Kinetics of Reactions of Cl Atoms with Ethane, Chloroethane, and 1,1-Dichloroethane

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Reactions of Cl atoms with ethane (1), chloroethane (2), and 1,1-dichloroethane (3) were studied experimentally with the discharge flow/resonance fluorescence technique over wide ranges of temperatures and at pressures between 2.3 and 9.2 Torr. Results of earlier investigations of the reactions of Cl atoms with ethane and chloroethanes are analyzed and compared with the results of the current work. The rate constants of the reaction of Cl atoms with ethane obtained in the current study (k1 = (4.91 × 10-12)T0.47 exp(−82 K/T) cm3 molecule-1 s-1, 299−1002 K) agree with the results of earlier determinations. Combination of the temperature dependence of k1 obtained in the current work with the existing (mostly at lower temperatures) literature data results in the expression k1 = (7.23 × 10-13)T0.70 exp(+117 K/T) cm3 molecule-1 s-1 (203−1400 K). Rate constants of the reactions of Cl atoms with chloroethane and 1,1-dichloroethane demonstrate different temperature dependences in the low-temperature (room temperature to 378 K) and the high-temperature (484−810 K) regions. The differences are due to the regeneration of Cl atoms at higher temperatures as a consequence of the fast thermal decomposition of radical products with a chlorine atom in the β position. This information enables quantitative differentiation between the site-specific reaction channels. The results of the current study, combined with those of earlier relative-rate experiments, were used to derive expressions for the temperature dependences of the rates of the site-specific abstraction channels: k2a(T) = (2.76 ± 0.28) × 10-11 exp(−455 ± 44 K/T) (296−810 K), k2b(T) = (1.92 ± 0.47) × 10-11 exp(−789 ± 84 K/T) (296−378 K), k3a(T) = (1.46 ± 0.21) × 10-11 exp(−733 ± 58 K/T) (293−810 K), and k3b(T) = (2.98 ± 1.42) × 10-11 exp(−1686 ± 160 K/T) (293−378 K) cm3 molecule-1 s-1, where channels a and b signify abstraction of hydrogen atoms in the α and β positions, respectively.