ESR Linewidths of Vanadyl β-Diketonate Complexes in Liquid Solutions
The electron spin resonance (ESR) spectra of a series of vanadyl β-diketonate complexes in dilute solutions in several inert solvents have been investigated. The widths of the lines in these spectra have been interpreted in terms of the Kivelson linewidth theory. Significant discrepancies between the experimental linewidths and those predicted by the theory were found at low temperatures and high solvent viscosities. It is concluded that the Stokes–Einstein relationship, which relates the reorientational correlation time to the solvent viscosity, is not valid in the low temperature region and that the simple description of spin relaxation by the spin–rotational interaction given by Atkins and Kivelson is inadequate.