Paramagnetic resonance of SO₂⁻radical-ion in solution: Spin-rotational relaxation mechanism

The E.P.R. linewidth of the SO2 - radical-ion in water solution has been studied as a function of temperature and viscosity. A strict dependence of the linewidth on T/η has been observed over the range of temperature and viscosity examined. The analysis of all possible broadening mechanisms shows that the spin-rotational interaction is the only process effective on the linewidth. The theory extended by Atkins and Kivelson [3] to E.P.R. relaxation has been checked quantitatively. From the slope of ΔH versus T/η and the principal values of the g tensor of the SO2 - radical-ion, the value of the hydrodynamic radius is r = 0·91 å. Comparison with the linewidth of the ClO2 isoelectronic radical has been made.