Binding energies and K-edge spectra of NO chemisorbed on Ru(0001)

The electronic structures, adsorption energies and equilibrium geometries of chemisorbed NO on the Ru(0001) surface for several adsorption sites were determined using cluster models and employing the first principles, local density theory. Ground state one-electron eigenvalues and wave functions were obtained using the discrete variational method with numerical atomic bases. K-edge X-ray absorption spectra of both nitrogen and oxygen for each geometry were obtained using a scattered wave method. The effects of the surface on these spectra were studied by comparison with results from an isolated NO molecule and with the XPS and UPS experiments of Umbach et al. Both the NO and the NO-substrate vibration frequencies were calculated. Comparison between these theoretical results, recent electron energy loss spectra of Conrad et al. and early experiments of Thomas et al. suggests that NO is adsorbed only at threefold and top sites.