Studies of the CuO bond in cupric oxide by X-ray photoelectron spectroscopy and ab initio electronic structure models

X-ray photoemission spectroscopy (XPS) and ab initio molecular orbital cluster model wavefunctions are used in a combined study of the electronic structure of CuO. High-resolution XPS spectra for single-crystal CuO identify and clarify several features of the core and valence level spectra. The molecular orbital cluster wavefunctions show that there is a significant covalent contribution to the ionic CuO bond. For the copper core hole final states, the states where the core hole is screened by charge transfer from O2p to Cud lie at lower binding energy than the states where charge transfer does not screen the core hole. The multiplet splitting of the higher binding energy 2p-hole states is large (ca. 3 eV).