Dissociation of dimethyl sulfide on water ice initiated by low-energy (<20 eV) electrons

Abstract

Dimethyl sulfide (CH₃SCH₃) is the most widespread of biogenic sulfur compounds responsible for sulfur aerosol production in the atmosphere. Here, we show that low-energy electrons, produced by ionization in the upper troposphere, can dissociate DMS and generate a variety of anion fragments, e.g., H⁻, CH₂⁻, CH₃⁻, S⁻, SH⁻, SCH₂⁻ and SCH₃⁻ as well as their neutral counterparts, e.g., CH₃SCH₂, HSCH₃, SCH₃, (CH₃)₂, CH₂CH₃, CH₄, CH₃, respectively. The ions H⁻, CH₂⁻ and CH₃⁻ arise from dissociative electron attachment (DEA) below 13 eV and from direct dipolar dissociation above that energy. The other anions, which contain a sulfur atom, appear to be formed only via DEA. The anion desorption yields for CH₃SCH₃ adsorbed on water ice were measured between 1 and 18 eV. In units of 10⁻³ anion per incident electron and per cm³, these yields averaged over the 1–18 eV range are 60 (H⁻), 0.1 (CH₂⁻), 1.0 (CH₃⁻), 1.2 (S⁻), 0.1 (SH⁻), 0.1 (SCH₂⁻) and 0.3 (SCH₃⁻).