Reading the transcript of the Royal Society of Chemistry podcast Helium Hydride, they state that helium hydride is possibly the most ancient compound to form in the Universe. They make the assertion that despite helium hydride being most stable as an ion, but:

The neutral molecule can briefly exist, but only as an excimer, where the excess electron has enough energy to keep it at a higher level.

Under what natural conditions could a stable neutral helium hydride molecule exist?


As explained in Emission Spectra of Bound Helium Hydride Physical Review Letters vol. 77 pages 2941-2944:

The ground state [of neutral HeH] is repulsive, as shown by numerous experiments and calculations.

but excited states of HeH that are bound exist (as first experimentally observed by this paper, but previously calculated).

Given that only excited states are bound, it don't think it proper to say HeH stably exists under any conditions natural or otherwise.

The paper does state:

Because of the abundance of He and $\ce{H_2}$ in stellar atmospheres and interstellar space, HeH is expected to be formed there. Therefore our data may be useful to find the HeH lines there.

However, that it exists does not mean it stably exists.

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