Spectroscopie dans l'infrarouge lointain de molécules d'intérêt astrophysique

Cette thèse a été consacrée à l étude en laboratoire plusieurs molécules d intérêt astrophysique par spectroscopie par transformation de Fourier dans l infrarouge lointain afin de montrer les possibilités offertes par cette gamme spectrale en matière de spectroscopie vibrationnelle et rotationnelle, notamment grâce à l utilisation du rayonnement synchrotron. Nous nous sommes intéressés à des molécules relativement lourdes, dérivées du naphtalène, pour lesquelles nous avons pu observer les bandes de vibrations de plus basses fréquences. Nous avons également développé différents dispositifs de décharge permettant d étudier la spectroscopie rotationnelle de molécules instables : molécules légères à haute température et radicaux de petite taille.This thesis has been dedicated to the laboratory far-infrared Fourier transform spectroscopy of several molecules of astrophysical interest in order to demonstrate the interest of this spectral region for vibrational and rotational spectroscopy, in particular using synchrotron radiation. Low frequency vibrational spectra of nine naphthalene derivatives, relatively heavy molecules, have been studied. Several discharge set-ups have also been developed in order to study rotational spectroscopy of transient species: high temperature light molecules and small radicals.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

A Real-Space Full Multigrid study of the fragmentation of Li11+ clusters

We have studied the fragmentation of Li11+ clusters into the two experimentally observed products (Li9+,Li2) and (Li10+,Li) The ground state structures for the two fragmentation channels are found by Molecular Dynamics Simulated Annealing in the framework of Local Density Functional theory. Energetics considerations suggest that the fragmentation process is dominated by non-equilibrium processes. We use a real-space approach to solve the Kohn-Sham problem, where the Laplacian operator is discretized according to the Mehrstellen scheme, and take advantage of a Full MultiGrid (FMG) strategy to accelerate convergence. When applied to isolated clusters we find our FMG method to be more efficient than state-of-the-art plane wave calculations.Comment: 9 pages + 6 Figures (in gzipped tar file

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $\mu$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $\mu$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photo-dissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, impacting planet formation within the disks. We report JWST and Atacama Large Millimetere Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modelling their kinematics and excitation allows us to constrain the physical conditions within the gas. We quantify the mass-loss rate induced by the FUV irradiation, finding it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk

PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula

The JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate

PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar

(Abridged) We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the HII region to the atomic PDR (crossing the ionisation front (IF)), and the subsequent transition to the molecular PDR (crossing the dissociation front (DF)). We use high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science Program. The NIRSpec data reveal a forest of lines including, but not limited to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. We observe numerous smaller scale structures whose typical size decreases with distance from Ori C and IR lines from CI, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the PDR. The H2 lines reveal multiple, prominent filaments which exhibit different characteristics. This leaves the impression of a "terraced" transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&

PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars

22 pags., 8 figs., 1 tab.Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter-and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.Support for JWST-ERS program ID 1288 was provided through grants from the STScI under NASA contract NAS5-03127 to STScI (K.G., D.V.D.P., M.R.), Univ. of Maryland (M.W., M.P.), Univ. of Michigan (E.B., F.A.), and Univ. of Toledo (T.S.-Y.L.). O.B. and E.H. are supported by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES, and through APR grants 6315 and 6410 provided by CNES. E. P. and J.C. acknowledge support from the National Science and Engineering Council of Canada (NSERC) Discovery Grant program (RGPIN-2020-06434 and RGPIN-2021-04197 respectively). E.P. acknowledges support from a Western Strategic Support Accelerator Grant (ROLA ID 0000050636). J.R.G. and S.C. thank the Spanish MCINN for funding support under grant PID2019-106110GB-I00. Work by M.R. and Y.O. is carried out within the Collaborative Research Centre 956, subproject C1, funded by the Deutsche Forschungsgemeinschaft (DFG)—project ID 184018867. T.O. acknowledges support from JSPS Bilateral Program, grant No. 120219939. M.P. and M.W. acknowledge support from NASA Astrophysics Data Analysis Program award #80NSSC19K0573. C.B. is grateful for an appointment at NASA Ames Research Center through the San José State University Research Foundation (NNX17AJ88A) and acknowledges support from the Internal Scientist Funding Model (ISFM) Directed Work Package at NASA Ames titled: “Laboratory Astrophysics—The NASA Ames PAH IR Spectroscopic Database.”Peer reviewe

Visible Photodissociation Spectra Of The 1-methyl And 2-methylnaphthalene Cations: Laser Spectroscopy And Theoretical Simulations

