Molecular hydrogen in the cosmic recombination epoch.

The advent of precise measurements of the CMB anisotropies has motivated correspondingly precise calculations of the cosmic recombination history. Cosmic recombination proceeds far out of equilibrium because of a "bottleneck" at the n = 2 level of hydrogen: atoms can only reach the ground state via slow processes--two-photon decay or Lyman-α resonance escape. However, even a small primordial abundance of molecules could have a large effect on the interline opacity in the recombination epoch and lead to an additional route for hydrogen recombination. Therefore, this paper computes the abundance of the H2 molecule during the cosmic recombination epoch. Hydrogen molecules in the ground electronic levels Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. can either form from the excited H2 electronic levels Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and C¹Πu or through the charged particles Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. HeH+, and H-. We follow the transitions among all of these species, resolving the rotational and vibrational sublevels. Since the energies of the Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (Lyman band) and (Werner band) transitions are near the Lyman-a energy, the distortion of the CMB spectrum caused by escaped H Lyman-line photons accelerates both the formation and the destruction of H2 due to this channel relative to the thermal rates. This causes the populations of H2 molecules in Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. energy levels to deviate from their thermal equilibrium abundances. We find that the resulting H2 abundance is 10-17 at z = 1200 and 10-13 at z = 800, which is too small to have any significant influence on the recombination history. [ABSTRACT FROM AUTHOR]