On the kinetic mechanism of the hydrogen abstraction reactions of the hydroxyl radical with CH3CF2Cl and CH3CFCl2: a dual level direct dynamics study.

By means of the dual-level direct dynamics method, the mechanisms of the reactions, CH(3)CF(2)Cl + OH --> products (R1) and CH(3)CFCl(2) + OH --> products (R2), are studied over a wide temperature range 200-2000 K. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) level, and then the energy profiles of the reactions are refined with the interpolated single-point energy method at the G3(MP2) level. The canonical variational transition-state theory with the small-curvature tunneling (SCT) correction method is used to calculate the rate constants. For the title reactions, three reaction channels are identified and the H-abstraction channel is the major pathway. The results indicate that F substitution has a significant (reductive) effect on hydrochlorofluorocarbon reactivity. Also, for all H-abstraction reaction channels the variational effect is small and the SCT effect is only important in the lower temperature range on the rate constants calculation.