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, H 2 O + CH 2 OH (R1) and H 2 O + CH 3 O (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), 13 CH 3 OH, CH 3 18 OH, and CD 3 OH, 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.

Computational study of the post-transition state dynamics for the OH + CH3OH reaction probed by photodetachment of the CH3O−(H2O) anion

“…The reaction between the hydroxyl radical and methanol holds significant importance across various research domains, such as high-temperature combustion chemistry, 12,13 atmospheric chemistry on Earth and other planets, 14 and low-temperature interstellar chemistry. 15,16 Consequently, numerous experimental 14,17–21 and theoretical 22–32 investigations have been conducted to explore the OH + CH 3 OH reaction. Recently, comprehensive full-dimensional potential energy surfaces (PESs) have been developed by three distinct research teams based on high-level ab initio quantum chemistry calculations.…”

“…Recently, comprehensive full-dimensional potential energy surfaces (PESs) have been developed by three distinct research teams based on high-level ab initio quantum chemistry calculations. 27,28,30 Utilizing these developed PESs, rate coefficients have been computed employing dynamic methods, including quasi-classical trajectory calculations 27,29,30 and ring-polymer molecular dynamics (RPMD) simulation. 32 Although the entrance channel has been extensively investigated through collisional simulations of OH + CH 3 OH, the dynamics occurring after the system crosses the transition state are not yet fully understood on the two PESs.…”