ESR linewidths in solution. VIII. Two-component diamagnetic solvents

The ESR spectra of dilute vanadyl acetylacetonate were studied in several two-component solvents as a function of component concentration. A modified Debye equation gives reasonable results for the rotational correlation time τϑ for a number of solvent systems; this equation has the form τϑ= (4π/3) r⊥3ηκ⊥/kT, where k is the Boltzmann constant, r⊥3 a volume which is constant for vanadyl acetylacetonate in all the systems, η is the solvent viscosity, and κ⊥ is a dimensionless coupling parameter. κ⊥ is κ⊥=κ⊥(A)xA +κ⊥(B)xB where κ⊥(A) and κ⊥(B) are the coupling parameters and xA and xB the mole fractions of solvent components A and B, respectively. In ’’ideal’’ cases, these two equations hold quite well. κ⊥ is independent of temperature, pressure, and viscosity (η), and the excess viscosity (η−η(A)xA−η(B) xB) is small. η(A) and η(B) are the viscosities of pure A and B, respectively. For butanol systems at temperatures decreasing towards room temperature the systems are nonideal and the equations above are not too useful.