Le milieu interstellaire (MIS) est la matière presente dans l'espace au sein des galaxies.Cette matière est composée de gaz et de grains de poussière. Jusqu'à présent, les radioastronomes principalement ont identifié plus de 170 molécules différentes dans le MIS.La présence de la plupart de ces molécules est expliquée à travers des réactions dans la phase gazeuse, mais la synthèse de beaucoup de ces molécules (comme H2, H2O, CO2) nécessite l'intervention d'uncatalyseur, donc des réactions dans la phase solide, sur la surface des grains de poussière. Les objectifs de cette thèse sont de comprendre quels sont les processus physico-chimiques qui ont lieu (par exemple, la diffusion et désorption) sur la surface des grains de poussière interstellaire et comment ils conduisent à la synthèse de molécules de plus en plus complexes.En particulier, l'objet de ma thèse est d'étudier:- le rôle de la diffusion des atomes d'oxygène (noté « O ») et les processus d'oxydation dans la formation des glaces interstellaires;- le couplage thermique et non thermique entre la phase gaz et la phase solide.L'astrochimie ne tendait à considérer que la diffusion des atomes d'hydrogène et les réactions d'hydrogénation, ignorant souvent le rôle de l'oxygénation ainsi que l'importance des processus d'adsorption et de désorption, d'où mes recherches approfondies sur ces thématiques.Évidemment, une meilleure connaissance de ces processus physico-chimiques et des réactions de surface aiderait les astronomes à comprendre la formation des glaces interstellaires, l'augmentation de la complexité moléculaire, et l'équilibre entre le gaz et la phase solide.Pour répondre à ces questions, de nombreuses expériences ont été réalisées avec le dispositif FORMOLISM, situé à l'Université de Cergy-Pontoise dans le cadre du LERMA (Observatoire de Paris). Via deux jets de particules avec un pompage différentiel, les atomes et les molécules sont déposés sur un échantillon froid (> 6,5 K) dans une chambre ultravide. Les produits des réactions sont ensuite sondés en utilisant la spectroscopie de masse et la spectroscopie infrarouge.Pour simuler différents environnements astrophysiques, la physique-chimie de l'état solide a été étudiée dans différentes conditions expérimentales:- La morphologie de substrat (glace d'eau amorphe soit poreuse, soit compacte, glace d'eau cristalline, silicate amorphe ou graphite)- Les espèces déposées et leur rapport relatif- La couverture des espèces déposées, de 0,1 à 2 monocouches- La température du substrat, de 6,5 à 60 K.En ce qui concerne les processus d'oxydation, les résultats montrent que l'O est très réactif avec de nombreuses espèces ; la diffusion des atomes d'O semble être beaucoup plus rapide que prévu et peut se produire par effet tunnel à des températures aussi basses que 6,5 K. Nous avons comparé les valeurs expérimentales des coefficients de diffusion et constaté que les taux de diffusion sur chaque surface, basés sur les résultats de la modélisation, étaient considérablement plus élevés que ceux prévus pour les atomes lourds tels que l'O. Nos résultats montrent que les atomes O peuvent rencontrer tous les partenaires disponibles de réaction à un taux plus rapide que le taux d'accrétion. En particulier, dans les nuages interstellaires très denses, le rapport O/H est tel que O devient l'un des partenaires réactifs dominants avec H. Ceci a un impact sur la formation de certaines espèces et sur l'abondance relative des produits formés.En ce qui concerne les processus de couplage solide-gaz (c'est à dire, l'adsorption, désorption thermique, désorption chimique), les résultats montrent que chaque processus est influencé d'une manière différente par le substrat (glace d'eau, de silicate ou graphite). Enfin, nous fournissons une liste utile des énergies de liaison de plusieurs espèces et de l'efficacité de désorption chimique des différentes réactions sur ces substrats. / The interstellar medium is the matter that exists in the space between the star systems in a galaxy. It is composed of gas and elongated tiny dust grains. To date, plenty of molecules (> 170) are known to exist in the interstellar medium. The presence of most of them can be understood in terms of gas phase reactions but the synthesis of some key species (H2, H2O, CO2) need the intervention of solid-state reactions on dust grains surface. The aims of this thesis are to understand what are the relevant physical-chemical processes (i.e., diffusion and desorption) occurring on the surface of interstellar