Showing papers in "International Journal of Chemical Kinetics in 1985"

Principal component analysis of kinetic models

Abstract: An €igenvalue-eiservect r aDalFis b ued lo exrra.r neaninsful kineric i omario, fhm linea. *nsitjvity @ficienl5 cohputad for eler.l speci€s of. reactiry 3Fr€n at evenl line points. The main advaDtag€ ofrhis Fethod lies in i!3 abitit' t! evesl th6e pait! of the Dechanish which @n.isr of strcnsly inre.acrins reacrio.s, md to indicai€ their importlnce wtbin rh€ nechsdsm. Results @n be usad ro &lve three seneral kinetic problems. FiBrly, an objelive condirjon fo. consrructing a hiDimat reaction *l b pres€nt d. S€condly, rhe uDcover.d depeDdencies 6mon8ltr p6ram€ieE arc shown Lo confm or deny lalidily of quasi,sready{tlt€ ldsunptjoB !nde! lhe @nsidered ex!€rimenral mndtions. Thirdty, rlkitrs inro a.@uDr only *tu ivities of obeded speci$, the snalysis b u@d to yield eftr estimtes on unknoh Dsam€reB dete@ined frch the exp€rimeDt6l obsftaiion!, 6nd t sug8et the pe@et€rs thar $ould b€ k.pt 6xed in the e.lihaiion pro.edure. To illustEre pe cho* rhe wel.knom hydrcsen-brcmine raction end the kiDeti@ of fomaldehyde oridarioD i! the Dresnce ofCO.

Kinetics of the gas phase reaction of Cl atoms with a series of organics at 296±2 K and atmospheric pressure

Abstract: Using a relative rate technique, rate constants have been determined for the gas phase reactions of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure of air. Using a rate constant of 1.97 × 10−10 cm3 molecule−1 s−1 for the reaction of Cl atoms with n-butane, the following rate constants (in units of 10−11 cm3 molecule−1 s−1) were obtained: ethane, 6.38 ± 0.18; propane, 13.4 ± 0.5; isobutane, 13.7 ± 0.2; n-pentane, 25.2 ± 1.2; isopentane, 20.3 ± 0.8; neopentane, 11.0 ± 0.3; n-hexane, 30.3 ± 0.6; cyclohexane, 31.1 ± 1.4; 2,3-dimethylbutane, 20.7 ± 0.6; n-heptane, 34.1 ± 1.2; acetylene, 6.28 ± 0.18; ethene, 10.6 ± 0.3; propene, 24.4 ± 0.8; benzene, 1.5 ± 0.9; and toluene, 5.89 ± 0.36. These data are compared and discussed with the available literature values.

Separation of polar and steric effects on absolute rate constants and arrhenius parameters for the reaction of tert‐butyl radicals with alkenes

Abstract: Absolute rate constants and their temperature dependencies were measured for the reaction of tert-butyl radicals with 24 substituted ethenes and several other compounds in 2-propanol solution by time-resolved electron spin resonance. At 300 K the rate constants cover the range from 60 M−1 s−1 (1,2-dimethylene) over 16,500 M−1 s−1 (vinyl-chloride) to 460,000 M−1 s−1 (2-vinylpyridine). For the mono- and 1,1-disubstituted ethenes log k300 increases and the activation energy decreases with increasing electron affinity of the olefins. The frequency factors are in the range log A/M−1 s−1 = 7.5 ± 1.0 as typical for addition reactions, with minor exceptions. Electron affinity (polar) and steric effects on reactivity are separated for the addition of tert-butyl to chloro- and methyl-substituted ethylenes. A comparison with rate data for methyl, ethyl, 2-propyl, and other radicals indicates both polar and steric effects on radical substitution.

