STAGE Nuclear spin Conversion of molecular hydrogen trapped on icy surfaces

Date de mise à jour de l’offre

Sorbonne Université :

Sorbonne Université - Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Description de la mission

Due to Pauli’s exclusion principle, molecules like H2, H2O or CH4 having protons in exchangeable positions exist in several nuclear spin configurations. In case of water, they are called ortho and para depending if the spins of the protons are parallel (total nuclear spin I=1) or anti-parallel (I=0). In gaseous phase, each rotational state is associated with only one of the nuclear magnetic species and in the high temperature limit (above 50 K), it is known that 1/4 of the molecules are para while 3/4 are ortho. Below 50 K, the Ortho-to-Para Ratio (OPR) at equilibrium becomes strongly temperature-dependent. Under stellar radiations, comets and interstellar dust release in space a great variety of hydrogenated molecules detected from space or ground-based telescopes. The abundances of ortho- and para- H2 are known to play a strong role in the chemistry of hydrogenated molecules like H2O, NH3, or c-C3H2. It is then crucial to understand and quantify the physical processes that may influence these abundances in the interstellar medium, especially on the surface of the icy mantles of interstellar grains. Performed in physical conditions close to the ones found in space, the measurement will help to answer to the following question: is the disequilibrium observed between the relative abundance of nuclear spin families a clue of the thermal history of the hydrogenated molecules in space?

Profil recherché

During this internship, we propose to develop with the members of the research group a set-up under high vacuum to investigate the nuclear spin conversion of molecular hydrogen H2 trapped on icy surface and the equilibration of the quantum nuclear spin states when the molecules are released in the gas by thermal desorption. The student will have the opportunity to use and develop state-of-the-art laser-based non-linear techniques, and high resolution infrared techniques for the rotational spectroscopy of simple molecules. He (She) will develop skills in vacuum systems and very low temperature (< 10 K) processes. By the end of the internship, the student will be strongly familiar with spectroscopy of the nuclear spin states of H2 and water. This work could be then extended in a PhD work in close collaboration with astronomers to investigate the role of the OPR of hydrogenated molecules in the Interstellar Medium and Comets.

Niveau de qualification requis

Bac + 4/5 et +
  • Employeur
    Sorbonne Université
  • Secteur d’activité de la structure
    Enseignement - Formation - Recherche
  • Effectif de la structure
    Plus de 250 salariés
  • Site internet de la structure
    https://lerma.obspm.fr
  • Type de stage ou contrat
    Stage pour lycéens et étudiants en formation initiale
  • Date prévisionnelle de démarrage
  • Durée du stage ou contrat
    Plus de 2 mois et jusqu'à 4 mois
  • Le stage est-il rémunéré ?
    Oui
  • Niveau de qualification requis

    Bac + 4/5 et +
  • Lieu du stage
    Tour 32-33, 3e étage LERMA - Sorbonne Université
    4 place Jussieu case 76
    75005 PARIS 5E ARRONDISSEMENT
  • Accès et transports
    Métro ligne 7 et 10 "Jussieu", bus 67 et 89