Introduction

Abstract

Electron and atom group transfer from a solvated donor to a solvated acceptor molecule, or between a solvated molecule and a macroscopic solid body such as an electrode or a membrane, have attracted attention since the days of Grotthuss, Davy, and Faraday(1). Such processes are of crucial importance in chemical, biological, and physical processes, which are conveniently viewed as individual or a series of consecutive reaction steps, the molecular nature of which involves electron or atom group transfer. Thus, in chemical and biological systems in liquid or solid media the elementary reaction steps most frequently consist of a synchronous bond break and bond formation in atom group transfer, or the transfer of an electron without accompanying bond breaks. Elementary chemical reaction steps are moreover conceptually closely related to such physical processes as radiative and radiationless electronic transitions in large isolated molecules(2,3) and in impurity centres in solid matrices(3,4), to defect diffusion in solids(5), and to nuclear tunnelling phenomena as manifested by ‘abnormal’ heat capacity effects(6–8) and vibrational level splitting(9,10).