Theoretical study on the methyl radical with chlorinated methyl radicals CH_3-nCl_n (n = 1, 2, 3) and CCl₂

Radical-radical reactions involving chlorinated methyl radicals are particularly important in the mechanism of combustion of chlorinated hydrocarbons. Yet, they are usually difficult to study experimentally. In this paper, four chloride-related radical-radical reactions, i.e., CH ₃+CH_3-nCl_n (n = 1, 2, 3) and CH ₃+CCl₂, are theoretically studied for the first time by means of the Gaussian-3//B3LYP potential energy surface survey combined with the master equation study over a wide range of temperatures and pressures. Our calculated results show that the three CH₃+CH_3-nCl _n reactions can barrierlessly generate the former two kinetically allowed products P₁ H₂C=C(H)_3-nCl _n-1+HCl and P₂ CH₃CH_3-nCl _n-1+Cl with the very high predominance of P₁ over P ₂. For the CH₃ reaction with the biradical CCl ₂, which inevitably takes place during the CH₃+CCl ₃ reaction and yet has never been studied experimentally or theoretically, H₂C=CCl₂+H and H₂C=C(H)Cl+Cl are predicted to be the respective major and minor products. The results are compared with the recent laser photolysis/photoionization mass spectroscopy study on the CH₃+CH_3-nCl_n (n = 1, 2, 3) reactions. The predicted rate constants and product branching ratios of the CH₃+CCl₂ reaction await future experimental verification.