Figure 6.

Schematic potential energy surface of the OH^– + CH₃I → I^– + CH₃OH S_N2 reaction showing the classical (without ZPE) relative energies of the stationary points corresponding to the composite analytical PES (ref (41)) compared with benchmark relativistic all-electron CCSDT(Q)/complete-basis-set-quality reference data (ref (74)). The stationary-point notations are as follows: front-side minimum (FSMIN), hydrogen-bonded minimum (HMIN), hydrogen-bonded transition state (HTS), post-reaction hydrogen-bonded minimum (PostHMIN), front-side attack transition state (FSTS), and double-inversion transition state (DITS). Note that double inversion via DITS is a non-IRC pathway. Adapted with permission from ref (41). Copyright 2020 the PCCP Owner Societies.