Quantum chaos, statistical equilibrium and resonant radiative capture of electrons by multicharged ions: $Au 24^{+}$

We show that the spectrum and eigenstates of open-shell multicharged atomic ions near the ionization threshold are chaotic, as a result of extremely high level densities of multiply excited electron states (1000 levels per eV in Au 24+) and a strong configuration mixing. This complexity enables one to use statistical methods to analyze the system. The orbital occupation numbers obey the Fermi-Dirac distribution, and temperature can be introduced. We show that radiative capture of electrons through the multielectron resonant states is strongly enhanced compared to the direct radiative recombination