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
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)5NO2– 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 SeO2–4 at low temperatures is presented.