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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., Les molécules H2, HD et D2 occupent une place fondamentale en physique moléculaire, en astrophysique et en physique des plasmas. H2 est la molécule la plus abondante dans l'univers. Les récentes observations à haute résolution des transitions VUV de cette molécule et de son isotope HD ont été effectuées par le satellite FUSE dans le domaine 90.5 -118.7 nm. Ces observations permettent de déterminer le rapport d'intensités des raies HD/H2, considéré comme un outil nouveau pour évaluer le rapport d'abondances D/H, qui est connu pour être un traceur efficace de l'évolution chimique de l'Univers. Par ailleurs, les molécules H2, HD et D2 sont formées dans le plasma de bord des tokamaks et contribuent aux pertes radiatives du milieu. Par conséquent, il est indispensable de disposer de données spectroscopiques de haute qualité obtenues en laboratoire pour une exploitation fiable des résultats d'observations ou pour une modélisation réaliste des plasmas de fusion. L'objectif de cette thèse est d'effectuer une étude expérimentale à haute résolution des spectres d'émission et d'absorption des isotopes D2 et HD de l'hydrogène moléculaire dans le VUV et de la compléter par une étude théorique des états électroniques excités en relation avec les transitions observées. Une telle étude avait été effectuée dans notre laboratoire et avait abouti à la réalisation d'un atlas VUV dans le domaine 78-170 nm. Les spectres d'émission de HD et D2 sont produits par une source à décharge Penning opérant sous faible pression, et sont enregistrés dans la région spectrale 78 -170 nm à l'aide du spectrographe sous vide de 10 mètres à haute résolution (~ 150 000) de l'Observatoire de Meudon, soit sur plaques photographiques, soit sur des écrans phosphore photostimulables pour mesure d'intensités. Les spectres enregistrés contiennent plus de 20 000 raies. Les longueurs d'onde sont mesurées avec une précision de Δλ/λ= 10-6.Les raies des molécules D2 et H2 étant inévitablement présentes dans le spectre de HD, nous avons d'abord cherché à réaliser l'analyse du spectre de D2, qui consiste à identifier et à assigner les raies aux transitions électroniques entre des niveaux d'énergie de la molécule. Nous avons par ailleurs réalisé une étude en absorption des molécules HD et D2 au Centre Laser LCVU d'Amsterdam. Nous avons mesuré par spectroscopie laser à deux photons 1XUV+1UV, de nouvelles longueurs d'onde avec une précision inégalée de Δλ/λ= 10-8 dans le domaine spectral 99.9-104 nm permis par l'accordabilité du laser XUV. Ces nouvelles longueurs d'ondes constitueront une base de données de raies de référence pour la calibration des spectres moléculaires, mais leurs intérêts ne s'arrêtent pas au laboratoire. En effet, les nouvelles raies de HD mesurées par spectroscopie laser, ajoutées aux raies de H2 déjà mesurées avec une précision similaire, seront utilisées comme référence pour mettre en évidence une possible variation cosmologique du rapport de masse proton-électron μ= mp/me, par comparaison avec des longueurs d'onde de raies de H2 ou de HD observées dans les spectres d'absorption de quasars à grands déplacements vers le rouge. Cette étude nécessite la connaissance des coefficients de sensibilité des longueurs d'onde par rapport à la possible variation de μ, que nous avons calculés par la résolution d'un système d'équations couplées pour les états électroniques B, B', C et D de la molécule H2 et HD pour diverses valeurs de μ. Durant ce travail de thèse, nous nous sommes également intéressés à des transitions entre états libres-libres et états libres-liés de la molécule H2. Ces transitions se produisent lors d'une collision H-H formant une quasi-molécule et sont responsables de l'apparition de satellites dans l'aile des raies de l'atome d'hydrogène. Nous avons effectué une étude quantique du satellite quasi-moléculaire de la raie Lymanβ et calculé le profil d'absorption du satellite en fonction de la température. Cette variation est un outil important de diagnostic pour la détermination des caractéristiques des atmosphères des naines blanches.

International audience; Vacuum-ultraviolet (VUV) high-resolution absorption spectroscopy is a unique tool for the study of gas-phase atomic and molecular electronic structure. To date, it has been performed by using lasers or synchrotron radiation-based grating spectrometers, but none of these techniques can offer simultaneous high resolution, wavelength accuracy and broad tunability. The only technique combining these three important features is Fourier-transform spectroscopy, but this is limited to the mid-UV range (down to 140 nm; ref. 1) because of a lack of beamsplitters. Here, we present a new instrument based on a wavefront-division scanning interferometer, applied for the first time to the VUV range. This instrument, coupled to the DESIRS beamline at synchrotron SOLEIL, covers a broad range of wavelengths (typically 7%, adjustable in the 250–40 nm range), a resolving power of ~1 × 106, an extrinsic absolute wavelength accuracy of 1 × 10−7 and a high signal-to-noise ratio.