Naphthalene (Np) and its methylated derivatives (1-Me-Np and 2-Me-Np) are prototype molecules for spectroscopists as first members of the polycyclic aromatic hydrocarbons (PAHs) family. High resolution studies are capable to explore the details of the internal rotation of the methyl group. Although this was achieved in neutral PAHs\footnote{see for instance Baba et al, \emph{J.Phys.Chem.A}, \textbf{2009}, 113, 2366}, the task is not the same in cations. Me-Np cations have been probed by resonance-enhanced multiphoton dissociation\footnote{Dunbar et al, \emph{J. Am. Chem. Soc.} \textbf{1976}, 98, 7994-7999 and \emph{J.Phys.Chem.} \textbf{1985}, 89, 3617}, showing only very broad and unresolved spectra, while absorption in argon matrix revealed more resolved vibronic bands\footnote{Andrews et al, \emph{J.Phys.Chem.} \textbf{1982}, 86, 2916}. The electronic absorption gas phase spectra of 1-Me-Np$^+$ and 2-Me-Np$^+$ were measured using an Ar-tagging technique. In both cases, a band system was observed in the visible range and assigned to the $D_2\leftarrow D_0$ transition. The 1-Me-Np$^+$ absorption bands revealed a red shift of 808 cm$^{-1}$, relative to Np$^+$ (14 906 cm$^{-1}$)\footnote{Pino et al, \emph{J. Chem. Phys.} \textbf{1999}, 111, 7337-7347} , while for 2-Me-Np$^+$ a blue shift of 226 cm$^{-1}$ was found. A short vibrational progression was also observed. Moreover, insights into the internal rotation motion of the CH$_3$ were inferred, although intrinsic broadening due to intramolecular relaxation was present. These measurements were supported by detailed quantum chemical calculations that allowed exploration of the potential energy curves, along with a complete simulation of the harmonic FC factors using the cumulant Gaussian fluctuations formalism, extended to include the internal rotation

Spectroscopie des transitions électroniques des cations hydrocarbures aromatiques polycycliques et de leurs agrégats

Ce travail est une étude expérimentale de la spectroscopie électronique des cations hydrocarbures aromatiques polycycliques (PAH) et de leurs agrégats dans des conditions simulant celles régnant dans le milieu interstellaire, froids et totalement isolés. L objectif principal est d obtenir des spectres au laboratoire qui puissent être comparés aux spetres des Bandes Diffuses Interstellaires et d explorer les propriétés des agrégats de PAH.This work is mainly an experimental study of the electronic spectroscopy of the polycyclic aromatic hydrocarbon cations and their clusters in conditions close to those of the interstellar medium. The aim of this study is to obtain data that can be compared with the spectrum of the diffuse interstellar bands and to explore the properties of PAH clusters.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Recherche de signatures spectrales de cations aromatiques dans l'absorption diffuse interstellaire (confrontation spectroscopie de laboratoire, observations astronomiques)

Les Hydrocarbures Aromatiques Polycycliques (PAHs) sont maintenant reconnus comme un constituant important de la phase gazeuse du milieu interstellaire. Cette famille de molécules et en particulier leurs dérives ioniques semble être l'un des candidats les plus prometteurs pour l'identification des Bandes Diffuses Interstellaires (DIBs). Ces bandes d'absorption sont observées dans le visible sur des spectres d'étoiles masquées par des nuages. L'identification de PAHs comme molécules responsables de ces bandes ne peut se faire que par comparaison directe avec des spectres de PAHs obtenus dans des conditions se rapprochant le plus possible de celles du milieu interstellaire. Ces conditions de basse température et d'absence de collisions ont été reconstituées en laboratoire grâce à la technique du jet supersonique. Un complexe de van der Waals PAH-Ar est alors ionise par ionisation résonnante à deux photons. L'absorption par cet ion d'un photon laser visible accordable provoque le départ de l'atome d'argon, et la détection de cette dissociation au spectromètre de masse permet, l'obtention du spectre du cation PAR. Grâce a cette technique, les spectres du phénylacétylène(+)-Ar et de l'acénaphthène(+)-Ar ont pu être enregistrés. Le profil spectral des bandes est large et lorentzien, indiquant une dynamique intramoléculaire dominée par des mécanismes de conversion interne ultrarapide. Deux campagnes d'observations au Télescope Bernard Lyot du Pic du Midi ont permis la recherche systématique de ces bandes larges grâce à un protocole d'observation et à un traitement des données spécifiques. Des limites supérieures d'abondance on été déterminées pour cinq cations PAHs. Les zones d'absorption interstellaire repérées dans nos spectres sont de largeur variable et certaines sont vraisemblablement le résultat d'une combinaison de l'absorption de plusieurs espèces. D'après nos mesures entre 525 et 840 nm, l'absorption interstellaire diffuse représente 87 % de l'absorption interstellaire.Polycyclic Aromatic Hydrocarbons (PAHs) are now recognized as an important constituent of the interstellar medium gaseous phase. This family of molecules and in particular their ionic derivatives seems to be one of the most promising candidates for identification of the Diffuse Interstellar Bands (DIBs). These absorption bands are observed in the visible spectral range in the spectra of stars partially masked by gas cloud. The possible identification of PAHs as molecules responsible for these bands must be done through direct comparison with PAHs spectra recorded in conditions as close as possible to those of the interstellar medium. These low temperature and collision-free conditions can be recreated in the laboratory with supersonic beams. A van der Waals complex PAH-Ar is then ionized by resonant two-photon ionization. The ion absorption of a tunable visible laser photon causes the argon departure, and the detection of this dissociation by a mass spectrometer allows the recording of the PAH cation spectrum. Using this technique, the spectra of phenylacetylene(+)-Ar and of acenaphthene(+)-Ar could be obtained. The spectral profile is wide and lorentzian, showing an intramolecular dynamics dominated by ultrafast internal conversion. Two observation campaigns with the Télescope Bernard Lyot at the Pic du Midi allowed us to perform a systematic search for this broad bands, thanks to specific observational protocole and data processing. Upper-limits of abundance were determined for five PAH cations. Interstellar absorption zones identified in our spectra are of variable width and some of them are very likely the result of a combination due to several species. According to our measurements between 525 and 840 nm, the diffuse interstellar absorption represents 87 % of the interstellar absorption in front of BD +404220 star.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF