HYDROGEN-BONDING AND PROTON-TRANSFER IN THE GROUND AND LOWEST EXCITEDSINGLET-STATES OF O-HYDROXYACETOPHENONE

The potential energy surface of the ground stare and lowest lying sing let of o-hydroxyacetophenone was calculated at the ab initio SCF and C IS 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 tauto mer, only one minimum appears in these potentials after correlation is added. S-0 --> S-1 excitation hence induces the tautomerization assoc iated with intramolecular proton transfer from the hydroxyl to the car bonyl oxygen. The excited state proton transfer may involve a nonradia tive transition from the S-1(n pi) state to S-1(pi pi*). The vibratio nal spectra of the two tautomers have certain strong differences. Anha rmonic adiabatic treatment of the OH...O segment of the molecule leads to improved reproduction of experimentally observed nu(O...O) and nu( OH) frequencies.