Some many-electron effects strongly influencing the X-ray photoabsorption and X-ray photoelectron spectra of atoms are reviewed. In particular, the following effects are analyzed:
- Intrashell and intershell correlations in photoionization of valence and subvalence shells;
- Polarization of valence shells by the vacancy in the subvalence shell;
- Influence of the doubly-excited states on the photoionization cross sections of the subvalence shells;
- Rearrangement of the outer shells in the photoionization of inner shells.
Changing the above effects is discussed when the absorbing atom is coordinated by ligands in simple molecules.
