Knowledge Bank

The pure rotational spectrum of the FeCN radical (X$4\Delta i$) has been measured using Fourier transform microwave (FTMW) techniques in the 4 - 40 GHz frequency range and a laser ablation source. The species was produced using Discharge Assisted Laser Ablation Spectroscopy (DALAS) in a supersonic jet expansion of iron vapor and (CN)$2$, diluted in argon carrier gas. The fundamental rotational transition, J = 9/2 $\to$ 7/2 ($\Omega$ = 7/2), was recorded near 36 GHz. Three hyperfine transitions, due to the nitrogen nuclear spin of I = 1, were observed in the spectrum. These data were combined with the previous millimeter/submillimeter measurements of FeCN in a global fit and nitrogen hyperfine constants were determined. These measurements confirm that the ground state of FeCN is $4\Delta i$, as suggested by previous millimeter/submillimeter measurements of Flory & Ziurys. Theoretical calculations have predicted that the ground state of this radical is $6\Delta i$. In a $6\Delta i$ state, the J = 9/2 $\to$ 7/2 transition does not exist in the lowest energy ladder ($\Omega$ = 9/2).