ESR Linewidths in Solution. III. Experimental Study of the Solvent Dependence of Anisotropic and Spin—Rotational Effects

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Abstract
The ESR linewidths of vanadyl acetylacetonate in diphenylmethane have been studied as a function of temperature. The results confirm the analysis made previously for the linewidths of vanadyl acetylacetonate in toluene. The major contributions arise from anisotropic g and hyperfine interactions and from spin—rotational effects. The parameter λ⅓=r/3.045 Å, where r, the hydrodynamic spherical radius of the radical, is introduced as an adjustable parameter. This one parameter is sufficient to enable the theory to explain the linewidth results in a number of solvents, but a slightly different value of λ is required for each solvent. This variation may be due to solvation effects. Studies of deuterated vanadyl acetylacetonate in carbon disulfide indicate that neither intermolecular dipolar interactions nor unresolved proton extrahyperfine splittings contribute appreciably to the linewidth.