Non-thermal photons and direct photodissociation of H2, HD and HeH+ in the chemistry of the primordial Universe

Abstract

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.