Precursor Adsorption of Oxygen on Ni(111) and the Activation Energy for Chemisorption

Measurements of electron transmission spectra and work function $\phi$ of a Ni(111) surface held at $T=5.5\mathrm{}$ K during exposure to ${\mathrm{O}}_2$ 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 $\phi$ that accompanies this transition gives an activation energy of ∼ 13 meV for the reaction.