A theoretical investigation of the reaction mechanisms for C-H and C-C bond activation processes in the reaction of Ni with cycloalkanes C,,H2. （n = 3-7） is carried out. For the Ni ＋ CnH2, （n = 3, 4） reactions, the major and minor reaction channels involve C-C and C-H bond activations, respectively, whereas Ni atom prefers the attacking of C-H bond over the C-C bond in CnH2n （n = 5=7）. The results are in good agreement with the experimental study. In all cases, intermediates and transition states along the reaction paths of interest are characterized, It is found that both the C-H and C-C bond activation processes are proposed to proceed in a one-step manner via one transition state. The overall C-H and C-C bond activation processes are exothermic and involve low energy barriers, thus transition metal atom Ni is a good mediator for the activity of cycloalkanes CnH2n （n = 3 -7）.
A dynamic method is employed to study the reaction mechanisms of CH3CH2OCF3 with the hydrogen trioxy （HOOO） radical. In our paper, the geometries and harmonic vibrational frequencies of all the stationary points and minimum energy paths （MEPs） are calculated at the MPW1K/6-31＋G（d,p） level of theory, and the energetic information along MEPs is further refined by the CCSD/6-31＋G（df, p） level of theory. The rate constants are evaluated with the conventional transition-state theory （TST）, the canonical variational transition-state theory （CVT）, the microcanonical variational transition-state theory （μVT）, the CVT coupled with the small-curvature tunneling （SCT） correction （CVT/SCT）, and the μVT coupled with the Eckart tunneling correction μVT/Eckart） based on the ab initio calculations in the temperature range of 200-3000 K. The theoretical results are important in determining the atmospheric lifetime and the feasible pathways for the loss of HFEs.
