(~Go'

Introduction of this value into Eq. (73) gives the activation energy in Eq. (76) for the forward reaction.* Thus it is seen from the latter equation that A/4 is equal to the "intrinsic activation barrier" ~Gi, that is, to the activation energy that would be obtained for ~G0 = 0. Thus if a series of electron transfers with virtually identical ),_ is considered, determination of the activation barrier for ~G0 ' = 0 gives direct access to the experimental value of A. Proponents of this second interpretation then prefer to reformulate Eqs. (64) or (76) under the equivalent form

(77)

To conclude, we discuss more deeply the energetic diagrams like that presented in Fig. Sa. As noted previously, the A and D orbitals must interact in order that the electron may be transferred. This simply means that an electronic coupling is observed between the initial system and the final system. This results in mixing of the two systems, which amounts to separating the potential energy curves in Fig. Sa into a lower (or fundamental) state and an upper ( or excited) state, as represented in Fig. Sb. Because the potential energies of the electron tend to be identical for the initial and final systems when the transition state is approached, the degree of mixing in this region is higher than near the bottom of each potential well. Thus the maximal effect is reached at the transition state, where a splitting of magnitude 2V; is observed [58].