Direct ab initio dynamics studies on the hydrogen-abstraction reactions of CH_nCl_3-n + HBr with n = 1, 2

The title reactions are investigated by ab initio direct dynamics method. The geometries for the reactants, products and transition states are optimized at the BH&H-LYP/6-311+G(d, p) level. With the aid of intrinsic reaction coordinate theory, the minimum energy path (MEP) is obtained at the same level, and the energies along the MEP are further refined by performing the single-point calculations at the QCISD(T)/6-311+G(3df, 2p) level. For both reactions, the calculated ICVT/SCT rate constants are in good agreement with the experimental results, and the variational effect is small and small-curvature tunneling effect is important only in the lower temperature range.