Intensity distribution in the rotational structure of1 Δ−2 Σ and1 Π−3 Σ transitions in diatomic molecules

Abstract

Rigorous analytic formulae are derived for the rotational intensity factors of the lines of all the branches resulting from the spin-forbidden electronic transitions1 Δ−3 Σ and1 Π−3 Σ in diatomic molecules. The present derivation incorporates a full-fledged intermediate coupling treatment of the3 Σ state which includes the effects of centrifugal distortion on spin uncoupling. These formulae when applied to the transitiona 1 Δ g −X 3 Σ − in diatomic sulphur predict an intensity pattern that markedly differs from the predictions of previous formulae based on case (b) treatment of3 Σ.