Theoretical Studies Of The Reactions Cl Atoms With Hydrofluoroethers

In the atmosphere, there are a large numbers of small molecule radicals, which can deplete ozone layer and cause a green house effect. But due to their especial character and the limitation of the existing experimental equipment, laboratory chemists can only do research of the small molecule radicals in a low-temperature. So it is necessary to research the small molecule radicals using the theoretical method.By using Gaussian03 program package and appropriate precision-group, we can obtain very accurate microscopic kinetics mechanism of these small molecule radicals. Using dynamics investigation, we can predict all possible channels and which channel is major and the potential energy surface information. Furthermore, we calculated the rate constant and compared with the experimental data.In this paper, we calculated the optimized geometries, energies and harmonic vibrational frequencies of reactants, complexes, transition states and products of the reactions Cl + CF₃CH₂OCH₃ (R₁), Cl + CF₃CH₂OCH₂F (R₂) and Cl + CF₃CH₂OCHF₂ (R₃) at MP2/6-31+G(d,p) level, and obtained the minimum energy path (MEP) using intrinsic reaction coordinate (IRC) method. In order to obtain the more accurate potential energy surface information, The MC-QCISD method is employed to refine the energy based on the MP2/6-31+G(d,p) geometries. At the same level, we also calculated the bond dissociation energies (BDEs) of the three reactants. From the potential energy surface information, the barrier heights of H-abstraction channel are lower than the others, so the H-abstraction channels are more likely to occur. The barrier heights of the others channels are so high that the rate constants can be neglectable. We calculated the TST, CVT and CVT/SCTrate constants of the H-abstraction channels in a wide temperature range from 200 to 1,500 K. using POLYRATE 9.1 program package. In order to validate the credibility of our conclusion, we compared the theoretical values with the experimental values. Furthermore, we also calculated the branching ratios of the two H-abstraction channels of the reactions and simulated the three-parameter fits for reactions R₁, R₂ and R₃. The conclusion indicates that the channels R1b, R2a and R3a are dominate channels for R₁, R₂ and R₃, respectively.