Interactions among the lower valence states of the OH radical

In order to define the origins of experimentally observed predissociations within the A²Σ⁺ state of OH, we have computed overlaps of the bound level vibrational wavefunctions in the A ²Σ⁺ state with the vibrational continua of states of OH arising from the ground electronic state separated atoms. Rapid variation of overlap with rotational quantum number is found to occur for the a ⁴Σ^- and X²II_i states with the A²Σ⁺ state. The resulting predissociation widths are compared with the experimental data, and shown to be able to reproduce it by assuming that the a⁴Σ^- state dominates in radiationless depopulation of the OH A²Σ⁺ state. The dependence of the transition moment upon internuclear distance is derived, and compared with previous results. Implications of this analysis in terms of the two body formation of OH are indicated.