FINE STRUCTURE OF 3Σ− AND 3Π STATES OF NH, OH+, PH, AND SH+

Abstract

A semi-empirical calculation of the fine structure of the 3Σ− ground states of several diatomic hydrides gives results in very good agreement with experiment. The Λ doubling of the 3Π0 first excited state, for J = 0, is shown to result from the algebraic sum of the spin–spin contribution and the spin–orbit interaction with Σ states. For the NH radical, the former effect predominates. For heavier molecules, the spin–orbit contribution dominates and the sign of the Λ doubling is reversed.The positions of the 3Π rotational levels do not agree with Gilbert's formulae. The apparent shift is interpreted by a simple model. In addition to the perturbation by the lower lying 3Σ− and 1Σ+ states and by a higher lying 1Π state, one must take into account perturbation by the lower lying 1Δ state. The values of the parameters obtained from fitting the experimental data support this interpretation.