Infrared spectroscopy of transient species

White cell - Axial view of the long optical path (200 m) White cell, equipped with two electrodes to produce a giant plasma (Source: ESA – D. Ducros, 2009)

The identification of new molecular species in astrophysical environments (interstellar medium, comets and planetary atmospheres) depends on the measurement of their gas-phase spectral signature. The development of radio-astronomy in the 70’s (mm and sub-mm domains), is at the origin of the discovery of most interstellar molecules. Mid and far infrared ranges, which usually complement this spectral region, become key for the detection of species devoid of permanent dipole moment. Many interstellar species (molecules, radicals, ions) are unstable under standard conditions of temperature and pressure, thus complicating their investigation.

Several of our experimental chambers are coupled to a high resolution Fourier Transform spectrometer Bruker HR 125. It includes a multi-pass White cell with a 200-m absorption path length, equipped with two facing electrodes to generate a “giant” plasma. This apparatus is employed for the investigation of charged species, which play a key role in a variety of diluted astrophysical environments.

The recent development of a planar plasma expansion source opens the way to the production of charged radical species at low temperatures (10-20 K) of interest for the interstellar medium. The source will be combined with the FTIR spectrometer for the investigation of the most absorbing species and to a diode laser spectrometer based on a high Finesse cavity (Cavity Ring Down Spectroscopy) for trace species.

Selected publications