Samarium atoms exist in two different electronic configurations, namely, divalent (Sm2+) and trivalent (Sm3+). Up to now, those two electronic configurations have been connected with the existence of Sm atoms in different valence states. Recent theoretical calculations performed by Yakovkin [9] show that both electronic configurations have similar LDOS around the Fermi level, and as a result, should give a similar photoelectron emission in the valence band region, which was identified earlier as the emission from the Sm2+ state. The Sm3+ signal in photoelectron emission could originate from contaminations of Sm by other elements, e. g. oxygen. To check the influence of O on the electronic structure of Sm, the XPS experiments of coadsorption of O and Sm have been performed. (C) 2010 Elsevier B. V. All rights reserved.