Entropy of reaction and number of active modes in the theory of electron-transfer reactions

The entropy of reaction is incorporated in a classical model by introducing frequency changes in the harmonic modes. Various properties, such as the rate constant dependence on the energy of reaction and on the temperature, are influenced by the number of active modes. This number is therefore an important parameter of the system. It becomes unimportant in the asymptotic limit, when its value is very large. In this limit one recovers the classical Marcus expression.