2014ApJ...794...57B

Carbon dioxide (CO₂) ices were irradiated with energetic D⁺ ions to simulate the exposure of oxygen-bearing solar system ices to energetic protons from the solar wind and magnetospheric sources. The formation of species was observed online and in situ by exploiting FTIR spectroscopy. Molecular products include ozone (O₃), carbon oxides (CO₃(C_2v, D_3h), CO₄, CO₅, CO₆), D2-water (D₂O), and D2-carbonic acid (D₂CO₃). Species released into the gas phase were sampled via a quadrupole mass spectrometer, and possible minor contributions from D2-formaldehyde (D₂CO), D4-methanol (CD₃OD), and D2-formic acid (DCOOD) were additionally identified. The feasibility of several reaction networks was investigated by determining their ability to fit the observed temporal column densities of 10 key species that were quantified during the irradiation period. Directly relevant to the CO₂-bearing ices of comets, icy satellites in the outer solar system, and the ice caps on Mars, this work illustrates for the first time that D2-water is formed as a product of the exposure of CO₂ ices to D⁺ ions. These findings provide strong support for water formation from oxygen-bearing materials via non-thermal hydrogen atoms, and predict reaction pathways that are likely to be unfolding on the surfaces of asteroids and the Moon.