Fluorescence from the CS22+ dication: Theory and experiment

The recently discovered CS22+ emission has been investigated experimentally and theoretically, leading to the identification of two separate fluorescent dicationic transitions (X3Σg-←13Σu- and 11Δg ← 11Δu). The vertical energies of the fluorescent electronic states were directly obtained by detecting photons in coincidence with electron pairs. Their assignment was aided by the use of glass filters to isolate the spectral region of each emission and by performing highly correlated MRCI calculations at a range of geometries. The potential energy curves thus generated predict bound potential energy functions for all linear Σ and Δ states of triplet and singlet spin multiplicities, throughout the energy range studied. Dissociation onsets for different fragmentation pathways are re-evaluated by detecting ions in coincidence with electron pairs. The C+ + S+ onset is revised downwards to 36.8 ± 0.4 eV and C++S2+ formation is found to arise from non-statistical dissociation of a limited number of precursor states, which have been identified to be the electronically excited CS22+ formed in bent structures at these internal energies. Assignments have been attempted for all fragment emissions observed by measuring quantum yields as a function of the selected spectral region.