Rotational line-strengths in the orbitally forbidden electric dipole transitions

Abstract Expressions have been developed for the branch intensity factors of orbitally forbidden electric dipole transitions of the type 3 ∑ ± - 3 ∑ ∓ in diatomic molecules. It is shown that, in general, the line intensities are governed by the following 13 transition moments: three vibronic moments reflecting spin-orbit effects, six rovibronic moments due to orbit-rotation interaction and four higher-order cross-moments of relatively smaller magnitude. Some special cases are discussed and a few useful sum rules of general validity are established.