Theoretical kinetics analysis of the OH + CH3OH hydrogen abstraction reaction using a full-dimensional potential energy surface

Abstract

Based on an analytical full-dimensional potential energy surface (PES), named PES-2022, fitted to high-level ab initio calculations previously developed by our group and specifically developed to describe this polyatomic reactive process, an exhaustive kinetics analysis was performed in the temperature range 50–2000 K, that is, interstellar, atmospheric and combustion conditions. Using the competitive canonical unified theory with multidimensional tunneling corrections of small curvature, CCUS/SCT, and low- and high-pressure limit (LPL and HPL) models, in this wide temperature range we found that the overall rate constants increase with temperature at T > 300 K and T < 200 K, showing a V-shaped temperature dependence, reproducing the experimental evidence when the HPL model was used. The increase of the rate constant with temperature at low temperatures was due to the strong contribution of the tunneling factor. The title reaction evolves by two paths, H₂O + CH₂OH (R1) and H₂O + CH₃O (R2), and the branching ratio analysis showed that the R2 path was dominant at T < 200 K while the R1 path dominated at T > 300 K, with a turnover temperature of ∼260 K, in agreement with previous theoretical estimations. Three kinetics isotope effects (KIEs), ¹³CH₃OH, CH₃¹⁸OH, and CD₃OH, were theoretically studied, reproducing the experimental evidence. The kinetics analysis in the present paper together with the dynamics study previously reported showed the capacity of the PES-2022 to understand this important chemical process.