Knowledge Bank

The rotational spectrum of the transition metal complex, butadiene iron tricarbonyl, was measured using a Flygare-Balle type microwave spectrometer. A total of 71 a-dipole and c-dipole transitions in the 5-17 GHz range were obtained for this asymmetric top transition metal complex. The ``best fit” rotational constants are $A=1005.4201(3)$ MHz, $B=958.0408(2)$ MHz and $C=933.6865(3)$ MHz. Centrifugal distortion constants were also obtained in the least squares fit to the measured transitions. The present measurements indicate an upper limit of 40 Khz for splittings due to internal rotation, which places a lower limit on the barrier height of $V3$ $\ge$ 1.2 THz. This appears to be only the second asymmetric top, transition metal complex to be studied by microwave spectroscopy.