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

Abstract

A semi-empirical calculation of the fine structure of the 3 Σ − ground states of several diatomic hydrides gives results in very good agreement with experiment. The Λ doubling of the 3 Π 0 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 3 Π 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 3 Σ − and 1 Σ + states and by a higher lying 1 Π state, one must take into account perturbation by the lower lying 1 Δ state. The values of the parameters obtained from fitting the experimental data support this interpretation.