MICROWAVE MEASUREMENTS OF RHENIUM QUADRUPOLE COUPLING IN CYCLOPENTADIENYL RHENIUM TRICARBONYL

Microwave measurements of rotational transitions for cyclopentadienyl rhenium tricarbonyl were performed in the gas phase using pulsed beam Fourier transform microwave spectroscopy. One hundred and sixty five t ransitions were assigned to two isotopomers of rhenium. The location o f the rhenium atom near the center of mass produced significant overla p between the spectra of the two isotopomers. The data were accurately fit using a symmetric top, rigid rotor Hamiltonian that included nucl ear quadrupole coupling and centrifugal distortion constants. The rota tional constants obtained were B(Re-187) = 724.9794(2), B(Re-185) = 72 4.9795(2). The quadrupole coupling constants obtained were eQq(Re-187) = 614.464(12) and eQq(Re-185) = 649.273(14) MHz. The successful fitti ng of the measured spectra to a symmetric top Hamiltonian indicates th at the cyclopentadienyl group retains C-5 upsilon symmetry, and the Re (CO)(3) group C-3 upsilon Symmetry in the gas phase. The measured rota tional constants are in reasonable agreement with those calculated fro m the structural parameters obtained in the earlier x-ray work. The Re quadrupole coupling constants obtained are compared with values for o ther complexes. (C) 1998 American Institute of Physics. [S0021-9606(98 )00921-0]