Millimeter-wave spectroscopy of the FeCO radical in the ν2 and ν3 vibrationally excited states

The pure rotational spectra of the FeCO radical in the ν2 (bending) and ν3 (Fe-C stretching) vibrational states of the ground X3Σ− electronic state were observed in the millimeter-wave region. The equilibrium rotational and centrifugal distortion constants were determined to be Be = 4374.631 (58) MHz and De = 1.1666 (20) kHz together with the spin-spin coupling constant λe = 691.89 (37) GHz and spin-rotation coupling constant γe = − 1079.4 (55) MHz with use of the millimeter-wave results and the ν1 IR data. The equilibrium bond length for Fe-C was derived to be 1.725 A assuming that for C-O to be 1.159 A. Since the vibronic symmetry of the excited state of bending vibration is 3Π, the analysis of spectrum in the ν2 state required an effective spin-orbit interaction constant of A2 = 6.0219 (61) GHz together with three parity doubling constants of o2 = 36.168 (10) GHz, p2 = 85.18 (34) MHz, and q2 = 4.7024 (17) MHz. The effective spin-orbit interaction constant A2 is attributed to the vibronic mixing of the...