that of cyclopentadiene. The rate difference is explained by a mechanism which includes a radical combination reaction of cyclopentadienyl and phenoxy. With literature and approximate rate coefficient data, the mechanism reproduced the experimental observations very well. The mechanism and data provide estimates of rate coefficients for the phenol decomposition initiation step, abstraction of hydrogen from phenol by cyclopentadienyl, and the phenoxy‐cyclopentadienyl combination, all of which have not been available in the literature.
Flash photolysis study for reactions of NO3· with sulfur compounds in acetonitrile solution
Authors: Akiho Seiji , Ito Osamu , Iino Masashi
Published: January 2005

The rate constants for the reaction of NO3· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 104 M−1s−1 at −10°C) is larger than that of the deuterium derivative, indicating that NO3· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 109 M−1 s−1 at −10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO3·, suggesting the electron transfer reaction from the sulfide to NO3·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 109 M−1 s−1 (at −10°C) was not practically affected by the deuterium substitution, suggesting that NO3· adds to sulfur atom forming (CH3)2Ṡ(O)‐ONO2. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.
Study of the reaction of MoOS2(S2CNR2)2 with PPh3 in 1,2‐dichloroethane: Part I. Kinetics of the teaction of MoOS2(S2CNR2)2 with triphenylphosphine PPh3
Authors: Xiaoqing Song , Huixing Yang , Degang Han
Published: January 2005

The kinetics of the reaction of MoOS2(S2CNR2)2 (R = CH3, C2H5, n‐C3H7) with PPh3 have been studied using a Stopped‐flow method. It was found that these MoOS2(S2CNR2)2 complexes react with PPh3 in the form of an irreversible second‐order reaction. The rate constants at 25°C are respectively 48.4, 23.8, and 20.8 mol−1 dm3 s−1 and the activation energies are 4.8, 4.9, and 5.0 Kcal/mol with R = CH3, C2H5, and n‐C3H7.
Kinetics of CH radical reactions with N2O, SO2, OCS, CS2, and SF6
Authors: Zabarnick S. , Fleming J. W. , Lin M. C.
Published: January 2005

Pulsed laser photolysis/laser‐induced fluorescence (LIF) is utilized to measure absolute rate constants of CH radical reactions as a function of temperature and pressure. Multiphoton dissociation of CHBr3 at 266 nm is employed for the generation of CH (X2Π) radicals. The CH radical relative concentration is monitored by exciting fluorescence on the R1(2) line of the (A2Δ – X2Π) transition at 429.8 nm. A resistively heated cell allows temperature studies to be performed from room temperature to ≈︂670 K. The following Arrhenius equations are derived:

With the exception of SF6, the reactions of sulfur containing species proceed at rates that are near the theoretical gas kinetic collision frequency. Additionally, these reactions all have activation energies that are near zero or slightly negative. These observations are consistent with an insertion‐decomposition mechanism being dominant under these conditions.
Laser photolysis/laser‐induced fluorescence studies of reaction rates of OH with CH3Cl, CH2Cl2, and CHCl3 over an extended temperature range
Authors: Taylor Philip H. , D'angelo Joe A. , Martin Marc C. , Kasner James H. , Dellinger Barry
Published: January 2005

A modified laser photolysis/laser‐induced fluorescence technique has been used to measure atmospheric pressure absolute rate coefficients for the reaction of hydroxyl (OH) radicals with the chlorinated methanes (CH3Cl, CH2Cl2, and CHCl3). Data have been obtained for these compounds over the widest temperature range (292–800 K) that has been reported in the literature using a single experimental apparatus. The temperature dependence of the rate data is best represented by the following three‐parameter expressions:

Uncertainties in the pre‐exponential and exponential term are expressed as 95% confidence intervals. For the temperature exponent, error limits represent a ±10% change in the total error of best fit.

The degree of curvature in the Arrhenius plots appeared to increase with increasing Cl substitution of the reactant. However, the uncertainty in the temperature exponent for the CH3Cl data was large in comparison with the other chlorinated methanes. Thus, data of greater precision at elevated temperatures are necessary to further explore this relationship. The rate coefficients were compared with recent semiempirical and transition state theory models for haloalkane‐OH hydrogen transfer reactions over a temperature range of 250–800 K. The transition state model of Cohen and Benson was in excellent agreement with the CH3Cl and CH2Cl2 data. The semiempirical structure activity relationship developed by Atkinson represented the best fit of the CHCl3 data, although it underestimated the experimental data by more than a factor of 2 at 800 K. The extreme care used to remove and alayze for reactive impurities along with the agreement with other experimental studies suggests that transition state and semi‐empirical models for CHCl3 must be modified to account its reaction behavior at high temperature.
Modeling and simulation of stationary catalytic processes
Authors: Salmi Tapio
Published: January 2005

Generalized models for steady state catalytic processes are presented in matrix form. Multistep reaction rate control is assumed. Numerical algorithms for solving of the created linear and nonlinear equation systems are developed and tested. Four examples are considered: an Eley–Rideal‐mechanism, a Langmuir–Hinshelwood mechanism, a dual route, dual site mechanism, and a monomolecular decomposition with steady state multiplicity. The overall reaction rates are simulated as a function of the reactant concentrations.

A maximum reaction rate is obtained in the case of a Langmuir–Hinshelwood mechanism (example 2), the location of the rate maximum in the concentration domain is shifted towards the concentration of the reactant with the lowest adsorption constants. An Eley–Rideal mechanism (example 1) has always monotonously increasing rate curves. In the case of steady state multiplicity (example 4) all steady states could be simulated with the proposed algorithm. The computation of reaction rate surfaces is important in investigating the behavior of complicated catalytic systems (e.g., systems with multistep rate control and/or steady state multiplicity), in planning of experiments and in chemical reactor simulation.
Fourier transform infrared study of the self reaction of C2H5O2 radicals in air at 295 K
Authors: Wallington T. J. , Gierczak C. A. , Ball J. C. , Japar S. M.
Published: January 2005

Fourier transform infrared spectroscopy was used to identify and quantify products of the self reaction of ethylperoxy radicals, C2H5O2, formed in the photolysis of Cl2/C2H6 mixtures in 700 torr total pressure of synthetic air at 295 K. From these measurements, branching ratios for the reaction channels
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of k1a/(k1a + k1b) = 0.68 and k1c/(k1a + k1b + k1c) ⩽ 0.06 were established. Additionally, using the relative rate technique, the rate constant for the reaction of Cl atoms with C2H5OOH was determined to be (1.07 ± 0.07) × 10−10 × cm3 molecule−1 s−1. Results are discussed with respect to the previous kinetic and mechanistic studies of C2H5O2 radicals.
An absolute and relative rate study of the reaction of oh radicals with dimethyl sulfide
Authors: Nielsen Ole J. , Sidebottom Howard W. , Nelson Linda , Treacy Jack J. , O'farrell Denis J.
Published: January 2005

The gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3, DMS) has been studied using both an absolute and a relative technique at 295 ± 2 K and a total pressure of 1 atm. The absolute rate technique of pulse radiolysis combined with kinetic spectroscopy was applied. Using this technique a rate constant of (3.5 ± 0.2) × 10−12cm3molecule−1s−1was obtained. For the relative rate method, rate constants for the reaction of OH with DMS were found to increase with increasing concentrations of added NO. These results are compared with the large body of kinetic and mechanistic data previously reported in the literature.
The gas phase reactivity of aliphatic polyethers towards OH radicals: Measurements and predictions
Authors: Dagaut Philippe , Liu Renzhang , Wallington Timothy J. , Kurylo Michael J.
Published: January 2005

Using the flash photolysis resonance fluorescence technique, absolute rate constants were determined for the gas phase reactions of hydroxyl radicals with a series of aliphatic polyethers. At 298 K, the measured rate constants (in units of 10−12 cm3 molecule−1 s−1) were: 2,2‐dimethoxypropane, (3.9 ± 0.2); 2,2‐diethoxypropane, (11.7 ± 1.3); 1,2‐dimethoxypropane, (14.3± 1.5); 2‐methoxyethylether, (17.5 ± 1.1); 2‐ethoxyethlyether, (26.8 ± 2.4); 1,1‐dimethoxyethane, (8.9 ± 1.0); and 1,1,3‐trimethoxypropane, (16.7 ± 1.0).

The temperature dependencies of the rate constants for 2,2‐dimethoxypropane and 2,2‐diethoxypropane, reactions (1) and (2), were studied over the temperature range 240–440 K and are expressed by the Arrhenius equations:

Implications of the results are discussed in terms of reaction mechanisms and the prediction of gas phase OH radical reaction rates for aliphatic polyethers.
Kinetic probe to study the structural behavior of the mixed aqueous‐organic solvents. Salt effects on the kinetics and mechanism of intramolecular general‐base‐catalyzed ethanolysis of ionized phenyl salicylate
Authors: Khan M. Niyaz , Audu A. A.
Published: January 2005

The reaction rates of ethanolysis of ionized phenyl salicylate, PS−, have been studied in the presence of different concentrations of various inorganic and organic salts in ethanol‐water solvent of different compositions. The observed pseudo first‐order rate constants,𝓀1, reveal a nonlinear increase with increase of thecontent of ethanol until it becomes ca. 85%, v/v. The rate constants, 𝓀1, begin to decrease with increase of ethanol content beyond ca. 85%, v/v. The observed data obtained at ethanol contents of <ca. 55%, v/v, follow the relationships 𝓀1 = 𝓀[EtOH]T/(1 + K[EtOH]T ) where 𝓀 and K represent the second‐order rate constant for thereaction of PS− with monomeric ethanol, EtOH, and association constant for dimerization of monomers of ethanol, respectively, and [EtOH]T is the total concentration of ethanol. The calculated values of 𝓀 and K obtained in the presence of 0.01 M tetraalkylammonium ions, R4N+, show ca. 15% and 40%, respectively, decrease with increase of the chain lengths of alkyl groups, R. The following conclusions have been derived from the observed data. (i) Lithium chloride causes ethanol structure‐making effect while NaCl, KCl, and CsCl show ethanol structure‐breaking effect. (ii) Tetraalkylammonium halide salts such as Me4NCl, Et4NI, andn‐Bu4NI reveal ethanol structure‐breaking effect due to the transfer of some water molecules from solvation shells of ethanol and R4N+ when favorable hydrophobic interaction between hydrophobic sites of ethanol and R4N+ results in. This effect is, however, partially off set by the direct interaction between monomeric ethanol and R4N+. Both inorganic and organic cations are preferentially solvated by only water molecules in EtOH‐H2O solvents with EtOH contents of <ca. 55%, v/v. The effects of 0.01 M LiOH on 𝓀1 values obtained within the ethanol content range of 35% to 97%, v/v, seemed to be unaffected due to the presence of 0.01 M NaCl.
Kinetics and mechanism of oxidation of excited state Tris‐(2,2′‐bipyridyl)‐ruthenium (II) complex by peroxomonosulfate, peroxodisulfate, and peroxodiphosphate
Authors: Venkatasubramanian Lakshmanan , Dharmalingam Periasamy , Maruthamuthu Pichai
Published: January 2005

Excitation of Ru(bipy)32+ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)33+. The kinetics of this photochemical oxidation of Ru(bipy)32+ by each peroxide was followed spectrophotometrically and found to obey a total second‐order, first‐order each in [Ru(bipy)32+] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)32+ occurred but only when at 1.0 M [H+] and > 10−2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)33+ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)32+] on the visible light induced oxidation of Ru(bipy)32+ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.
Toward a comprehensive mechanism for methanol pyrolysis
Authors: Norton T. S. , Dryer F. L.
Published: January 2005

A single kinetic mechanism for methanol pyrolysis is tested against multiple sets of experimental data for the first time. Data are considered from static, flow, and shock tube reactors, covering temperatures of 973 to 2000 K and pressures of 0.3 to 1 atmosphere. The model results are highly sensitive to the rates of unimolecular fuel decomposition and of various chain termination reactions that remove CH2OH and H radicals, as well as to experimental temperature uncertainties. The secondary fuel decomposition reaction CH3OH = CH2OH + H, which has previously been included only in mechanisms for high temperature conditions, is found to have a significant effect at low temperatures as well, through radical recombination. The reaction CH3O + C = CH3 + CO2, rather than CH3OH + H = CH3 + H2O, is found to be the dominant source of CH3 at low temperatures. The reverse of CH3 + OH = CH2OH + H is important to CH3 production at high temperatures.
A kinetic study of the autocatalytic permanganate oxidation of formic acid
Authors: Perez‐Benito Joaquin F. , Arias Conchita , Brillas Enrique
Published: January 2005

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations

The activation energies associated with the true rate constants, 𝓀, 𝓀, 𝓀, 𝓀, 𝓀, and 𝓀 are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol−1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed.
Kinetics of the reactions of O(3P) and Cl(2P) with HBr and Br2
Authors: Nicovich J. M. , Wine P. H.
Published: January 2005

A laser flash photolysis‐resonance fluorescence technique has been employed to study the kinetics of reactions (1)–(4) as a function of temperature.
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In all cases, the concentration of the excess reagent, i.e., HBr or Br2, was measured in situ in the slow flow system by UV‐visible photometry. Heterogeneous dark reactions between XBr (X = H or Br) and the photolytic precursors for Cl(2P) and O(3P) (Cl2 and O3, respectively) were avoided by injecting minimal amounts of precursor into the reaction mixture immediately upstream from the reaction zone. The following Arrhenius expressions summarize our results (errors are 2σ and represent precision only, units are cm3 molecule−1 s−1): 𝓀1 = (1.76 ± 0.80) × 10−11 exp[(40 ± 100)/T]; 𝓀2 = (2.40 ± 1.25) × 10−10 exp[−(144 ± 176)/T]; 𝓀3 = (5.11 ± 2.82) × 10−12 exp[−(1450 ± 160)/T]; 𝓀4 = (2.25 ± 0.56) × 10−11 exp[−(400 ± 80)/T]. The consistency (or lack thereof) of our results with those reported in previous kinetics and dynamics studies of reactions (1)–(4) is discussed.
A pyrolysis mechanism for ammonia
Authors: Davidson D. F. , Kohse‐Höinghaus K. , Chang A. Y. , Hanson R. K.
Published: January 2005

The mechanism of NH3pyrolysis was investigated over a wide range of conditions behind reflected shock waves. Quantitative time‐history measurements of the species NH and NH2were made using narrow‐linewidth laser absorption. These records were used to establish an improved model mechanism for ammonia pyrolysis. The risetime and peak concentrations of NH and NH2in this experimental database have also been summarized graphically.

Rate coefficients for several reactions which influence the NH and NH2profiles were fitted in the temperature range 2200 K to 2800 K. The reaction and the corresponding best fit rate coefficients are as follows:with a rate coefficient of 4.0 × 1013exp(−3650/RT) cm3mol−1s−1,with a rate coefficient of 1.5 × 1015T−0.5cm3mol−1s−1andwith a rate coefficient of 5.0 × 1013exp(−10000/RT) cm3mol−1s−1. The uncertainty in rate coefficient magnitude in each case is estimated to be ±50%. The temperature dependences of these rate coefficients are based on previous estimates.

The experimental data from four earlier measurements of the dissociation reactionwere reanalyzed in light of recent data for the rate of NH3+ H → NH21 + H2, and an improved rate coefficient of 2.2 × 1016exp(−93470/RT) cm3mol−1s−1in the temperature range 1740 to 3300 K was obtained. The uncertainty in the rate coefficient magnitude is estimated to be ± 15%.
Comment: A re‐evaluation of the rate constant for abstraction of hydrogen from isobutane by methyl radicals
Authors: Zhang H.‐X. , Back M. H.
Published: January 2005

The rate constant for abstraction of hydrogen from isobutane by methyl radicals has been re‐examined making use of new measurements at temperatures above 660 K. Most of the data over the temperature range 300–855 K can be accommodated by the following values for the rate constants for abstraction from primary and tertiary hydrogen atoms:

This activation energy for abstraction of the tertiary hydrogen atom in isobutane is essentially the same as expressed in a previous evaluation, which considered data only below 500 K, but the magnitude of the rate constant is about 0.25 log units greater.
High temperature pyrolysis of methane in shock waves. Rates for dissociative recombination reactions of methyl radicals and for propyne formation reaction
Authors: Hidaka Yoshiaki , Nakamura Takuji , Tanaka Hiroya , Inami Koji , Kawano Hiroyuki
Published: January 2005

The pyrolysis of 2% CH4 and 5% CH4 diluted with Ar was studied using both a single–pulse and time–resolved spectroscopic methods over the temperature range 1400–2200 K and pressure range 2.3–3.7 atm. The rate constant expressions for dissociative recombination reactions of methyl radicals, CH3 + CH3 → C2H5 + H and CH3 + CH3 → C2H4 + H2, and for C3H4 formation reaction were investigated. The simulation results required considerably lower value than that reported for CH3 + CH3 → C2H4 + H2. Propyne formation was interpreted well by reaction C2H2 + CH3 → P‐C3H4 + H with 𝓀 = 6.2 × 1012 exp(−17 kcal/RT) cm3 mol−1 s−1.
The mechanism of the homogeneous pyrolysis of acetylene
Authors: Kiefer John H. , Von Drasek William A. , Von Drasek William A.
Published: January 2005

The experimental literature on the pyrolysis of C2H2 is reviewed and summarized. These observations divide naturally into three temperature regimes: (i) T < 1100 K, where the homogeneous reaction is a molecular polymerization; (ii) 1100 < T < 1800 K, where the process is still dominated by a molecular polymerization, but a fragment radical chain is clearly involved; and (iii) T > 1800 K, where a fragment chain carried by C2H and H drives a polymerization to polyacetylenes. A combined molecular/fragment chain mechanism is developed and applied to the modeling of three shock‐tube studies which span the two higher‐temperature regimes. The core of the mechanism is a set of 5 mainly molecular reactions whose rates are derived from an application of unimolecular rate theory and detailed balance to recent measurements on the decomposition of vinylacetylene. The combination of this core with consequent fragment radical reactions provides a satisfactory description of most features of the chosen experiments including several‐isotope exchange, hydrogenation to C2H4, and C6H2 formation‐which are almost entirely the result of fragment radical chain reaction. Possible detailed paths for the molecular dimerization are suggested and some possible molecular paths for the “Berthelot synthesis” of benzene are also proposed.
UV‐Absorption spectrum of the methylperoxy radical and the kinetics of its disproportionation reaction at 300 K
Authors: Simon Franz‐Georg , Schneider Wolfgang , Moortgat Geert K.
Published: January 2005

Molecular modulation spectroscopy combined with ultraviolet spectroscopic techniques have been used to observe the behavior of the CH3O2 radicals generated in the gas phase by near‐ultraviolet modulated photolysis of flowing Cl2CH4O2 mixtures. The kinetics of the disproportionation reaction (1)
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and the absorption cross‐sections of CH3O2 were measured by computer fitting of the modulated absorption traces obtained in the wavelength range 220 to 270 nm at 300 K and 240 torr. The rate constant for the elementary self‐reaction 𝓀1 = 𝓀1(a) + 𝓀1(b) + 𝓀1(c) was determined to be (3.61 ± 0.55) × 10−13 cm3 molecule−1 s−1. The parameter 𝓀obs/σ (where 𝓀obs is the observed apparent second‐order rate constant) was measured from the decay curves in the dark phase of the modulated photolysis period in the wavelength range 230–260 nm, and had a value 1.16 × 105 cm2 s−1 at 250 nm. At 250 nm the absorption cross‐section was determined as σ(CH3O2) = 4.14 × 10−18 cm2 molecule−1, leading to a value of 𝓀obs, = (4.8 ± 0.5) × 10 13 cm3 molecule−1 s−1. In addition, the absorption spectrum of CH3O2 was measured in the range 210–295 nm using diode array spectroscopy. A detailed review of all previous studies concerning the kinetics and spectrum of the CH3O2 radical is presented, and a recommended spectrum, representing an average from selected recent studies, is proposed.
The rate constant for the intramolecular isomerization of pentyl radicals
Authors: Marshall Roger M.
Published: January 2005

The thermal decomposition of n‐pentane has been investigated in the temperature range 737 to 923 K. Making various assumptions, the detailed distribution of major products (methane, ethane, ethene, propene, and 1‐butene) is used to evaluate the rate constant for the unimolecular isomerization
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which proceeds via a five‐membered, cyclic transition state. Two alternative sets of assumptions are used. Common to both of them are assumptions concerning the thermochemistry and rate constants for decomposition of the C5H11 radicals. Method 1 assumes that all secondary CH bonds are equally reactive towards hydrogen abstraction in which case, in addition to the value of 𝓀10, the ratio of the rate constants for abstraction from primary and secondary CH bonds is evaluated. Values about a factor of two higher than published values for similar molecules are obtained. The alternative, method 2, assumes that the ratio of abstraction from the 1‐ and 2‐ positions of n−pentane is the same as that published for n−butane, in which case, in addition to the value of 𝓀10, the ratio of the rates of abstraction from the 3‐ and 2‐ positions of n‐pentane is obtained. The value obtained is 0.401 which is to be compared with the statistically expected (and assumed in method 1) 0.5. Detailed discussions of the values of 𝓀10 obtained leads to the conclusion that method 1 leads to the best value

where θ = 2.303RT in kcal/mol and error limits are two standard deviations. Combination of this value with values recalculated from published lower temperature data gives

which, it is concluded, is the best value in the range 438 to 923 K.
Kinetics and products of the gas‐phase reactions of the OH radical and O3 with allyl chloride and benzyl chloride at room temperature
Authors: Tuazon Ernesto C. , Atkinson Roger , Aschmann Sara M.
Published: January 2005

The kinetics of the gas‐phase reactions of allyl chloride and benzyl chloride with the OH radical and O3 were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of 𝓀(O3 + allyl chloride) = (1.60 ± 0.18) × 10−18 cm3 molecule−1 s−1 and 𝓀(O3 + benzyl chloride) < 6 × 10−20 cm3 molecule−1 s−1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of 𝓀(OH + allyl chloride) = (1.69 ± 0.07) × 10−11 cm3 molecule−1 s−1 and 𝓀(OH + benzyl chloride) = (2.80 ± 0.19) × 10−12 cm3 molecule−1 s−1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT‐IR absorption spectroscopy indicated that the co‐products ClCH2CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH2CHO, (ClCH2)2CO, and CH2  CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH2CHO and the CH2Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ⩽4%, respectively), with the remainder of the products being unidentified.
cis‐RuCl2(DMSO)4‐catalyzed oxidation of sulfides by N‐methylmorpholine N‐oxide (NMO)
Authors: Caroling G. , Rajaram J. , Kuriacose J. C.
Published: January 2005

The induction period observed in the cis‐RuCl2(DMSO)4 catalyzed oxidation of thioethers (S) to sulfoxides by N‐methylmorpholine N‐oxide (NMO) is attributed to the rate of formation of the active species viz. RuCl2(DMSO)3S. Cyclic voltammetric studies indicate formation of the RuIV = 0 species. Based on the variable orders in NMO and first order in each of the other reactants, a mechanism is proposed where the active species generated in situ reacts with NMO in a slow step to form RuIV oxo complex which then decomposes to give the product.
Kinetic modeling of the reactions of C3H3+ with acetylene, deuteroacetylene, and diacetylene
Authors: Wiseman Floyd L. , Ozturk Feza , Zerner Michael C. , Eyler John R.
Published: January 2005

The reactions of ℓ‐C3H3+ (propargylium cation) with acetylene and diacetylene have been modeled kinetically. Data were obtained from Fourier Transform Ion Cyclotron Resonance (FTICR) experiments on these systems, which are themselves models for soot particle initiation. Acetylene forms an encounter complex with ℓ‐C3H3+, but, in the absence of a third body collision, the complex decomposes to acetylene and c‐C3H3+ (cyclopropenylium cation) at about 1/3 the rate it decomposes to acetylene and ℓ‐C3H3+, in spite of the fact that c‐C3H3+ is ca. 115 kJ/mol more stable than ℓ‐C3H3+. The encounter complex is long enough lived, and energetic enough, to scramble deuterium in reactions between ℓ‐C3H3+ and C2D2. These reactions have been successfully modeled, yielding a nearly statistical distribution of deuterium, and a rather large kinetic isotope effect. The more complex reactions of ℓ‐C3H3+ with diacetylene have also been modeled.
A product study of the gas‐phase reaction of Isoprene with the OH radical in the presence of NOx
Authors: Tuazon Ernesto C. , Atkinson Roger
Published: January 2005

The gas‐phase reaction of isoprene with the OH radical, in the resence of NOx, was investigated at 298 ± 2 K and atmospheric pressure of air by long path length FT‐IR spectroscopy. The primary products identified and their formation yields were: methacrolein, 0.21 ± 0.05; methyl vinyl ketone, 0.29 ± 0.07; and HCHO, with the observed yield being consistent with the sum of the methacrolein and methyl vinyl ketone yields. Combined with the previously reported yield of 0.044 ± 0.006 for 3‐methylfuran, these products accounted for 55 ± 9% of the isoprene which reacted. Under conditions where the dark reaction of isoprene with NO2is not significant, the balance of the isoprene consumed could possibly be accounted for by the “organic nitrates” and “other carbonyl compounds” formed in estimated overall yields of ca. 12% and ca. 25%, respectively.
Effect of solvent on the reactions of coordination complexes: Part 15: Base hydrolysis ofCis‐(Chloro)(benzimidazole)‐Bis‐(ethylenediamine)cobalt(III) ion in mixed solvent media
Authors: Dash Anadi C. , Dash Neelamadhab
Published: January 2005

