Correlation diagrams for Hund's coupling cases in diatomic molecules with high rotational angular momentum

Abstract

A diatomic molecule has in general three angular momenta: electronic orbital angular momentum L, electronic spin angular momentum S, and nuctear rotation angular momentum R. They couple together to form the total angular momentum J. Nuclear spin angular momentum I, if present, usually couples to J to form F, but this coupling is ignored in this paper. In general, L, S, and R are not conserved, whereas J is. We consider the limit J≫L, S, where angular momentum addition can be treated semiclassically. We present correlation diagrams that connect five limiting coupling cases (Hund's cases (a)-(e)) for a given value of J at a fixed internuclear separation r. The results pertain to bound states of a molecule as well as to two atoms ‘in collision’.