Molecular orientation of CN adsorbed on Pd(110)

Abstract

The bonding geometry of the C–N molecule in the saturated c(2×2) 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 25°±4° 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.