The kinetics of base hydrolysis ofthecis‐(chloro)‐(benzimidazole)bis(ethylenediamine) cobalt(III) ion was investigated in Methanol‐water and Ethyleneglycol‐water media of varying compositions and at isodielectric conditions(Ds ≃ 61 at 25°C) in isopropanol‐ and Acetonitrile‐water media at 35°C in the pH range, 7.2–8.9. It is of interesttonote that the aquation rate constant of the conjugate base, cis‐[Co(en)2(bzm)Cl]+ (Bzm = N H deprotonated benzimidazole, en = ethylenediamine) is virtually insensitive to the compositions of the mixed solvents studied, unlike the aquation rate constant of the conjugate acid form of the title complex. This is indicative of a true dissociative mode of activation (Dcb) of the conjugate base.
Kinetics and mechanism of oxidation of indigo carmine by hypohalites
Authors: Puttaswamy  , Mahadevappa D. S. , Gowda N. M. Made
Published: January 2005

Kinetics of oxidation of indigo carmine (IC) by sodium hypohalites, NaOX (X  Cl or Br), in alkaline buffer of pH 9–11 has been studied spectrophotometrically at λ = 610 nm. The experimental rate law obtained is −d[IC]/dt = k[OX−][IC][OH−]x where x <1. Variation of ionic strength or dielectric constant of the medium had no effect on the reaction rate while the addition of halide ions slightly retarded the rate. A most plausible mechanism proposed on the basis of experimental results involves the formation of isatin sulphonate which undergoes further oxidation to anthranilate. Activation parameters have been evaluated.
Kinetics and mechanism of chloramine‐T oxidation of cinnamaldehyde in two acid media
Authors: Mythily C. K. , Rangappa K. S. , Made Gowda N. M.
Published: January 2005

Kinetics of oxidation of cinnamaldehyde (Cinn) by chloramine‐T (CAT) has been studied in solutions containing HCl and H2SO4 at 313 K. The respective experimental rate laws obtained in HCl and H2SO4 media are as follows:
equation image
and
equation image

Here the value of x varies from 0.9 to zero while the values of y and z are 0.83 and 0.72, respectively. Effects, on the reaction rate, of ionic strength, reaction product (p‐toluenesulfonamide), dielectric constant of the solvent medium, and the anions, Cl− and SO42−, have been investigated. Activation parameters have been computed, based on the rate constants determined at different temperatures. Mechanisms proposed and the rate laws derived are consistent with the observed kinetic data represented by the experimental rate laws.
Kinetic study of some reactions related to the Mn(II)‐catalyzed bromate‐saccharide oscillating reactions
Authors: Ou Chin‐chou , Jwo Jing‐jer
Published: January 2005

In the stirred batch experiment, the Mn(II)‐catalyzed bromate‐saccharide reaction in aqueous H2SO4 or HClO4 solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second‐order rate constants of the Mn(III)‐saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M−1 s−1 in 1.00 M H2SO4 and (4.69, 7.51, 10.2, 13.5, and 36.2) M−1 s−1 in (2.00–4.00) M HClO4 for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo‐first‐order rate constant of the Mn(III)‐Br− reaction is kobs = (0.2 ± 0.1) [Br−] + (130 ± 5)[Br−]2 + (2.6 ± 0.1) × 103[Br−]3 + (1.2 ± 0.2) × 104[Br−]4 s−1 and the rate constant of the Br2Mn(II) reaction is less than 1 × 10−4 M−1 s−1. The second‐order rate constants of the Br2‐saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10−4 M−1 s−1 at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.
Kinetics of the solvolysis of [Co(3Rpy)4Cl2]+ (R = Me or Et) in water + propan‐2‐ol mixtures
Authors: El‐subruiti Gehan M. , Wells Cecil F. , Sidahmed Ibrahim M.
Published: January 2005

Rates of solvolysis of complex ions [Co(3Rpy)4Cl2]+ with R = Me and Et have been determined in mixtures of water with the hydrophobic co‐solvent propan‐;2‐ol for a range of temperatures. The variations of the enthalpies and entropies of activation with the solvent composition have been correlated with the physical properties of the solvent and it has been shown that the linear plot found for ΔH* against ΔS* in water + propan‐2‐ol is coincident with that found for water + methanol mixtures. A free energy cycle has been applied to the dissociative‐type process of initial state (Cn+) going to the transition state (M(n+1)+…‥ Cl−) using values for the free energy of transfer of the chloride ion from water into the mixture, ΔG(Cl−), derived from the solvent sorting technique or from the TATB/TPTB method. Irrespective of the source of ΔG(Cl−), it is found that ΔG(Co(3Rpy)4Cl2+*) ca. ΔG(Co(3Rpy)4Cl2+) (where * indicates a species in the transition state) for mol fractions of propan‐2‐ol x2 ≳ 0.04–0.05 with ΔG(Co(3Rpy)4Cl2+*) becoming increasingly more negative than ΔG(Co(3Rpy)4Cl2+) as x2 increases above 0.05. These variations are compared with those for the solvolysis of the same ions in water + methanol mixtures and of a range of other ions in water + propan‐2‐ol mixtures. It is concluded that, using values for ΔG(Cl−) from either source, the stabilizing influence of changes in solvent structure is greater on the cation in the transition state than on the cation in the initial state for the solvolyses of complexes [Co(Rpy)4Cl2+] and [Coen2LCl]n+.
A shock tube study of the reactions of NH with NO, O2, and O
Authors: Mertens John D. , Chang Albert Y. , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

The reactions of NH(X3Σ−) with NO, O2, and O have been studied in reflected and incident shock wave experiments. The source of NH in all the experiments was the thermal dissociation of isocyanic acid, HNCO. Time‐histories of the NH(X3Σ) and OH(X2Π) radicals were measured behind the shock waves using cw, narrow‐linewidth laser absorption at 336 nm and 307 nm, respectively. The second‐order rate coefficients of the reactions:
equation image
were determined to be:

and

cm3 mol−1 s−1, where ƒ and F define the lower and upper uncertainty limits, respectively.

The branching fraction of channel
equation image
defined as k3b/k3total, was determined to be 0.19 ± 0.10 over the temperature range of 2940 K to 3040 K.
Kinetics and mechanism of oxidation of hydrazinium ion with peroxomonophosphoric acid in acid perchlorate solutions and role of trace iodide ions
Authors: Dhas T. Peter Amala , Mishra D. K. , Mittal R. K. , Gupta Y. K.
Published: January 2005

The reaction of peroxomonophosphoric acid and hydrazinium ion in acid perchlorate solutions occurs as per stoichiometry (i), and the rate law (ii) at large [N2H5 +],
equation image
where K′d is the first acid dissociation constant of H3PO5 and k 1 and k 2 are rate constants found to be 2.6 × 10−4 s−1 and 5.0 × 10−2 M−1 s−1, respectively, at 35°. The reaction is greatly catalyzed by iodide ions. The mechanism involves a redox cycle I−/I2 and the rate is independent of [N2H5 +] in the presence of iodide ions. K′d was found to be 0.55 M−1 and independent of temperature.
Kinetics of the reactions of the IO radical with dimethyl sulfide, methanethiol, ethylene, and propylene
Authors: Maguin F. , Mellouki A. , Laverdet G. , Poulet G. , Bras G. Le
Published: January 2005

The reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6 have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3 → products (1): k1 = (1.5 ± 0.2) × 10−14; IO + CH3SH → products (2): k2 = (6.6 ± 1.3) × 10−16; IO + C2H4 →products (3): k3 < 2 × 10−16; IO + C3H6 → products (4): k4 < 2 × 10−16 (units are cm3 molecule−1 s−1). CH3S(O)CH3 and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k1 compared to our previous determination is discussed.
Kinetic modeling of the reduction of nitric oxide in combustion products by isocyanic acid
Authors: Miller James A. , Bowman Craig T.
Published: January 2005

The RAPRENOx process for NO reduction in combustion products involves reaction of nitric oxide with isocyanic acid. We have developed a mechanism for the gas‐phase reaction of isocyanic acid with nitric oxide in the presence of various amounts of O2, H2O, and CO. Kinetics calculations using the mechanism are compared with the experimental data of Siebers and Caton, and the model reproduces all trends of these data. Sensitivity and rate‐of‐production analyses show that the reactions of HNCO with OH, O, and H play a major role in the NO‐removal process and that NO removal occurs primarily by reaction of NO with NCO to form N2O, which subsequently reacts slowly to form N2. The overall reaction is critically dependent on production of radicals. When O2, H2O, and CO are present, the radicals are supplied by the moist‐CO chain branching sequence. When any of these species is absent, radicals must be supplied by other reactions, principally the N2O decomposition reaction and the reaction of the NH2 radical with NO.