Adsorption of gases activated by electron impact

Abstract

Adsorption of nitrogen which has been activated by electron impact is shown to result from dissociation of the nitrogen molecule and from the interaction of energetic ions with a nickel surface. Excitation of N2 to states at about 10.3, 12.2, and 14.0 eV causes dissociation. Dissociative ionization at 24.5 eV also leads to additional pumping. Energetic N2+ ions have an adsorption probability of approximately 0.85 when they collide with a nickel surface. It is shown that the ion adsorption probability is practically independent of energy between 30 and 100 eV. It is also shown that thermal energy ions have a very low adsorption probability. These results lead to the postulate that the N2+ ions dissociate in impact and that the atomic nitrogen is subsequently adsorbed. Results have also been obtained which indicate that the adsorption probability of Ar+ is strongly dependent on surface structure. Annealing of the surface greatly reduces the adsorption probability.