Reaction Mechanism and Product Branching Ratios of OH+C₂H₃F Reaction: A Theoretical Study

Ab initio CCSD(T)/CBS//B3LYP/6-311G(d, p) calculations of the potential energy surface for possible dissociation channels of HOC_2H_3F, as well as Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of rate constants, were carried out, in order to predict statistical product branching ratios in dissociation of HOC_2H_3F at various internal energies. The most favorable reaction pathway leading to the major CH_2CHO+HF products is as the following: OH+C_2H_3F\rightarrowi2\rightarrowTS14\rightarrowi6\rightarrowTS9\rightarrowi3\rightarrowTS3\rightarrowCH_2CHO+HF, where the rate-determining step is HF elimination from the CO bridging position via TS11, lying above the reactants by 3.8 kcal/mol. The CH_2O+CH_2F products can be formed by F atom migration from C_\beta to C_\alpha position via TS14, then H migration from O to C_\alpha position via TS16, and C-C breaking to form the products via TS5, which is 1.8 kcal/mol lower in energy than the reactants, and 4.0 kcal/mol lower than TS11.