Distortion of the CMB Spectrum by Primeval Hydrogen Recombination
  We solve the recombination equation by taking into account the induced recombinations and a physical cut off in the hydrogen spectrum. The effective recombination coefficient is parametrized as a function of temperature and free electron density and is about a factor of four larger than without the induced recombination. This accelerates the last stage of the recombination processes and diminishes the residual ionization by a factor of about 2.6. The number and energy distribution of photons issuing from the hydrogen recombination are calculated. The distortion of the cosmic microwave background (CMB) spectrum depends strongly on the cosmological parameters \Omega, \Omega_b and H_0 and differs essentially from the Planck-spectrum for wavelengths < 190 \mu m. 
Peter Boschan and Peter Biltzinger