Relative Reaction Rates of Hydrogenation and Deuteration of Solid CO at Very Low Temperatures

Abstract

Using cold atomic hydrogen and deuterium beams, hydrogenation and deuteration of solid CO on the surface of H2O ice were investigated in the surface‐temperature range 8–20 K. In hydrogenation experiments, formaldehyde and methanol were produced efficiently by successive hydrogenation of CO below 20 K in conditions similar to those in molecular clouds. In deuteration experiments, we found, for the first time, that D2CO and CD3OD are formed from CO, with the reaction proceeding similarly to hydrogenation although at a much slower rate. From the attenuation curve of the parent CO at 15 K, the relative reaction rate of CO‐deuteration to ‐hydrogenation was determined to be about 0.1. This isotope effect is considered to be due to tunneling reaction.