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Etude expérimentale et théorique des spectres d'émission et d'absorption VUV des molécules H2, D2 et HD

Abstract : H2, HD and D2 molecules take a fundamental place in molecular physics, astrophysics and plasma physics. H2 is the most abundant molecule in the universe. The recent observations with high resolution of VUV transitions of this molecule and its isotope HD were carried out by the FUSE satellite in the range 90.5-118.7 nm. These observations make it possible to determine the intensity ratio HD/H2 of lines, considered as a new tool to evaluate the abundance ratio of D/H, which is known to be a tracer of the chemical evolution of the Universe. In addition, the H2, HD and D2 molecules are formed in the plasma of edge of the tokamaks and contribute to the radiative losses of the medium. Consequently, it is important to have spectroscopic data obtained in laboratory with high accuracy for a reliable exploitation of the results of observations or for a modeling of plasmas of fusion.

The aim of this thesis is to carry out an experimental study of the absorption and emission spectra of the D2 and HD isotopes, with high resolution, in the VUV and to supplement it by a theoretical study of the excited electronic states involved in the observed transitions. Such a study had been carried out in our laboratory and had led to the realization of an atlas VUV in the range 70-170 nm for the H2 molecule.

The emission spectra of HD and D2 are produced by Penning discharge source operating under low pressure, and are recorded in the spectral range 78 -170 nm using the high resolution vacuum spectrograph of 10 m (~150 000) of Meudon Observatory, either on photographic plates, or on image plates for measurement of intensities. The recorded spectra contain more than 20 000 lines. The wavelengths are measured with a precision of Δλ/λ= 10-6.

The lines of the D2 molecules and H2 being present in the spectrum of HD, we initially start to carry out the analysis of the spectrum of D2, which consists to identify and to assign the lines to the electronic transitions between energy levels of the molecule. The present analysis is based on our theoretical calculations of the ro-vibrational energy levels of the excited electronic states and the transition probabilities from these states towards the energy levels of the fundamental state.

In addition, we carried out a study of the absorption spectra of the HD and D2 molecules in the Laser Center LCVU of Amsterdam, using the two photons 1 XUV+1 UV laser spectroscopy. New wavelengths with a very high precision of Δλ/λ= 10-8 in the spectral range 99.9 -104 nm has been measured.

These new wavelengths will constitute a data base of reference lines for the calibration of the molecular spectra, but their importance goes beyond the laboratory uses. Indeed, the new lines of HD measured by laser spectroscopy, added to the H2 lines already measured with a similar precision, will be used as references to study a possible cosmological variation of the masses ratio proton-to-electron μ= mp/me, by comparison with wavelengths of lines of H2 or HD observed in the absorption spectra of quasars at high red shift. This study requires the knowledge of the sensitivity coefficients of the wavelengths to the possible variation of μ, which we calculated by the resolution of coupled equations system for the electronic states B, B', C and D of the molecule H2 and HD for various values of μ.

During my thesis, we were also interested in transitions between free-free and free-bound states of the H2 molecule. These transitions occur during the H-H collision forming a quasi-molecule and leads to the formation of satellites in the wing of the lines of the hydrogen atom. We carried out a quantum study of the quasi-molecular satellite of the Lymanβ line and calculated the profile of absorption of the satellite according to the temperature. This variation is an important tool for diagnosis for the determination of the characteristics of the atmospheres of dwarf white.
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Contributor : Mourad Roudjane <>
Submitted on : Sunday, February 10, 2008 - 2:17:27 PM
Last modification on : Monday, December 14, 2020 - 9:41:14 AM
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  • HAL Id : tel-00208073, version 3


Mourad Roudjane. Etude expérimentale et théorique des spectres d'émission et d'absorption VUV des molécules H2, D2 et HD. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2007. Français. ⟨tel-00208073v3⟩



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