Figure 1.

Idealized parabolic PESs for reactants (G₁(x), red) and products (G₂(x), blue) in the electron self-exchange process, M^– ↔ M, as functions of the reaction coordinate. The two parabolas have the same curvature near the respective local minimum (x₁ and x₂). The activation energy ΔG^† is given by the reorganization energy λ and the driving force ΔG⁰ = G₂⁰ – G₁.