Photoion–fluorescence photon coincidence study of radiative and dissociative relaxation processes in VUV photoexcited SO2. Fluorescence of SO+2, SO+, and SO

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Abstract
Line photoexcitation sources in the range 10.2–21.2 eV are used to produce excited electronic states of SO2 and/or SO+2. Photoion–fluorescence photon coincidence measurements show that SO+2 states in the 16 eV region fluoresce at λF(? 2B2+? 2A1)∼6×10−5, in competition with predissociation. The products of predissociation of excited states of SO+2 are identified by their TOF mass spectra and/or dispersed optical emission. SO+(A 2Π–X 2Π), SO(B 3Σ−–X 3Σ−), and SO(A 3Π–X 3Σ−) emissions are observed when the excited products are formed with ionic or (super) excited states of SO2. The measured lifetime of the SO+A 2Π state is 2.4±0.4 μs. The results are discussed in relation to photoion–photoelectron measurements and in the context of unimolecular dissociation models.