The authors study the chemical shift of the Cu 2p core level for Cu2O, CuO and NaCuO2, where Cu is formally monovalent, divalent and trivalent, respectively. They find that the binding energy increases with the valence, as expected, although the variation in the number of 3d electrons is small and the trivalent Cu atom is found to have a smaller net positive charge than the monovalent or divalent Cu. The origin of the calculated chemical shifts is analysed and the relation with the chemical valence is discussed.
 

Journal of Physics: Condensed Matter, 4 895-909, 1992.