Methanol Formation\nin Hyperthermal Oxygen Collisions\nwith Methane Clathrate Ice

The presence of small organic molecules at airless icy\nbodies may\nbe significant for prebiotic chemistry, yet uncertainties remain about\ntheir origin. Here, we consider the role of hyperthermal reactive\nions in modifying the organic inventory of ice. We employ molecular\ndynamics using the ReaxFF formalism to simulate bombardment of carbon-bearing\nice by hyperthermal water group molecules (H<sub><i>x</i></sub>O, <i>x</i> = 0–2) with kinetic energy between\n2 and 58 eV. Methanol is the dominant closed-shell organic product\nfor a CH<sub>4</sub> clathrate irradiated at low dose by atomic oxygen.\nIt is produced at yields as high as 10%, primarily by a novel hot-atom\nreaction mechanism, while radiolysis makes a secondary contribution.\nAt high irradiation doses (≳1.4 × 10<sup>15</sup> cm<sup>–2</sup>), the composition is driven toward greater carbon\noxidation states with formaldehyde being favored over methanol production.\nOther water group impactors are less efficient at inducing chemistry\nin the ice, and alternate clathrate guest species (CO, CO<sub>2</sub>) are very robust against hydrogenation.