Knowledge Bank

The pure rotational spectrum of the iron carbonyl radical FeCO produced by a de discharge of iron pentacarbonyl $Fe(CO)5$ was observed in the millimeterwave region. Ten rotational transitions, split into triples by the electron spin-spin interaction, were assigned to the electronic ground state of FeCO, definitely confirming that the FeCO radical has $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$ symmetry. Molecular constants in the ground state were derived from an analysis of the MMW spectrum combined with the rotational lines in the lowest spin component $\Omega =0$ observed by Fourier transform microwave (FTMW) spectroscopy [1]. The rotational and centrifugal distortion constants were determined as $B0=4363.88342(40)$ MHz, and $D0$ = 1.217 99(84) kHz. The spin-spin coupling constant and the spin-rotation coupling constant are $\gamma 0=684.470(51)$ GHz and $\gamma 0=1127.80(35)$ MHz, respectively, where the figures in the parentheses are a standard error to be attached to the last digits.