H2S-CIMS: Theoretical calculations of the energies and structures of secondary ions in the ion source

The most stable structures of the plasma ions H3S+, S2+, H2S2+, H3S2+, [H2S···H3S]+, H2S3+, H3S4+ and HSn+ were obtained by the ab initio G3B3 method, in which the G3 method is extended with B3LYP/6-31G(d). Of the three isomers of H2S3+, the C2V structure, with terminal hydrogen atoms, proved to be the lowest energy. The structure of the adduct [H2S···H3S]+ was found to be comparable with that of the water adduct [H2O···H3O]+. An enthalpy of −59.9 kJ mol−1 was calculated for the reaction H3S+ + H2S → [H2S···H3S]+ and the exothermic reaction enthalpies of the polysulfonium ions, formed according to the equation HSn+ + S → HSn+1+, lie in the range 225-347 kJ mol−1 for n = 1-8.