Theoretical study of the near-edge Cu L x-ray absorption spectrum of copper phthalocyanine

Copper tetraazaporphyrin is used as a model for copper phthalocyanine in theoretical simulations of the features observed at the Cu L_2,3 near-edge x-ray absorption spectra. Theoretical results obtained by a density-functional theory approach provided interpretations of the different features observed experimentally, including the so-called white line and the satellite structures, leading to the conclusion that the solid phase arrangement exerts no significant influence on the shape of the Cu L_2,3 copper molecular spectrum. The calculations show that the unoccupied 3d levels are essentially located in the plane (3d_x2-y2) of the molecule with a small contribution that bas an out-of-plane 3d_z2-r2 and 3d_xz,yz character. The angular dependence of the copper unoccupied electronic levels could be used to confirm the orientation of the copper tetraazaporphyrin on the substrates.