Some anomalies in the electronic spectra of GeH, GeD, SnH, and SnD related to Hund's coupling case (c)

Abstract

Expressions for the rotational energy and fine structure based on Hund's coupling case (c) are applied to the 2Π, 4Σ −, and 2Δ states of the heavy hydrides and deuterides GeH, GeD, SnH, and SnD. The 2Π ground state is found to be very well described by the case (a) coupling model, while a considerable case (c) character is found for the 4Σ − state, thus accounting for the observation of the forbidden 2 Π - 4 Σ − transition. For the 2Δ state the case (c) model yields very reasonable explanations for several apparent anomalies, in particular for the irregular isotopic shifts of the coupling constants.