Electronic structure and photoionization dissociation studies of dimethyl monothiocarbonate, CH3OC(O)SCH3

Dimethyl monothiocarbonate, CH3OC(O)SCH3, was synthesized by reaction of methyl chlorothioformate with dried methanol, the product was separated and purified by trap-to-trap condensation before detection and characterization by the photoelectron and photoionization mass spectroscopy. The geometric and electronic properties of CH3OC(O)SCH3 were investigated by the combination of experimental and theoretical studies. The assignment of the bands in the photoelectron spectrum is reasonably supported by previous studies on analogous molecules, as well as the outer-valence Green’s function (OVGF) calculations. The first ionization process happens on the 3p out-of-plane lone pair of sulfur atom n′′S, and the experimental first vertical ionization potential is 9.46 eV. It is worth mentioning that the CSCO dihedral angle twists after ionization and the cationic-radical form becomes non-planar. In the PIMS, it shows six peaks: CH3+, CH3O+, CH3S+, CH3OCO+, CH3SCO+ and CH3OC(O)SCH3+ (M·+), with the dominant features being the CH3SCO+ peak. According to the calculated bond dissociation energies, the dissociation process was discussed. The calculated results indicate that the most preferred dissociation pathway for the parent ion is to form CH3SCO+ and CH3O.