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