Showing papers in "International Journal of Chemical Kinetics in 1984"

Pyrolysis of methyl chloride, a pathway in the chlorine-catalyzed polymerization of methane

Abstract: The reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 - initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol):

An Investigation of the Dark Formation of Nitrous Acid in Environmental Chambers

Abstract: The formation of nitrous acid (HONO) in the dark from initial concentrations of NO2 of 0.1–20 ppm in air, and the concurrent disappearance of NO2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300- and 5800-L volume (both with surface/volume ratios of 3.4 m−1). In these environmental chambers the initial HONO formation rate was first order in the NO2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-order consumption rate of NO2 was (2.8 ± 1.2) × 10−4 min−1 in the 5800-L Teflon-coated evacuable chamber and (1.6 ± 0.5) × 10−4 min−1 in a 4300-L all-Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO2 reacted in the evacuable chamber and ca.10–30% in the all-Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NOx− organic-air mixtures, and of HONO formation in polluted atmospheres, are discussed.

The high temperature oxidation of the methyl side chain of toluene

Abstract: From the results of order of magnitude analyses, it is concluded that during the oxidation of toluene, radical-atom and radical-radical reactions (1) and (3) play an unusually important and approximately equal role in the formation of benzaldehyde, an intermediate that leads eventually to the complete removal of the side chain. An additional radical-radical system, reaction (2), is shown to be the most likely source of benzyl alcohol observed during toluene oxidation.

Rate constants for the reaction of OH radicals with a series of alkenes and dialkenes at 295 ± 1 K

Abstract: Using a relative rate technique, rate constants for the gas phase reactions of the OH radical with n-butane, n-hexane, and a series of alkenes and dialkenes, relative to that for propene, have been determined in one atmosphere of air at 295 ± 1 K. The rate constant ratios obtained were (propene = 1.00): ethene, 0.323 ± 0.014; 1-butene, 1.19 ± 0.06; 1-pentene, 1.19 ± 0.05; 1-hexene, 1.40 ± 0.04; 1-heptene, 1.51 ± 0.06; 3-methyl-1-butene, 1.21 ± 0.04; isobutene, 1.95 ± 0.09; cis-2-butene, 2.13 ± 0.05; trans-2-butene, 2.43 ± 0.05; 2-methyl-2-butene, 3.30 ± 0.13; 2,3-dimethyl-2-butene, 4.17 ± 0.18; propadiene, 0.367 ± 0.036; 1,3-butadiene, 2.53 ± 0.08; 2-methyl-1,3-butadiene, 3.81 ± 0.15; n-butane, 0.101 ± 0.012; and n-hexane, 0.198 ± 0.017. From a least-squares fit of these relative rate data to the most reliable literature absolute flash photolysis rate constants, these relative rate constants can be placed on an absolute basis using a rate constant for the reaction of OH radicals with propene of 2.63 × 10−11 cm3 molecule−1 s−1. The resulting rate constant data, together with previous relative rate data from these and other laboratories, lead to a self-consistent data set for the reactions of OH radicals with a large number of organics at room temperature.

High‐temperature kinetics of thermal decomposition of acetic acid and its products

Abstract: Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300–1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.

The role of electronically excited states in recombination reactions

Abstract: Methods are described for including the participation of bound electronically excited states in calculations on radical recombination reactions. These methods are illustrated by applying them to the reactions For O2, accurate ab initio potentials are used in calculations which show that the electronic degeneracy and long-range part of the potential are likely to be crucial in determining the contribution of a given electronic state to the overall reaction, as long as the state is not so weakly bound that it dissociates thermally before being electronically quenched. Weak collision effects are allowed for using a Monte Carlo technique and an assumed exponential form for the distribution of energies transferred in collisions with a third body. For larger systems it is evident that the role of bound excited states in the low-pressure regime falls rapidly as the size of the system increases. As the high-pressure limit is approached, however, the contribution of excited states is likely to come close to that expected simply on the basis of electronic degeneracy.

Kinetics of rich ammonia flames

Abstract: We report laser absorption measurements of NH3 decay within the flame front region of rich, atmospheric pressure ammonia flames. These data are combined with earlier OH, NH, and NH2 measurements to obtain new estimates for the oscillator strength of NH2. This value, fi = 6.4 × 10−5 for the PQ1,7 line in the (0,9,0) (0,0.0) vibrational band of the A2A1 X2B1 transition, suggests ΔH(NH) ≅ 87 kcal/mol. The ammonia profiles were also combined with previous data on NO, NH, NH2, and OH to provide an extensive database at fuel equivalence ratios (o) of 1.28, 1.50, and 1.81 for comparison to our kinetic model predictions. This modeling used a one-dimensional flame code which explicitly accounts for the diffusional component in our flame experiments. Modeling results using a conventional mechanism predicted concentration profiles which deviated markedly from our observations. It was possible to obtain much more satisfactory fits by postulating reactions between various NHi (i = 1, 2) species to form N—N bonds. The N2Hj (j = 1–3) species could then lose H atoms via dissociation to ultimately form N2. Inclusion of these reactions in the mechanism allowed us to predict concentration—distance profiles for five different species at three different equivalence ratios that are in good agreement with experiment. The most important component of this mechanism is the recognition that the NHi + NHi reactions dominate the kinetics in rich flames. A most satisfying aspect of these calculations is that the key rate constants in the NHi + NHi sequence were estimated using simple RRK theory.

Gas phase reaction of NO2 with alkenes and dialkenes

Abstract: The kinetics of the gas phase reactions of NO2 with a series of organics have been studied at 295 ± 2 K. It was observed that only 2,3-dimethyl-2-butene and the conjugated dialkenes studied reacted at observable rates, with rate constants which ranged from 1.5 × 10−20 cm3 molecule−1 s−1 for 2,3-dimethyl-2-butene to 1.3 × 10−17 cm3 molecule−1 s−1 for α-phellandrene. These rate constants are compared with the available literature data and the mechanisms of these reactions are discussed.

Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO

Abstract: The yields of C5 and C6 alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH3ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10−12 cm3 molecule−1 s−1, these OH radical rate constants are (in units of 10−12 cm3 molecule−1 s−1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO2 radicals reacting with NO to form RONO2) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.

Kinetics of the gas‐phase reactions of NO3 radicals with a series of aromatics at 296 ± 2 K

Abstract: Rate constants have been determined at 296 ± 2 K for the gas phase reaction of NO3 radicals with a series of aromatics using a relative rate technique. The rate constants obtained (in cm3 molecule−1 s−1 units) were: benzene, <2.3 × 10−17; toluene, (1.8 ± 1.0) × 10−17; oxylene, (1.1 ± 0.5) × 10−16; mxylene, (7.1 ± 3.4) × 10−17; pxylene, (1.4 ± 0.6) × 10−16; 1,2,3-trimethylbenzene, (5,6 ± 2.6) × 10−16; 1,2,4-trimethylbenzene (5.4 - 2.5) × 10−16; 1,3,5-trimethylbenzene, (2.4 ± 1.1) × 10−16; phenol, (2.1 ± 0.5) × 10−12; methoxybenzene, (5.0 ± 2.8) × 10−17; o-cresol, (1.20 ± 0.34) × 10−11; m-cresol, (9.2 ± 2.4) × 10−12; p-cresol, (1.27 ± 0.36) × 10−11; and benzaldehyde, (1.13 ± 0.25) × 10−15. These kinetic data, together with, in the case of phenol, product data, suggest that these reactions proceed via H-atom abstraction from the substituent groups. The magnitude of the rate constants for the hydroxy-substituted aromatics indicates that the nighttime reaction of NO3 radicals with these aromatics can be an important loss process for both NO3 radicals and these organics, as well as being a possible source of nitric acid, a key component of acid deposition.

Kinetics of OH reactions with aliphatic thiols

Abstract: The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10−11 cm3 molecule−1 s−1, -Eact = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10−11 cm3 molecule−1 s−1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.

Kinetics of OH reactions with furan, thiophene, and tetrahydrothiophene

Abstract: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254–425 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule−1 S−1): k1 = (1.33 ± 0.29) × 10−11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10−12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10−11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.

Kinetics of the reaction of OH with pernitric and nitric acids

Abstract: The absolute rate constants for the reactions of OH + HO2NO2 (1) and OH + HNO3 (2) have been measured with the technique of flash photolysis resonance fluorescence over the temperature ranges of 240–330 K at 760 torr He for reaction (1) and of 240–370 K at 50 and 760 torr He for reaction (2). Reactant concentrations were monitored continuously by ultraviolet and infrared spectrophotometry. The data can be fitted to the following Arrhenius expressions: These results are in very good agreement with recent studies of reaction (2), and also of reaction (1) at 295 K.

Shock tube study of cyanogen oxidation kinetics

Abstract: Mixtures of cyanogen and nitrous oxide diluted in argon were shock-heated to measure the rate constants of A broad-band mercury lamp was used to measure CN in absorption at 388 nm [B2Σ+(v = 0) X2Σ+(v = 0)], and the spectral coincidence of a CO infrared absorption line [v(2 1), J(37 38)] with a CO laser line [v(6 5), J(15 16)] was exploited to monitor CO in absorption. The CO measurement established that reaction (3) produces CO in excited vibrational states. A computer fit of the experiments near 2000 K led to An additional measurement of NO via infrared absorption led to an estimate of the ratio k5/k6: with k5/k6 ≃ 103.36±0.27 at 2150 K. Mixtures of cyanogen and oxygen diluted in argon were shock heated to measure the rate constant of and the ratio k5/k6 by monitoring CN in absorption. We found near 2400 K: and The combined measurements of k5/k6 lead to k5/k6 ≃ 10−3.07 exp(+31,800/T) (±60%) for 2150 ≤ T ≤ 2400 K.

Sensitivity analysis in chemical kinetics: Recent developments and computational comparisons

Abstract: The advantages and disadvantages of various methods of parametric sensitivity analysis in chemical kinetic modeling are discussed. Particular attention is given to estimates of computational labor for realistic problems, and quantitative comparisons are made utilizing a 52-reaction, 11-species CO oxidation mechanism. The authors′ CHEMSEN/AIM program compares favorably to other techniques in many circumstances, and provides the additional convenience of accepting input information in familiar chemical notation. This paper also reviews recent developments in theory of sensitivity analysis, relevant to chemical kinetic modeling.

Kinetics of the reaction of oh radicals with a series of branched alkanes at 297 ± 2 K

Abstract: Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10−12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2-methylbutane, 3.97 ± 0.11; 2,2-dimethylbutane, 2.66 ± 0.08; 2-methylpentane, 5.68 ± 0.24; 3-methylpentane, 5.78 ± 0.11; 2,2,3-trimethylbutane, 4.21 ± 0.08; 2,4-dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3-tetramethylbutane, 1.06 ± 0.08; and 2,2,4-trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2-dimethylbutane, 2,4-dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.

High temperature study of the reactions of O and OH with NH3

Abstract: Mixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750–2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration—time histories. The early-time NH3 and OH concentration profiles were sensitive to the rate constants of the reactions leading to the following best-fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(−4470/T) and k3 = 1013.91±0.2 exp(-4230/T) cm3 mol−1 s−1. The results of this study combined with previous low-temperature data suggest a significant non-Arrhenius behavior for both k2 and k3.

The rate of the reaction of OH with HCl

Abstract: Using the techniques of laser/flash photolysis-resonance fluorescence, the absolute rate constant for the OH + HCl reaction is measured from 240 to 295 K. Ultraviolet and infrared spectrophotometry are used to continuously monitor the HCl concentrations. It is shown that the rate constant values obtained in the study are 20-30 percent larger than those recommended by Smith and Zellner (1974) and Ravishankara et al. (1977) for modeling of stratospheric chemistry.

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Abstract: Rate constants for the reactions of O3 and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O3 with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10−21 cm3/molecule · s, (1.43 ± 0.15) × 10−20 cm3/molecule · s, and (1.97 ± 0.26) × 10−20 cm3/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3/molecule · s, were determined to be (8.8 ± 1.4) × 10−13 cm3/molecule · s, (6.21 ± 0.31) × 10−12 cm3/molecule · s, and (8.25 ± 0.23) × 10−12 cm3/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.

Kinetics and mechanism of diethanolamine degradation in aqueous solutions containing carbon dioxide

Abstract: The problem of diethanolamine (DEA) degradation in gas-treating processes was quantified through a detailed kinetic study. This reaction was found to be catalyzed by CO2, and degradation occurs in a successive manner to 3-(2-hydroxyethyl)oxazolidone-2, to N,N,N′-tris(2-hydroxyethyl)ethylenediamine and then to N,N′-bis(2-hydroxyethyl)piperazine. A reaction mechanism consistent with these observations was proposed and tested through kinetic analyses. A satisfactory kinetic model which can be of practical use was derived.

Rate constant for the OH + CO reaction: Pressure dependence and the effect of oxygen

Abstract: The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10 percent. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40 percent at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

The heat of formation of the ethyl radical

Abstract: An examination of the results of measurements of the forward and reverse rate constants for the reaction shows that agreement between the kinetics and the thermochemistry is achieved only through use of a value of ΔHf(C2H5) = 28 kcal mol−1. This system therefore provides further support for the recent measurement of this quantity.

A pulse radiolysis study of I and (SCN) in aqueous solutions over the temperature range 15–90°C

Abstract: The extinction coefficients and the decay kinetics of I2 and (SCN)2 have been characterized over the 15-90C-temperature range. The extinction coefficients of I2 at 385 and 725 nm were determined to be 10,000 and 2560M cm , respectively, based on the extinction coefficient of (SCN)2 at 475 nm being equal to 7600M cm . At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I2 and (SCN)2 was found to be a function of I and SCN concentration, respectively, as well as temperature. 28 references, 5 figures.

The very‐high‐temperature pyrolysis of ethane: Evidence against high rates for dissociative recombination reactions of methyl radicals

Abstract: The pyrolysis of 1 and 2% ethane in krypton has been studied in shock waves by the laser-schlieren technique over 1700–4800 K. For 2400–2800 K an effective zero density gradient is seen following the rapid dissociation of the ethane. Through simulation with various mechanisms it is evident that the high rates for the dissociative recombination reactions of methyl radicals obtained in recent shock-tube studies, are incompatible with this observation; these rates must be reduced at least an order of magnitude. On the basis of theory and previous low-temperature (T) measurements, k = 7.8 × 1011 (-6562/T) (cm3/mol s) is recommended for the second of these reactions.

Kinetics of the reactions of CCl3 with O and O2 and of CCl3O2 with NO at 295 K

Abstract: The reactions of CCl3 with O(3P) and O2 and those of CCl3O2 with NO have been studied at 295 K using discharge flow methods with helium as the bath gas. The rate coefficient for the reaction of CCl3 with O was found to be (4.2 ± 0.6) × 10−11 cm3/s and that for CCl3O2 with NO was (18.6 ± 2.8) × 10−12 cm3/s with both coefficients independent of [He]. For reaction between CCl3 and O2 the rate coefficient was found to increase from 1.51 7times; 10−14 cm3/s to 7.88 × 10−14 cm3/s as the [He] increased from 3.5 × 1016 cm−3 to 2.7 × 1017 cm−3. There was no evidence for a direct two-body reaction, and it is concluded that the only product of this reaction is CCl3O2. Examination of these results for CCl3 + O2 in terms of current simplified falloff treatment suggests that the high-pressure limit for this reaction is ∼ 2.5 × 10−12 cm3/s, which may be compared with a direct measurement of the high-pressure limit of 5 × 10−12 cm3/s. A value of (5.8 ± 0.6) × 10−31 cm6/s has been obtained for k0, the coefficient in the low-pressure region. This value is compared with corresponding values found earlier for the (CH3, O2) and (CF3, O2) systems and with estimates based on unimolecular rate theory.

Rate constants for the reactions of OH radicals with alkyl substituted olefins

Abstract: Relative rate constants for the reactions of hydroxyl radicals with a series of alkyl substituted olefins were measured by competitive reactions between pairs of olefins at 298 ± 2 K and 1 atmospheric pressure. Hydroxyl radicals were produced by the photolysis of H2O2 with 254-nm irradiation. The obtained rate constants were (× 10−11 cm3 molecule−1 s−1): 2.53 ± 0.06, propylene; 5.49 ± 0.17, cis-2-butene; 5.47 ± 0.1, isobutene; 6.46 ± 0.13, 2-methyl-1-butene; 6.37 ± 0.16, cis-2-pentene; 6.23 ± 0.1, 2-methyl-1-pentene; 8.76 ± 0.14, 2-methyl-2-pentene; 6.24 ± 0.08, trans-4-methyl-2-pentene; 10.3 ± 0.1, 2,3-dimethyl-2-butene; 9.94 ± 0.1, 2,3-dimethyl-2-pentene; 5.59 ± 0.07, trans-4,4-dimethyl-2-pentene. A trend in alkyl substituent effect on the rate constant was found, which is useful to predict kOH on the basis of the number of alkyl substituents on the double bond.

High‐pressure range of the recombination O + O2 → O3

Abstract: The recombination reaction O + O2 O3 was studied by laser flash photolysis of pure O2 in the pressure range 3–20 atm, and of N2OO2 mixtures in the bath gases Ar, N2, (CO2, and SF6) in the pressure range 3–200 atm. Fall-off curves of the reaction have been derived. Low-pressure rate coefficients were found to agree well with literature data. A high-pressure rate coefficient of k∞ = (2.8 ± 1.0) × 10−12 cm3 molecule−1 s−1 was obtained by extrapolation.

Kinetics and equilibria of the reaction between bromine, and ethyl ether. The C-H bond dissociation energy in ethyl ether

Abstract: The kinetics and equilibria of the reaction: have been studied in the temperature range 298–333 K by using the very low pressure reactor (VLPR) technique. Combining the estimated entropy change of reaction (1), ΔS = 8.1 ± 1.0 eu, with the measured ΔG, we find ΔH = 4.2 ± 0.4 kcal/mol; ΔH(CH3CHOC2H5) = −20.2 kcal/mol, and DH° [Et OCH(Me)-H] = 91.7 ± 0.4 kcal/mol. We find: where θ = 2.3 RT in kcal/mol. It has been shown that the reaction proceeds via a loose transition state and the “contact TS” model calculation gives a very good agreement with the observed value.

Updated chemical mechanism for atmospheric photooxidation of toluene

Abstract: A new reaction mechanism describing the atmospheric photochemical oxidation of toluene is formulated and tested against environmental chamber data from the University of California, Riverside, Statewide Air Pollution Research Center (SAPRC). On simulations of toluene—NO_x and toluene—benzaldehyde—NO_x irradiations, the average predicted O_3 and PAN maxima are within 3% of the experimental values. Simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. Specific areas that are investigated include benzaldehyde photolysis, organic nitrate formation, alternate ring fragmentation pathways, and conjugated γ-dicarbonyl condensation to the aerosol phase.

A shock tube study of the reaction of the hydroxyl radical with propane

Abstract: The rate coefficient for the reaction of the hydroxyl radical, OH, with propane has been measured at 1220 K in shock tube experiments, and a value of (1.58 ± 0.24) × 1013 cm3/mol s was obtained. This measured value is compared with previous experimental results and a transition-state theory calculation.