Helium Hydride Ion

The hydrohelium(1+) cation, HeH+, also known as the helium hydride ion, is a positively charged ion formed by the reaction of a proton with a helium atom in the gas phase, first observed in 1925 and isoelectronic with molecular hydrogen. It is the strongest known acid, with a proton affinity of 177.8 kJ/mol. This ion is also called the helium-hydride molecular ion. It has been suggested that it should occur naturally in the interstellar medium. It is the simplest heteronuclear ion, and is comparable with the hydrogen molecular ion, H+
2. Unlike H+
2, however, it has a permanent dipole moment, which makes its spectroscopic characterization easier.