Ion—Molecule Reactions of [C,H 3,S] + Ions and Evidence for Long-Lived Triplet CH 3 S +

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.

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