Emission of metallic ions from oxide surfaces. I.—Identification of the ions by mobility measurements

Abstract

In two recent papers an account was given of the determination of the mobility of ions of the alkali metals in various gases. It was shown that in argon, krypton, xenon and nitrogen the experimental results could be represented with considerable accuracy by the relation K = A/√ρ (D - 1)·(1 + m /M) ½ cm./sec./unit electrostatic field, (1) where K is the speed of an ion of mass M in a gas of molecular weight m , density ρ and dielectric constant D, at a pressure of 760 mm. of mercury and a temperature of 20°C. For a given gas A is a constant; it changes slightly from one gas to another, the extreme values being 0·48 for nitrogen and 0·56 for xenon. The equation is very similar to one deduced by Langevin using a simple atomic model. In his equation A depends upon the “size” and polarizability of the gas molecules, but for the particular case of a highly polarizable gas it approaches a limiting value of 0·51. The experimental facts summarized above suggest that in the more polarizable gases the “size” of the ions has little influence on their mobility. This view was confirmed by further experiments in nitrogen which showed that the mobility of even large clustered ions like (Na + , NH 3 ) and (Na + , 2NH 3 ) is also given by the same relation which holds for the simple alkali ions.