Stationary points for the OH^- + CH₃F → CH₃OH + F^- potential energy surface

Ab initio calculations at the HF, MP2, and CCSD(T) levels of theory, utilizing a range of basis sets including the large bases 6-311++G(2df,2pd) and aug-cc-pVTZ, are used to study the OH^-+CH₃F→CH₃OH+F^- potential energy surface (PES). Structures, vibrational frequencies, and energies are determined for the reactant and product asymptotic limits, the OH⋯CH₃F ion-dipole potential minimum, the [OH⋯CH₃⋯F]^- central barrier, and the CH₃OH⋯F^- hydrogen-bonded minimum. This PES does not have a post-reaction F^-⋯CH₃OH minimum complementary to the pre-reaction OH^-⋯CH₃F minimum. Except for the CH₃OH⋯F^- minimum, the large basis sets and MP2 theory give a consistent set of structures and frequencies for the stationary points. Neither the structure nor the vibrational frequencies of the CH₃OH⋯F^- minimum are converged by the MP2 and large basis set calculations. RHF theory does not describe the energy of the [OH⋯CH₃⋯F]^- central barrier nor the reaction exothermicity, however, it does give OH^-+CH₃F→OH^-⋯CH₃F and F^-+CH₃OH→CH₃OH⋯F^- well depths in good agreement with the CCSD(T) values. Overall good agreement is found between the MP2/6-31+G* and much higher level CCSD(T) energies for the stationary points. The MP2 and CCSD(T) calculations give a reaction exothermicity and F^-+CH₃OH→CH₃OH⋯F^- well depth in good agreement with the experimental values.