Water Catalysis of the Reaction of Methanol with OH Radical in the Atmosphere is Negligible.

Abstract

Faced with the contradictory results of two recent experimental studies [Jara-Toro et al., Angew. Chem. Int. Ed. 2017, 56, 2166 and Chao et al., Angew. Chem. Int. Ed. 2019, 58, 5013] of the possible catalytic effect of water vapor on CH3 OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH3 OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high-level electronic structure and kinetics calculations. The Wuhan-Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high-frequency and low-frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small-curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200-400 K.