Van Der Waal's Adsorption as a Determinant of Joshi Effect

The significance as a determinant of Joshi effect Δi in H2O vapor of the predischarge adsorption consisting of an instantaneous uptake of molecules due to van der Waal's forces and slow process of sorption on Langmuir sites was investigated. Joshi effect corresponding to 15—20-percent reversible current suppression was detected with a predischarge interval = ½ min; it was not altered by increase of this last to 5 hr or favored by ``aging'' under discharge, which indicated that the instantaneous process, viz, van der Waal's adsorption, which was quite distinct from Langmuir sorption formed during the predischarge interval and/or under discharge, was the chief seat of Δi. It was suggested that under light, surface molecules dissociated into atoms and/or radicals which possessed large electron affinity, to increase the work function of the cathode and, therefore, to give Δi. Observation of Δi even with longer wavelengths than those corresponding to dissociation energy of H2O suggested that the adsorbed molecules possessed, prior to irradiation, certain energy h(vd—v) obtained by ionic bombardment under applied fields (vd is the frequency corresponding to dissociation energy of a molecule, and v is that employed for observing Δi).