A theoretical and experimental study of the SO22+ dication

The double photoionization spectrum of SO2 has been measured using the TOF-PEPECO technique and contains one resolved band. Detailed electronic structure calculations and experimental comparisons allow the resolved band to be identified as the A 1A2 state of the SO2(2+) dication, with its adiabatic ionization energy at 35.284+/-0.02 eV. According to the most accurate calculations, the ground state level of SO2(2+) must be located near 33.48 eV, well below the range accessed by vertical transitions from neutral SO2. Transient SO2 (2+) molecules detected by mass spectrometry may be identified either as the sharp levels of the A 1A2 state or as ground state levels populated by nonvertical ionization pathways.