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ARNAUD CUISSET, MARIE-ALINE MARTIN-DRUMEL, FRANCIS HINDLE, GAEL MOURET, DMITRII A. SADOVSKII, Laboratoire de Physico-Chimie de l'Atmosphère, 189A Ave. Maurice Schumann, 59140 Dunkerque, France.
Benefiting of the exceptional properties of the AILES synchrotron beamline, the gas phase Far-IR spectrum of DMSO has been recorded and resolved . The rovibrational analysis allowed to discover a new rotational behaviour for a polyatomic molecule: the gyroscopic destabilization. In order to explain this phenomenon, we looked for four-fold energy clusters in the high resolution ground state THz spectrum of DMSO recorded with a sub-THz spectrometer based on a frequency multiplication chain . Pure rotational lines in the 5 lowest vibrationnally excited levels have been recorded below 700 GHz. With near 1000 rotational transitions assigned, high quantum numbers have been reached allowing to discover sequence of four-fold clusters in the out of plane bending mode of DMSO and to study the vibrational dependence of an unusual rotational dynamics.