Abstract

Abstract THE sequence of events leading to the trapping of hydrogen atoms in X-irradiated glasses and ices at 77 K (refs. 1 to 8) has been thoroughly analysed by Moorthy and Weiss9 and Kevan10, with special emphasis on the evidence obtained in e.s.r. experiments. They have found the following reactions to be the most important in producing trapped hydrogen atoms: where X2− is an oxyanion like SO42−. Their conclusion is based on the change in the yield of trapped hydrogen as acidity and oxyanion concentration are increased. In the situations represented by equations (1) and (2) the mobile electron, e−m, is the presumed precursor of the hydrogen atom which is supposed to be trapped immediately after formation. A good electron scavenger should therefore compete for the mobile electrons, and cause a reduction in the yield of H atoms. Evidence in apparent support of this has been obtained by Kevan8, who presumably measured the relative electron scavenging rates of several solutes by e.s.r. observation of the decrease in the yield of trapped H atoms. Thus he found a remarkable proportionality between electron reactivities in the solid and the aqueous phase, the latter being known from pulse radio-lysis experiments.