https://doi.org/10.1351/goldbook.I03346
A molecular ion containing one or more of the less abundant naturally occurring isotopes of the atoms that make up the molecular structure. Thus, for ethyl bromide there exist isotopic molecular ions such as: 13CCH5Br+·, C2H4DBr+·, C2H581Br+·, 13C2H581Br+·, etc.