Microwave Spectrum of Germacyclopentane

The microwave spectrum of four Ge isotopic species of the five-membered heterocycle germacyclopentane (C4H10Ge) has been investigated in the region 8–22 GHz. Rotational constants for the ground state of the 74Ge species are: A = 5323.7, B = 2842.20, C = 2041.52 MHz. From excited states assigned to the lowest ring-deformation mode, a lower limit of about 500 cm−1 has been estimated for the barrier to pseudorotation. The molecule is found to be permanently twisted into a C2 conformation with a twist angle of 18°, and ∠CGeC = 98°, ∠GeCC = 106°, and ∠CCC = 115°. Stark-effect measurements give a dipole moment of 0.665 ± 0.007 D. For the 73Ge species, the nuclear quadrupole coupling constants are found to be χaa = 15.89 MHz, χbb = −10.29 MHz, χcc = −5.60 MHz.