Characterization of the excited electronic states of the SH radical byab initiomethods

Abstract

Ab initio MRD-CI calculations have been performed for the SH radical in its low-lying valence states as well as vertically for the first Rydberg terms (2π²4s, 2π²4p and 2π²3d). The lowest 1 ^4,2Σ^-, 1 ²Δ and 2 ²Σ⁺ states are found to be of valence character in the vertical region, while a Rydberg structure was suggested by an earlier ab initio study. For the bound X ²Π _i and A ²Σ⁺ various molecular constants such as spectroscopic parameters, dipole moments, Franck-Condon factors and spin-orbit constant are reported. The predissociation of A ²Σ⁺ in its low-vibrational levels observed by Ramsay is confirmed to be caused by the repulsive 1 ^4,2Σ^- states. Furthermore, a complete reassignment of the electronic structure of the experimentally measured Rydberg levels is given: all these states are found to have a 2π²4s (B ²Σ^- and C ²Δ), 2π²3d _σ (E ²Σ^-) and 2π² nd _σ, n = 3–6 (D, F, G, H ²Δ) electronic configuration respectively. The E ²Σ^- and C ²Δ states are classified here for the first time, while the B ²Σ^- has been reclassified with respect to prior theoretical work. An earlier experimental assignment of the higher ²Δ levels given by Morrow, namely 2π² ns (n = 5–8), is found to be in contradiction with an applied ionization limit correlating with SH⁺ in its X ³Σ^- state.