Three-dimensional quantum dynamics of H2O and HOD photodissociation

Abstract

Three-dimensional quantum mechanical calculations of the VUV photodissociation of H2O and HOD on realistic potential surfaces are presented. The dynamical equations in the ground and excited states are solved by a coupled channels expansion using the artificial channel method. The photoabsorption spectrum in the 1360–1290 Å range is computed. A progression of ‘‘Feshbach-type’’ rotational resonances, whose positions coincide very nicely with the well-known diffuse bands of water is obtained. A bimodal rotational state distribution of the OH(2Σ) photofragment is shown to exist. It is a result of an interplay between the direct process (giving rise to an inverted ‘‘abnormal’’ distribution) and a compound process (resulting in a substantial contribution of a thermal-like component). The branching ratio for OH/OD production is shown to be a sensitive function of photon energy, as are the OH versus OD rotational state distributions. General implications concerning our ability to theoretically analyze and predict the dynamical behavior of the three-body system, as a result of this calculation are discussed.