CONVERSION OF H_2CO TO CH_3OH BY REACTIONS OF COLD ATOMIC HYDROGEN ON ICE SURFACES BELOW 20 K

摘要

The conversion of formaldehyde (H_2CO) to methanol (CH_3OH) by successive hydrogenation on H_2O ice was measured at 10, 15, and 20 K using atomic hydrogen beams of 30 and 300 K. The conversion rates and CH_3OH yields under the 30 K beam are very similar to those under the 300 K beam at all ice temperatures, demonstrating that the reaction is independent of beam temperature. The dependence of the conversion rates on ice temperature is consistent with that for previous experiments on CO hydrogenation. The conversion rate for H_2CO → CH_3OH at 15 K was found to be about half that for CO → H_2CO. The dependence of the reactions on the initial thickness of H_2CO was also measured. More than 80% of H_2CO was converted to CH_3OH for H_2CO layers of less than 1 monolayer in average thickness. Irradiation of CH_3OH with H atoms did not produce H_2CO, demonstrating that the reverse process, CH_3OH → H_2CO (H abstraction), is minor compared to the forward process.