Mechanism of the silane decomposition. I. Silane loss kinetics and rate inhibition by hydrogen. II. Modeling of the silane decomposition (all stages of reaction)

Abstract: Part I: Kinetic data for the static system silane pyrolysis (from 640–703 K, 60–400 torr) are presented. For conversion from 3–30%, first-order kinetics are obtained, with silane loss rates equal to half the hydrogen formation rates. At conversions greater than 40%, rate inhibition attributable to the back reaction of hydrogen with silylene occurs. Overall reaction rates are not surface sensitive, but disilane and trisilane yield maxima under some conditions are. A nonchain mechanism capable of describing quantitatively all stages of the silane pyrolysis is proposed. Post 1.0% initiation is both homogeneous (gas phase) and heterogeneous (on the walls), and reaction intermediates are silylenes and disilenes. Free radicals are not involved at any stage of the reaction. Rate data at high conversions and with added hydrogen provide kinetics for the addition of silylene to hydrogen [reaction (−1)1] relative to its addition to silane [reaction (2)]: k−1,/k2 = 10−0.65 × e−3200 cal/RT. With E2 = 1300 cal, this gives a high pressure activation energy for silylene insertion into hydrogen of E−1 = 8200 cal. Part II: An analysis is made of each rate constant of the silane mechanism and the modeling results are compared with experimental results. Agreement is excellent. It is concluded that the dominant sink reaction for silylene intermediates is 1,2—H2 elimination from disilane (followed by Si2H4 polymerization and wall deposition). The model is in accord with slow isomerization between disilene and silylsilylene and near exclusive 1,2—H2 elimination from Si2H6. It is also concluded that disilene is about 10 kcal/mol more stable than silylsilylene and that the activation energy for isomerization of silylsilylene to disilene is greater than 26 kcal/mol.

Termolecular reaction of nitrogen monoxide and oxygen: A still unsolved problem

Abstract: The oxidation of nitrogen monoxide has been studied extensively between 226 and 758 K at pressures of NO and O2 ranging from about 0.2 to 30 torr. It has been shown that (i) the reaction is properly first order against oxygen and second order against nitrogen monoxide, as well under initial conditions as during the course of the reaction; (ii) the termolecular rate constant, k, first decreases with increasing temperature and reaches a minimum value at 600 K; (iii) the transition state theory is unable to describe this behavior correctly, (iv) under the present experimental conditions k can be represented either by (Formula Presented.) or by (Formula Presented.) The latter equation is compatabile with a multiple‐step mechanism. Copyright © 1985 John Wiley & Sons, Inc.

A continuous stirred tank reactor investigation of the gas‐phase reaction of hydroxyl radicals and toluene

Abstract: A continuous stirred tank reactor (CSTR) was used to study the gas-phase reaction between HO⋅ and toluene. HO⋅ was generated by the in situ photolysis of nitrous acid. Flow reactor operation at steady-state conditions with a residence time of 20 min allowed investigation of primary and very rapid secondary reactions. CSTR and batch reactor experiments were also performed with selected products. Both gas-phase and aerosol products were identified by chromatography and mass spectroscopy, with total product yields between 55 and 75% of reacted carbon. Toluene reaction products included cresols, nitrocresols, nitrotoluenes, 3,5-dinitrotouluene, benzaldehyde, benzyl nitrate, nitrophenols, methyl-p-benzoquinone, glyoxal, methylglyoxal, formaldehyde, methyl nitrate, PAN, and CO. The fraction of HO⋅ methyl hydrogen abstraction was calculated to be 0.13 ± 0.04. The ratio of reaction rate constants for nitrotoluene versus cresol formation from the HO⋅-adduct was calculated to be about 3.3 × 104. Also, the ratio of cresol formation versus O2 addition to the HO⋅-adduct was estimated to be ≥0.5 for atmospheric conditions. Comparisons of these measurements with previous values and the implications with respect to photochemical kinetics modeling of the atmosphere are discussed.

An outdoor smog chamber and modeling study of toluene–NOx photooxidation

Abstract: An experimental investigation of the gas-phase photooxidation of toluene–NO_x–air mixtures at part-per-million concentrations has been carried out in a 65-m^3, outdoor smog chamber to assess our understanding of the atmospheric chemistry of toluene. In addition, six CO-NO_x–air irradiations were conducted to characterize the chamber with regard to any wall radical sources. Measured parameters in the toluene–NO_x experiments included O_3, NO, NO_2, HNO_3, peroxyacetyl nitrate (PAN), CO, toluene, benzaldehyde, o-cresol, m-nitrotoluene, peroxybenzoyl nitrate (PBZN), temperature, relative humidity, aerosol size distributions, and particulate organic carbon. Predictions of the reaction mechanism of Leone and Seinfeld [7] are found to be in good agreement with the data under a variety of initial conditions. Additional simulations are used to investigate various mechanistic pathways in areas where our understanding of toluene chemistry is still incomplete.

