Alizadeh, Esfandiar and Hirata, Christopher M. (2011) Molecular hydrogen in the cosmic recombination epoch. Physical Review D, 84 (8). Art. No. 083011. ISSN 0556-2821 http://resolver.caltech.edu/CaltechAUTHORS:20111219-075610258
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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 H_2 molecule during the cosmic recombination epoch. Hydrogen molecules in the ground electronic levels X^1Σ_g+ can either form from the excited H_2 electronic levels B^1Σ_u^+ and C^1Π_u or through the charged particles H_2^+, HeH^+, and H^-. We follow the transitions among all of these species, resolving the rotational and vibrational sublevels. Since the energies of the X^1Σ_g^+-B^1Σ_u^+ (Lyman band) and X^1Σ_g^+-C^1Π_u (Werner band) transitions are near the Lyman-α energy, the distortion of the CMB spectrum caused by escaped H Lyman-line photons accelerates both the formation and the destruction of H_2 due to this channel relative to the thermal rates. This causes the populations of H_2 molecules in X^1Σ_g^+ energy levels to deviate from their thermal equilibrium abundances. We find that the resulting H_2 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.
|Additional Information:||© 2011 American Physical Society. Received 21 February 2011; published 27 October 2011. E. A. thanks Ben Wandelt for his support, Laura Book for her constant help, and Yacine Ali-Haїmoud and Dan Grin for useful conversations. He acknowledges financial support from the National Science Foundation (Grant No. AST 07-08849). C. H. is supported by the U.S. Department of Energy (DOE-FG03-92-ER40701), the National Science Foundation (NSF AST-0807337), and the David & Lucile Packard Foundation.|
|Classification Code:||PACS: 98.70.Vc, 95.30.Ft, 98.62.Ra|
|Official Citation:||Molecular hydrogen in the cosmic recombination epoch Esfandiar Alizadeh and Christopher M. Hirata Published 27 October 2011 (14 pages) 083011|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||19 Dec 2011 18:56|
|Last Modified:||26 Dec 2012 14:37|
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