Implantation of multiply charged sulfur ions in water ice

Abstract Sulfuric acid has been suggested to be present on the surface of the jovian moon Europa where it is mixed with the dominant water ice. The formation mechanism of sulfuric acid is still under discussion. We present new experimental results on the implantation of S q + ( q  = 7, 9, 11) ions at an energy range between 35 and 176 keV in water ice at 80 K. Previous results on 200 keV S + implantation in H 2 O at 80 K have also been included in the data analysis. Experiments with multiply-charged ions at different energies are particularly relevant to simulate the complexity of the irradiation environment to which the surface of Europa is exposed being embedded in the jovian magnetosphere. The experiments were performed at the low energy ion beam facility ARIBE of GANIL in Caen (France). 35–176 keV S q + ( q  = 7, 9, 11) ions were implanted in solid H 2 O layers which were frozen at 80 K. Fourier Transform Infrared Spectrometry (FTIR) was used to analyze the sample in the 5000–600 cm −1 (2–16.7 μm) region with a spectral resolution of 1 cm −1 . The results of our experiments indicate that implantation produces hydrated sulfuric acid with yields that increase with ion energy, from 0.12 molecules ion −1 for 35 keV ions to 0.64 molecules ion −1 for 200 keV ions. We have also searched for the production of SO 2 and H 2 S, but we were not able to find any evidence for their synthesis. We conclude that sulfur ion implantation is the dominant formation mechanism of hydrated sulfuric acid at Europa. The suggestion that the observed distribution of sulfuric acid on the surface is well correlated with the local flux of sulfur ions find a full explanation by present experimental data.