Carbonic acid production in H2O : CO2 ices - UV photolysis vs. proton bombardment

We have the unique ability to perform ultraviolet photolysis (similar to 10 eV photon(-1)) and ion irradiation (0.8 MeV p(+)) in the same experimental set-up, with ices created under identical conditions. We present experimen ts that show the formation of carbonic acid (H2CO3) from H2O:CO2 ice mixtur es exposed to either UV photons or high-energy protons. CO and CO3 were als o formed in these experiments. Results show that while H2CO3 is readily for med by p(+) bombardment, its formation by UV photolysis is limited by the p enetration of UV photons into the ice. H2CO3 production pathways are invest igated. Intrinsic IR band strengths are determined for eight IR features of H2CO3. Implications for ices found in various astrophysical environments a re discussed.