Nuclear electron double resonance and scalar interactions in solutions

Abstract
The electron-nuclear Overhauser effect at two magnetic fields has been investigated for solutions of 2,4,6-tri-tert.-butyl phenoxy radical in several protonated and fluorinated organic solvents. In some cases the enhancement of the nuclear resonance is positive in sign, and the results have been interpreted in terms of the theory of Hubbard (1966) in which both dipolar and scalar interactions between the electrons and nuclei are considered. Hubbard assumes two models for the scalar interaction which he calls the sticking and diffusion models. The experimental results may be best explained in terms of the diffusion model. The theory permits calculation of the diffusional correlation times, distances of closest approach of the nuclei to the electrons, and relative diffusion coefficients of the solvent and radical molecules. Reasonable values are obtained for the systems investigated.