MICROWAVE MEASUREMENTS OF THE ROTATIONAL SPECTRUM FOR CYCLOPENTADIENYL COBALT DICARBONYL

Rotational transitions in the 6-18 GHz range were measured for cyclopentadienyl-cobalt dicarbonyl (CpCo(CO)2) using a Flygare-Balle type pulsed beam spectrometer. Splitting and additional transitions due to hindered internal rotation and cobalt quadrupole coupling were observed in the spectrum. Analysis of the spectrum provided the rotational constants A = 1625(20), B = 1257(2) and C = 876(2) MHz. This molecule appears to have a tenfold barrier to rotation of the -Co(CO)2 fragment about the C5 axis of the Cp group. The potential energy barrier to internal rotation is V10 = 0.82(20) THz (0.3 kJ/mol). The value of the OC-Co-CO angle was found to be theta = 98(5)-degrees. This and other structure parameters will be compared with electron diffraction results. The Co-59 quadrupole coupling components are eQq(aa) = 12(4) MHz and eQq(bb) = 132(4) MHz.