HYDROGEN–DEUTERIUM EXCHANGE IN PHOTOLYZED METHANE–WATER ICES

Abstract

Previous work has concluded that H–D exchange occurs readily in polycyclic aromatic hydrocarbons frozen in deuterated water (D2O) irradiated with ultraviolet light. Here, we examine H–D exchange in methane–water ices following exposure to ultraviolet radiation and analyze the products formed as a result. We find that H–D exchange also occurs in methane–water ices by means of ultraviolet photolysis. Exchange proceeds through a radical mechanism that implies that almost all organic species will undergo significant H–D exchange with the matrix in water ices exposed to ultraviolet radiation. Given sufficient energetic processing of the ice, the H/D ratio of an ice matrix may be transferred to the organic species in the ice.