Fourier-transform microwave spectroscopy of FeCN (X4Δi): Confirmation of the quartet electronic ground state

► Microwave spectra of FeCN (X4Δ) and NiCN (X2Δ) have been measured for the first time, using FTMW/laser ablation methods. ► Nitrogen hyperfine structure was observed in both species, giving insight into the electronic structure. ► The 4Δi ground state of FeCN has been confirmed, in contrast to theoretical predictions.