The near-edge X-ray-absorption fine-structure of O2 chemisorbed on Ag(110) surface studied by density functional theory

In this computational work a finite cluster model approach has been employed to simulate the adsorption of O2 molecule on the Ag(110) surface by means of density functional theory. O 1s NEXAFS spectra have been calculated with the transition potential scheme in order to include the core hole relaxation effect. From the analysis of the density of states, experimental and calculated NEXAFS spectra found that the O2 molecule upon adsorption on Ag(110) has completely filled π* orbitals consistent with a closed shell electronic structure of peroxide. The only virtual valence molecular orbital still belonging to the O2 fragment is the antibonding σ*, which will be responsible for the most intense resonance observed and calculated in the O 1s NEXAFS spectra. The simulated polarized spectra are in good agreement with two different sets of experimental data, with the exception of grazing incidence, for which a disagreement between theory and experiment is found. We attributed this disagreement to a slight deviation of the adsorption geometry with respect to the ideal case, suggesting a tilt angle of about 10°-15° of the OO bond with respect to the surface plane.