  Some models of Big Bang nucleosynthesis suggest that very high baryon density
regions were formed in the early Universe, and generated the production of
heavy elements other than lithium such as fluorine F. We present a
comprehensive chemistry of fluorine in the post-recombination epoch.
Calculation of F, F- and HF abundances, as a function of redshift z, are
carried out. The main result is that the chemical conditions in the early
Universe can lead to the formation of HF. The final abundance of the diatomic
molecule HF is predicted to be close to 3.75 10(-17) when the initial abundance
of neutral fluorine F is 10(-15). These results indicate that molecules of
fluorine HF were already present during the dark age. This could have
implications on the evolution of proto-objects and on the anisotropies of
cosmic microwave background radiation. Hydride of fluorine HF may affect
enhancement of the emission line intensity from the proto-objects and could
produce spectral-spatial fluctuations.
