THERMAL-DISSOCIATION AND POSITIVE IONIZATION OF POTASSIUM-CHLORIDE ON TUNGSTEN

The efficiency (beta+) of dissociative positive surface ionization (DPSI) of KCl impinging on a polycrystalline tungsten surface heated in a high vacuum was found to bc unity only in an intermediate temperature range (T congruent-to 1250-1750 K). Analysis of the data by our original theory of DPSI yields the following results: (1) at temperatures above and below this range, beta+ is determined only by the degree of ionization of potassium and that of dissociation of KCl respectively, (2) both ionization of potassium and dissociation of KCI are strongly governed by the effective work function (phi+) for DPSI; and (3) phi+ increases from 5.1 to almost-equal-to 6eV mainly owing to residual gas adsorption when T decreases from almost-equal-to 2000 to 1200 K. Temperature dependence of the effective work function for thermal electron emission has virtually the same pattern as that of phi+, thus giving additional evidence to support our theory.