Production of oxidants by ion irradiation of water/carbon dioxide frozen mixtures.

We present new experimental results on the formation of oxidants, such as hydrogen peroxide, ozone, and carbonic acid, under ion irradiation of icy mixtures of water/carbon dioxide at different ratios and temperatures (16 and 80 K). Pure water ice layers and mixtures with carbon dioxide were irradiated by 200 keV He+ ions. We found that the CO2/H2O ratio progressively decreased to a value of about 0.1, the H2O2 production increased with increasing CO2 abundance at both 16 and 80 K, and the CO and H2CO3 production increased with increasing CO2 abundance at 16 K. At 80 K, the synthesis of CO was less efficient because of the high volatility of the molecule that partially sublimed from the target. The production of carbonic acid was connected with the production of CO3. O3 was detected only after ion irradiation of CO2-rich mixtures. The experimental results are discussed with regard to the relevance they may have in the production of an energy source for a europan or a martian biosphere. Astrobiology 5, 612...