MILLIMETER-WAVE SPECTROSCOPY OF THE IRON CARBONYL RADICAL(FeCO) IN THE $\nu_{2}$ BENDING VIBRATIONAL STATE

$^{a}$K. Tanaka, M. Shirasaka and T. Tanaka, J. Chem. Phys. 106, 6820 (1997)Author Institution: Department of Chemistry, Faculty of Science, Kyushu University 33The rotational spectrum of iron carbonyl radical FeCO in the $\nu_{2}$ bending vibrational state of the ground $X^{3}\Sigma^{-}$ electronic state was observed in the millimeter-wave region. The radical was produced by a dc discharge of iron pentacarbonyl $Fe(CO)_{5}$. Seven rotational lines, split into sextet by the electron spin-spin interaction and A-type doubling, were identified in the frequency region of 154-254 GHz. Molecular constants derived, the rotational and c***ntrifugal distortion constants, the spin-spin coupling constant $\gamma_{0} = 679.37(291)GHz$ and the spin-rotation coupling constant $A_{0} = -1180.0(19)$ MHz, are reasonably similar to those of the ground $state^{a}$. Although the electronic state is $^{3}\Sigma^{-}$, a large spin-orbit coupling constant $A = 14.0746(57)$ GHz was derived, indicating the vibronic coupling with the $^{3}\Pi$ electronic state located about $6500 cm^{-1}$ above the ground state. From the A-type doubling, large interaction constants, $o = -18.2899(55)$ GHz, $p = -355.36(64)$ MHz, and $q = 9.5167(69)$ MHz, were determined, where the figurs in parentheses are a standard error to be attached to the last digits