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

Spectra of the FeCN radical have been measured using Fourier-transform microwave (FTMW) techniques. This species was created in a supersonic jet by laser-ablation of iron, coupled with a dc discharge, in the presence (CN)2. The lowest rotational transition of FeCN near 36 GHz was recorded. The observation of this transition, the J = 9/2 → 7/2 line in the Ω = 7/2 spin–orbit component, conclusively establishes that FeCN has a 4Δi ground electronic state, rather a 6Δ state, as predicted by theory. The FTMW spectrum of NiCN (X2Δi) was also measured; small nitrogen hyperfine splitting was observed in both molecules.