THEORY ASSISTED INTERPRETATION OF COPPER PHTHALOCYANINE CORE LEVELS XPS SPECTRA

X-ray photoemission spectroscopy (XPS) and ab initio quantum mechanica l calculations (SCF, Cl, MCSCF) are used in combination to study the e lectronic structure of copper phthalocyanine (CuPc). The XPS core leve l spectra as well as the molecular orbital calculations suggest that i n this molecule, the CuN bonds are ionic to a large extent. In the Cu2 p spectrum, the final state corresponding to the main line, at the low er binding energy side, appears as a large mixing of two configuration s; 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 an d Cu3p core holes the screening by the ligand to metal (L --> M) charg e transfer is less important. For the Cu2p and Cu3p core levels, the h igher binding energy states (satellites) correspond to shake-up proces ses exhibiting L --> M charge transfer as well as M --> M transitions, whereas in the case of Cu3s these are purely L --> M.