Thermal decomposition of ethane in shock waves

Abstract: The thermal decomposition of ethane was studied behind reflected shock waves over the temperature range 1200–1700 K and over the pressure range 1.7−2.5 atm, by both tracing the time variation of absorption at 3.39 μm and analyzing the concentration of the reacted gas mixtures. The mechanism to interpret well not only the earlier stage of C2H6 decomposition, but also the later stage was determined. The rate constant of reactions, C2H6 CH3 + CH3, C2H6 + C2H3 C2H5 + C2H4, C2H5 C2H4 + H were calculated. The rate constants of the other reactions were also discussed.

Kinetics of the reactions of hydroxyl radical with aliphatic aldehydes

Abstract: Les coefficients de vitesse des reactions de OH avec des aldehydes aliphatiques a 2-5 carbones sont mesures sous des conditions de pseudo-ordre 1 par rapport a OH. La reactivite de l'aldehyde vis-a-vis de OH est pratiquement independante de l'identite de la chaine laterale hydrocarbonee

“Complex” versus “free radical” mechanism for the catalytic decomposition of H2O2 by ferric ions

Abstract: Kinetic and spectrophotometric measurements made during the Fe3+ ion catalyzed decomposition of H2O2 have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k3/KM = 4.94 M−1 min−1, k4 = 193 M−1 min−1, eI/KM = 52.3 M−2 cm−1, eII = 25.7 M−1 cm−1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O2 evolved in the reaction using [H2O2] ∼ 10−2 M has been calculated and found to be nearly stoichiometric. O2 evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O2 and the “free radical mechanism” predicting exactly stoichiometricamounts of O2. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H2O2 both with Fe2+ and Fe3+ ions, as well as other reactions assumed to proceed via free radicals.

Tables of rate constants extracted from chemical kinetics and photochemical data for use in stratospheric modeling. Evaluation number 7

Abstract: These tables of evaluated rate constants for use in stratospheric modeling have been taken from the most recent report of the NASA Panel that has been periodically producing such reviews. They are reproduced here to make a broader community aware of their existence. This article should NOT be cited, nor should these rate constants be used without consulting the full report. All citations should be to that original report (JPL Publ. 85-37), which contains extensive documentation and discussion of the rationale of the evaluation. Copies may be obtained by requesting JPL Publ. 85-37 from Documentation Services, 111-116B, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109.

Rates of OH radical reactions. XII: The reactions of OH with c-C3H6, c-C5H10, and c-C7H14. Correlation of hydroxyl rate constants with bond dissociation energies

Abstract: Absolute rate constants for H-atom abstraction by OH radicals from cyclopropane, cyclopentane, and cycloheptane have been determined in the gas phase at 298 K. Hydroxyl radicals were generated by flash photolysis of H2O vapor in the vacuum UV, and monitored by time-resolved resonance absorption at 308.2 nm [OH(A2Σ+X2Π)]. The rate constants in units of cm3 mol−1 s−1 at the 95% confidence limits were as follows: k(cC3H6) = (3.74 ± 0.83) × 1010, k(cC5H10) = (3.12 ± 0.23) × 1012, k(cC7H14) = (7.88 ± 1.38) × 1012. A linear correlation was found to exist between the logarithm of the rate constant per CH bond and the corresponding bond dissociation energy for several classes of organic compounds with equivalent CH bonds. The correlation favors a value of D(cC3H5–H) = (101 ± 2) kcal mol−1.

Kinetic study for the reactions of OH radicals with dimethylsulfide, diethylsulfide, tetrahydrothiophene, and thiophene

Abstract: The reactions of OH radicals with dimethylsulfide (DMS) diethylsulfide (DES), tetrahydrothiophene (THT), and thiophene have been studied at room temperature for DES and THT, at 273, 293, and 318 K for DMS, and at 293 and 318 K for thiophene by the discharge flow EPR technique in a halocarbon wax coated reactor. The following rate constants were obtained at room temperature. For the reaction OH + DMS (1), a very low temperature dependence was noticed. Some additional results concerning the mass spectrometric analysis of the products are also reported.

