Tributyl phosphate (TBP) is a liquid, viscous solvent used in various industrial sectors such as plastic coatings, metallurgy, hydraulic brakes, etc. It is known in the atomic industry as a solvent for the extraction and separation of actinides (uranium, thorium) and rare earth elements. For this reason, it is considered as an excellent tracer of nuclear activity and its detection in the gas phase is a subject of considerable importance. Unfortunately, at room temperature, with a vapor pressure of the order of 0.1 Pa, the gas phase of TBP is practically undetectable by conventional spectroscopic methods.

Its detection by infrared spectroscopy has become possible by coupling synchrotron radiation of the AILES beamline to a multi-passage cell (L = 20 m) configured in such a way as to create a temperature gradient during the passage through the beam. In this way the vibration spectrum of TBP in the 600 cm^-1 – 3500 cm^-1 region has been recorded, starting at a temperature of 60°C. By comparing the observed spectra with those calculated by ab initio methods, all the observed bands can be attributed to normal vibration modes of the molecule. The infrared spectrum of TBP constitutes a unique fingerprint, which can distinguish it unambiguously from other chemically close organophosphorus compounds, whose spectra have also been recorded by the AILES beamline of the SOLEIL synchrotron.

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