Structure and Energetics of Ionized Water Clusters : ( H 2 O ) n + , n ) 2 - 5

Energetics and geometrical structures of neutral, (H2O)n, and ionized, (H2O)n, water clusters, with n ) 2-5, are investigated using local-spin-density functional electronic structure calculations with exchange-correlation gradient corrections. While the ground-state structures of the neutral clusters are hydrogen-bonded cyclic ones, those of the molecular ions are noncyclic. The lowest energy isomers of the ionized (H2O)n clusters contain a hydrazine-like fragment, (H2OOH2), hydrogen-bonded to the extra water molecules. Higher energy isomers of the cluster ions are based on hydrogen bonding to a disproportionated fragment, (H3O)OH.