NEXAFS study of the О$_2$–Yb–Si(111) nanofilm system

The near-edge X-ray absorption fine structure of the adsorbed oxygen layer on the ytterbium nanofilm has been studied. It is shown that oxygen is chemisorbed in the form that is close to singly charged O$_2^-$ ions. The O–O bond length in such ions is determined (1.33 $\mathring{\mathrm{A}}$). X-ray dichroism of chemisorbed molecules is detected. It is due to the orientation of intramolecular $\sigma^*$ orbitals predominantly along the normal to the ytterbium surface.