Theoretical studies on sulfur-containing radical ions

Structures and properties are reported for pi*-radical cations and for sigm a*-radical cations and anions, containing SS, SN and SO odd-electron bonds, from a variety of ab initio molecular orbital techniques and Density Funct ional Theory (DFT). Characteristic frequencies and absorption bands are det ermined to aid in the assignment of transient vibrational and optical spect ra detected in pulse radiolysis experiments. Hyperfine coupling tensors are evaluated to facilitate the identification of these radicals by EPR spectr oscopy. By comparison with predictions from accurate coupled-cluster based calculations in some simple model systems, DFT is shown to have difficultie s in correctly describing the electronic structure of these radical ions. U seful linear relationships are uncovered between the computed length of the odd-electron bond and both the wavelength of maximum optical absorption an d the bond stretching frequency.