Evidence for Halogen Films on Tungsten in the Surface Ionization of Potassium Halides

Abstract

Molecular rays of the potassium halides were directed in high vacuum against tungsten and tungsten‐oxygen surfaces, and the positive ion current to a collector cylinder was measured as a function of the surface temperature. Degrees of ionization on oxygen‐free surfaces were calculated upon the assumption that each halide molecule produced one positive ion on striking a tungsten‐oxygen surface. The high temperature results on oxygen‐free filaments (1800°‐2380°K) were interpreted as indicating surfacedissociation of the potassium halide molecule, followed by partial ionization of the potassium atom and by the escape of the halogen as an atom. In the approximate temperature range 1800–1600°K a progressive change in the surface, with decreasing temperature, toward a higher work function was observed. This change led to surfaces of constant high work function, which were interpreted as due to the formation of halogen layers on the tungsten.