Figure 3.

Illustration of Marcus-like models as expressed in Equation (1). The orthogonal coordinates presented are the Marcus-term (isotopically insensitive), and the fluctuation of the DAD (gating, isotopically sensitive). R is the reactant state and P is the product state. The Franck–Condon term is presented by the probability of finding the hydrogen at the reactant or the product states and is illustrated for the tunneling-conformation as a dark probability function along the gating coordinate.