Many-body effects in valence and core photoionization of molecules

The spectral function of ionization is discussed for the whole energy range. It is found that different energy regions are likely to exhibit different types of many-body effects. For the ionization out of an outer valence orbital most of the intensity appears in one main line. The many-body effects explain the additional satellite lines and, in addition, can lead to an ordering of main lines which is different from the ordering determined from one-particle calculations. For the ionization out of an inner valence orbital the intensity may be distributed over several lines and in many cases it is not possible to identify any of these lines as the main line representing the orbital. Such a breakdown of the quasiparticle picture of ionization is stressed to be a common phenomenon. Ionization of core orbitals can usually be viewed within a quasiparticle picture, i.e., the process leads to a main line accompanied by satellite lines. In cases, however, where the creation of the core hole leads to a strong charge transfer, the shake-up energies can become small or even negative and the quasiparticle picture may break down. The origin of the above effects is discussed and typical examples are presented.