EPR-Untersuchungen an elektrolytisch erzeugtem SO2

Abstract

From the triatomic molecule SO2 with 18 valency electrons we generated the mononegative radical ion with the aid of electrolytic techniques. In this way we could vary the radical concentration over a wide range and could also study the influence of counter ions and solvent molecules. The semi-empirical LCAO-MO theory of WALSH was used to calculate the g-factor shift. UV spectroscopic data of SO2 and Hückel-MO-calculations of the spin density distribution of the unpaired electron in the antibonding MO of SO2 - resulted in Δgtheor = (3.9 ± 0.6) x 10-3 which agrees rather well with Δgexp = (3.414 ± 0.003) x 10-3. The quoted error of the theoretical value refers to approximations, which have to be introduced in addition to the approximations of the LCAO-MO theory of WALSH. The HMO spin density distribution compares nicely with the distribution calculated from anisotropic hfs constants of SO2 - in a KCl single crystal which have been measured recently by SCHNEIDER et al. Higher concentrations of SO2 molecules resulted in another EPR line with Δgexp = 4.6 x 10-3 which we attribute to the solvated radical ion (SO2)xSO2 -. From the temperature dependance of the concentration ratio of the radical species in we determined W = - 6.9 kcal mol-1, x = 2, and K(0 °C) = 8.0 x 10-5 mol2 lit-2.