Electron tunnelling in aqueous LiCl at low temperatures. Evidence for tunnelling to acceptors via deep and shallow traps

Abstract

Rates of reaction of trapped electrons produced by pulse radiolysis in 9.5 mol dm^–3 LiCl solutions have been measured for electron acceptors which show widely differing reactivities with trapped and dry electrons. In the glass at 138 K where tunnelling occurs the reaction rate reflects the ability of the acceptor to react with dry electrons rather than with trapped electrons. For those acceptors which do not react with dry electrons the reaction rate is much slower.

At higher temperatures, where the glass is softer, the reaction rates correspond more closely to the reactivities of the acceptors with trapped electrons.

These phenomena are interpreted in terms of a trap-to-trap electron tunnelling mechanism involving tunnelling from deep to very shallow traps in the glass. At higher temperatures, where the electron can deepen its trap by relaxation, it is suggested that shallow traps are not accessible from deep traps.