An electron paramagnetic resonance study of rotational and translational motion in solution

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Abstract
Electron paramagnetic resonance (E.P.R.) spectra of dilute and concentrated solutions of two nitroxide spin probes differing in size and shape have been examined in toluene and in the isotropic phase of the liquid crystal MBBA. The results are discussed in detail using the hydrodynamic theory of molecular relaxation in liquids. The feasibility of using electron spin relaxation data to test the Hynes-Kapral-Weinberg theory of molecular dynamics in liquids is also examined. It appears that electron spin relaxation results are useful for testing theories of reorientational relaxation in liquids; however, the translational diffusion constants obtained from E.P.R. linewidth studies are not accurate enough to test molecular theories of translational motion in liquids.