The flash photolysis—shock tube technique using atomic resonance absorption for kinetic studies at high temperatures

Abstract: A flash photolysis-shock tube technique is described for making kinetic measurements at high temperature. Coupled with sensitive atomic resonance absorption detection, this method allows bimolecular rate constants for atom-molecule reactions to be measured directly under conditions free from kinetic complications. Experiments were performed in the reflected shock regime, and the temperature and density were calculated using ideal shock wave theory in this initial work. Results for the reaction of atomic hydrogen with ammonia are presented to illustrate the potential of the technique. The values of the Arrhenius rate parameters found in these experiments, 900 K less than or equal to T less than or equal to 1850 K, were A = (1.14 +/- 0.12) x 10/sup -10/ cm/sup 3/ molecule/sup -1/ s/sup -1/ and E/sub ..cap alpha../ = 13,216 +/- 242 cal mol/sup -1/. This result gives rate constants that are about five times larger than those from previous studies. Although corrections for nonidealities in the reflected shock region are anticipated and under investigation, the expected changes will be relatively small and thus the large discrepancy noted here will remain. 21 references, 5 figures, 1 table.

Complex dynamical behavior in a new chemical oscillator: The chlorite–thiourea reaction in a CSTR

Abstract: The reaction between chlorite ion and thiourea has been studied both in a closed (batch) system and in a flow reactor (CSTR). The principal stoichiometry is given by In batch, the reaction displays an induction period, whose length is proportional to [CS(NH2)2]/[ClO] [H+], followed by the rapid buildup and disappearance of a ClO2 intermediate. At [ClO]/[CS(NH2)2] ratios between 2.5 and 3.5, a second peak in the ClO2 absorbance is observed. In the CSTR, this iodine-free system displays simple and complex periodic oscillation, bistability, aperiodic oscillation, and birhythmicity.

Kinetic study of the reaction of OH with HCl from 240–1055 K

Abstract: Absolute rate coefficients for the reaction of OH with HCl (k1) have been measured as a function of temperature over the range 240–1055 K. OH was produced by flash photolysis of H2O at λ > 165 nm, 266 nm laser photolysis of O3/H2O mixtures, or 266 nm laser photolysis of H2O2. OH was monitored by time-resolved resonance fluorescenceor pulsed laser–induced fluorescence. In many experiments the HCl concentration was measured in situ in the slow flow reactor by UV photometry. Over the temperature range 240–363 K the following Arrhenius expression is an adequate representation of the data: k1 = (2.4 ± 0.2) × 10−12 exp[−(327 ± 28)/T]cm3 molecule−1 s−1. Over the wider temperature range 240–1055 K, the temperature dependence of k1 deviates from the Arrhenius form, but is adequately described by the expression k1 = 4.5 × 10−17T1.65 exp(112/T) cm3 molecule−1 s−1. The error in a calculated rate coefficient at any temperature is 20%.

The pyrolysis of dimethyl sulfide, kinetics and mechanism

Abstract: The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system at 681–723 K by monitoring total pressure-time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths: with a slow, minor, secondary reaction: In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by with θ = 2.303 RT in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data: which agrees well with the experimental one over the range studied. The reaction is initiated by Me2S Me + MeS⋅ and propagated by metathetical radical attack on Me2S. C2H4 is formed by an isomerization reaction which may in part be due to a hot radical: Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.

Temperature coefficients for reactions of OH radicals with alkanes between 300 and 1000 K

Abstract: Recently, Atkinson et al. have developed a more sophisticated approach than simple additivity to determine group rate constants at room temperature for reactions of OH radicals with alkanes. In this article, use is made of reliable experimental data at room temperature and at 753 K to determine temperature coefficients for these reactions. Evidence based on experiment is cited in support of the expression k = AT1e−E/RT as a suitable quantitative expression for the variation of k with temperature between 300 and 1000 K for OH attack at any particular specific group in an alkane. Values are given for A and E for a number of groups found in both linear and branched alkanes. With highly branched alkanes, steric effects may limit the use of even the more sophisticated additivity approach used here. Use of the group values permits the calculation of both the overall rate constant for OH + alkane, the agreement with the limited amount of experimental data available being very good, and the proportions of each species of alkyl radical formed in the overall attack. Such information is vital to quantitative modeling of combustion processes currently being carried out extensively. The values given in the article are recommended for use over the temperature range 300–1000 K.

