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 be en assigned for the first time using microwave-microwave double resona nce 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 becaus e of the large-amplitude motion displayed by the molecule. This motion , consisting of a concerted torsion of both OH groups, leads to a tunn eling splitting of 7 GHz and significantly alters the rotational energ y level pattern because it is coupled to the overall rotation of the m olecule through a Coriolis coupling. This coupling is accounted for us ing an IAM-like theoretical model, and this allows us to satisfactoril y analyze the microwave frequencies of the normal and of the O-d(2) sp ecies. Information on the equilibrium geometry of the molecule and on the tunneling path is extracted through the values obtained for the pa rameters involved in this Coriolis coupling. A dipole moment analysis yields values of all three dipole moments components and a determinati on of their relative signs is attempted. (C) 1995 Academic Press, Inc.