Esr and structure of sulfur-centered radicals and radical ions. γ-Irradiated dimethyl disulfide and methane thiol single crystals at 77°k

Abstract

Single crystals of dimethyl disulfide and methane thiol were irradiated at 77°K. CH 3S radicals were produced in both compounds and measurement of the isotropic coupling constant from the methyl protons gave a value of 7.6 G. In the dimethyl disulfide crystal both the anion, CH 3SSCH 3, and the cation, CH 3SSCH + 3, radicals were observed. The disulfide anion radical exhibited an isotropic septet of lines with a = 5.0 G. Comparison with measurements on a polycrystalline sample gave g⊥ = 2.020 and g‖ = 2.000 for this radical. The disulfide cation radical exhibited an evenly spaced septet of lines with a = 9.1 G and a maximum value for the g factor of 2.032. On illumination with IR radiation (λ > 590 mm) the disulfide cation radicals were easily bleached together with about 50% of the disulfide anion radicals suggesting a photoinduced neutralization process. The presence of weak 33S satellite lines in the anion radical spectrum indicates that 12% of the unpaired spin is localized to the two sulfur 3s orbitals. The structure of the disulfide cation radical is discussed in relation to earlier studies and a dihedral angle of 180° is proposed. The mechanisms for radical formation and decay in dimethyl disulfide and methane thiol are also discussed.