Discovery in ionization experiments Hydridohelium(1+), specifically {{chem2|[^{4}He^{1}H](+)}}, was first detected indirectly in 1925 by
T. R. Hogness and E. G. Lunn. They were injecting protons of known energy into a rarefied mixture of hydrogen and helium, in order to study the formation of hydrogen ions like , and . They observed that appeared at the same beam energy (16
eV) as , and its concentration increased with pressure much more than that of the other two ions. From these data, they concluded that the ions were transferring a proton to molecules that they collided with, including helium.
Early theoretical studies The first attempt to compute the structure of the HeH+ ion (specifically, {{chem2|[^{4}He^{1}H](+)}}) by quantum mechanical theory was made by J. Beach in 1936. Improved computations were sporadically published over the next decades.
Tritium decay methods in chemistry H. Schwartz observed in 1955 that the decay of the tritium molecule = {{chem2|^{3}H2}} should generate the helium hydride ion {{chem2|[^{3}HeT](+)}} 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. In a variant of that technique, exotic species like
methanium are produced by reacting organic compounds with the {{chem2|[^{3}HeT](+)}} that is produced by the decay of that is mixed with the desired reagents. Much of what we know about the chemistry of came through this technique.
Implications for neutrino mass experiments 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. The claim was disputed, and several other groups set out to check it by studying the decay of molecular tritium . It was known that some of the energy released by that decay would be diverted to the excitation of the decay products, including {{chem2|[^{3}HeT](+)}}; and this phenomenon could be a significant source of error in that experiment. This observation motivated numerous efforts to precisely compute the expected energy states of that ion in order to reduce the uncertainty of those measurements. Many have improved the computations since then, and now there is quite good agreement between computed and experimental properties; including for the isotopologues {{chem2|[^{4}He^{2}H](+)}}, {{chem2|[^{3}He^{1}H](+)}}, and {{chem2|[^{3}He^{2}H](+)}}.
Spectral predictions and detection In 1956, M. Cantwell predicted theoretically that the spectrum of vibrations of that ion should be observable in the infrared; and the spectra of the deuterium and common hydrogen isotopologues ({{chem2|[^{3}HeD](+)}} and {{chem2|[^{3}He^{1}H](+)}}) should lie closer to visible light and hence easier to observe. The first detection of the spectrum of {{chem2|[^{4}He^{1}H](+)}} was made by D. Tolliver and others in 1979, at wavenumbers between 1,700 and 1,900 cm−1. In 1982, P. Bernath and T. Amano detected nine infrared lines between 2,164 and 3,158 waves per cm.
Interstellar space HeH+ has been conjectured since the 1970s to exist in the
interstellar medium. Its first detection, in the nebula
NGC 7027, was reported in an article published in the journal
Nature in April 2019. ==Natural occurrence==