An FTIR spectroscopic study of the reactions Br + CH3CHO → HBr + CH3CO and CH3C(O)OO + NO2 ⇌ CH3C(O)OONO2 (PAN)

Abstract: Based on an FTIR-product study of the photolysis of mixtures containing Br2CH3CHO and Br2CH3CHOHCHO in 700 torr of N2, the rate constant for the reaction Br + CH3CHO HBr + CH3CO was determined to be 3.7 × 10−12 cm3 molecule−1 s−1. In addition, the selective photochemical generation of Br at λ > 400 nm in mixtures containing Br2CH3CHO14NO2 (or 15NO2)O2 was shown to serve as a quantitative preparation method for the corresponding nitrogen-isotope labeled CH3C(O)OONO2 (PAN). From the dark-decay rates of 15N-labeled PAN in large excess 14NO2, the rate constant for the unimolecular reaction CH3C(O)OO15NO2 CH3C(O)OO + 15NO2 was measured to be 3.3 (±0.2) × 10−4 s−1 at 297 ± 0.5 K.

Self-Reaction of HO2 and DO2: Negative temperature dependence and pressure effects

Abstract: The negative temperature dependence, pressure dependence, and isotope effects of the self-reaction of HO2 are modeled, using RRKM theory, by assuming that the reaction proceeds via a cyclic, hydrogen-bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO2 self-reaction is due to the approach to the high-pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high-pressure limit of the self-reaction of HO2.

Extent of H‐atom abstraction from the reaction of the OH radical with 1‐butene under atmospheric conditions

Abstract: Products of the reaction of OH radicals with 1-butene have been investigated in the presence of NO in one atmosphere of air at room temperature using gas chromatography and in situ long pathlength Fourier transform infrared absorption spectroscopy. The major product observed was propionaldehyde, with a formation yield (after allowing for its subsequent loss processes) of 0.94 ± 0.12. Minor yields of organic nitrates (RONO2) and of peroxypropionyl nitrate, a secondary product arising from propionaldehyde, were also observed. However, none of the products expected from the reactions subsequent to H-atom abstraction from 1-butene by OH radicals were observed, allowing an upper limit of 10% for this process to be derived. These data are compared with the available literature results and the implications are discussed.

Mechanism and kinetics of the silane decomposition in the presence of acetylene and in the presence of olefins

Abstract: Kinetic data and product studies are reported for the silane pyrolysis in the presence of olefins and acetylene. The kinetics of silane loss in the presence of acetylene was found to be identical to the initial gas phase silane decomposition step (SiH4 + M → SiH2 + H2 + M) when corrected for pressure fall-off effects. This result and the absence of methane or ethane from the pyrolysis of SiH4 in the presence of 1-butene or 1-pentene demonstrate that silyl radicals and H atoms are not involved in silane-olefin or silane-acetylene reactions. Qualitative aspects and kinetic data from the SiH4 pyrolysis in the presence of propylene are in accord with propylsilane formation via propylsilylene formed by silylene addition to propylene.

Thermal decomposition of methane: Autocatalysis

Abstract: The origin of autocatalysis in the pyrolysis of methane has been investigated by kinetic modeling. A mechanism is presented that provides good agreement with experimental data at 1038 K and 433 torr into the autocatalytic region. The main causes of autocatalysis are secondary initiation by hydrocarbon products larger than C2H6 and chain radical methylation sequences.

Intramolecular catalysis and the rate‐determining step in the alkaline hydrolysis of ethyl salicylate

