THEORY ASSISTED INTERPRETATION OF COPPER PHTHALOCYANINE CORE LEVELS XPS SPECTRA

X-ray photoemission spectroscopy (XPS) and ab initio quantum mechanical calculations (SCF, Cl, MCSCF) are used in combination to study the electronic structure of copper phthalocyanine (CuPc). The XPS core level spectra as well as the molecular orbital calculations suggest that in this molecule, the CuN bonds are ionic to a large extent. In the Cu2p spectrum, the final state corresponding to the main line, at the lower binding energy side, appears as a large mixing of two configurations; in one of them the core hole is fully screened by a charge transfer from the ligand 2p orbitals to the Cu3dx2-y2 orbital. For the Cu3s and Cu3p core holes the screening by the ligand to metal (L --> M) charge transfer is less important. For the Cu2p and Cu3p core levels, the higher binding energy states (satellites) correspond to shake-up processes exhibiting L --> M charge transfer as well as M --> M transitions, whereas in the case of Cu3s these are purely L --> M.