Reaction Rates and Kinetic Isotope Effects of H$_2$ + OH $\rightarrow$ H$_2$O + H

TL;DR

This study calculates reaction rate constants and isotope effects for H$_2$ + OH reactions down to 50 K, revealing significant tunneling effects and relevance to astrochemistry.

Contribution

It applies advanced quantum tunneling theories to all isotopologues of H$_2$ + OH, providing detailed low-temperature reaction rates and isotope effects.

Findings

Atom tunneling increases below 250 K.

Rate constants remain significant at 50 K.

Hydrogen transfer dominates isotope effects.

Abstract

We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling (CVT/$\mu$OMT) were applied using a fitted potential energy surface [J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval $ 4 \cdot 10^{-20}$ to $4 \cdot 10^{-17}$ cm$^3$ s$^{-1}$ , demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures.