Rate constants calculation of hydrogen abstraction reactions CH 3 CHBr + HBr and CH 3 CBr 2 + HBr

Dual‐level direct dynamics method is used to study the kinetic properties of the hydrogen abstraction reactions of CH 3 CHBr + HBr → CH 3 CH 2 Br + Br (R1) and CH 3 CBr 2 + HBr → CH 3 CHBr 2 + Br (R2). Optimized geometries and frequencies of all the stationary points and extra points along the minimum‐energy path are obtained at the MPW1K/6‐311+G(d,p), MPW1K/ma‐TZVP, and BMK/6‐311+G(d,p) levels. Two complexes with energies less than that of the reactants are located in the entrance of each reaction at the MPW1K/6‐311+G(d,p) and MPW1K/ma‐TZVP levels, respectively. The energy profiles are further refined with the interpolated single‐point energies method at the G2M(RCC5)//MPW1K/6‐311+G(d,p) level of theory. By the improved canonical variational transition‐state theory with the small‐curvature tunneling correction (SCT), the rate constants are evaluated over a wide temperature range of 200–2000 K. Our calculations have shown that the radical reactivity decreases from CH 3 CHBr to CH 3 CBr 2 . Finally, the total rate constants are fitted by two modified Arrhenius expression. © 2012 Wiley Periodicals, Inc.