Three-dimensional quantum dynamics of H2O and HOD photodissociation

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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.