VUV Photolysis of CH4-H2O mixture in methane-rich ices: Formation of large complex organic molecules in astronomical environments

Abstract

The present work aims to highlight the influence of water molecules in the photo-decomposition of methane ice and reveal the photoproducts formed in solid phase upon VUV irradiation of CH4-H2O mixture in methane-rich ices. The analysis of our IR spectra shows that even with very low concentrations of water in methane ices, several oxygenated hydrocarbons are formed as photoproducts derived from the photodecomposition of water and methane at cryogenic temperatures. We show that both alka[e]nes and oxygen bearing organics are efficiently formed at temperatures as low as 3 K. However, while the IR signatures of the alka[e]nes such as C2H6, C2H4 and C2H2 dominate the IR spectra of the irradiated CH4-H2O ices at temperatures lower than 50 K, the heating of the sample to 110 K reveals the formation of large carbon chain complex organic molecules such as ethanol, pronanol, propanal and glycolaldehyde.