15min:

A. PERRIN, J.-M. FLAUD, M. SMIRNOV, Laboratoire de Photophysique Moléculaire, CNRS, Université Paris Sud, Campus d'Orsay, Bat 210, 91405 Orsay Cedex, France; M. LOCK, Physikalisch-Chemisches Institut, Justus Liebig Universität, Heinrich-Buff-Ring 58, D-35392 Gieß en, Deutschland.

Using new Fourier transform spectra recorded with high resolution at Giessen, it has been possible to perform an extensive study of the absorption spectra of the HDCO isotopomer of formaldehyde in the 900-1400cm^-1 spectral range. This analysis of the ₅ and ₆ bands was performed starting from the results obtained previously in the same spectral region and using the ground state parameters of Bocquet et al

For the ₅ band (CHD rocking) both A- and B- type transitions were observed, while the ₆ band (out of plane bend) involves C- type and forbidden transitions. The energy level calculation was performed using first the model previously proposed by Allegrini et al.: i.e. for the v- diagonal blocks a Watson A-type Hamiltonian in Ir representation and for the off- diagonal blocks, A- and B- type Coriolis operators. Surprisingly, this model appeared unsuitable because a new type of resonance was observed. We propose a new model which satisfactory reproduces the observed energy levels.