A Thermal Motion Effect in the Electron Spin Resonance of a Free Radical in Solution

The electron resonance hyperfine triplet at 9.5 mm wavelength of the peroxylamine disulphonate ion has been measured in a series of solutions of water and glycerol from 20% to 72% glycerol by weight and over a temperature range from -46° to 65°C. There is a temperature and solution dependent broadening which affects the individuals of the triplet differently. The high field line is broadened first with falling temperature. The effect is thought to be due to the motionally attenuated anisotropic electron-nuclear interaction. The anisotropic interaction is estimated to be comparable with the isotropic one. The anisotropy of the g factor, δ g / g , is 2 x 10 -3 . These parameters allow the prediction of a static spectrum of the ion in agreement with experiment (Weissmann and Banfill 1953). The effect of thermal motion of the ion is shown by the close relation between the value and temperature dependence of the thermal reorientation correlation frequency and the variation of the electron resonance signal with temperature and nature of the solvent.