Emission of organic products from the surface of frozen methane under MeV ion irradiation

IO km layers of CH, freshly condensed onto a cold finger at 10~1.5 K were irradiated with IOk MeV protom and ‘Hc’ ’ ions. The gases emitted during irradiation and successive warming to ambient temperature were monitored by qundrupole mass apectrometry (QMS). C,H, and C?H, were the primary volatile products at low temperatures. They were converted with increasing irradiation time and dose into C,H,. c‘,H,, and heavier hydrocarbons up to C,. During the warmup phase even more complex hydrocarbons up to C,, were emitted including substituted henrenes (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 suprathermnl reactions as one of the most prominent processes.