Benchmark ab initio potential energy surface mapping of the F + CH 3 NH 2 reaction.

This electronic structure study reveals four exothermic and two endothermic reaction pathways of the F + CH 3 NH 2 system: the barrierless hydrogen abstraction from the methyl/amino group (HF + CH 2 NH 2 /CH 3 NH), amino/methyl substitution (NH 2 + CH 3 F and CH 3 + NH 2 F) and hydrogen substitution from the two functional groups (H + CH 2 FNH 2 /CH 3 NHF). 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 CH 2 NH 2 ⋯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.