A unified theory of electron transfer and internal conversion based on solitary electronic states

A description of electron transfer processes is presented which makes use of the concept of solitary states for the construction of the initial and the final state wave functions. Even though this concept is closely related to an adiabatic description in the sense that it provides partial delocalization of these states it also assures localization for a symmetric donor-acceptor system. The theory can be applied to arbitrary values of the internal parameters characterizing the system, that is the electronic donor-acceptor coupling V, the free energy change ΔE, and the coupling of the electron to nuclear motions represented by a Stokes shift S. This way the theory of nonadiabatic electron transfer processes is put on equal footing with the theory of adiabatic transitions and even more interestingly the same concept unifies the common electron transfer theory and the theory of internal conversion processes if |ΔE| and (or) |V| exceed S. It is shown analytically how the results of the conventional treatments for adiabatic, nonadiabatic, and internal conversion processes fall out of this theory as special cases. It is further examplified how the system develops from the so-called normal regime with |ΔE| <S into the inverted regime with |ΔE| >S as function of ΔE for fixed parameters of V and S and as function of V for fixed parameters of ΔE and S.