Scanning tunnelling microscopic observations of a (111) surface revealed that O adatoms at 300K were essentially immobile. Low-coverage overlayers, which were formed by the dissociative chemisorption of O2, consisted only of single isolated atoms rather than pairs of adjacent atoms. Upon dissociation, some of the chemisorption energy was transformed into translational energy which was available for movement parallel to the surface. This caused the two O atoms to separate from each other, by at least 8nm, before the excess energy was dissipated. The lifetime of these activated adatoms was estimated to be of the order of more than 1ps.

H.Brune, J.Wintterlin, R.J.Behm, G.Ertl: Physical Review Letters, 1992, 68[5], 624-6