Microscopic reversibility of the rate constants given by the generalized Marcus equation

The microscopic reversibility of the rate constants given by the generalized Marcus equation which was recently presented by Tachiya has been proved. It is concluded that although in the original Marcus equation the energy gap is expressed in terms of thermodynamical free energy, there is no necessity to do so. Theoretically it is more appropriate to express the energy gap in terms of the internal energy of the solute pair and the solvation energy due to the electronic polarization, which are independent of temperature and entropy.