Electron Transfer in Homogeneous and Heterogeneous Systems

The mechanism o f electron transfer in solution and at electrodes is described. A theoretical analysis involving the fluctuations in the chemical bond distances and in the dielectric polarization of the partially oriented solvent molecules about the reactants leads to an expression for the rate constant of these reactions. Relations are obtained between the rate constants of cross reactions k_(12) self-exchange reactions k_(11), [e.g., k_(12)≅ (k_(11)k_(22)K_(12)f_(12)1/2, and reactions at surfaces (electrodes, both metal and semiconductor type). There are many comparisons between theory and experiment and a survey is given. The effect of standard free energy of reaction and of electrode potential is included, as in the Co^(+3) (aq) anomaly, and the occurrence of chemiluminescence. The discussion is preceded by a brief description of reaction rate theory in general and of atom versus electron transfer mechanisms in particular.