Limitations of the ionic model in describing core-hole decay molecular versus crystalline KCl

Normal Auger decay spectra of the 2p core hole in potassium have been measured both for molecular gas-phase and crystalline solid-state samples of KCl. While the spectrum for the latter is easily interpreted using a strictly ionic approach, the molecular spectrum gives evidence of strong additional effects. The observed differences between the two phases are discussed from the viewpoint of the ionic model, considering also the perturbation by the different environments and symmetries. The uniquely molecular effects seen in the Auger electron spectra are attributed to the sudden change in character of the valence (Cl 3p) orbital upon core-hole decay, accompanied by dynamic relaxation processes.