dust grains and how these processes influence synthesis of more and more complex molecules. In particular, the focus of my thesis is the investigation of:1) the role of O-atom diffusion and the oxidation processes in the formation of interstellar ices;2) the thermal and non-thermal processes coupling gas and solid phase.The reasons of these investigations lie on the realization that, up to now, only hydrogen diffusion and hydrogenation reactions are commonly considered in solid astrochemistry and the role of oxygenation as well as the importance of adsorption and desorption processes are often disregarded.Evidently, a better knowledge of such physical-chemical processes and, in general, of the solid state physical-chemistry could help astronomers to understand the formation of interstellar ices, the increase on molecular complexity, and the equilibrium between gas and solid phase.To answer these questions, many experiments have been performed with the FORMOLISM set-up, i.e., FORmation of MOLecules in the ISM, located in the Universitè de Cergy Pontoise, Observatoire de Paris. Via two triply differentially pumped beams, atoms and molecules were aimed at a cold (>6.5 K) sample held in a Ultra high vacuum chamber. The products were probed using Mass spectroscopy and Reflexion Absorption Infrared Spectroscopy.To simulate different astrophysical environments, the solid state physical-chemistry has been studied in different experimental conditions:-The substrate morphology (Amorphous water ice, porous (p) and compact (np), crystalline (c) ice, amorphous silicate, and graphite)-The species deposited and their relative ratio-The coverage of deposited species, from 0.1 to 2 ML-The substrate temperature, from 6.5 to 60 KConcerning oxidation processes and O-atom reactivity, the results show that oxygen is very reactive with many species (i.e., H, CO, NO, H2CO, HCOOH); O diffusion appears to be much faster than previously expected and can occur via quantum mechanical tunnelling at temperatures as low as 6.5 K. We compared the experimental values of the diffusion coefficients and found that the rates of diffusion on each surface, based on modelling results, were considerably higher than those expected for heavy atoms such as oxygen. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O, OH, CO) at a faster rate than that of accretion. In particular, in very dense interstellar clouds, the O/H ratio is such that O becomes one of the dominant reactive partners together with H. This has an impact on the chemistry occurring at the surface of dust grains as either the formation of some species may be enhanced, or at least the relative abundances of the final products will be affected. An important example of how O-atom mobility can modulate the abundances of key species of ices in the ISM is the case of the H2O/CO2 ratio via the CO+O and H2CO+O pathways.Concerning gas-solid coupling processes (i.e., adsorption, sticking, thermal desorption, chemical desorption), the results show that each processes is influenced in a different way by the substrate (i.e., water ice, silicate or graphite). Moreover, we provide a useful list of binding energies of several species and chemical desorption efficiency for different reactions on different subst

Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-29T22:11:50Z No. of bitstreams: 1 TESE_GIL.pdf: 2275297 bytes, checksum: 45e4c2a7be1a4d3eeb37b526cabd2cae (MD5) / Approved for entry into archive by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-30T02:23:20Z (GMT) No. of bitstreams: 1 TESE_GIL.pdf: 2275297 bytes, checksum: 45e4c2a7be1a4d3eeb37b526cabd2cae (MD5) / Made available in DSpace on 2014-10-30T02:23:20Z (GMT). No. of bitstreams: 1 TESE_GIL.pdf: 2275297 bytes, checksum: 45e4c2a7be1a4d3eeb37b526cabd2cae (MD5) / CNPq / A poluição atmosférica é, dentre os diversos tipos de poluição, a que mais tem causado incômodo a população com implicações à saúde, originando desde simples irritações até o desenvolvimento de câncer. A concentração de alguns poluentes do ar em ambientes ocupacionais pode ser muitas vezes, superior aos valores estabelecidos por lei, devido à localização de fontes potenciais de emissão e pela ausência de sistemas de ventilação adequados. A princípio, o objetivo deste trabalho foi fazer uma pesquisa exploratória de caráter quantitativo/qualitativo com trabalhadores de postos de combustíveis de cidades do Recôncavo Sul da Bahia e realizar uma reflexão crítica sobre suas percepções sobre os efeitos à saúde