Photodissociation of vibrationally excited water in the first absorption band

We investigate the photodissociation of highly excited vibrational states of water in the first absorption band. The calculation includes an ab initio potential energy surface for the Ã-state and an ab initio X̃→Ã transition dipole function. The bending angle is fixed at the equilibrium value within the ground electronic state. Most interesting is the high sensitivity of the final vibrational distribution of OH on the initially prepared vibrational state of H2 O. At wavelengths near the onset of the absorption spectrum the vibrational state distribution can be qualitatively understood as a Franck–Condon mapping of the initial H2 O wave function. At smaller wavelengths final state interaction in the excited state becomes stronger and the distributions become successively broader. Our calculations are in satisfactory accord with recent measurements of Vander Wal and Crim.