15min:

A. PERRIN, J.-M. FLAUD, Laboratoire de Photophysique Moléculaire, CNRS, Université Paris Sud, Campus d'Orsay, Bat 350, 91405 Orsay Cedex, France; J. DEMAISON, L. MARGULÈS, Laboratoire PhLAM, CNRS, Université de Lille I, Bat. P5, 59655 Villeneuve d'Ascq Cedex, France; H. MÄDER, S. WÖRMKE, Institut für Physikalische Chemie, Olshausenstrasse 40, D-24098 Kiel, Germany.

The rotational spectrum of HDCO in the 4¹, 5¹ and 6¹ excited vibrational states has been investigated in Lille and Kiel using a sample enriched in D. In Lille the measurements were performed in the millimeter (160-600 GHz) region. The spectra in Kiel were recorded using Fourier transform microwave spectrometers in the regions of about 8-18 GHz and 18-26 GHz, employing a rectangular waveguide of 12 m length and a circular waveguide of 36 m length, respectively. These results were combined with the 4¹, 5¹ and 6¹ infrared energy levels obtained in a previous analysis of FTS spectra of the ₄ band (CHD bend), ₅ band (CHD rocking) and ₆ band (out of plane bend) recorded in the 10 µm region at Giessen in order to get the best possible Hamiltonian constants.

The energy levels calculation of the 4¹, 5¹ and 6¹ interacting states accounts for the usual A- and B-type Coriolis resonances in the 5¹ - 6¹ and 6¹ - 4¹ off diagonals blocks. On the other hand, in order to reproduce the observed microwave transitions and infrared energy levels, it was necessary to use a $1J_x,J_z$1 non orthorhombic term in the 5¹ and 6¹ v- diagonal blocks of the Hamiltonian matrix. Therefore, HDCO exhibits an example of vibrational induced rotational axis switching.