Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères

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High resolution VUV spectroscopy of interstellar molecules

par Mathieu Bertin - publié le , mis à jour le


M. Eidelsberg (voluntary researcher), M. Glass-Maujean (Prof. emeritus), A.-M. Vasserot (Ass. Prof.), S. Leach (voluntary researcher), J.-L. Lemaire (voluntary researcher), W-Ü L. Tchang-Brillet (Prof.), C. Blaess (tech.), N. Champion (engineer)


The huge improvements of observational data supplied by new generation of space and ground-based telescope, increase, for their interpretation, the need for highly accurate laboratory data. The group has expertise in high resolution studies of electronic spectra of small molecules, which occur in the vacuum ultraviolet (VUV) range. High resolution is necessary for determination of energy levels of these quantum systems, for probing their fundamental radiative properties, and for photodynamics studies.

Complementary laboratory techniques are involved, including mass spectrometry and ionic dissociation channels. Emission studies are carried out using the 10-meter vacuum spectrograph (resolution R=150000) of the Meudon Observatory.

Absorption studies are performed at synchrotron facilities, either on the SOLEIL-DESIRS beamline using the Fourier Transform Spectrometer (R=350000) or at BESSY (R=100000). Wavelengths with a precision better than 10-7 are obtained, as well as absorption cross-sections and predissociation and/or ionization widths.

The interpretation of experimental spectra is closely related to theoretical calculations based on ab initio potentials and coupling operator.

Current studies

The species under study are of interest to a variety of astrophysical environments.

  • H2/HD/D2 : We are conducting experimental and theoretical investigations of the complex line spectra of the most abundant molecule of the Univers and of its isotopologues, which show strong non adiabatic perturbations. H2 and HD lines are candidats for probing possible cosmological variation of the fundamental constant mass ratio mu= mp/me. These studies participate to the enrichment of the MOLAT database.
  • CO : The CO molecule is a tracer for H2 and gives rise to a rich photochemistry in the ISM. We are conducting exhaustive study of Rydberg series in CO and in its isotopologues, including the Rydberg-valence predissociating interactions, which are isotopically dependent.
  • Molecules relevant to exobiology : Recent investigation of formamide and its methyl derivatives, diacetylene, cyanoacetylene and dicyanoacetylene, by absorption studies and electron-ion coincidence technique in the far UV. /Measurement, through CN radical interstellar UV absorption spectra, of the cosmic background radiation temperature. /Study of the part played by VUV radiation in exoplanets. /Testing the validity of published values of the heat of formation for neutral and ionic molecules.


Mourad Roudjane, Wim Ubachs (VU Amsterdam), Christian Jungen (LAC Orsay), I. Haar, A. Ehresmann (Kassel), Steve Federman (Univ. of Toledo, Ohio) and Glenn Stark (Wellesley College, Massachussets), Martin Schwell (LISA, Crêteil), H. Baumgärtel (Berlin)

Séminaires à venir

Vendredi 20 septembre 2019, 14h00
Atelier, Paris
Challenging a Newtonian prediction through Gaia wide binaries
UNAM, Mexico
résumé :
Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. After reviewing recent work evidencing the existence of a critical acceleration scale in Elliptical Galaxies and Globular Clusters, I will show new results showing such a phenomenology in Gaia wide binaries using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical a0 value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.

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