PARAMAGNETIC RELAXATION OF RADICAL SPECIES IN GAMMA-IRRADIATED GLASSY ETHANOL SOLUTION OF TETRACYANOETHYLENE ANION RADICAL - ROLE OF SPECTRAL DIFFUSION IN CROSS RELAXATION

The mechanism of paramagnetic relaxation for hydroxyethyl radicals and chemically prepared tetracyanoethylene anion radicals in γ-irradiated solid ethanol has been studied at 77 K by an electron spin echo method. Cross relaxation between anion radicals and hydroxyethyl radicals is much faster than that between anion radicals themselves. The cross relaxation between the anion radicals and hydroxyethyl radicals is induced by spectral diffusion of off-resonant hydroxyethyl radicals into the on-resonant spectral region of the anion radicals, which in turn is induced by the time fluctuation of the hyperfine fields due to the rotation of methyl groups on the hydroxyethyl radicals. Spectral diffusion by rotation of the methyl group is so fast that only hydroxyethyl radicals with methyl proton spin states of ±(1/2, 1/2, 1/2) are observed on the electron spin echo detected ESR spectrum. The theoretical cross relaxation rate of the anion radicals agrees with the observed one. © 1990 American Chemical Society.