Millimeter and submillimeter wave spectroscopic investigations into the rotation-tunneling spectrum of gGg' ethylene glycol, HOCH2CH2OH

The rotation-tunneling spectrum of the second most stable gGg' conformer of ethylene glycol (1,2-ethanediol) in its ground vibrational state has been studied in selected regions between 77 and 579 GHz. Compared to the study of the more stable aGg' conformer, a much larger frequency range was studied, resulting in a much extended frequency list covering similar quantum numbers, J less than or equal to 55 and K-a less than or equal to 19. While the input data were reproduced within experimental uncertainties up to moderately high values of J and K, larger residuals remain at higher quantum numbers. The severe mixing of the states caused by the Coriolis interaction between the two tunneling substates is suggested to provide a considerable part of the explanation. In addition, a Coriolis interaction of the gGg' ground vibrational state with an excited state of the aGg' conformer may also contribute. Relative intensities of closely spaced lines have been investigated to determine the signs of the Coriolis constants between the two tunneling substates relative to the dipole moment components and to estimate the magnitudes of the dipole moment components and the energy difference between the gGg' and the aGg' conformers. Results of ab initio calculations on the total dipole moment and the vibrational spectrum were needed for these estimates. The current analysis is limited to transitions with quantum numbers J less than or equal to 40 and K-a less than or equal to 6 plus those having J less than or equal to 22 and K-a less than or equal to 17 which could be reproduced within experimental uncertainties. The results are aimed at aiding radioastronomers to search for gGg' ethylene glycol in comets and in interstellar space. (C) 2004 Elsevier Inc. All rights reserved.