On the Sudden Removal of Two Outer-shell Electrons in Atoms

Electron correlation (EC) in atoms is at the same time very important and challenging investigation topic due to its many-body interactions, nevertheless it may be the main process to describe the absolute electron impact cross section for the ionization of atoms and molecules. The outer-shell double photoionization of a multielectron target is usually a less important process in comparison to ionization of a single electron by a photon and it is determined completely by electron-electron interaction. The objective in this chapter has been upon a review of the recently found relationship between SO amplitudes and the number of target electrons as well as their density (electrons per volume). Through the comparison between the asymptotic values of the experimental ratios of the double-to-single photoionization cross-sections from the literature, a scaling law was achieved. This scaling allows us to predict the SO amplitudes for several atomic elements up to xenon within a factor two. The electron SO amplitudes following outer-shell photoionization have been plotted as a function of the target atomic number, Z, and static polarizability, α . Our results are in qualitative agreement with the experimental data.