Off-diagonal spin–orbit and apparent spin–spin parameters in carbon monosulfide

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Abstract
From a detailed study of the uv spectrum of carbon monosulfide (including new line measurements to be reported elsewhere) we report here values for the vibronic spin–orbit perturbation interactions, the reduced electronic interactions, and the apparent molecular orbital spin–orbit integral, a, for perturbations between A 1Π or a 3Π states and the d 3Δi, e 3Σ−, or a′ 3Σ+ states. Although for four of six of these pairs of coupled states, the empirical values for a are within the range 289–297 cm−1, the set of six values ranges from 243 to 314 cm−1, each being about 20% larger than the results of configuration interaction calculations by Robbe and Schamps. Hence the hypothesis that a is effectively constant is not entirely substantiated for CS. We find that the effective Coriolis interaction elements within the triplet manifold are surprisingly small; from six 3Π–3Σ± perturbations we obtain 〈L+〉 =0.04±0.04. We also present values for effective spin–spin parameters for a number of 3Σ+ and 3Σ− vibrational levels and consider the off‐diagonal spin–orbit contributions from coupling with A 1Π and a 3Π. After these terms are subtracted out, the residual spin–spin terms are −2.89 and 3.02 cm−1 for a′3Σ+ and e3Σ−, respectively, which represent primarily the effect of the 3Σ+1–3Σ−1 spin–orbit interaction.