Ion—Molecule Reactions of [C, H3, S]+ Ions and Evidence for Long-Lived Triplet CH3S+

Abstract

Gas-phase [C, H3, S]+ ions obtained by electron impact from (CH3)2S at 14 eV undergo two distinct low-pressure ion–molecule reactions with the parent neutral: proton transfer and charge exchange. The kinetics of these reactions studied by Fourier transform ion cyclotron resonance (FT-ICR) techniques clearly suggests the [C, H3, S]+ species to be a mixture of isomeric ions. While proton transfer is consistent with reagent ions displaying the CH2SH+ connectivity, the observed charge exchange strongly argues for the presence of thiomethoxy cations, CH3S+, predicted to be stable only in the triplet state. Charge exchange reactions are also observed in the reaction of these same [C, H3, S]+ ions with benzene, toluene and phenetole. For these substrates, the CH2SH+ ions can promote proton transfer and electrophilic methylene insertion in the aromatic ring with elimination of H2S. The results obtained for the different substrates suggest that the fraction of long-lived fraction of thiomethoxy cations obtained at 14 eV by electron ionization of dimethyl sulfide amounts to ∼(22 ± 4)% of the [C, H3, S]+ fragments.