Autoionization
The autoionization is an effect that can occur with atoms or molecules when an excited state above the ionization energy is located. This can happen when two or more electrons are excited at the same time. The transfer of the energy from the first to the second electron can lead to ionization .
However, an electron can also be sent out if only one electron was previously excited. When this excited state decays, the energy released can be emitted directly as a photon ( fluorescence ), or the excited electron transfers its energy to a more weakly bound electron, which can then be emitted as a so-called Auger electron .
Excitation of two electrons
If in an atom with two valence electrons (e.g. beryllium - 2s) both are excited into higher states, the total excitation energy of the atom results:
where and are the energies of the individual excitations of the electrons and is the interaction energy between the excited and the remaining electrons (in the lower shells), which is changed by the excitation.
This doubly excited state can be balanced either by sending out two photons or by transferring energy from one electron to the other. Since energy conservation must also apply in the latter process, the energy transfer is i. A. only possible if a suitable state for highly excited single electron excitation exists. For discrete energies this is very unlikely and so the process can only be observed for energies , since free electrons do not have a discrete energy spectrum. If the total energy is above the ionization energy of a singly excited electron, the transfer of the energy to the second electron can lead to ionization, in which the electron leaves the atom and this leads to a positive ion with a total charge .
