Low-Energy Rate Enhancement in Recombination Processes of Electrons into Bare Uranium Ions

Based on the Dirac--Fork--Slater method combined with the multichannel quantum defect theory, the recombination processes of electrons into bare uranium ions (U ⁹²⁺ ) are investigated in the relative energy range close to zero, and the x-ray spectrum emitted in the direct radiative recombination and cascades processes are simulated. Compared with the recent measurement, it is found that the rate enhancement comes from the additional populations on high Rydberg states. These additional populations may be produced by other recombination mechanisms, such as the external electric-magnetic effects and the many-body correlation effects, which still remains an open problem.