A theoretical derivation of closed form expressions for the intensities of all the rotational branches arising out of4Σ-4Π electronic transition in a diatomic molecule is described. In the present theory the tradition of treating the coupling in the4Σ state as belonging to Hund’s case (b) is discarded; instead a full-fledged intermediate coupling treatment which rigorously takes into account the spin-spin and second order spin-orbit effects is presented. Since accurate intermediate coupling treatment of4Π, in analytically closed form, is not possible, the4Π is first restricted to the extreme coupling scheme Hund’s case (a)(or case (b)); the effect of spin uncoupling (or spin-orbit and spin-spin interactions) is then incorporated through a first order perturbation calculation.
Volume 94, 2020
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