Interactions between bare and tri-solvated (Eigen) hydronium with water and methanol is investigated with ab initio methods. Unexplored configurations on the oxygen side of H3O+ are covered to improve our understanding of the solvation energetics. Results indicate that the interaction between the charged and polar species, with oxygen atoms oriented toward H3O+ oxygen ('back to back' or 'O-side' to 'O-side' interaction), is similar to or stronger than a hydrogen bond. The repulsion along the O-O directrix onset in the range 2.2-2.7 angstrom, indicating H2O short-range O-O contacts with (H3O+) as possible despite water coordination. (C) 2012 Elsevier B. V. All rights reserved.