The pure rotational spectrum of FeCN has been recorded in the frequency range 140-500 GHz using millimetersub-millimeter direct absorption techniques. The species was created in an ac discharge of Fe(CO)5 and cyanogen. Spectra of the 13C, 54Fe, and 57Fe isotopologues were also measured, confirming the linear cyanide structure of this free radical. Lines originating from several Renner-Teller components in the v2 bending mode were also observed. Based on the observed spin-orbit pattern, the ground state of FeCN is 4Δi, with small lambda-doubling splittings apparent in the Ω = 5/2, 3/2, and 1/2 components. In addition, a much weaker spectrum of the lowest spin-orbit component of FeNC, Ω = 9/2, was recorded; these data are consistent with the rotational parameters of previous optical studies. The data for FeCN were fit with a Hunds case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling parameters were determined. Rotational constants were also established from a case (c) analysis for the other isotopologues, excited vibronic states, and for FeNC. The r0 bond lengths of FeCN were determined to be rFe-C = 1.924 Å and rC-N = 1.157 Å, in agreement with theoretical predictions for the 4Δ i state. These measurements indicate that FeCN is the lower energy isomer and is more stable than FeNC by ∼1.9 kcalmol.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry