The interfacial Barrier and Its Penetration

The first ideas about this were given by R. Gurney, whose best-known work resides in a paper given early after the beginning of the quantum theory pertaining to the escape of radioactive particle from nuclei, i.e., the beginning of the quantum theory of radioactivity. 

Gurney applied the thinking which he had made for the radioactive case to electrodes and considered the mechanism of electron escape, the cathodic case. Taking the clue from the situation within the nucleus, Gurney regarded the metal itself as a kind of box in which electrons were con- 

The origin of this barrier is mainly due to image potential and field drop at the interface. However, most readers will be familiar with the general idea of an activation barrier in chemical reactions. There, of course, is the energy of activation which controls the rate of electrode reactions and has appeared in this chapter already in the of the Arrhenius equation quoted above. If this barrier is high, the reaction is slow because the value of the exponential function in the Arrhenius equation is small. Fast reactions are associated, then, with small energies of activation. 

The physical origin of energies of activation has to be discussed individually in the case of every situation. In general, however, it can be stated that when the reactants arrive at the interface for reaction, most of them are not in an energetic state appropriate to electron transfer. Such a state, which involves rearrangement of the atoms within the molecule, and perhaps some stretching of bonds, is only attained if one waits a certain time (of the order of magnitude of s) while some of the 

Gurney then invoked the quantum mechanical phenomena of tun- 

---