One can now discuss the electronic structure implications for the system's behavior when traversing the PES. In the scenario of fully aligned PC and ET motions, the electronic structure change that accompanies the proton movement drags along the electron, or equivalently, the motion that drives ET fully incorporates the proton movement from reactants to products. In the other limiting case of orthogonal PC and ET motions, the electronic structure changes when moving purely along one of them must be fully independent of each other. Any angle 0°< 90°between the PC and ET motions implies that there is a degree of similarity between the nuclear movements and the electronic structure changes that occur along the vectors, which provides a degree of flexibility to the system to complete the overall proton and electron movement from reactants to products. Taking the HAT scenario shown in the middle of Figure , it may be beneficial to move along the ET dimension depending on the curvature of the PES, even though the net movement along the ET vector will be zero once the product minimum has been reached. Such effects will likely be particularly pronounced for asymmetric donor-acceptor systems.