Exploring the Role of Ion–Molecule Reactions on Interstellar Icy Grain Surfaces

The synthesis of organic molecules in the interstellar medium involves various gas-phase and surface reactions, with dust-grain surfaces playing a particularly crucial catalytic role. While ion-neutral gas-phase reactions and surface reactions are relatively well modeled and documented in databases, the interactions between gaseous ions and neutral species on granular surfaces are less understood. Recent theories propose that ion–molecule reactions on icy interstellar grains could offer efficient and barrierless pathways for the formation of complex organic molecule intermediates. This area remains underexplored in astrochemistry, highlighting the need for standardized modeling and data handling. Our study introduces an Eley–Rideal reaction model, focusing on reactions between gas-phase ions such as C+ and HCO+ and water ice on grain surfaces within a gas–grain model of cold interstellar clouds. The evolution of the model, including ion–molecule surface reactions, was studied via a three-phase gas–grain chemical network.