A new impurity-cluster configuration-interaction model that treats charge transfer and exchange correlations on the same footing is applied to interpret the 3s core-level X-ray photoelectron spectra of NiO, CoO, K2NiF4 and K2CoF4. The interplay between charge transfer and exchange correlations in determing the final state satellite structures is clarified and an estimate of the exchange integrals between the 3s hole and the 3d electrons is given. The results are consistent with the electronegativity scale, as regards charge transfer energy, and with the trend suggested by the Van Vleck rule, as concerns the exchange integrals.
