Rotational line strengths in a 5Σ – 5Π transition with application to the A – X system of CrO

Abstract

Detailed calculations of the line strengths in a 5Σ – 5Π transition as a function of J show that the relative branch intensities in the A – X system of CrO, which do not follow the published formulae for 5Σ(b) – 5Π(a) transitions, can be explained very well in terms of strong spin uncoupling in the5Π state, with a single perpendicular transition moment dominating. It is emphasized that spin uncoupling affects line strengths by an amount that increases very rapidly with multiplicity, so that algebraic formulae for the pure coupling cases quickly lose their value. An unusual cancellation effect occurs in the main branches of a 5Σ – 5Π transition, nine of which have intensities that drop to zero and then rise again with increasing J.