Theoretical investigation of the hydrogen abstraction from CF3CH2CF3 by OH radicals, F, and Cl atoms: A dual-level direct dynamics study

The hydrogen abstraction reactions of the CF3CH2CF3 with the OH radicals (R1), F (R2), and Cl (R3) atoms have been studied theoretically over a wide temperature range 200-1000 K. In this study, the recently developed hybrid density functional theory BB1K is used to obtain reaction path information including the geometries and frequencies of the stationary points. To refine the energies, single-point energy calculations were performed at the BMC-CCSD level using the BB1K geometries. The rate constants are carried out by the canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT). It is found that the activation energies for the title reactions are on the order of R3 > R1 > R2 and the rate constants exhibit just the opposite order, i.e., k2 > k1 > k3. The calculated CVT/SCT rate constants are compared with the available experimental values in the temperature region 269-413 K. The temperature dependence of the rate constants can be expressed by three-parameter Arrhenius expressions (cm3 mol−1 s−1): k1 = 1.18 × 10−19T2.51 exp(−1761.16/T), k2 = 2.47 × 10−15T1.36 exp(−689.34/T), and k3 = 4.24 × 10−21T3.22 exp(−2819.55/T) cm3 mol−1 s−1, respectively. Furthermore, in order to further reveal the thermodynamics properties, the enthalpies of formation of CF3CH2CF3 and CF3CHCF3 are studied using isodesmic reactions.