Kinetic Peculiarities of Electron Tunneling Reactions

Two main conclusions about the kinetics of electron tunneling follow from theoretical works on electron tunneling. One of them is that the dependence of the tunneling probability, W, on distance R between the donor and the acceptor can be well approximated by the exponential function 

Describing electron tunneling reactions in vitreous matrices it is convenient to use such a characteristic as the tunneling distance, R  

As is seen from Eqs. (1) and (2), it makes sence to choose parameters ve and ae as the basic kinetic characteristics for electron tunneling reactions. Knowing them, it is easily possible to find, with the help of Eq. (1), the probabilities W(R) of electron tunneling for various distances R between the reagents or to calculate with the help of Eq. (2), the distance R, to which the electron will tunnel within time t. 

The ability of electron tunneling to provide PET at large and various distances when put together with a rather sharp exponential dependence of the tunneling probability on the distance can result in a rather unusual character of the reaction kinetics. The details of these kinetics depend substantially on the character of the spatial distribution of the reagents as well as on how mobile they are. We shall discuss this problem here only very briefly, just to provide better understanding of the data presented below on electron tunneling in PET. For a more detailed discussion see Chapter 4 of Ref. [31], 

Consider first the kinetics of electron tunneling between immobile reagents. In this case the character of the spatial distribution of the reagents has the strongest influence on the reaction kinetics. From the practical point of view two types of 

---