The potential energy surface of the ground stare and lowest lying singlet of o-hydroxyacetophenone was calculated at the ab initio SCF and CIS levels, respectively, using a split-valence basis set to which was added polarization functions on atoms involved in the intramolecular H-bond. Whereas these potentials each contain one minimum corresponding to the normal form and a second well for the proton-transferred tautomer, only one minimum appears in these potentials after correlation is added. S-0 --> S-1 excitation hence induces the tautomerization associated with intramolecular proton transfer from the hydroxyl to the carbonyl oxygen. The excited state proton transfer may involve a nonradiative transition from the S-1(n pi*) state to S-1(pi pi*). The vibrational spectra of the two tautomers have certain strong differences. Anharmonic adiabatic treatment of the OH...O segment of the molecule leads to improved reproduction of experimentally observed nu(O...O) and nu(OH) frequencies.