The distance distribution of radical—paramagnetic ion pairs studied by the electron spin echo method. Spatial regularities of radical diffusion in glassy alcohols

Abstract

Applications of the electron spin echo (ESE) technique to determine the distance distribution function for radical-ion pairs stabilized in solids are described. The ESE signal intensity depends on the ion spin-lattice relaxation time T 1, thus on temperature, as well as on the function n( r), n( r) can be determined up to a distance of 50 A. At r < 10 - 20 A it is possible to estimate the portion of radicals stabilized at these distances in the vicinity of a paramegnetic ion. The photochemical reaction Fe 3+ + R 2CH(OH)→Fe 2+ +_R 2C(OH) + H + has been studied in glassy methanol and isopropanol. The pair distribution function n( r) has been obtained at 17 < r < 26 A. Its changes induced by radical diffusion have been studied. The portion of radicals stabilized at distance r < 17 A was about 80% for both alcohols.