The reactions of H atoms with methane, four chlorinated methanes, and isobutene have been studied experimentally using the discharge flow/resonance fluorescence technique over wide ranges of temperatures. The rate constants were obtained in direct experiments as functions of temperature. The experimentally obtained activation energies of the reactions of H atoms with chlorinated methanes demonstrate a correlation with the enthalpies of the reactions. Transition state theory reaction models were created on the basis of ab initio calculations, the Marcus expression for correlation between reaction barriers and reaction energetics, and analysis of experimental data. It is demonstrated that the formalism based on the Marcus expression adequately describes the observed temperature dependencies of the rate constants of the overall reactions. According to the models, abstraction by H atoms of hydrogen atoms from chloromethanes is an important process accounting for significant fractions of the overall rate constants. The models result in expressions for the rate constants of Cl and H atom abstraction channels and the corresponding reverse reactions over wide ranges of temperatures.

The reactions of Cl atoms with methane and three chlorinated methanes (CH 3 Cl, CH 2 Cl 2 , and CHCl 3 ) have been studied experimentally using the discharge flow/resonance fluorescence technique over wide ranges of temperature and at pressures between 1.4 and 8.8 Torr. The rate constants were obtained in direct experiments as functions of temperature: k 1 (Cl + CH 4 ) ) 1.30 × 10 -19 T 2.69 exp(-497 K/T) (295-1104 K), k 2 (Cl + CH 3 Cl) ) 4.00 × 10 -14 T 0.92 exp(-795 K/T) (300-843 K), k 3 (Cl + CH 2 Cl 2 ) ) 1.48 × 10 -16 T 1.58 exp(-360 K/T) (296-790 K), and k 4 (Cl + CHCl 3 ) ) 1.19 × 10 -16 T 1.51 exp(-571 K/T) (297-854 K) cm 3 molecule -1 s -1 . Results of earlier experimental and theoretical studies of the reactions of Cl atoms with methane and chloromethanes are analyzed and compared with the results of the current investigation. It is demonstrated that the existing theoretical models of reactions 2-4 are in disagreement with the experiments and thus are not suitable for use in extrapolating the experimental results to conditions outside the experimental ranges. Thus, no better alternative to the use of experimental modified Arrhenius fits can be proposed at this time. A transition-state theory model of reaction 1 (Cl + CH 4 ) was created on the basis of ab initio calculations and analysis of the experimental data and was used to extrapolate the latter to temperatures outside the experimental ranges. The model results in the expression k 1 (Cl + CH 4 ) ) 5.26 × 10 -19 T 2.49 exp(-589 K/T) cm 3 molecule -1 s -1 (200-3000 K) for the temperature dependence of the rate constant. Temperature dependences of the rate constants of the reverse R + HCl f Cl + RH reactions were derived on the basis of the experimental data, modeling, and thermochemical information.

The reaction of hydroxyl radicals with hydrogen chloride (reaction 1) has been studied experimentally using a pulsed-laser photolysis/pulsed-laser-induced fluorescence technique over a wide range of temperatures, 298-1015 K, and at pressures between 5.33 and 26.48 kPa. The bimolecular rate coefficient data set obtained for reaction 1 demonstrates no dependence on pressure and exhibits positive temperature dependence that can be represented with modified three-parameter Arrhenius expression within the experimental temperature range: k1 = 3.20 x 10(-15)T0.99 exp(-62 K/T) cm3 molecule(-1) s(-1). The potential-energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed for the reaction 1 on the basis of calculations and experimental data. The model results in modified three-parameter Arrhenius expressions: k1 = 8.81 x 10(-16)T1.16 exp(58 K/T) cm3 molecule(-1) s(-1) for the temperature range 200-1015 K and k1 = 6.84 x 10(-19)T2.12 exp(646 K/T) cm3 molecule(-1) s(-1) for the temperature dependence of the reaction 1 rate coefficient extrapolation to high temperatures (500-3000 K). A temperature dependence of the rate coefficient of the Cl + H2O --> HCl + OH reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.

The reactions of OH with molecular chlorine (reaction 1), methane (reaction 2), and propane (reaction 3) have been studied experimentally using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over wide ranges of temperatures (297-826, 298-1009, and 296-908 K, respectively) and at pressures between 6.68 and 24.15 kPa. The rate coefficients obtained for reactions 1-3 demonstrate no dependence on pressure and exhibit positive temperature dependences that can be represented with modified three-parameter Arrhenius expressions within their corresponding experimental temperature ranges: k 1 ) 3.59 × 10 -16 T 1.35 exp(-745 K/T) cm 3 molecule -1 s -1 , k 2 ) 3.82 × 10 -19 T 2.38 exp(-1136 K/T) cm 3 molecule -1 s -1 , and k 3 ) 6.64 × 10 -16 T 1.46 exp(-271 K/T) cm 3 molecule -1 s -1 . For the OH + Cl 2 reaction, the potential energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed on the basis of calculations and experimental data. Model predictions suggest OH + Cl 2 f HOCl + Cl as the main channel of this reaction. The model results in the expression k 1 ) 1.35 × 10 -16 T 1.50 exp(-723 K/T) cm 3 molecule -1 s -1 for the temperature dependence of the reaction 1 rate coefficient extrapolation outside the experimental range to low temperatures down to 200 K and to high temperatures up to 3000 K. A temperature dependence of the rate coefficient of the HOCl + Cl f OH + Cl 2 reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.