Hydrogenation of CO on pure solid CO and CO-H2O mixed ice

Using a cold ( 30 K) atomic hydrogen beam, hydrogenation of CO on pure solid CO and CO-H2O mixed ice is investigated at temperatures below 20 K. Hydrogenation proceeds efficiently on both pure solid CO and CO-H2O mixed ice below 12 K, but the rate of reaction on pure CO decreases significantly at 15 K compared to CO-H2O mixed ice. Hydrogenation of CO at 12 K and above is found to be promoted by H2CO and H2O molecules on the CO surface.