Mechanism of OH-initiated atmospheric oxidation of E/Z-CF₃CF=CFCF₃: a quantum mechanical study.

A detailed theoretical investigation was performed on the mechanisms for the reactions of E/Z-CF₃CF= CFCF₃ with OH radicals by means of density functional theory (DFT). The geometries and frequencies of all the stationary points and the minimum energy path (MEP) are calculated at the M06-2X/aug-cc-pVDZ level. To obtain more reliable energy information, the high-level single-point energies are further refined at the MCG3/3 level. Possible reaction pathways including the addition-elimination and the OH-initiated oxidation pathways are considered. A complete description of the possible degradation mechanisms of E/Z-CF₃CF = CFCF₃ in the absence and presence of O₂/NO has been presented. The calculated results demonstrate that the most accessible products are CF₃, CF(OH)= CFCF₃, CF(O)CHFCF₃, CF₃C(O)F, and CHFCF₃ via the dissociation reactions starting from the addition intermediates IM1E/IM1Z in the absence of O₂/NO. While in the atmosphere, IM1E/IM1Z can further react with O₂/NO to form the likely products CF₃C(O)F and HO₂. The calculated results are consistent with the experimental results.