causados pelos compostos orgânicos voláteis (COV) durante suas atividades laborais. Após essa análise inicial, foi desenvolvido um método analítico para determinação das concentrações de BTEX (benzeno, tolueno, etilbenzeno e xilenos) em amostras de ar ambiente de postos de combustíveis por amostragem ativa em tubos adsorventes contendo carvão ativo, seguido de dessorção química e análise por cromatografia a gás com detector de ionização em chama (CG/DIC). Foram realizados testes com diversos solventes a fim de se verificar a taxa de recuperação (TR) de cada um deles. Os testes revelaram que o diclorometano (CH2Cl2) apresentou os melhores resultados de TR, com valores acima de 75% de extração dos compostos BTEX. Os parâmetros analíticos utilizados para validação do método cromatográfico foram: seletividade, linearidade, precisão, exatidão, limite de detecção e limite de quantificação. A amostragem foi realizada em ar ambiente dos postos de combustíveis da cidade de Amargosa, Bahia. As concentrações encontradas no ar ambiente dos postos de combustíveis variaram de 16,9 a 44,5 μg m-3 para o benzeno; de 39,9 a 247 μg m-3 para o tolueno; de 15,6 a 29,4 μg m-3 para o etilbenzeno; de 12,7 a 68,5 μg m-3 para o m-xileno; de 13,7 a 63,3 μg m-3 para o pxileno e de 13,1 a 42.2 μg m-3 para o o-xileno. Os resultados obtidos pelo método proposto foram comparados com os resultados obtidos por um método usando dessorção térmica e não apresentou diferenças significativas para a faixa de concentração estudada, ratificando a validade do método. As concentrações dos compostos encontrados neste trabalho são consideradas pela NR-15 do Ministério do Trabalho e Emprego, com exceção do benzeno, como não cancerígeno para seres humanos. Segundo estudo realizado pela Organização Munidal da Saúde (OMS), os níveis de benzeno encontrados são classificados como possíveis causadores de câncer devido seu caráter cumulativo durante o tempo de vida laboral de um trabalhador nesses ambientes. / Air pollution is the type of pollution that has caused more discomfort for the population. This type of pollution has caused damage to human health resulting from simple irritations to the development of cancer. Many times, the concentration of some air pollutants in occupational environments can be greater than the values established by law due to the location of potential emission sources and the default of adequate ventilation systems. First, this work aimed to develop an exploratory quantitative/qualitative research with gas station attendants in cities located in the Southern Recôncavo of Bahia and promoting a critical reflection on their perceptions about the effects on human health caused by volatile organic compounds (VOC) during their work activities. After this initial analysis, an analytical method was developed to determination of BTEX (benzene, toluene, ethylbenzene and xylenes) concentrations in samples of ambient air of gas stations by active sampling on adsorbent tubes containing activated charcoal followed by chemical desorption and analysis by gas chromatography with flame ionization detector (GC/FID). Tests were done using various solvents in order to verify the recovery rate (RR) of each one of them. So, tests indicated that dichloromethane (CH2Cl2) presented the best results of RR, with values above 75% of extraction of BTEX compounds. The selectivity, linearity, precision, accuracy and detection and quantification limits of the chromatographic method were validated. Sampling was performed in ambient air of gas stations located in Amargosa city in Bahia. The concentrations found in ambient air of gas stations ranged from 16.9 to 44.5 μg m-3 for benzene; 39.9 to 247 μg m-3 for toluene; 15.6 to 29.4 μg m-3 for ethylbenzene; 12.7 to 68.5 μg m-3 for m-xylene; 13.7 to 63.3 μg m-3 for p-xylene and 13.1 to 42.2 μg m-3 for o-xylene. The results obtained in this proposed method were compared with the results obtained in a method using thermal desorption and showed no significant differences for the studied analytical range, confirming the validity of the method. The concentrations of the compounds found in this study are classified not carcinogenic to humans by NR- 15 from the Ministério do Trabalho e Emprego, with the exception of Benzene. According to a study developed by the World Health Organization (WHO), the levels of Benzene found are classified as possible causes of cancer because of its cumulative feature during the work lifetime of a gas station attendant in those environments.