The structure of (H3O2)−

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.