Schematic view of the experimental protocol. The IFs are condensed by injection of a gas mixture on a substrate window at 10 K. A first isotopically unlabeled ice layer is deposited (light blue, (1)), followed by a thin layer of isotopically labled ice (red, (2)) and a final unlabeled ice layer (light blue, (3)). The whole IF is irradiated by heavy ions (4), resulting in the radiolysis of initial species and the formation of new molecules (5). At the end of the irradiation, the IF is slowly annealed from 10 K to 300 K, causing the sublimation of remaining volatile species (6) and the formation of a refractory OR (7).