Intramolecular resonances afterK-shell excitation of C2H2n adsorbed on Ag and Cu(100) surfaces

The near edge X-ray absorption fine structure (NEXAFS) at the C K-edge of C2H2, C2H4, C2H6 on Cu(100) and Ag(100) surfaces is studied. The oriented character of the molecules on the surface combined to the dipole selection rules for photon absorption allows an experimental assignment of the nature of the various final states. A careful fitting of the NEXAFS spectra reveals final states of C–H character and shake-up satellites of the C(1 s) to π* (C–C) transition. The asymmetric line shape of the C(1 s) to σ* (C–C) transition is described in a scattering model of the photoelectron from the molecular potential.