Study on resonance-enhanced multiphoton ionization (REMPI) of SO2 in the range 365–405 nm

The resonance-enhanced multiphoton ionization (REMPI) of SO2 in the range 365–405 nm has been studied using mass-distinguished excitation spectra. Most of the resonance peaks for both parent ion SO2+ and fragment ions SO+, S+ and O+ in the excitation spectra have been assigned to the transition SO2(ã 3B1) ← SO2(X̃ 1A1). It has been reasonably assumed that SO2(C̃ 1B2), produced by the subsequent excitation of SO2(ã 3B1), plays a key role in generating the fragment ions. It seems that tragment ions come mainly from the photoionization of neutral fragments dissociated from SO2(C̃ 1B2) while the parent ion is formed directly by further photoionization of SO2(C̃ 1B2). That the resonance peaks of the parent ion appear generally narrower than those of fragment ions can also be explained by the known spectral properties of SO2(C̃ 1B2).