A comprehensive benchmark ab initio survey of the stationary points and products of the OH· + CH3OH system

Reactions between methanol and the hydroxyl radical are of significant interest for combustion, atmospheric and astrochemistry. While the two primary product channels (the formation of H2O with either CH3O· or ·CH2OH) have been the subject of numerous studies, the possibility of other products has seen little attention. Here, we present a comprehensive thermochemical survey of the stationary points and plausible products of the reaction, featuring 29 geometries optimized at the UCCSD(T)-F12b/aug-cc-pVTZ level, followed by accurate composite ab initio computations for all stationary points (including ·CH2OH dissociation and isomerization) and five product channels, with a detailed evaluation of basis set convergence and efficiency. The computations reveal that the formation of methanediol and the hydroxymethoxy radical is thermodynamically favorable and the endothermicity of formaldehyde formation is low enough to be a plausible product channel. We also observe unexpectedly large energy deviations between the partially-spin-adapted ROHF-RCCSD(T) method and ROHF-UCCSD(T), as well as between UHF-UCCSDT(Q) and ROHF-UCCSDT(Q) results.