The role of long range tunneling in electron transfer processes in condensed media

Experimental evidence is given for the importance of long range tunneling in electron transfer reactions in condensed media: the unusually weak effect of electrostatic repulsion on the rate of some electron transfer and spin exchange processes; electron transfer between distant (up to ≈ 30 A) species in solids at a rate considerably exceeding that of thermal diffusion; the unusual concentration dependence of radiation yields in the presence of scavengers, etc. The concept of long range tunneling is shown to permit quantitative explanation and correlation of experimental data on electron transfer in quite different fields.The factors determining the efficiency of tunneling, as well as some peculiar features of tunneling kinetics are considered.The role of long range tunneling in various chemical processes involving electron transfer in condensed media are discussed (ion reactions in solutions, photochemistry, radiation chemistry, reactions with polymers, some biochemical reactions).