Full-dimensional, ab initio potential energy surface for CH3OH → CH3+OH

Abstract

An accurate, ab initio potential energy surface (PES) is reported for CH3OH including the bound region as well as the barrierless dissociation to CH3+OH. The surface is a linear least-squares fit to a total of 45,199 ab initio energies, most of which were computed using CCSD(T)-F12b/aug-cc-pVDZ theory and a small number using CASPT2/aug-cc-pVDZ theory. The latter set was done in the multi-reference region of the PES in order to obtain a realistic description of the OH–CH3 interaction in the near asymptotic region. The geometries and harmonic frequencies of the stationary points agree very well with direct CCSD(T)-F12b calculations. The three-fold barrier to internal rotation of CH3OH is also accurately described by the PES. The zero-point energies of methanol and CH3+OH are determined by Diffusion Monte Carlo calculations. The D0 dissociation energy is 90.1 kcal/mol, in very good agreement with the recent IUPAC evaluation [Ruscic et al., J. Phys. Chem. Ref. Data 34, 573 (2005)] result of 90.25 kcal/mol.