Multiphoton dissociation/ionisation of dimethyl sulfide

Abstract

Multiphoton dissociation/ionisation studies have been carried out at 355 nm for dimethyl disulfide (CH₃SSCH₃) using a time-of-flight-mass spectrometer. The prominent ion signals observed are CH₃⁺, S⁺, HCS⁺ and S₂⁺. No evidence for the formation of a parent ion signal was observed. The laser power variation experiments show a two-photon dependence for the most prominent HCS⁺ ion. The presence of a signal at m/e 30 is explained in terms of concerted elimination of ethane from the excited neutral CH₃SSCH₃ via a cyclic transition state. It is inferred that the multiphoton dissociation of CH₃SSCH₃ at 355 nm involves both S-S and C-S bond cleavage. Based on these results, it has been suggested that CH₃S⁺ isomerises to CH₂SH⁺, which undergoes unimolecular decay to produce HCS⁺ by H₂ elimination. The results have been interpreted in terms of the dissociation of the parent molecule using two photons, followed by the ionisation of the fragments.