Electron Transfer and Single Molecular Events

Electrochemical electron transfer reactions are reviewed, starting with the works of Marcus and Hush, who evolved the concept of solvent reorganization. The resulting equations for the electrochemical rate constants are derived, and interpreted within the Gerischer formulation. A quantum mechanical version points out the importance of the electronic interaction between reactant and electrode, and allows an investigation into adiabatic and non-adiabatic reactions. The transitions between these two regimes, the effects of the solvent friction, and of the electronic overlap are discussed in detail. The introduction of the tip of a scanning tunneling microscope into the electrochemical systems makes it possible to observe electron transfer through single molecules.