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

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Science  16 Aug 2019:
Vol. 365, Issue 6454, pp. 676-679
DOI: 10.1126/science.aax5921
  • Fig. 1 Dissociative recombination in the cryogenic storage ring, CSR.

    (A) Scheme of the CSR ring structure with the injected and stored HeH+ ion beam (red), merged electron beam (blue), reaction products (green), and particle detector. (B) Reaction scheme and position-sensitive detection of coincident fragments. (C) Equilibrium rotational state populations of HeH+ for previous studies (300 K) and the estimated radiation field in the CSR.

  • Fig. 2 DR for rotationally cold HeH+.

    (A) Blue circles indicate the merged-beams rate coefficient αDR as a function of the detuning energy Ed after relaxation to >50% J = 0 (this experiment, 10 s < t < 50 s, mean ± SD); absolute scaling uncertainty ±20% (SEM). Red symbols represent room temperature data from (11) (squares, absolute scaling uncertainty ±10% SEM) and from (12) [triangles, scaled to (11) at 0.03 eV]. (B) Fragment distance distribution projected into the detector plane for Ed = 0 (blue) with fit (19) for isotropic angular distribution (red). (C) Projected fragment distance distribution for Ed = 0.044 eV (blue) with fit (19) for a |Y10|2 angular distribution of the fragments (red). The angular dependences in (B) and (C) are indicated schematically. arb., arbitrary units.

  • Fig. 3 DR during the rotational relaxation of HeH+.

    (A) Relative rotational level populations as functions of ion storage time t from the radiative model (starting temperature: 3000 K; CSR radiation field: 99% at 6 K, 1% at 300 K) for J as given and with time slices I to IV in which the dominant J varies from 3 to 0. (B) Rate coefficient αDR(Ed) measured in the marked time slices (mean ± SD).

  • Fig. 4 Rotational-state selective DR rates for HeH+.

    (A) Merged-beams rate coefficients αDRJ(Ed) for J ≤ 2 and average for J ≥ 3 (mainly 3 and 4; mean ± SD). The dashed lines mark the shift of the maximum as J increases. (B) Solid lines indicate single-J plasma rate coefficients αDR,plJ(Tpl) for J ≤ 2 and average (av) for J ≥ 3 (mainly 3 and 4; mean with shaded areas denoting ±SD). The dotted line represents the fully thermal rate coefficient αDR,therm(Trot=Tpl). Dashed-dotted lines indicate values applied in early-Universe models (21, 22) and astrochemistry databases (2325). See (19) for further discussion, numerical fitting functions, and parameters.

Supplementary Materials

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

    Oldřich Novotný*, Patrick Wilhelm, Daniel Paul, Ábel Kálosi, Sunny Saurabh, Arno Becker, Klaus Blaum, Sebastian George, Jürgen Göck, Manfred Grieser, Florian Grussie, Robert von Hahn, Claude Krantz, Holger Kreckel, Christian Meyer, Preeti M. Mishra, Damian Muell, Felix Nuesslein, Dmitry A. Orlov, Marius Rimmler, Viviane C. Schmidt, Andrey Shornikov, Aleksandr S. Terekhov, Stephen Vogel, Daniel Zajfman, Andreas Wolf

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 and S2
    • Table S1
    • References

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