Dynamics of OH Λ-doublet production through photodissociation of water in its first absorption band. I. Formal theory

Abstract

The formal theory is presented for the photofragmentation of water into a hydrogen atom and an OH radical in its ground 2Π state. Full account is taken of the electron spin angular momentum, the electronic orbital angular momentum and the angular momentum generated by motion of the nuclei. A formula is presented which permits the calculation of the differential cross section for the production of individual OH(X 2Π)Λ-doublet states. From this formula others for less detailed cross sections are derived. In particular, an expression is presented for the integral photodissociation cross section for the production of OH Λ-doublet fragments. In all cases the formulas are specialized to apply to the à 1B1 ← X 1A1 photodissociative transition of water. The general formalism that is developed however, transcends this particular application. It is clearly apparent how the formalism may be extended to apply to many other cases of current experimental interest. Simplified formulas are derived to permit approximate Franck–Condon estimates of the photodissociation cross sections and product state distribution to be made.