Pulse radiolysis of deuterated aqueous LiCl glasses. Dependence of the yields and rates of reaction of visible and infrared absorbing trapped electrons on LiCl concentration

Abstract

The yields and reactions of trapped electrons which absorb in the visible (evis−) and infrared (eir−) have been studied by pulse radiolysis in deuterated aqueous 6–15 M LiCl glasses at low temperatures. At 76 K G(evis−) increases and G(eir−) decreases as the concentration of LiCl is increased, but [Formula: see text] over the whole concentration range. Because the hydration number of Li+ is 4, G(eir−)/G(evis−) was plotted against [free D2O]/[LiCl•4D2O] and found to give a straight line passing through the origin, for [D2O]/[LiCl] > 4. From this proportionality it is concluded that eir− is an electron trapped in a purely amorphous water environment and evis− is mainly associated with water bound to Li+.The reactions of eir− and evis− with Cu(II) and SeO42− have been investigated. At 138 K the rate of reaction of evis− with SeO42− increases with decreasing [LiCl] whereas its rate of reaction with Cu(Il) is slower and independent of [LiCl]. At 76 K, where the rates of reaction of eir− with the scavengers can also be measured, it is found that in each case evis− and eir− react more slowly in 12 M LiCl glass than in 6 M LiCl glass, the difference being more marked for SeO42−. In the absence of scavenger the electron in the smaller yield decays faster. These observations can be rationalized on the basis that electrons can tunnel in either direction between visible and infrared traps before being scavenged, and it seems they cannot be rationalized in terms of direct tunnelling only.G(Cl2−) is found to be proportional to the electron fraction of Cl−•3D2O in the glass and its extrapolated value for pure Cl−•3D2O is 3.4. It is inferred that Cl2− arises mainly from ionization of the D2O bound to Cl−.