Adsorption of nitrogen on clean and modified single-crystal Ni surfaces

N2 chemisorbs on (100), (110) and (111) single-crystal faces at 80 K without any dissociation. A molecular precursor species at the threshold of dissociation is formed at 80 K on a Ni(110) surface covered with atomic carbon or nitrogen; the precursor species dissociates at higher temperatures. At low C concentrations, however, dissociative adsorption occurs on Ni(110) at 80 K without forming any precursor species, accompanied by molecular chemisorption on the open Ni sites.