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L‘objectif de la thèse consiste à caractériser expérimentalement sous vide les propriétés d’émission électronique de matériaux utilisés dans des applications spatiales tels que l’argent et l’aluminium dans leur état de contamination naturel, afin de fournir des données précises à la communauté du spatial tout en contribuant à comprendre et quantifier le rôle joué par la contamination naturelle sur leurs propriétés d’émission électronique. Afin de répondre à cet objectif, un moyen expérimental nommé CELESTE permettant de caractériser les différentes propriétés d’émission électronique de ces matériaux sous ultravide a été développé. Il permet d’effectuer des mesures de rendement d’émission électronique ainsi que des mesures de rendement de rétrodiffusion. Afin d’établir un lien entre la physique d’émission bien connue des matériaux purs et la physique d’émission des matériaux d’utilité pratique, un protocole expérimental spécifique a été mis en place. Il permet de caractériser l’évolution du rendement d’émission et de la distribution énergétique des électrons émis à partir d’un matériau exposé à l’air jusqu’à l’élimination par décapage ionique successifs de tous les contaminants déposés à la surface. Une corrélation a été établie entre évolution du rendement d’émission et évolution de la composition de la surface de l’argent et de l’aluminium. Ce travail a permis de mettre en évidence l’influence prépondérante des contaminants naturels sur leurs propriétés d’émission électronique. En effet, les propriétés d’émission de ces deux matériaux exposés à l’air dépendent d’avantage de la nature de la couche de contamination déposée à la surface que du matériau pur sous-jacent. / The aim of this study is to provide accurate data on electronic emission properties of technical materials used in spacecraft applications such as silver and aluminium and to understand and to quantify the effect of natural contamination on their electron emission properties.In order to reach this goal, an experimental facility named CELESTE allowing electronic emission properties characterization under ultra-high vacuum had been developed. The facility can be used to perform electron emission yield measurements and also backscattering yield measurements thanks to special experimental setup developed during this phD. To establish a link between the well-known emission physic of pure materials and those of “technical” materials, a specific protocol has been implemented. It allows the study of emission proprieties starting from a sample exposed to ambient atmosphere and reaching a cleaned sample, using Ar ion etching step by step technic.A link has been established between electron emission yield and surface composition evolution of silver and aluminium sample. This work highlights the leading influence of natural contamination on the electron emission proprieties of metals.

The main purpose of this Thesis is the experimental characterization of the electronic and geometric structures of objects called clusters. A cluster consists of a finite group of bound atoms or molecules. Due to its finite size, it may present completely different properties than those of the isolated atom and the bulk. The clusters studied in this work are constituted by rare-gas atoms, organic molecules, and metal atoms. Intense cluster beams were created using either an adiabatic expansion source or a gas-aggregation source, and investigated by means of synchrotron radiation based photoelectron spectroscopy. The reports presented in this Thesis may be divided into three parts. The first one deals with results concerning homogeneous molecular clusters (benzene- and methyl-related clusters) highlighting how molecular properties, such as dipole moment and polarizability, influence the cluster structure. The second part focuses on studies of solvation processes in clusters. In particular, the adsorption of polar molecules on rare-gas clusters is studied. It is shown that the doping method, i.e. the technique used to expose clusters to molecules, and the fraction of polar molecules are important factors in determining the location of the molecules in the clusters. Finally, a summary of investigations performed on metal clusters is presented. The applicability of solid state models to analyse the cluster spectra is considered, and the differences between the atomic, cluster and solid electronic structures are discussed.

<p>In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies.</p><p>We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl₂ and C1s⁻¹π*¹ states of allene molecules. The combined use of high-resolution spectroscopy with <i>ab initio</i> calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl₂ which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N₂O.</p><p>We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH₃X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.</p>

<p>Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects.</p><p>In this thesis, some atomic, molecular and cluster systems (clusters of O₂, CH₃Br, Ar/O₂, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using <i>ab initio</i> methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of <i>ab initio</i> and molecular dynamics (MD) methods.</p><p>Results on the dissociation behavior of CH₃Br and O₂ molecules in clusters are presented. The dissociation of the Na₂ molecule has been characterized and the molecular field splitting of the Na 2<i>p</i> level in the dimer has been measured. The molecular field splitting of the CH₃Br 3<i>d</i> level has been measured and the structure of CH₃Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O₂, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.</p>

Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects. In this thesis, some atomic, molecular and cluster systems (clusters of O2, CH3Br, Ar/O2, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using ab initio methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of ab initio and molecular dynamics (MD) methods. Results on the dissociation behavior of CH3Br and O2 molecules in clusters are presented. The dissociation of the Na2 molecule has been characterized and the molecular field splitting of the Na 2p level in the dimer has been measured. The molecular field splitting of the CH3Br 3d level has been measured and the structure of CH3Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O2, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.

In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies. We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl2 and C1s−1π*1 states of allene molecules. The combined use of high-resolution spectroscopy with ab initio calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl2 which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N2O. We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH3X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.