Wave-vector-dependent symmetry analysis of a photoemission matrix element: The quasi-one-dimensional model system Cu(110)(2X1)O

We derive orbital symmetry character from the study of peak intensities in angle-resolved photoemission spectra taken at different incidence angles of p-polarized light. Our method of analysis is tested at the oxygen-derived antibonding band on the Cu(110)(2 x 1)O surface. This band has all initial state energy E-i = -1.37 eV (T = 300 K) at the (Y) over bar point and shows even symmetry with respect to the Gamma LUX mirror plane (along <(<Gamma>Y)over bar>). The intensity analysis reveals that orbitals both of z-like (along surface normal) and y-like symmetry (y along the Cu-O chains) are mixed into this band. This interpretation is supported by several calculations. The ground-state symmetry character was studied by a full-potential linearized augmented planewave method using a seven-layer supercell geometry. For a direct comparison with the experimental intensities, photoemission spectra at the (Y) over bar point were calculated using the one-step model of photoemission, Our results contribute to a long-standing discussion about the orbital character of the even antibonding band. In particular we demonstrate that this kind of intensity analysis can supply valuable information about symmetry properties.