Helium hydride ion

Helium hydride ion

Names
Systematic IUPAC name Hydridohelium(1+)[1]
Other names Helonium Helium hydride
Identifiers
3D model (JSmol)	Interactive image
ChEBI	CHEBI:33688 CHEBI:33689 neutral excimer
ChemSpider	21106447 Y
Gmelin Reference	2
CompTox Dashboard (EPA)	DTXSID801018818
InChI InChI=1S/HHe/h1H/q+1 Y Key: HSFAAVLNFOAYQX-UHFFFAOYSA-N Y
SMILES [HeH+]
Properties
Chemical formula	HeH+
Molar mass	5.01054 g·mol−1
Conjugate base	Helium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The helium hydride ion, hydridohelium(1+) ion, or helonium is a cation (positively charged ion) with chemical formula HeH⁺. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated helium. It is the lightest heteronuclear ion, and is believed to be the first compound formed in the Universe after the Big Bang.^[2]

The ion was first produced in a laboratory in 1925. It is stable in isolation, but extremely reactive, and cannot be prepared in bulk, because it would react with any other molecule with which it came into contact. Noted as the strongest known acid—stronger than even fluoroantimonic acid—its occurrence in the interstellar medium had been conjectured since the 1970s,^[3] and it was finally detected in April 2019 using the airborne SOFIA telescope.^[4][5]