Hydrogen Atoms and Solvated Electrons in Irradiated Aqueous Solutions at 77° K

Abstract

It is well known that Samuel and Magee's theory (1) for the formation of radicals in water postulates H atoms and OH radicals with the same initial yields and distribution. On the other hand, the Lea-Gray-Platzman (2) theory postulates the formation of OH radicals and solvated electrons. Since several of these initial products in irradiated aqueous solutions possess unpaired electrons, they may give rise to electron spin resonance (ESR) spectra. In liquid solutions the radicals have very short lifetimes, and in order to apply the ESR technique it is necessary to introduce some type of stabilization of the induced species. The radicals may be trapped in frozen solutions at low temperatures, and in this way Livingston et al. (3) succeeded in observing directly radiation-induced H atoms in concentrated acids at 77?K. Recent experiments (4) have shown that H atoms are very unstable in pure water and have already disappeared at about 20?K. The water resonance at 77?K has been ascribed mainly to hydroxyl radicals which disappear in the temperature range 100? to 130?K (5-7). Hart and Boag (8), using pulse radiolysis, have obtained evidence for the existence of solvated electrons in liquid water, and recent ESR observations (9-12) on alkaline solutions seem to demonstrate that solvated electrons may also be produced and trapped in frozen ionic solutions at 77?K. In the present work the formation and properties of the ESR centers induced in acid, neutral, and alkaline solutions at 77?K have been studied. Special attention has been focused on the formation of H atoms and solvated electrons and how their resonance patterns are influenced by the type and physical state of the solution. The interesting result was obtained that both H atoms and solvated electrons may be observed in alkaline solutions at the same time, a fact that may be important concerning the mechanism for the formation of radicals in aqueous solutions.