Non-thermal photons and direct photodissociation of H2, HD and HeH+ in
  the chemistry of the primordial Universe
  Non-thermal photons deriving from radiative transitions among the internal
ladder of atoms and molecules are an important source of photons in addition to
thermal and stellar sources in many astrophysical environments. In the present
work the calculation of reaction rates for the direct photodissociation of some
molecules relevant in early Universe chemistry is presented; in particular, the
calculations include non-thermal photons deriving from the recombination of
primordial hydrogen and helium atoms for the cases of H2, HD and HeH+. New
effects on the fractional abundances of chemical species are investigated and
the fits for the HeH+ photodissociation rates by thermal photons are provided.
