Benchmark ab initio potential energy surface mapping of the F + CH3NH2 reaction

Abstract

This electronic structure study reveals four exothermic and two endothermic reaction pathways of the F + CH₃NH₂ system: the barrierless hydrogen abstraction from the methyl/amino group (HF + CH₂NH₂/CH₃NH), amino/methyl substitution (NH₂ + CH₃F and CH₃ + NH₂F) and hydrogen substitution from the two functional groups (H + CH₂FNH₂/CH₃NHF). The benchmark classical and adiabatic energies are obtained using a high-accuracy composite ab initio approach, where the gold-standard explicitly-correlated coupled cluster method (CCSD(T)-F12b) is applied with the correlation-consistent polarized valence quintuple-zeta F12 basis set (cc-pV5Z-F12) and further additive energy contributions. Considering indispensable post-(T) correlation, core correlation, scalar relativistic, spin–orbit and harmonic zero-point energy corrections, the obtained global minimum of the potential energy surface is the post-reaction CH₂NH₂⋯HF complex in the product channel. Although each substitution pathway has a high barrier, the energies of amino-substitution and methyl-hydrogen-substitution products are below the energy of the reactants, as well as the submerged-barrier hydrogen-abstraction pathways.