Rate constants calculation of hydrogen abstraction reactions CH3CHBr + HBr and CH3CBr2 + HBr.

Dual-level direct dynamics method is used to study the kinetic properties of the hydrogen abstraction reactions of CH3CHBr + HBr → CH3CH2Br + Br (R1) and CH3CBr2 + HBr → CH3CHBr2 + 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 CH3CHBr to CH3CBr2. Finally, the total rate constants are fitted by two modified Arrhenius expression. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]