It is the lightest heteronuclear ion, and is believed to be the first compound formed in the Universe after the Big Bang.

Noted as the strongest known acid—stronger than even fluoroantimonic acid—its occurrence in the interstellar medium had been conjectured since the 1970s,[4] and it was finally detected in April 2019 using the airborne SOFIA telescope.

[8] The calculated dipole moment of HeH+ is 2.26 or 2.84 D.[9] The electron density in the ion is higher around the helium nucleus than the hydrogen.

The decay of tritium to 3He+ followed by its extraction of a hydrogen atom from the compound yields 3HeH+, which is then surrounded by the organic material and will in turn react.

[22][23] HeH+ cannot be prepared in a condensed phase, as it would donate a proton to any anion, molecule or atom that it came in contact with.

They observed that H+3 appeared at the same beam energy (16 eV) as H+2, and its concentration increased with pressure much more than that of the other two ions.

From these data, they concluded that the H+2 ions were transferring a proton to molecules that they collided with, including helium.

[16] The first attempt to compute the structure of the HeH+ ion (specifically, [4He1H]+) by quantum mechanical theory was made by J.

[28][29] H. Schwartz observed in 1955 that the decay of the tritium molecule T2 = 3H2 should generate the helium hydride ion [3HeT]+ with high probability.

In 1963, F. Cacace at the Sapienza University of Rome conceived the decay technique for preparing and studying organic radicals and carbenium ions.

[31] In 1980, V. Lubimov (Lyubimov) at the ITEP laboratory in Moscow claimed to have detected a mildly significant rest mass (30 ± 16) eV for the neutrino, by analyzing the energy spectrum of the β decay of tritium.

This observation motivated numerous efforts to precisely compute the expected energy states of that ion in order to reduce the uncertainty of those measurements.

[3] 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.

These included cool helium stars,[3] H II regions,[39] and dense planetary nebulae,[39] like NGC 7027,[36] where, in April 2019, HeH+ was reported to have been detected.