Recombination of low energy electrons with U$^{28+}$
  We performed an extensive study of configuration mixing between the doubly excited (doorway) states and complex multiply excited states of U$^{28+}$ near its ionization threshold. The detailed investigation of complex spectrum and analysis of the statistics of eigenstate components show that the dielectronic (doorway) states weakly mixed with each other. However, they show substantial mixing with the complex multiply excited states. This situation explains the mechanism of low energy electron recombination with U$^{28+}$. We calculated the energy averaged capture cross sections as a sum over dielectronic doorway states and found our present calculation interprets well the experimental recombination rates in the energy range of 1 to 100 eV. 
S Sahoo, G. F. Gribakin and V Dzuba