Quantum chaos in multicharged ions and statistical approach to the calculation of electron-ion resonant radiative recombination

We show that the spectrum and eigenstates of open-shell multicharged atomic ions near the ionisation threshold are chaotic, as a result of extremely h igh level densities of multiply excited electron states (10(3) eV(-1) in Au 24+) and strong configuration mixing. This complexity enables one to use st atistical methods to analyse the system. We examine the dependence of the o rbital occupation numbers and single-particle energies on the excitation en ergy of the system, and show that the occupation numbers are described by t he Fermi{Dirac distribution, and the temperature and chemical potential can be introduced. The Fermi{Dirac temperature is close to the temperature def ined through the canonical distribution. Using a statistical approach we es timate the contribution of multielectron resonant states to the radiative c apture of low-energy electrons by Au25+ and demonstrate that this mechanism fully accounts for the 10(2) times enhancement of the recombination over t he direct radiative recombination, in agreement with recent experimental ob servations.