Soft X-ray appearance potential spectroscopy of O chemisorbed on Ti,Cr, Fe and Ni

We wish to report the observation of O 1s level soft X-ray appearance potential spectra for O adsorbed on clean polycrystalline surfaces of Ti, Cr, Fe and Ni. The spectra are detectable in the chemisorption regime and are then characterized by one single peak at the threshold. The peak is thought to be related to an enhanced local density of unfilled valence states on the oxygen atoms. These simple spectra are in sharp contrast to the multipeaked O 1s level spectra observed from the surface oxides grown after prolonged oxygen exposures.