International audience; Absorption spectroscopy in the vacuum ultraviolet (VUV) domain was performed on the hydrogen-deuteride molecule with a novel Fourier-Transform spectrometer based upon wavefront division interferometry. This unique instrument, which is a permanent endstation of the undulator-based beamline DESIRS on the synchrotron SOLEIL facility, opens the way to Fourier-Transform spectroscopy in the VUV range. The HD spectral lines in the Lyman and Werner bands were recorded in the 87-112~nm range from a quasi-static gas sample in a windowless configuration and with a Doppler-limited resolution. Line positions of some 268 transitions in the $B^1\Sigma^+_u\,(v'=0-30) \leftarrow X^1\Sigma^+_g\,(v''=0)$ Lyman bands and 141 transitions in the $C^1\Pi_u(v'=0-10) \leftarrow X^1\Sigma^+_g(v''=0)$ Werner bands were deduced with uncertainties of 0.04$\wn$(1$\sigma$) which correspond to $\Delta\lambda/\lambda \sim 4 \times 10^{-7}$. This extensive laboratory database is of relevance for comparison with astronomical observations of H$_2$ and HD spectra from highly redshifted objects, with the goal of extracting a possible variation of the proton-to-electron mass ratio ($\mu=m_p/m_e$) on a cosmological time scale. For this reason also calculations of the so-called sensitivity coefficients $K_i$ were performed in order to allow for deducing constraints on $\Delta\mu/\mu$. The $K_i$ coefficients, associated with the line shift that each spectral line undergoes as a result of a varying value for $\mu$, were derived from calculations as a function of $\mu$ solving the Schr\"{o}dinger equation using \emph{ab initio} potentials.

International audience; In this work, we have extended our previous high resolution study of the vacuum ultraviolet emission spectrum of the D2 molecule [M. Roudjane, et al. J. Chem. Phys. 125, 214305 (2006)] up to 124.2 nm in order to investigate the B' 1Sigmau+-->X 1Sigmag+ band system. The analysis of the spectrum has been carried out by means of a complex spectrum visual identification code IDEN [V. I. Azarov, Phys. Scr. 44, 528 (1991); 48, 656, (1993)] and supported by theoretical calculations using ab initio data [L. Wolniewicz, J. Chem. Phys. 103, 1792 (1995); 99, 1851 (1993); G. Staszewska and L. Wolniewicz, J. Mol. Spectrosc. 212, 208 (2002); L. Wolniewicz and G. Staszewska, 220, 45 (2003)] which provided level energies and transition probabilities. More than 1480 new emission lines have been observed and 109 bands belonging to the B' 1Sigmau+-->X 1Sigmag+ system have been identified between 84.1 and 121.6 nm. Except for the upsilo'-0 bands that were reported in absorption [I. Dabrowski and G. Herzberg, Can. J. Phys. 52, 1110 (1974)], all the upsilo'-upsilo'' bands are reported here for the first time. The analysis led to the determination of 111 rovibronic energy levels in the B' 1Sigmau+ state, of which 31 with higher rotational numbers J are new. Observed perturbations are accounted for through a set of coupled equations involving the four excited electronic states B 1Sigmau+, B' 1Sigmau+, C 1Piu, and D 1Piu and including nonadiabatic couplings. The solution of this set provides the percent contribution of these four states to each of the observed rovibronic level.

International audience; The emission spectrum of the D2 molecule has been studied at high resolution in the vacuum ultraviolet region 78.5-102.7 nm. A detailed analysis of the two D 1Piu-->X 1Sigmag+ and D' 1Piu--->X 1Sigmag+ electronic band systems is reported. New and improved values of the level energies of the two upper states have been derived with the help of the program IDEN [V. I. Azarov, Phys. Scr. 44, 528 (1991); 48, 656 (1993)], originally developed for atomic spectral analysis. A detailed comparison is made between the observed energy levels and solutions of coupled equations using the newest ab initio potentials by Wolniewicz and co-workers [J. Chem. Phys. 103, 1792 (1995); 99, 1851 (1993); J. Mol. Spectros. 212, 208 (2002); 220, 45 (2003)] taking into account the nonadiabatic coupling terms for the D 1Piu state with the lowest electronic states B 1Sigmau+, C 1Piu, and B' 1Sigmau+. A satisfactory agreement has been found for most of the level energies belonging to the D and D' states. The remaining differences between observation and theory are probably due to nonadiabatic couplings with other higher electronic states which were neglected in the calculations.