Abstract: The alkaline hydrolysis of ethyl salicylate has been studied at 35°C within the [ŌH] range of 0.001–2.00 M. The observed hydroxide ion concentration dependence of rate has been explained by proposing the occurrence of two parallel kinetic steps shown as in the rate law: rate = k1[H2O] [ES] + k2[ŌH] [ES] where ES− represents ionized ethyl salicylate. The value of k1, is ca. 106 times larger than the expected value of rate constant for uncatalyzed aqueous cleavage of ethyl-p-hydroxybenzoate. This rate advantage is attributed to intramolecular general base catalysis. The analysis of observed activation parameters indicates that ca. 106 times rate enhancement is entirely due to favorable entropy change. The Bronsted-type plots show an extremely low sensitivity of rate constants k1 and k2 with respective Bronsted coefficient of β = −0.03 ± 0.01 and β = −0.01 ± 0.05, on the basicity of leaving groups of salicylate esters (alkoxide and phenoxide ions). The low values of these Bronsted coefficients indicate essentially little or an insignificant amount of bond cleavage between carbonyl carbon and leaving group in the rate-determining step in both the k1 and k2 steps. The rate constants obtained at different ethanol concentration follow Grunwald-Winstein mY equation with m = 0.14 ± 0.01.

Rate constants for the reactions of alkyl radicals with 1,4‐cyclohexadiene

Abstract: An electron paramagnetic resonance (EPR) technique was used to show that simple alkyl radicals readily abstract hydrogen from 1,4-cyclohexadiene. Rate constants for the reaction were ca. 104–105 M−1 s−1 at 300 K and activation energies 5–7 kcal mol−1. For the stabilized radicals, allyl and benzyl, the rate constants were <102 M−1 s−1 at 300 K. The data suggest that 1,4-cyclohexadiene could be used as an effective trap to probe rearrangement reactions of carbon centered radicals and biradicals.

Reactions of alkoxy radicals with O2. I. C2H5O radicals

Abstract: C2H5ONO was photolyzed with 366 nm radiation at −48, −22, −2.5, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of CH3CHO, Φ{CH3CHO}, was measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ϕ1a = 0.29 ± 0.03 independent of temperature. The C2H5O radicals can react with NO by two routes The C2H5O radical can also react with O2 via Values of k6/k2 were determined at each temperature. They fit the Arrhenius expression: Log(k6/k2) = −2.17 ± 0.14 − (924 ± 94)/2.303 T. For k2 ≃ 4.4 × 10−11 cm3/s, k6 becomes (3.0 ± 1.0) × 10−13 exp{−(924 ± 94)/T} cm3/s. The reaction scheme also provides k8a/k8 = 0.43 ± 0.13, where

High temperature measurements of the rate of the reaction of OH with NH3

Abstract: Low pressure (4.67 kPa) CH4/O2/Ar flames were seeded with approximately 5300 ppm NH3. The concentration profiles of stable and radical species in lean (ϕ = 0.92) and rich (ϕ = 1.13) flames were determined by molecular beam sampling mass spectrometry. Temperature profiles in these flames were measured with thermocouples whose readings were corrected for radiative losses by the Na-line reversal method. Regions of the flames were selected where the principal reaction leading to the destruction of NH3 was By correcting the measured concentrations for diffusion, the net rate of NH3 loss rate was determined in the temperature range 2080–2360 K. The rate constant k1 was determined from the net loss rate with correction for the reaction using measured values of (O) and k2 values given by Salimian, Hanson, and Kruger [1]. The best-fit Arrhenius expression for k1 in the temperature range 2080–2360 K is 1013.88 exp(−4539/T) cm3/mol-s. The results of this study combined with previous lower temperature data confirm the non-Arrhenius behavior of k1 suggested by Salimian, Hanson, and Kruger [1]. The best-fit modified three parameter expression for the range 300–2360 K is 106.33±0.2T2 exp(−169/T) cm3/mol-s.

An FTIR study of the Cl-atom-initiated reaction of glyoxal

Abstract: The kinetics and mechanism of Cl-atom-initiated reactions of CHOCHO were studied using the FTIR detection method to monitor the photolysis of Cl2–CHOCHO mixtures in 700 torr of N2–O2 diluent at 298 ± 2 K. The observed product distribution in the [O2] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHOCHO HCl + CHOCO with a rate constant of [3.8 ± 0.3(σ)] × 10−11 cm3 molecule−1 s−1; (2) the primary product CHOCO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10−7 s; (3) alternatively, the CHOCO reacts with O2 leading to the formation of CO, CO2, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO2 radical, formed in the secondary reaction CHO + O2 HO2 + CO, reacts with the CHOCHO with a rate constant ca. 5 × 10−16 cm3 molecule−1 s−1 to form HCOOH and a new transient product resembling that detected previously in the HO2 reaction with HCHO.