The emission of electrons under the influence of chemical action Part V—The theory of the chemical electron emission and its application to certain reactions involving haloids

Abstract

The chemical electron emission studied is that of the electrons emitted from the liquid alloy of sodium and potassium, K 2 Na, when it is acted an by different chemically active gases, such as the halogens, at very low pressures of the order of 10 -5 mm of Hg. The electron emission is looked upon as an immediate result of a bombardment, by free metallic electrons, of the unstable (excited) chemical bonds formed on the metal surface during collisions of the gas molecules with the metal. When an electron collides with an excited bond, the latter reverts spontaneously through an electronic rearrangement to the normal polar state and the available energy of the electronic rearrangement is simultaneously transferred to the electron which is thus enabled to escape from the metal. The fundamental physical problems underlying the observed phenomena, on this view, relate to (1) collisions of the second kind between free electrons and the electronically excited chemical bonds, and (2) the escape of electrons from the metal surface. Problem (2) is well known is connection with the thermionic and photo-electric effects. Problem (1) is treated by introducing, a priori , a mathematical expression, as general as possible, for the electron de-excitation, or excitation, function which represents the chance of a successful collision. An application of the theory to the experiments has enabled us to determine accurately the values of the constants included in the electron de-excitation, or excitation, function and also the value of an important constant—the total potential barrier of the alkali metal.