Molecular hydrogen in the cosmic recombination epoch

Journal Article · Sat Oct 15 00:00:00 EDT 2011 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.84.083011· OSTI ID:21607859

Alizadeh, Esfandiar ^[1]; Hirata, Christopher M ^[2]

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1. Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States)
2. Caltech M/C 350-17, Pasadena, California 91125 (United States)

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-{alpha} 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{sub 2} molecule during the cosmic recombination epoch. Hydrogen molecules in the ground electronic levels X{sup 1}{Sigma}{sub g}{sup +} can either form from the excited H{sub 2} electronic levels B{sup 1}{Sigma}{sub u}{sup +} and C{sup 1}{Pi}{sub u} or through the charged particles H{sub 2}{sup +}, HeH{sup +}, and H{sup -}. We follow the transitions among all of these species, resolving the rotational and vibrational sublevels. Since the energies of the X{sup 1}{Sigma}{sub g}{sup +}-B{sup 1}{Sigma}{sub u}{sup +} (Lyman band) and X{sup 1}{Sigma}{sub g}{sup +}-C{sup 1}{Pi}{sub u} (Werner band) transitions are near the Lyman-{alpha} energy, the distortion of the CMB spectrum caused by escaped H Lyman-line photons accelerates both the formation and the destruction of H{sub 2} due to this channel relative to the thermal rates. This causes the populations of H{sub 2} molecules in X{sup 1}{Sigma}{sub g}{sup +} energy levels to deviate from their thermal equilibrium abundances. We find that the resulting H{sub 2} abundance is 10{sup -17} at z=1200 and 10{sup -13} at z=800, which is too small to have any significant influence on the recombination history.

• OSTI ID: 21607859
• Journal Information: Physical Review. D, Particles Fields, Vol. 84, Issue 8; Other Information: DOI: 10.1103/PhysRevD.84.083011; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANISOTROPY
ATOMS
ELECTRONIC STRUCTURE
ENERGY LEVELS
GALACTIC EVOLUTION
GROUND STATES
HYDROGEN
HYDROGEN IONS 1 MINUS
HYDROGEN IONS 2 PLUS
LYMAN LINES
MOLECULES
OPACITY
PHOTONS
RECOMBINATION
RELICT RADIATION
RESONANCE
SPECTRA
THERMAL EQUILIBRIUM
ANIONS
BOSONS
CATIONS
CHARGED PARTICLES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ELEMENTS
EQUILIBRIUM
EVOLUTION
HYDROGEN IONS
IONS
MASSLESS PARTICLES
MICROWAVE RADIATION
MOLECULAR IONS
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS