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-H 2 O mixed ice is investigated at temperatures below 20 K. Hydrogenation proceeds efficiently on both pure solid CO and CO-H 2 O mixed ice below 12 K, but the rate of reaction on pure CO decreases significantly at 15 K compared to CO-H 2 O mixed ice. Hydrogenation of CO at 12 K and above is found to be promoted by H 2 CO and H 2 O molecules on the CO surface.