Literatura académica sobre el tema "Astrophysical ices"

The universe is a vast chemical and physical factory consisting of large collections of stars, gas and dust. Energetic processing of ices and subsequent molecular synthesis in astrophysical environments, including icy Solar System bodies and grain mantles in the interstellar medium, are responsible for the observation of some of the molecular species found in space. Gas phase processes alone cannot explain the reaction mechanisms and the observed abundances of some of these molecules. This thesis reviews the current state of knowledge on solid state molecular synthesis in astrophysical ices and highlights the relevance of this work to understanding the chemical origins of life. The nature and origin of astrophysical ices and their environments is discussed to provide a background for the design and implementation of a new apparatus built to simulate astrophysical environments. An outline is given of the relevant collisional and chemical processes associated with interactions between radiation and matter pertinent to astrochemistry, e.g. ion, photon and electron processing of ices. A detailed description of the design and construction of the new apparatus is given and the theory and instrumentation in the spectroscopic techniques used are discussed. This is followed by a detailed explanation of the experimental procedures implemented at both ion and synchrotron radiation sources. The first results of ion and photon irradiation of H₂O and CO₂ ices (both pure and binary) using this apparatus are presented and discussed in detail. Ion irradiation is carried out using both reactive and unreactive ions. Reactive carbon ion implantation in pure H₂O is investigated and the production of CO and CO₂ monitored. Experiments involving both high (100 keV) and low (1 – 5 keV) energy ion irradiation of mixed H₂O:CO₂ ices are described and the production of H₂CO₃ (carbonic acid) and CO investigated. The production of CO and CO₃ is described in UV irradiation experiments of mixed H₂O:CO₂ ices. Particular attention is paid to the infrared band profile of CO in each of the irradiation experiments. The CO band profile shows a great degree of complexity, particularly in the carbon ion implantation experiments in H₂O. Differences in the types and yields of molecular products formed and their infrared band profiles in ion and photon irradiated ices suggest different chemical and physical processes taking place. Trial experiments of VUV synchrotron photoabsorption experiments of H₂O and NH₃ ices are also described. Results reveal a blueshift of 20 – 25 nm in the peak absorption of the first excited electronic state, observed in both species, and is attributed to the effect of hydrogen bonding. The thesis ends with suggestions of the possible modifications to the apparatus and plans for future work.

Dans les nuages denses, les manteaux glacés sont des condensats de petites molécules sur des grains solides. Ces manteaux glacés représentent des sites prometteurs pour certains processus chimiques. Ils sont constamment irradiés et de nouvelles molécules organiques complexes peuvent être ainsi formées. Une fois que les nuages denses se transforment en disque d'accrétion et, éventuellement, en système planétaire, ces manteaux glacés peuvent potentiellement contribuer au réservoir de molécules complexes des planètes. Dans cette thèse, les effets de l'irradiation ionique sur deux molécules aromatiques, la pyridine et le pyrène, ont été étudiés. Les échantillons ont été exposés à une irradiation ionique sur les lignes des accélérateurs du GANIL (Caen, France) et de l'ATOMKI (Debrecen, Hongrie). Leur évolution a été suivie par spectroscopie infrarouge in situ. Il a été constaté que la structure initiale (amorphe ou cristalline) et la température d'irradiation n'affectent pas la section efficace de destruction de la pyridine pure. De plus, il a été observé que la dose locale n'est pas un paramètre clé comme cela était affirmé précédemment. En effet, la destruction du pyrène provoquée par des ions lourds, à partir du carbone, est significativement plus importante que celle provoquée par des ions plus légers comme l'hydrogène et l'hélium pour une même dose locale déposée. Pour les deux molécules, une augmentation significative de la section efficace de destruction a été observée lorsque la concentration des molécules dans la matrice d'eau diminue. Le temps de demi-vie de la pyridine et du pyrène dans les nuages denses a été estimé à environ 13 et 20 millions d'années, respectivement. Cela suggère qu'une fois formées dans ces environnements, ces molécules pourraient survivre et contribuer à la formation planétaire<br>Formed in the dense clouds, icy mantles are condensates of small molecules on solid grains. These icy mantles are promising sites for rich chemical processes, where complex organic molecules can form, as these mantles are continuously exposed to ionizing radiation. Once dense clouds transform into an accretion disc and eventually into a planetary system, these icy mantles may potentially contribute to the reservoir of the complex molecules of the planets.In this thesis, the effects of ion irradiation on two aromatic molecules, pyridine and pyrene were investigated. The samples were exposed to ion irradiation at the GANIL (Caen, France) and ATOMKI (Debrecen, Hungary) ion beam facilities. Their evolution was monitored using in-situ infrared spectroscopy. It was found that the initial structure (amorphous or crystalline) and the irradiation temperature do not affect the destruction cross section of pure pyridine. Additionally, it was observed that the local dose is not a key parameter as previously assumed. Indeed, since the destruction of pyrene caused by heavy ions, starting from C, is significantly greater than that caused by lighter ions such as H and He for the same deposited local dose. For both molecules, a significant increase in the destruction cross section was observed for decreasing molecule concentration in the water matrix. The half-life time of pyridine and pyrene in dense clouds was estimated to be around 13 and 20 millions of years, respectively. This suggests that once formed in these environments, they could survive and contribute to planetary formation

In this thesis the formation of molecular species in cold icy mantles, typical of those in the interstellar medium (ISM) has been studied. The construction of an ultra high vacuum system for the formation and containment of these astrophysical ice analogues is described. The method of preparation of these ices is detailed and analysis methodologies are discussed. VUV spectra of molecular ices (e.g. SO2, CH3NH2, OCS) measured on the UV1 beam line of the Astrid Synchrotron facility at the University of Aarhus in Denmark, are presented. Molecular synthesis (e.g. CO3, CO, H2CO3) induced by ion irradiated CO2/H 2O ices using facilities at Queens University Belfast are also reported. In particular this thesis focuses on the irradiation studies of the binary ice mixture of Methylamine (CH3NH2) and Carbon Dioxide (CO2). The results of irradiation of CH3NH2 and CO2 binary ice mixtures by ultraviolet photons, and electrons are presented. The apparent production of the amino acid - glycine - in our irradiated samples is discussed together with possible production processes.

Polycyclic aromatic hydrocarbons (PAHs) are the most abundant large organic molecules in space. They are thought to be the main contributor to the unidentified infrared (UIR) emission bands from the interstellar medium (ISM) for several reasons: UIR intensities correspond to carbon abundance, indicating the presence of a carbon-based molecule; UIRs are found in extremely harsh environments which means the source must be a stable molecule. The most important evidence is if the bands in mid-infrared (MIR) or 'fingerprint' region match those of PAHs. Through the infrared spectroscopy of matrix-isolated polycyclic aromatic hydrocarbons a compound's unique neutral and ionized vibrational modes can be identified. In this work, the PAH anthracoronene (AntCor, C36H18) is suspended in a matrix of water-ice, irradiated with ultraviolet (UV) light, and then analyzed using Fourier Transform Infrared (FTIR) spectroscopy. AntCor has not been studied in water ice before, and therefore the vibrational transition data collected (i.e. band positions and intensities) has been compared to coronene and anthracene, the parent molecules, and with theoretical predictions made using density functional theory. The data from this work will be incorporated into the NASA Ames PAH IR Database, where it will be applied to astronomical observations of the unidentified infrared emissions of the ISM, as well as observations of infrared absorption features in dense molecular clouds.

Les glaces sont présentes dans notre système solaire par exemple sur les comètes, les lunes de Jupiter et de Saturne ainsi que sur les objets trans-neptuniens. Dans le milieu interstellaire, ces glaces forment une fine couche à la surface de grains des nuages denses. L’eau (H2O) est la molécule la plus abondante dans ces glaces. Ces glaces sont constamment exposées aux rayons cosmiques, au vent solaire et aux ions piégés dans la magnétosphère des planètes géantes. Les simulations de ce type d’irradiation associées aux observations peuvent nous amener à comprendre la grande variété des processus physicochimiques induits par l’irradiation. Nous avons donc irradié des glaces avec les ions produits par le GANIL afin de simuler les effets des rayons cosmiques pour les ions lourds rapides et les effets du vent solaire pour les ions lents. Les modifications induites sont étudiées par spectroscopie infrarouge dans le domaine 500-5000 cm-1. L’irradiation induite des changements de structure tels que la compaction et l’amorphisation. Plusieurs ions ont été utilisés afin de déterminer la dépendance de ces processus physiques en fonction du pouvoir d’arrêt du projectile. A basse énergie l’implantation d’ions soufre a permis de mesurer le taux de production de l’acide sulfurique H2SO4, molécule observée à la surface d’Europa. La comparaison avec les observations et les mesures de flux des ions soufre à la surface d’Europa amène à penser que le processus d’implantation est primordial pour expliquer la présence de H2SO4 sur cette lune de Jupiter. Finalement, une étude préliminaire sur le rôle de l’interface entre un substrat carboné et une glace de NH3+H2O est présentée<br>Ices can exist in our solar system for example on comets, the moons of Jupiter and Saturn, and trans-Neptunian objects. In the cold interstellar medium, they form thin layers on dust grains. Water (H2O) is the most abundant molecules in those ices, which are continuously exposed to the irradiation by cosmic rays, solar wind, and ions trapped in the magnetosphere of the giant planets. Simulation in the laboratory compared to telescopic observations can provide information to understand the large variety of radiation induced physicochemical processes. Therefore, we simulated the effects of swift heavy ion (cosmic ray analogs) and slow ion (solar wind, magnetosphere ions) irradiation of water ice at different beam lines of the GANIL accelerator facility. Fourier transform infrared spectroscopy (FTIR) was used to analyze the ices. The irradiation induced structural changes of water ice such as amorphization and compaction were studied. The efficiency to amorphize and compact the ice was established as a function of projectile stopping power with several swift heavy ions. Furthermore, by implantation of sulfur ions in water ice, the formation yield of sulfuric acid was measured and found to increase with projectile energy. From comparison to measure sulfur ion fluxes and sulfuric acid concentrations by the Galileo spacecraft, strong evidence was found that H2SO4 on Europa’s surface can be formed by sulfur ion implantation of magnetosphere ions in water ice. Finally, we also performed a first preliminary experiment to study the radiation induced chemistry with a carbonaceous solid substrate covered with a NH3+H2O ice mantle

The work presented in this thesis is an experimental investigation into the sputtering of oxygen and water ice by 4 ke V ions under conditions existing in the Interstellar Medium (ISM). This work is divided into two main parts : 1) sputtering of oxygen ice by singly and doubly charged ions He+, Ar+, C+, N+ ,0, C2+, N2+ and 0 2+ and 2) sputtering of water ice by C+, N+, 0+, C2+, N2+ and 0 2+. The experimental sputter yield obtained for both oxygen and water ice is compared with those from a theoretical obtained model and found to be in reasonable agreement within the experimental errors. For oxygen and water ice, deposited at 10 K, the refractive index was experimentally determined and found to have values of 1.285 and 1.282 respectively that are in good agreement with previous results. In the case of oxygen ice the sputtering yields are at least nine times larger compared to that of water ice. For water ice the doubly charged ions have, the same sputtering yield ,as the singly charged ions within the experimental errors. In the case of oxygen ice the doubly charged ions have the same sputtering yield as the singly charged ions, except 0+ and 0 2+, where 0 2+ has a significantly lower sputtering yield.

L’excitation électronique de molécules condensées sur des surfaces froides (10-100 K) peut mener à la désorption de certaines de ces molécules. Ce processus fondamental a des conséquences dans de nombreuses disciplines, dont deux ont guidé ce travail : l’astrochimie et la dynamique du vide dans les accélérateurs. La désorption induite par photons et électrons est étudiée pour des films amorphes de molécules condensées (glaces) telles que CO, H2O, NO ou CH4. Un objectif de cette thèse est la quantification de la désorption des différentes espèces, et d’explorer les paramètres pouvant affecter l’efficacité du processus. Le second objectif est de déterminer l’évolution et la relaxation des excitations électroniques initiales et par quel mécanisme cela mène à la désorption. La photodésorption est étudiée au LERMA en utilisant le rayonnement synchrotron dans la gamme du VUV (5-14 eV) et des X mous (520-600 eV). Cela permet d’obtenir une information spectrale cruciale pour la compréhension des mécanismes et pour l’implémentation dans les modèles. La désorption induite par les électrons est étudiée au CERN dans la gamme d’énergie 150-2000 eV. Les résultats obtenus étendent les données de photodésorption UV disponibles et permettent de déterminer la pertinence de la désorption par les électrons ou les rayons X pour l’astrochimie. Des progrès sont faits dans la compréhension des mécanismes, notamment sur le rôle du transport d’énergie ou de particules depuis l’intérieur de la glace vers la surface, ou sur la désorption indirecte. Un nouveau dispositif expérimental a aussi été mis en place au LERMA pour des expériences de désorption par laser et de spectroscopie laser, permettant d’obtenir l’énergie interne et cinétique des molécules désorbées<br>The deposition of energy in the form of electronic excitations in molecules condensed on cold surfaces (10-100 K) can lead to the desorption of some of these molecules. This basic surface science process has consequences in a variety of fields, two of which are of concern here : astrochemistry and vacuum dynamics. Photon and Electron-Induced desorption are studied in this manuscript for thin films of condensed molecules (ices), e.g. CO, H2O, NO or CH4. The first objective is to obtain a quantification of the desorption of the various desorbing species, and to look for the parameters that affect the efficiency of the process. The second objective is to understand the mechanisms of evolution and relaxation of the initial electronic excitations that lead to desorption. Photon-induced desorption is studied at LERMA using synchrotron radiation in the VUV range (5-14 eV) and soft X-ray range (520-600 eV). This allows to obtain spectrally-resolved information, which is crucial both for model implementation and fundamental understanding of the mechanisms. Electron-induced desorption is studied at CERN in the 150-2000 eV range. The results expand the available data on UV photodesorption and allow to determine the relevance of electron or X-ray desorption for astrochemistry. Progress has also been made on the understanding of mechanisms, particularly on the role of energy or particle transport from the bulk to the surface of the ice, on indirect desorption, or on the desorption of ions in the soft X-ray range. A new experimental set-up has also been developed at LERMA for laser desorption and laser spectroscopy experiments, allowing quantum-state and kinetic energy resolved measurements of desorbed molecules