Dimethyl sulfoxide (DMSO) occupies an important place amongst industrial solvents since it is used in the oil industry, textiles, biology and even in the manufacture of pesticides. As a volatile organic compound, it is a pollutant well-known for its involvement in atmospheric reactions. This molecule has, moreover, been targeted in NRBC* (nuclear, radiological, biological and chemical) protection programs as a simulation chemical of yperite, better known as “mustard gas”.
The infra-red spectrum of DMSO was recorded in the gas phase more than 35 years ago, using the means available at the time (low resolution, limited tunability, access to mid- and near- infrared (ν > 600 cm^-1)). Information on active far-infrared modes (ν < 600 cm^-1) came mainly from microwave data. Recent articles on spectroscopic analysis of DMSO are still based on these old experimental data. In spite of the interest in this molecule, there seemed to be little or no new data on it.
The combined use of synchrotron radiation on the AILES beamline, a IFS125 Fourier Transform spectrometer and a multi-passage cell permitting an optical path of 150 m., has made it possible to record the high resolution spectrum of DMSO (0.001 cm^-1) using sub-millimeter wavelengths up to the far-infrared. The pure rotation spectrum was recorded between 10 and 50 cm^-1 and could be compared, for the first time, to data obtained in the laboratory by optoelectronics means, using a THz generating spectrometer. For the first time, it has been possible to resolve the rotational structures of two low frequency vibration modes observed between 300 and 400 cm^-1. The analysis of hundreds of observed transitions should lead to the determination of new and pertinent spectroscopic and structure parameters for this molecule.

These experiments  were carried out  in collaboration with Arnaud Cuisset ( Université du Littoral - Dunkerque).