15min:

GEORGES WLODARCZAK, JEAN DEMAISON, LAURENT MARGULES, BILAL BAKRI AND FRANCOIS HERLEMONT, Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, Université de Lille 1, F-59655 Villeneuve d'Ascq, France ; ANDRE FAYT, Molecular Spectroscopy Laboratory, Université Catholique de Louvain, Chemin du Cyclotron 2, B-1348 Louvain-La-Neuve, Belgium .

The rotational spectra of deuterated isotopomers of ethylene, H₂C=CH₂, have already been measured . The parent species in its ground vibrational state, as far as it is concerned, has no rotational spectrum because it has no permanent dipole moment. However, the vibrational states v₇=1 and v₈=1 are close in energy (at 948.77 and 939.86 cm^-1, respectively) and some allowed transitions between these two states lie in the millimeterwave range. The ₇ state is known with an accuracy better than 10^-6 cm^-1 thanks to CO₂ laser sideband spectra . The ₈ state has been estimated with an accuracy of the order of 10^-3 cm^-1 by combining the ₇ + ₈ band with the hot band ₇ ! + ₈ - ₈, both analysed in F.T. spectra (unpublished results). The spectrum has been measured from 180 to 500 GHz and more than 30 transitions have been assigned without ambiguity to ethylene, with a systematic deviation of about -27 MHz from the predictions. A new analysis of the ₈ state has been performed, including the a-type Coriolis interaction with the ₆ state, and a good agreement has been obtained.