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Quantum-state–selective electron recombination studies suggest enhanced abundance of primordial HeH+

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Science  18 Jul 2019:
eaax5921
DOI: 10.1126/science.aax5921

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Abstract

The epoch of first star formation in the early universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a dramatic decrease of the electron recombination rates for the lowest rotational states of HeH+, compared to previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.

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