EMISSION OF ORGANIC-PRODUCTS FROM THE SURFACE OF FROZEN METHANE UNDER MEV ION IRRADIATION

10-mu-m layers of CH4 freshly condensed onto a cold finger at 10-15 K were irradiated with 10-20 MeV protons and 3He2+ ions. The gases emitted during irradiation and successive warming to ambient temperature were monitored by quadrupole mass spectrometry (QMS). C2H2 and C2H4 were the primary volatile products at low temperature. They were converted with increasing irradiation time and dose into C2H6, C3H6 and heavier hydrocarbons up to C-8. During the warmup phase even more complex hydrocarbons up to C-12 were emitted including substituted benzenes (xylols), naphthalene derivates and anthracene and/or phenanthrene. The preferential formation of unsaturated compounds in the first reaction steps underlines the role of hot carbon atoms in the radiation induced complexation of solid organic matter, starting with their insertion into C-H bonds. The interaction of cosmic rays with organic solids in space includes these suprathermal reactions as one of the most prominent processes.