A fluorescence polarisation study of the CS2+ and the transitions

Abstract

Abstract The fluorescence yields and polarisations of the CS 2 + A 2 Π u → X 2 Π g and the B 2 Σ u + → X 2 Π g transitions have been measured between their thresholds and 30 eV using synchrotron radiation. In the outer valence region the fluorescence yields display prominent structure due to autoionising Rydberg states. New features, associated with multi-electron transitions, have been observed between 16 and 30 eV, and most have been assigned through reference to the inner valence shell photoelectron spectrum. Some of the new features exhibit vibrational progressions involving excitation of the ν 1 ′ mode. The influence of shape resonances on the photoionisation partial cross-sections has been considered. The polarisation measurements for the A 2 Π u → X 2 Π g and the B 2 Σ u + → X 2 Π g transitions have been compared with predictions derived from theoretical photoionisation partial cross-sections. The predictions for the B 2 Σ u + → X 2 Π g fluorescence polarisation display a rapid increase in the threshold region, in agreement with the experimental results. Resonant excitation and decay processes produce significant variations in the fluorescence polarisation, and these changes can be used to deduce the symmetry of the excited state. This information has allowed the assignments of some of the Rydberg series converging onto the B 2 Σ u + or the C 2 Σ g + ionisation thresholds to be clarified.