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

Abstract

ABSTRACTThe 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 (Fa) of SF5CF3 molecule is easier to be extracted than others [the F atom perpendicular to the molecular axis (Fb) or in -CF3 group(Fc)] 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.