Electronic structure of atomic adsorbates from x-ray-absorption spectroscopy: Threshold effects and higher excited states

Atomic C, N, and O chemisorbed on Ni(100) have been studied by x-ray-absorption spectroscopy. The atomic 2p orbitals are shown to form hybrid orbitals with the Ni 3d and 4sp bands. The spectral contributions from these hybrids are identified at the absorption threshold and in a region 6-12 eV above this. Between those regions, states derived from atomic 3p and higher np orbitals are observed. The threshold region shows vibrational and dynamical effects, which are discussed in connection with the corresponding photoemission spectra. The substrate Ni 2p3/2 x-ray-absorption spectrum is also presented. Its large similarity to the Ni 2p3/2 x-ray photoemission spectrum is discussed.