Rotational spectrum of five isotopologues of cyclopropylmethylgermane: Ab initio calculations, barrier to internal rotation and nuclear quadrupole coupling constants for the 73Ge nucleus

Rotational spectra have been measured for five naturally occurring isotopologues of germanium in the gauche conformer of the cyclopropylmethylgermane molecule by Fourier-transform microwave spectroscopy. Internal rotation of the methyl group caused all rotational transitions to be doubled and analysis of these A and E states with an internal rotation Hamiltonian furnished a barrier to rotation of approximately 4.7 kJ mol−1 for each isotopic species. In addition, the quadrupolar nature of the I = 9/2 73Ge nucleus caused nuclear quadrupole hyperfine structure to be observed for all transitions belonging to this isotopologue, allowing a determination of nuclear quadrupole coupling constants for the 73Ge nucleus. Dipole moment components have also been measured via the Stark effect. Ab initio results will be presented and compared with experimental rotational constants, dipole moment components and electric field gradients at the Ge nucleus.