Low-Temperature Kinetic Isotope Effects in CH3OH+H -> CH2OH+H2 Shed
  Light on the Deuteration of Methanol in Space
  We calculated reaction rate constants including atom tunneling for the
hydrogen abstraction reaction CH3OH+H -> CH2OH+H2 with the instanton method.
The potential energy was fitted by a neural network, that was trained to
UCCSD(T)-F12/VTZ-F12 data. Bimolecular gas-phase rate constants were calculated
using microcanonic instanton theory. All H/D isotope patterns on the CH3 group
and the incoming H atom are studied. Unimolecular reaction rate constants,
representing the reaction on a surface, down to 30 K, are presented for all
isotope patterns. At 30 K they range from 4100 for the replacement of the
abstracted H by D to ~ 8 for the replacement of the abstracting H to about 2--6
for secondary KIEs. The $^\text{12}$C/$^\text{13}$C kinetic isotope effect is
1.08 at 30 K, while the $^\text{16}$O/$^\text{18}$O kinetic isotope effect is
vanishingly small. A simple kinetic surface model using these data predicts
high abundances of the deuterated forms of methanol.
