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Under the title 'Angle Resolved Photoelectron Spectroscopy Study of Small Molecules', the thesis discussed the following aspects: Processes after the interaction of photons with atoms or molecules, including photoscattering, photoexcitation and fluorescence, photoabsorption, photodissociation and photoionization; Concepts of photoionization and photoelectron spectroscopy, including ionization potentials, photoionization cross sections, photoelectron angular distributions, shape resonances and autoionization; Theory of photoionization and photoelectron angular distributions, including central field approximation, Hartree-Fock calculations and multichannnel quantum defect theory; Apparatus for an angle resolved high resolution photoelectron experiment, including the synchrotron radiation source at Daresbury Laboratory, UK and an angle resolved electron spectrometer system from NIST/ANL, USA; The experiment on <i>CO</i>₂ at Daresbury Laboratory, including electron spectrometer calibrations, experimental procedures and data processing; Results and discussion, including results for the photoionization cross sections of the <i>CO</i>^+₂<i>X</i>^{2 Π_h} state, vibrational branching ratios and asymmetry parameters for the synmmetric stretch vibrations (000) to (500) in the <i>CO</i>^+₂<i>X</i>^{2 Π_h} state in the photon wavelength region of 687 - 790AA with a resolution of about 0.1AA, analysis of photoelectron spectra taken at the Tanaka-Ogawa resonances and result for the Franck-Condon factors for transitions from the autoionizing states to different vibrational levels of the molecule.

De façon générale, la physique des collisions concerne l'étude des phénomènes induits par l'interaction de particules en mouvement. En physicochimie moléculaire et en physique atomique, cadres dans lesquels s'inscrit cette thèse, les interactions mises en jeu sont coulombiennes et les partenaires de la collision sont des espèces atomiques ou moléculaires, neutres ou chargées. Celles-ci sont susceptibles de subir au cours de la collision des modifications importantes de leur cortège électronique, à la source même de processus secondaires variés présentant un grand intérêt, par exemple, dans la modélisation de systèmes complexes tels que les plasmas, les milieux astrophysiques ou biologiques. Notre étude s'appuie sur une description théorique semi-classique non-perturbative des processus multi-électroniques au cours de collisions atomiques et moléculaires, à des énergies telles que la vitesse relative des partenaires est comparable à celle de leur électrons de valence. Dans deux systèmes " benchmark " (H+ - Li , He - H2+), nous avons mis en évidence respectivement l'existence de couplages complexes entre voies de réaction impliquant les électrons internes et de valence du lithium et des phénomènes d'interférences et de diffraction d'ondes de matière. Nous avons également étudié des systèmes de collision plus complexes impliquant le carbone, en analysant tout particulièrement des phénomènes multi-électroniques (collisions C(+) - He) - hors approximation des électrons indépendants - et multi-centriques (collisions proton-graphène). Pour ce dernier système, les résultats obtenus ont permis de mettre en évidence les principes d'une nouvelle technique d'imagerie de matériaux 2D. / In general, the Physics of collisions concerns the study of phenomena induced by the relative motion of interacting particles. In chemical physics and atomic physics, which are the area covered by this PhD, the interactions are Coulombic and the colliding partners are atoms or molecules which can be neutral or charged. During the collision, they are likely to undergo important modifications of their electronic environment, which can be the source of various secondary processes that are of great interest, for example, in the modelling of complex systems such as plasmas or astrophysical and biological media. Our study is based on a close-coupling semi-classical description of the multielectronic processes occurring in the course of atomic and molecular collision at impact energy such as the relative velocity of the partners are of the same order of magnitude than the classical velocity of their valence electrons. We have studied two ?benchmark? systems (H+ - Li , He ? H2+), for which we have respectively highlighted the existence of couplings between channels involving inner and outer-shell electrons of lithium, and, wave matter interferences and diffraction phenomena. We have also studied more complex colliding systems involving the carbon nucleus in analyzing multielectronic (C(+) ? He collisions) and multicentric (proton-graphene collisions) phenomena. For the latter system, the results obtained have allowed us to bring out the principles of a new two-dimensional material imaging technique.