Resonant soft-x-ray emission spectroscopy of surface adsorbates:  Theory, computations, and measurements of ethylene and benzene on Cu(110)

Soft-x-ray emission spectra from C₂H₄/Cu(110) and C₆H₆/Cu(110) have been obtained for two excitation energies, resonant and nonresonant, and resolved in all three spatial components (x,y,z). The one-step theory for resonant soft x-ray spectroscopy and Raman scattering is extended to adsorbates on metal surfaces and is implemented within a density-functional theory framework. The calculations are performed for ethylene and benzene chemisorbed on Cu(110) using cluster models (up to 86 Cu atoms) of the metal surface; the calculations are performed for both resonant and nonresonant excitation with the focus on the polarization and symmetry selectivity and the role of channel interference. The molecular mirror plane symmetry is maintained for the chemisorbed system, and for the generated core hole, which leads to an energy-dependent symmetry and polarization selectivity in the emission process. The calculations and experiment show good agreement both with regard to intensities and energy positions of the peaks.