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

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Study of van der Waals systems for Astrophysics and for Planetology

par Mathieu Bertin - publié le , mis à jour le


M.L. Dubernet (Astronomer, Observatoire de Paris), C. Boursier (50%, Lecturer, UPMC), E. Quintas-Sanchez (Post-Doc 2015-2016, Observatoire de Paris), P. Tuckey (Syrte, Astronomer, Observatoire de Paris), C. M. Zwölf* (Senior Software Engineer, Observatoire de Paris), N. Moreau* (Software Engineer, Observatoire de Paris), Y.A. Ba* (Software Engineer, Observatoire de Paris)
* on databases and VAMDC


The study of the dynamics of van der Waals systems allows to calculate microscopic quantities that are of interest both for the analysis of spectra and the modelisation of the interstellar medium, of solar planetary, exo-planets and cometary atmospheres.
By van der Waals systems we mean 2-body non-reactive systems between an atom and a molecule, and/or between molecules (the 3-body systems are irrelevant for the above astrophysical applications).

Potential energy surface of HCS+ - He (M.-L. Dubernet, P. Tuckey, E. Sanchez-Quintas, submitted to JCP 2015)

Our theoretical activities include :

  • the calculation of non-reactive potential energy surfaces via ab initio quantum chemistry
  • the calculation of van der waals bound states, the comparison between experimental results and theoretical values allowing to test some range of the potential energy surface
  • the determination of collisional excitation rate coefficients of neutral/ionic molecules by atoms and/or molecules. These calculations use the above potential energy surfaces combined with either quantum or semi-classical dynamical calculations
  • the determination of pressure molecular line broadening and shitfting coefficients using quantum and/or semi-classical methodologies

Our expertise includes an experimental expertise on collisional relaxation of molecules, the collection, evaluation and diffusion of collisional data through the BASECOL database and the interoperable access to many atomic and molecular databases through the VAMDC Consortium that we lead at present. The activities related to databases and VAMDC are linked to the "Tâche de Service" SO5 of CNRS-INSU-AA.

"Rotational excitation of 45 levels of ortho/para—H2O by excited ortho/para—H2 from 5K to 1500K : state-to-state, effective and thermalized rate coefficients (F. Daniel, M.L. Dubernet, A. Grosjean, A.&A., 2011, 536 p A76+"
State-to-state cross-sections in _A2 as a function of relative kinetic energy (in cm-1) for the para-H2O transitions : from level 4(211) to 1(000) (1a), to 2(111) (1b), to 3(202) (1c) ; from level 7(322) to 1(000) (2a), to 2(111) (2b), to 4(211) ; and from level 16(440) to 2(111) (3a), to 10(331) (3b), to 14(524) (3c), with the following para-H2 transitions : j2 = 0 -> j’2 = 0 (black), j2 = 0 -> j’2 = 2 (red), j2 = 2 -> j’2 = 0 (green) and j2 = 2 -> j’2 = 2 (blue)

Research Collaborations

Our activities are carried out in collaboration with astrophysical colleagues who regularly use our results in their modelisation and/or in their interpretation of observed spectra. We have co-directed the FP6-RTN project "Molecular Universe" and we were part of a key project in HERSCHEL. At present C. Boursier is co-I of a project called « Non-LTE diagnostics of CIRS observations of Titan’s mesosphere ». This is a CDAPS project (Cassini Data Analysis and Participating Scientists from NASA whose PI is Dr. A. Kutepov (the Catholic University of America).
Some of the theoretical activities are carried out in collaboration with groups exploring either new methodologies or new dynamical effects (Dr T. Stoecklin’s group from University of Bordeaux and Prof. D. Babikov’s group from Milwaukee University, USA).


The activities are supported via european projects (FP6-RTN "Molecular Universe", the overheads of the e-science FP7 "VAMDC project", the ASTRONET CATS project, via the national program : " Physico-Chimie du Milieu Interstellaire (PCMI)" and "Planétologie (PNP)". Calculations are carried out on the group’s cluster, on Paris Observatory clusters, on MesoPSL and on national facilities at IDRIS and CINES.
The BASECOL database and the VAMDC activities have been supported by 2 european FP7 e-science contracts (2009-2012, 2012-2014), by the ASTRONET CATS project and by some support from Paris Observatory Scientific Councel.

Past Members

• F. Daniel (PhD - 2004-2007), (calculations on N2H+ — He, H2O—H2), PhD de l’Ecole Doctorale Astronomie et Astrophysique, ED127, at present post-doc at Grenoble Observatory
• S. Marinakis (Post-Doc, 2009-10) (calculations on CS-H2 and BASECOL), ASTRONET CATS contract, presently Oxford University
• L. Nenadovic (Software Engineer, 2010-2012) (VAMDC, SPECTCOL, VAMDC contract, at present student
• M. Doronin (Software Engineer, 2010-2012) (VAMDC standards, Portal, BASECOL), VAMDC Contract, presently PhD LERMA-LCT
• S. Pilon (Communication, 2013) (VAMDC), VAMDC Overheads
• Y.A. Ba (Software Engineer, 2011-2014) (BASECOL, SPECTCOL), VAMDC Contract, VAMDC Overheads, SUP@VAMDC Contract, at present permanent staff at Paris Observatory
• F. Portier (Technology Transfer, 2014), (SUP@VAMDC), SUP@VAMDC Contract & SUP@VAMDC Overheads
• M. Ivanov (Post-Doc, 2013) (semi-classical method, H2O-He), VAMDC Overheads
• E. Quintas-Sanchez (Post-Doc, 2014) (QCT calculations, PES of H2O- HCN), VAMDC Overheads


• A. Semenov (PhD of Prof. D. Babikov, Milwaukee University), (semi-classical method, H2O-He), 2014

Key References

• The water series of papers (M.L. Dubernet, F. Daniel, A. Grosjean)
• The BASECOL reference paper (M.L. Dubernet et al, A.&A., 2013, vol. 553, p A50)
• The VAMDC reference paper (M.L. Dubernet et al., JQSRT, 2010, vol. 210, p 2151)

Séminaires à venir

Vendredi 17 janvier 2020, 14h00
Salle de l'atelier, Paris
The role of feedback- and accretion-driven turbulence in galaxy build-up
résumé :
Cosmological models describe accurately the growth of large scale, dark matter-dominated, structures, but largely fail to reproduce the baryon content and physical properties of galaxies. Why? Essentially because the build-up of galaxies is regulated by a complex interplay between gravitational collapse, galaxy merging and feedback related to AGN and star formation, for which we still miss a robust theory. The energy released by these processes has to dissipate for gas to cool, condense, and form stars. How gas cools is thus a key to understand galaxy formation and why it such an inefficient process. In this seminar, I will discuss a few examples where turbulence driven by gas accretion, feedback, and galaxy interactions, which is largely ignored in models of galaxy formation, and captured in current simulations only over a limited range of scales, may have a major impact on galaxy and halos properties.

Vendredi 24 janvier 2020, 14h00
Salle de l'atelier, Paris
The accretion-ejection connection in planet-forming disks. New perspectives from high angular resolution observations
Vendredi 7 février 2020, 14h00
Salle de l'atelier, Paris
Redistribution of angular momentum from core to disk scales in Class 0 stars
Mathilde GAUDEL
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