Free energy and entropy of formation of water clusters on hydronium ions under conditions of exposure of the atmosphere to ionizing radiation: A computational study

Monte Carte simulation of H3O+(H2O)(N) clusters, where N = 1,..., 20, is reported. The intermolecular potential was reconstructed from experimental data on the internal and free energies of clusters having N = 1,..., 7. The interactions in the system are essentially of a nonpair character. The most significant nonpair contributions are observed at the distance of closest approach to the ion. The work of clustering shows a minimum with a well depth of about 0.5 eV corresponding to the thermodynamically stable state of the hydration shell. Under normal atmospheric conditions, all ions are hydrated and bear 5-6 water molecules.