Department of Chemistry & Biochemistry, University of Mississippi, University, MS 38677-1848, USA.
Laboratoire Aimé-Cotton, CNRS & Université Paris-Saclay, 91405 Orsay, France.
Molecules. 2020 May 7;25(9):2183. doi: 10.3390/molecules25092183.
HeHHe + is the only potential molecule comprised of atoms present in the early universe that is also easily observable in the infrared. This molecule has been known to exist in mass spectrometry experiments for nearly half-a-century and is likely present, but as-of-yet unconfirmed, in cold plasmas. There can exist only a handful of plausible primordial molecules in the epochs before metals (elements with nuclei heavier than 4 He as astronomers call them) were synthesized in the universe, and most of these are both rotationally and vibrationally dark. The current work brings HeHHe + into the discussion as a possible (and potentially only) molecular candle for probing high- and any metal-deprived regions due to its exceptionally bright infrared feature previously predicted to lie at 7.43 μ m. Furthermore, the present study provides new insights into its possible formation mechanisms as well as marked stability, along with the decisive role of anharmonic zero-point energies. A new entrance pathway is proposed through the triplet state ( 3 B 1 ) of the He 2 H + molecule complexed with a hydrogen atom and a subsequent 10.90 eV charge transfer/photon emission into the linear and vibrationally-bright 1 Σ g + HeHHe + form.
HeHHe + 是早期宇宙中仅有的由原子组成的潜在分子，也很容易在红外波段观测到。这种分子在质谱实验中已经存在了近半个世纪，并且很可能存在于冷等离子体中，但尚未得到证实。在金属（天文学家称之为核质量大于 4 He 的元素）被合成之前的时期，宇宙中可能只存在少数几种合理的原始分子，而且大多数都是旋转和振动都很暗的。由于其先前预测的位于 7.43 μ m 的异常明亮的红外特征，HeHHe + 作为一种可能的（可能是唯一的）分子烛，被引入到探测高金属和任何金属缺乏区域的讨论中。此外，本研究提供了对其可能的形成机制以及显著稳定性的新见解，以及非谐零点能的决定性作用。通过三重态（ 3 B 1 ）的 He 2 H + 分子与氢原子的复合物，提出了一种新的进入途径，随后是 10.90 eV 的电荷转移/光子发射到线性和振动明亮的 1 Σ g + HeHHe + 形式。
