Irradiation of Water Ice by C⁺ Ions in the Cosmic Environment

We present a first-principles MD (FPMD) study of the interaction of low-energy, positively charged carbon (C⁺) projectiles with amorphous solid water clusters at 30 K. Reactions involving the carbon ion at an initial energy of 11 and 1.7 eV with a 30-molecule cluster have been investigated. Simulations indicate that the neutral isoformyl radical, COH^•, and carbon monoxide, CO, are the dominant products of these reactions. All of these reactions are accompanied by the transfer of a proton from the reacting water molecule to the ice, where it forms a hydronium ion. We find that COH^• is formed either via a direct, “knock-out”, mechanism following the impact of the C⁺ projectile upon a water molecule or by creation of a COH₂⁺ intermediate. The direct mechanism is more prominent at higher energies. CO is generally produced following the dissociation of COH^•. More frequent production of the formyl radical, HCO^•, is observed here than in gas-phase calculations. A less commonly occurring product is the dihydroxymethyl, CH­(OH)₂^•, radical. Although a minor result, its existence gives an indication of the increasing chemical complexity that is possible in such heterogeneous environments