Conformation of ethylene glycol from the rotational spectra of the nontunneling O-monodeuterated species

The microwave spectrum of the two possible O-monodeuterated species has been measured in a mixture containing roughly 25% of each of the four possible OH/OH, OH/OD, OD/OH, and OD/OD isotopic species. Both spectra follow a semirigid rotor model without effects due to the tunneling of the two hydroxyl protons. Only one conformer has been detected: one oxygen is gauche with respect to the other; one hydroxyl hydrogen participates in the hydrogen bond, while the second one is trans with respect to the C---C bond. Precise values for the quartic centrifugal distortion constants have been obtained for both species. A measure of the dipole moment is given.