High-resolution angular-resolved measurements of the fragmentation of the core-excited OCS molecule

The sulfur $2p$ and carbon $1s$ core-electron excited states of the OCS molecule have been studied in high-resolution angular-resolved photoion experiments. Vibrationally resolved total ion yield spectra of this molecule have been recorded and several previously unobserved states have been revealed and tentatively assigned to the singly excited $ns,$ $np,$ and $\mathrm{nd}$ Rydberg levels. The $\mathrm{LS}$-split ${\ensuremath{\pi}}_{1/2}^{*}$ and ${\ensuremath{\pi}}_{3/2}^{*}$ states show significant bond length changes observed as very different intensity distributions of vibrational progressions of these states. Variations of the bond lengths of the Rydberg states have also been revealed by analyzing their vibrational structure. However, in the latter case the effect is found to be mainly dependent on the symmetry of the Rydberg electron orbital, while the state of the core electron plays a minor role. Asymmetric dissociation from the core-excited levels has been studied using the angular-resolved photoelectron-photoion technique. In general the derived values of the asymmetry parameters \ensuremath{\beta} support the proposed classification of the observed resonances. Remarkably, the differences between the theoretical and experimental values of the \ensuremath{\beta} parameters are large. The analysis of this discrepancy is supported by the results of separate triple coincidence measurements from which main fragmentation mechanisms are deduced. The coincidence measurements consistently indicate a bent geometry of the $\mathrm{S}{(2p}^{\ensuremath{-}1}){\ensuremath{\pi}}_{1/2}^{*}$ and $\mathrm{S}{(2p}^{\ensuremath{-}1}){\ensuremath{\pi}}_{3/2}^{*}$ states.