THE ROTATIONAL CONCERTED TORSIONAL SPECTRUM OF THE G'GA CONFORMER OF ETHYLENE-GLYCOL

The microwave spectrum of the g'Ga conformer of ethylene glycol has been assigned for the first time using microwave-microwave double resonance and molecular beam Fourier transform microwave spectroscopy. Such techniques were necessary in order to select the desired lines in the crowded spectrum, which does not follow a rigid rotator pattern because of the large-amplitude motion displayed by the molecule. This motion, consisting of a concerted torsion of both OH groups, leads to a tunneling splitting of 7 GHz and significantly alters the rotational energy level pattern because it is coupled to the overall rotation of the molecule through a Coriolis coupling. This coupling is accounted for using an IAM-like theoretical model, and this allows us to satisfactorily analyze the microwave frequencies of the normal and of the O-d(2) species. Information on the equilibrium geometry of the molecule and on the tunneling path is extracted through the values obtained for the parameters involved in this Coriolis coupling. A dipole moment analysis yields values of all three dipole moments components and a determination of their relative signs is attempted. (C) 1995 Academic Press, Inc.