Experimental and theoretical study on the ethane and acetylene formation from electron irradiation of methane ices

In this work we present an experimental and theoretical study on the formation of ethane and acetylene from solid methane condensed at 20 K and irradiated with a 500 - 3000 eV electron beam. The experiments were monitored with Thermal Desorption Spectroscopy. We observe that the electron irradiation induced a dehydrogenation of methane and a consequent formation of CHx (x = 1, 2, 3) fragments. Furthermore, in the solid during irradiation, a simple recombination reaction in the solid between two adjacent CHx molecules may form HC≡CH, H2C=CH2, and H3C-CH3 with a triple, double, and single carbon-carbon bond, respectively. The formed amount of ethane and acetylene increases with irradiation time and reaches a saturation value.