Precursor adsorption of oxygen on Ni(111) and the activation energy for chemisorption

Measurements of electron transmission spectra and work function φ of a Ni(111) surface held at T=5.5 K during exposure to O2 provide direct evidence for a precursor adsorption preceding dissociative chemisorption. The form of the electron transmission spectra indicates that the precursor adsorption involves oxygen molecules. Subsequent warming of the oxygen-covered surface leads to the chemisorption state. An analysis of the kinetics of the increase in φ that accompanies this transition gives an activation energy of ∼ 13 meV for the reaction.