Rotational spectroscopy of rare iron monoxide isotopologues: A mass-independent analysis

We present pure rotational transitions of the rare iron monoxide isotopologues.,andin their lowest spin states. For, the rotational spectrum reveals hyperfine splitting due to the nuclear spin of. We use Dunham-like parameters to analyse the new laboratory data together with data from the literature. In particular, we are able to derive the Born-Oppenheimer breakdown parametersandand the corresponding equilibrium bond length of. With these new accurate molecular parameters line positions on a sub-MHz accuracy level can be calculated, including those of the radioactive isotopologue. The new data allow for an astronomical search for the rareisotopologues using sensitive radio telescopes, like the Atacama Large Millimetre/submillimetre Array.