Fourier transform microwave spectroscopy of monobromogermylene (HGeBr and DGeBr), a heavy atom carbene analog

Eight isotopologues of HGeBr and nine of DGeBr have been studied in natural abundance by pulsed-jet Fourier transform microwave spectroscopy. The reactive germylene species were produced in an electric discharge at the exit of a pulsed molecular beam valve using precursor mixtures of H(3)GeBr or D(3)GeBr in high pressure neon. In the 5-25 GHz operating range of the spectrometer, only a-type transitions were observed; K = 0 transitions for HGeBr and K = 0 and 1 transitions for DGeBr. From the observed transitions, an improved molecular geometry has been determined and nuclear quadruple constants for Ge and Br have been determined. The Townes-Dailey model has been extended to obtain the electron densities of the 4p orbitals on the germanium and bromine atoms from the quadruple coupling constants. These results are discussed in terms of qualitative molecular orbital theory.