Reaction Rate Maxima at Large Distances between Reactants

One commonly thinks that two reactants need to come very close to one another in order for a chemical reaction to occur. This is true for most reaction types, but electron transfer is an exception in this regard. It is a well-documented fact that electron transfers can occur over long distances (≥15 Å), but it is much less well-known that theory predicts a regime in which electron transfer rates in crease with increasing distance between reactants. This contribution explains the physical origin of this counter-intuitive behavior, and it identifies a set of conditions that might facilitate its experimental observation.