Chemistry of heavy elements in the Dark Ages
  Primordial molecules were formed during the Dark Ages, i.e. the time between
recombination and reionization in the early Universe. The purpose of this
article is to analyze the formation of primordial molecules based on heavy
elements during the Dark Ages, with elemental abundances taken from different
nucleosynthesis models. We present calculations of the full non-linear equation
set governing the primordial chemistry. We consider the evolution of 45
chemical species and use an implicit multistep method of variable order of
precision with an adaptive stepsize control. We find that the most abundant
Dark Ages molecules based on heavy elements are CH and OH. Non-standard
nucleosynthesis can lead to higher heavy element abundances while still
satisfying the observed primordial light abundances. In that case, we show that
the abundances of molecular species based on C, N, O and F can be enhanced by
two orders of magnitude compared to the standard case, leading to a CH relative
abundance higher than that of HD+ or H2D+.
