The sticking probabilities of gases chemisorbed on the surfaces of solids—II

Abstract An earlier treatment of the sticking probability tor chemisorption is extended to include diatomic molecules which dissociate on chemisorption. It is shown that if it is assumed that all incoming molecules are physisorbed and come to thermal equilibrium with the adsorbent, the lack of dependence of the sticking probability on coverage found for nitrogen on tungsten can be reasonably explained only if the sticking probability on the clean metal is nearly unity. Experimentally, it is found to be in the range 0.1–0.5. It can be shown, however, both theoretically and experimentally, that this assumption is not valid, and that many of the molecules desorbed arise from the portion of the physisorbed molecules not yet in thermal equilibrium with the substrate. The discrepancy between the present theory and experiment is reduced if this fact is taken into account.