METHANOL FORMATION FROM ELECTRON-IRRADIATED MIXED H_2O/CH_4 ICE AT 10 K

摘要

In order to investigate the role of cosmic rays in the formation of methanol on dust grains, low-energy electron irradiation (～10-300 eV) on mixed H_2O/CH_4 ice was studied by infrared (IR) spectroscopy and thermal desorption spectrometry (TDS). CH_3OH was formed as a major product along with H_2CO, C_2H_4, C_2H_6, and C_2H_2 as minor products when the mixed H_2O/CH_4 (10/1) ice was irradiated by electrons at 10 K. There were found to be two pathways for the formation of methanol with about equal importance, i.e., the recombination reaction, CH_3 + OH → CH_3OH, and the insertion reaction, CH_2 + H_2O → CH_3OH. One CH_3OH molecule was formed per 60 electron irradiations with an electron energy of 100 eV. By using mixed H_2O/CD_4 ice, it was confirmed that formaldehyde was formed by the insertion reaction, C + H_2O → H_2CO.