Vertical double ionization of the sulphur dioxide molecule Original Research Article

Vertical double-ionization energies, for transitions from the ground state of the neutral sulphur dioxide molecule to both singlet and triplet energetically low-lying electronic states of the SO22+ dication, have been studied both experimentally with double-charge-transfer spectroscopy and theoretically with ab initio propagator calculations; consistently good agreement is found between the theoretical and experimental results. The experimental data for transitions to singlet states of SO22+ are also found to be consistent with the results of earlier studies of SO2 employing Auger spectroscopy, which also match closely the theoretical predictions in the higher-energy range not currently accessible with double-charge-transfer spectroscopy. The results of this paper, therefore, provide a comprehensive survey of the vertical double ionizations of SO2 up to 50 eV in energy, allowing an analysis of some earlier PIPICO data for SO2.