Low-Energy Isomers of the Magic Number H(HO) Cluster.

Electronic structure calculations are used to characterize low-energy isomers of H(HO). Eleven different classes of isomers, based on the (HO) pentagonal dodecahedron with the excess proton localized on the surface (as a hydrated hydronium ion) and the "extra" water molecule located in the interior of the cluster, are characterized. In 10 of these classes, the internal water molecule is engaged in six 5-membered rings, but in the remaining class, which is predicted to start at only 0.6 kcal/mol above the global minimum, the internal water is engaged in a 4-membered ring, an additional 6-membered ring, and four 5-membered rings. In addition, isomers with two 4-membered rings and two 6-membered rings on the cluster surface are predicted to start at only ∼1.3 kcal/mol above the lowest-energy dodecahedral-based structure.