The helium hydrogen ion is isoelectronic with molecular hydrogen ().
Unlike the dihydrogen ion , the helium hydride ion has a permanent dipole moment, which makes its spectroscopic characterization easier. The calculated dipole moment of HeH is 2.26 or 2.84 D. The electron density in the ion is higher around the helium nucleus than the hydrogen. 80% of the electron charge is closer to the helium nucleus than to the hydrogen nucleus.
Spectroscopic detection is hampered, because one of its most prominent spectral lines, at 149.14 μm, coincides with a doublet of spectral lines belonging to the methylidyne radical ⫶CH.
The length of the covalent bond in the ion is 0.772 Å or 77.2 pm.