Molecular orientation of CN adsorbed on Pd(110)

The bonding geometry of the C-N molecule in the saturated c(2 x 2) layer on the Pd(110) surface has been determined by combining polarization-dependent near edge x-ray absorption fine structure and full-solid-angle x-ray photoelectron diffraction (PED). The N K-edge spectra display a strong dependence on the polar and azimuthal orientation of the light polarization with respect to the sample surface. A strong forward scattering peak along the [001] direction is present in the full-solid-angle photoelectron diffraction data of the C1s core level. Both the position of the C1s PED forward scattering peak and the angular dependence of the N K-shell absorption spectra provide direct evidence that the CN molecules is oriented with the molecular axis along the [001] surface direction, at variance with earlier conclusions based on angle-resolved valence level photoemission data. The forward scattering peak in the C1s PED data further indicates that the N atoms lie above the C atoms, with the C-N molecular axis tilted by 25degrees +/- 4degrees with respect to the surface plane. The close analogy of this geometry with the results of previous structure determinations of CN adsorbed on Ni and Rh (110) surfaces is discussed.