Solid water (H2O) ice is found in high abundances in a large variety of astrophysical environments: e.g. icy mantles coating interstellar dust grains, in icy bodies like comets and satellites like Europa where exposure to energetic photons, ions and electrons is significant. In these conditions, solid H2O is known to dissociate into H and OH fragments under VUV irradiation while promoting ionization of organic impurities such as polycyclic aromatic hydrocarbons (PAHs). This was explained in terms of the relatively high electron affinity of the H2O molecules and of the OH fragments which, in synergy with the thermodynamic stability associated with the solvation of ions in solid H2O, enhances the ionization of positively charged PAHs [1-3]. If such ions are indeed produced, these will change the dielectric properties of the ice and can move inside the H2O matrix when a bias is applied, depending on the ice temperature. Our work reports on the investigation of photocurrents in millimeter-sized, water-rich ices containing organic impurities (e.g. toluene) and aims at understanding how these measurements correlate with the desorption of volatiles during vacuum ultraviolet (VUV, e.g. 121.6 nm) and electron (2 keV) irradiation.

Photo-conductivity measurements of water-rich ices at cryogenic temperatures

253rd National Meeting (2017)

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