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

The resonance-enhanced multiphoton ionization (REMPI) of SO, 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((a) over tilde B-3(1)) <-- SO2((X) over tilde (1)A(1)). It has been reasonably assumed that SO2((C) over tilde B-1(2)), produced by the subsequent excitation of SO2((a) over tilde B-3(1)), plays a key role in generating the fragment ions. It seems that the fragment ions come mainly from the photoionization of neutral fragments dissociated from SO2((C) over tilde B-1(2)) while the parent ion is formed directly by further photoionization of SO2((C) over tilde B-1(2)). 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((C) over tilde B-1(2)).