Reaction probability and defluorination mechanisms of a potent greenhouse gas SF₅CF₃ attacked by CH₃ radical: a theoretical study

The defluorination mechanisms for the reactions between SF₅CF₃ and CH₃ radicals were investigated by using the B3PW91/6-311++G(d,p) method. Optimised geometries of all the species (reactants, transition states, products and intermediates) were verified by the analysis of vibration frequency and intrinsic reaction coordinate. The energies were refined by the higher method of G3MP2. The results show that SF₅CF₃ is easier to be attacked by the carbon rather than the hydrogen atom of CH₃ radical. Moreover, the F atom on the molecular axis (F_a) of SF₅CF₃ molecule is easier to be extracted than others [the F atom perpendicular to the molecular axis (F_b) or in -CF₃ group(F_c)] because the barrier of transition state TS1 is 26.9 or 92.7 kJ mol⁻¹ lower than that of TS2 or TS3, respectively. The most favourable channel for the title reactions are R→TS1→Dp1→TS7→CP-1→Dp4[CF₃SF₃+CH₂F+HF]. The three-parameter-fitted Arrhenius expressions of the two elemental steps R→TS1→Dp1 and Dp1→TS7→CP-1 are and , respectively. The tunnelling effect is more significant for the reactions involving lighter atom or molecule group, especially in lower temperatures.