Theoretical study of the C-F bond activation in methyl fluoride by alkaline-earth metal monocations

Reactions of methyl fluoride with bare alkaline-earth metal monocations (Mg+, Ca+, Sr+, and Ba+) were studied using theoretical methods. Thermochemical data were calculated using density functional theory in conjunction with polarized 3-zeta and 4-zeta basis sets. Variational/conventional microcanonical transition state theory was used for the calculation of the reaction rate constants over a large range of temperatures. According to our calculations, the Ca+, Sr+, and Ba+ reactions with CH3F proceed to yield CaF+, SrF+, and BaF+, in agreement with the experimental observation. The theoretically predicted global rate constants are in reasonable agreement with the experimental data. In the case of Mg+, the large value of the computed energy barrier associated with the "inner" transition structure is fully consistent with the limited progress experimentally observed for this reaction. The importance of bottlenecks other than the "inner" transition state is highlighted and its mechanistic implications discussed. Particularly, our calculations suggest that the studied processes proceed through a "harpoon-like" mechanism.