Theoretical study of the state-to-state photodissociation dynamics of the vibrationally excited water molecule in the B band.

The state-to-state photodissociation dynamics for the vibrationally excited H2O in its second absorption band has been investigated on the recent three-dimensional potential energy surfaces based on a large number of high-level ab initio points. The photodissociassion dynamics from three fundamental vibrational states of H2O were explored from quantum dynamical calculations including the electronic X̃ and B̃ states on the basis of a Chebyshev real wave packet method. Because of the different shapes of various initial vibrational wave functions, the photoexcited wavepackets access different portions of the upper-state potential energy surface, which yields different absorption spectra, ro-vibrational distributions, and branching ratios. The bending excited vibrational state (0,1,0) generates two lobes with a shallow minimum on the absorption spectrum, a dominant vibrational inverted population OH(X̃, ν = 1) fragment at higher energy, and a nearly single rotational product propensity. The bond-stretching vibrational states (0,0,1) and (1,0,0) show a high OH(Ã)/OH(X̃) ratio at short photon wavelength, which indicates that dissociation proceeds mainly via the adiabatic channel.