Natural Occurrence
The helium hydride ion is formed during the decay of tritium in the HT or tritium molecule T2. Although excited by the recoil from the beta decay the molecule remains bound together.
HeH+ is thought to exist in the interstellar medium, although it has not yet been unambiguously detected. It is believed to be the first compound to have formed in the universe, and is of fundamental importance in understanding the chemistry of the early universe. This is because hydrogen and helium were almost the only types of atoms formed in Big Bang nucleosynthesis. Stars formed from the primordial material should contain HeH+, which could influence their formation and subsequent evolution. In particular, its strong dipole moment makes it relevant to the opacity of zero-metallicity stars. HeH+ is also thought to be an important constituent of the atmospheres of helium-rich white dwarfs, where it increases the opacity of the gas and causes the star to cool more slowly.
Several locations have been suggested as possible places HeH+ might be detected. These include cool helium stars, H II regions, and dense planetary nebulae (in particular NGC 7027). Detecting HeH+ spectroscopically is complicated by the fact that one of its most prominent spectral lines, at 149.14 μm, coincides with a doublet of spectral lines belonging to the methylidyne radical ⫶CH.
HeH+ could be formed in the cooling gas behind dissociative shocks in dense interstellar clouds, such as the shocks caused by stellar winds, supernovae and outflowing material from young stars. If the speed of the shock is greater than about 90 km/s, quantities large enough to detect might be formed. If detected, the emissions from HeH+ would then be useful tracers of the shock.
Read more about this topic: Helium Hydride Ion
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