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Theses

Interaction d'atomes et de molécules d'hydrogène
avec des glaces d'eau à très basse température :
formation de H2 dans le milieu interstellaire

Abstract : The molecular hydrogen, a major component of the interstellar medium (ISM) is
formed on dust grains through surface catalysis. This key reaction is a source of uncertainty
in the description of the dynamic of the ISM, as well for the reaction efficiency
and for its energy budget. This reaction and its sub-processes (sticking and diffusion on
the grain surface, desorption) are studied here experimentally in the case of molecular
hydrogen formation on water ice surfaces similar to those covering dust in the cold dense
ISM.
Ultra-high vacuum, cryogenics, atomic beams, mass spectrometry and UV spectroscopy
are combined in the experimental setup named FORMOLISM. We have studied
the effects of surface heterogeneity and porosity on the reaction. We have focused on
molecular hydrogen desorption to improve the interpretation of formation experiments
and because the molecular hydrogen adsorbed on grains modify the formation efficiency.
Adsorption energies of H2, HD and D2 on these ices are obtained. A mechanism of isotopic
segregation is highlighted and the deuteration of molecular hydrogen on ice mantles
is quantified. The study of molecular formation reveals that on porous ices the reaction
energy is released to the surface because of the efficient recapture of the formed
molecules, and that the reaction is effective up to temperatures higher (20 K) than for
nonporous ices (13 K). For these latter, the formed molecules are directly released into
the gas phase where they are detected in rovibrationally excited states.
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-00124797
Contributor : Lionel Amiaud <>
Submitted on : Tuesday, January 16, 2007 - 11:04:54 AM
Last modification on : Tuesday, September 22, 2020 - 3:58:23 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 9:01:23 PM

Identifiers

  • HAL Id : tel-00124797, version 1

Citation

Lionel Amiaud. Interaction d'atomes et de molécules d'hydrogène
avec des glaces d'eau à très basse température :
formation de H2 dans le milieu interstellaire. Astrophysique [astro-ph]. Université de Cergy Pontoise, 2006. Français. ⟨tel-00124797⟩

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