Low temperature pulse radiolysis of concentrated aqueous solutions. Evidence for trap-to-trap tunnelling in 50/50 v/v ethylene glycol + water and 10 mol dm–3 OH– aqueous solutions

Abstract

Reactions of e^–_t with several solutes have been investigated over a wide range of temperature in 50/50 v/v ethylene glycol + water (EG + H₂O) and 10 mol dm^–3 OH^– aqueous solutions.

In the fluid media the reactions are generally diffusion controlled, and values of the encounter radius, r, between e^–_t and solute have been estimated by applying the theory of time-dependent rate constants to the kinetics.

In the rigid media the reaction rate of e^–_t with solutes is independent of temperature and proportional to log (time). The rate varies from one solute to another, and is faster in 10 mol dm^–3 OH^– than in EG + H₂O. The kinetics are consistent with e^–_t tunnelling from trap to trap in the matrix and reacting with the solute when it becomes trapped within the encounter radius r. Independent assessments of r from tunnelling kinetics agree well with those obtained from diffusion kinetics.

The e^–_dry capture efficiency of each solute has been estimated from its effect on G(e^–_t). The efficiencies of H⁺, Cu²⁺ and Fe(CN)₅NO^2– are negligibly small, which is in marked contrast to their high reactivities with e^–_t.

Evidence for long lived encounter pairs of e^–_t and H⁺, e^–_t and Cu²⁺, and e^–_t and SeO^2–₄ at low temperatures is presented.