High-resolution investigation of the excited electronic states of CaSH and SrSH by laser excitation spectroscopy.

A laser ablation/pulsed molecular jet system has been used to record high-resolution laser excitation spectra of the [image omitted]2A'- [image omitted]2A' transition of CaSH and the [image omitted]2A'- [image omitted]2A', [image omitted]2A''- [image omitted]2A', and [image omitted]2A'- [image omitted]2A' transitions of SrSH. The rotationally-resolved data were analysed using an asymmetric top Hamiltonian (A-reduction) to determine rotational and fine structure parameters. A combined fit of all the newly measured and the previously recorded spectroscopic data for both CaSH and SrSH was performed. In the excited states observed in this study, both species were found to have a bent geometry. The spin-rotation parameters were analysed in terms of the pure precession and unique perturber approximations. In the excited electronic states of SrSH, the large spin-rotation interaction was found to cause perturbations between the Ka = 0 and 1 levels within each state. In the [image omitted]2A' and [image omitted]2A'' states of both species, the metal-sulfur bond length was found to decrease relative to the ground state, which is consistent with previous observations of other calcium and strontium radicals. [ABSTRACT FROM AUTHOR]