We present analysis of the molecular orbitals of an isolated water molecule physisorbed on the rutile TiO2 (1 1 0) surface and MgO (1 0 0) surface. On the TiO2 surface the 3a(1) and 1b(1) orbitals split due to the interactions with the surface atoms. This resembles the features of the experimental electronic spectra that were interpreted as an evidence for water dissociation. On MgO surface the water molecular orbitals exhibit some splitting for the 1b(1) orbital, but not sufficient to produce a pi orbital-like peak in the electronic spectra. Perturbations of the 1b(2) and 3a(1) orbitals also contribute to broadening observed in the experimental electronic spectra. (C) 2003 Elsevier Science B.V. All rights reserved.