The microwave spectrum and quadrupole coupling in tricarbonyl(methylcyclopentadienyl) manganese

The rotational spectrum of tricarbonyl(methylcyclopentadienyl) manganese ha s been recorded in the range from 1-23 GHz using an FTMW spectrometer worki ng on a molecular beam. This spectrum is assigned for the first time, yield ing the rotational constants of the molecule and quartic centrifugal distor tion constants. The fine structure due to the quadrupole interaction of the Mn-55 nucleus could be solved and gave the quadrupole coupling tensor (whi ch is compared with that of tricarbonyl(cyclopentadienyl) manganese, and th e spin-rotation constants. An additional splitting of a few kHz, which coul d be observed for some transitions, is interpreted as arising from the inte rnal rotation of the methyl group.