Structure and Energetics of Ionized Water Clusters: (H2O)n+, n = 2−5

Energetics and geometrical structures of neutral, (H 2 O) n, and ionized, (H 2 O) 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 (H 2 O) n + clusters contain a hydrazine-like fragment, (H 2 OOH 2 ) +, hydrogen-bonded to the extra water molecules. Higher energy isomers of the cluster ions are based on hydrogen bonding to a disproportionated fragment, (H 3 O) + OH.