Hydrogen peroxide formation by ion implantation in water ice and its relevance to the Galilean satellites

We have carried out, by in situ infrared spectroscopy, experiments on the implantation of ions into water ice at 16 and 77 K. The samples have been irradiated with 30 keV single charged ions: H, C, N, O and Ar. In all the cases, the sample thickness was larger than the penetration depth of the corresponding ion. The formation of the hydrogen peroxide band, with a peak position that varies between 3.50 and 3.52 μm (2860 and 2844 cm−1), has been studied. We have found that H2O2 is produced at the two different temperatures by all the different ions. This result shows that H2O2 may be produced by radiolysis on the surface of the satellite Europa even if water ice is the only component, i.e. in the absence of a further oxidant such as carbon dioxide, as previously suggested (Icarus (2000) 282). We have also obtained that the amount of H2O2 produced by N and Ar implantation does not vary significantly with the temperature. In contrast, marginally for C, notably for H and especially for O, more H2O2 is produced at 77 K than at 16 K.