Hot precursors in the adsorption of molecular oxygen on Ag(110)

The molecular adsorption of oxygen on a Ag(110) surface was investigated by scanning tunneling microscopy at 60-70 K, where thermal mobility is suppressed. The data provide evidence for a hot precursor state of the molecules existing prior to their final accommodation in the chemisorption well. The molecules in the precursor state are highly mobile on the surface and can be trapped by collision with the equilibriated species, lending to the formation of pairs or short strings of molecules in the troughs of the Ag(110) surface along [1(1) over bar0$].