The structure of (H3O2)−

Abstract
Global geometry optimizations of the hydroxide hydrate anion (H3O2) are performed at the 4‐31G, 6‐31G*, and 6‐31G** levels to determine its structure. Further geometry searches are carried out using configuration interaction with double substitutions, and Mo/ller‐Plesset perturbation theory to second and third order. An asymmetric hydrogen bond is found at the SCF level, while a symmetric structure results when correlation is included. Comparisons are made to previous theoretical studies of (H3O2), and also to recent x‐ray crystallography results. An analysis of the larger correlation energy in the symmetric case is given.