On Quantum and Classical Treatments of Radiative Recombination
  A quantum-mechanical solution to the problem of radiative recombination of an
electron in the Coulomb field has long been known. However, in astrophysics,
the classical approach is sometimes used to describe similar processes in
systems of magnetic monopoles or interacting dark matter particles. The
importance of such problems is determined by the fact that recombination
processes play a decisive role in the evolution of the large-scale structure of
the Universe. It is shown that the applicability of the quantum and classical
approaches to radiative recombination is closely related to the magnitude of
the radiated angular momentum and its quantization. For situations where the
classical approach is not suitable, a semiclassical approach based on
consideration of the quantization of the angular momentum is proposed. It can
be useful for an approximate description of radiative recombination in a
variety of systems.
