MANIFESTATION OF THE PARAMAGNETIC SPLITTING OF PHYSISORBED O-2 IN-CORE AND VALENCE SPECTROSCOPIES

We have investigated the core excited sigma resonance region in 1 mon olayer of O-2, physisorbed on several substrates. Comparisons with the paramagnetic splitting obtained in X-ray photoelectron spectroscopy ( XPS) and in ultraviolet photoelectron spectroscopy (UPS) are made. The paramagnetic splitting in XPS and UPS remains the same for the differ ent systems studied, whereas the lineshape of the sigma resonance cha nges considerably, There is a strong indication that the 3 eV double s tructure seen in the NEXAFS spectrum of O-2 is not due to the splittin g of the sigma resonance, but rather due to Rydberg states of differe nt symmetry. We also present ab initio calculations which support this interpretation. The calculations give a value of the (1s --> 3 sigma( u)) (3) Sigma exchange splitting of 0.73 eV.