GAS-GRAIN PROCESSES FOR THE FORMATION OF CH4 AND H2O - REACTIONS OF H-ATOMS WITH C, O, AND CO IN THE SOLID-PHASE AT 12 K

The reactions of H atoms with C, O, CO, and CH3CN in solid phase at 12 K were investigated by temperature-programmed mass spectrometry. In t he reaction of H atoms with C atoms trapped in the CO matrix, H atoms migrate in the CO matrix and react with trapped C atoms selectively to form CH4. D2O was the major product from the reactions of D atoms wit h O atoms trapped in a N2O matrix. CH4 was found to be one of the fina l products from the reactions of H atoms with solid CO. The precursor for the formation of CH4 may be the CH2OH radical. No products were de tected from the reaction of H atoms with CH3CN, suggesting that the ni trile group is not amenable to the hydrogenation reactions by H atoms at 12 K. When CH4 molecules are trapped in matrices such as CH3OH and H2O, the desorption of CH4 is greatly suppressed, i.e., from similar t o 50 K for neat CH, to similar to 100 K for CII, in the CH3OH matrix a nd to similar to 150 K for CH4 in the H2O matrix.