Lors de ce travail de thèse, nous avons effectué des recherches sur des chromophores organiques. Notre étude s’est portée sur la commutation des propriétés optiques linéaires et non linéaires via l’étude d’interrupteurs organiques multi-adressables. Notre étude s’est portée plus particulièrement sur la famille des dérivés de l’indolino-oxazolidine. Ce type de molécule présente l’avantage d’avoir deux voix de commutations distinctes par photochromisme et acidochromisme. Nous avons recherché le lien entre la structure des molécules et leurs propriétés optiques par une étude combinée originale théorie/expérience avec l’utilisation de calculs quantiques sophistiqués et par diffusion hyper-Rayleigh de la lumière. / In this work we have investigated the commutation of linear and non linear optical properties in organic multifunctional switches. Indolino-oxazolidine compounds and their derivatives were chosen as example of multifunctional systems, because they combine both acidochromic and photochromic properties. The relationships between the molecular structure of these compounds and their optical properties were established by means of high level the quantum chemical approach and hyper-Rayleigh Scattering of light approaches.

La présence croissante de diverses substances dans notre environnement, conséquencedes activités anthropiques de ces dernières décennies, a entraîné un besoingrandissant et urgent de nouveaux matériaux et dispositifs dans la quête de senseurschimiques efficaces et fiables. D'énormes progrès technologiques ont permis de mettreà disposition toute une gamme d'outils techniques pour leur développement, enprenant en compte les exigences à respecter en terme de sélectivité ou de rapidité deréponse, entre autres. Dans ce contexte, les méthodes de chimie quantique permettentune compréhension fondamentale des processus en jeu dans la détection des espèceschimiques, et par extension, l'élaboration de manière rationnelle de nouveauxmatériaux sensibles. Certaines molécules organiques pouvant être largementfonctionnalisées, elles constituent un point de départ idéal en raison des importantesmodulations possibles de leurs propriétés par des modifications structuralesappropriées.Cette étude vise à développer de manière rationnelle des chromoionophores pour lacomplexation de cations par une approche combinant méthodes de chimiecomputationnelles et caractérisation par spectroscopie optique. Deux pointsprincipaux ont été traités à l'aide de la Théorie de la Fonctionnelle de la Densité(DFT) et son extension dépendante du temps (TD-DFT): d'une part les relationsstructure moléculaire-propriétés optiques de chromophores, d'autre part le phénomènede complexation. En particulier, la détection de l'ion Zn2+, démontrée de manièrethéorique et expérimentale, est finalement réalisée après intégration du senseurmoléculaire dans un dispositif à fibre optique. / The increasing presence of various substances in our environment has brought abouta growing need for rapid emergence of new materials and devices in the quest forefficient and reliable chemical sensors. Massive technological progress have madeavailable an extensive range of technical tools to serve their development, accountingfor the requirements to be fulfilled (selectivity, quick response..). In this context,quantum chemistry methods provide a fundamental understanding of the processes atstake in the detection of chemical species and allow for rational design of sensingmaterials. Certain organic molecules can be extensively functionalised and thusconstitute an evident starting point owing to the tunability of their propertiesprovided by appropriate choice of structural modifications. The versatility of somechromophores associated to the selectivity offered by receptor units constitute theresearch playground for the development of ever better chemosensors.The present research aims at the rational development of chromoionophores for thecomplexation of cations, combining computational chemistry methods with basicspectroscopic characterisation. Using Density Functional Theory (DFT) and its timedependentextension (TD-DFT), two main aspects were treated, namely therelationship between molecular structure and optical properties of organicchromophores featuring valuable characteristics, and the complexation phenomenon.Photophysics of Zn2+ ion detection were more specifically studied, and recognitionwas demonstrated with both quantum-chemical calculations and experiments,accounting for the future integration of the chemical sensor in an optical fibre device.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A clorpropamida (C10H13ClN2O3S, (1-[4-chlorobenzenesulphonyl]-3-propyl urea)) à uma droga usada para tratar o diabetes tipo II (nÃo dependente da insulina), em particular em pessoas cujo diabetes nÃo pode ser controlada sà pelo regime alimentÃcio. O polimorfismo desta droga se encontra amplamente documentado exibindo, pelo menos, cinco diferentes formas cristalinas. Neste trabalho apresentamos um estudo de quatro destes polimorfos atravÃs das espectroscopias Raman, infravermelho e infravermelho prÃximo. O objetivo desta investigaÃÃo vibracional à estabelecer correlaÃÃes entre os modos vibracionais e as possÃveis estruturas cristalinas, alÃm de avaliar estes mÃtodos como ferramentas para a identificaÃÃo e controle de qualidade das matÃrias primas e produtos formulados. No intuito de prover uma caracterizaÃÃo detalhada tambÃm empregamos anÃlises tÃrmicas e difraÃÃo de raios- X para a identificaÃÃo prÃvia das formas cristalinas. Finalmente, a classificaÃÃo das bandas observadas nos espectros vibracionais em termos dos modos normais de vibraÃÃo da molÃcula foi realizada com a ajuda de cÃlculos computacionais baseados na teoria do funcional de densidade. Estes resultados tambÃm nos permitiram investigar a estabilidade conformacional da clorpropamida e estabelecer correlaÃÃes com o polimorfismo da mesma. / Chlorpropamide (C10H13ClN2O3S, (1-[4-chlorobenzenesulphonyl]-3-propyl urea)) is a drug used to treat type II diabetes (non-dependent of insulin), especially when the diabetes can not be controlled by alimentary regimes. The polymorphism of this drug is widely documented exhibiting at least five crystalline forms. In this work, we present a vibrational study of four of these polymorphs by using Raman, infrared and near-infrared spectroscopies. The objective of this vibrational investigation is to correlate the vibrational modes with the possible crystalline structures, as well as, to evaluate these methods as a tool for identification and quality control of raw materials and formulated products. In order to provide a detailed characterization we also applied thermal analyses and x-ray powder diffraction techniques to identify the crystalline forms. Finally, the assignment of the bands observed in the vibrational spectra in terms of the normal vibrational modes was performed with the help the quantum mechanical calculations based on the density functional theory. These results allow us to investigate the conformational stability of chlorpropamide establishing correlations with the polymorphism of this drug.

Com o crescimento da população, os países, estados e cidades identificam a necessidade de realizar investimentos em infraestrutura, transporte e outros. A proposta do presente trabalho é apresentar uma ferramenta, utilizada para atender a demanda de um edital de licitação, expondo à Companhia de Trens Metropolitanos de São Paulo, um exemplo da parte de um edital internacional para aquisição de um meio de transporte rápido e eficiente. Para tal finalidade, são analisadas e filtradas as informações contidas no edital para realizar a simulação de marcha de uma composição ferroviária, através de um software específico. Por fim, na forma gráfica ilustram-se os cálculos cinemáticos e elétricos do comportamento que o sistema de potência irá desempenhar, mostrando que atende aos requisitos do edital de licitação. / With growing of population, countries, states and cities have identified the necessity to perform investiments in infrastructure, transportation, among others. The purpose of this dissertation is to present a tool, used to meet the request of a bidding document, presenting to Metropolitan Train Company of São Paulo one example of part of an international bidding to an acquisition of a rapid and efficient transportation. For this purpose, information of bidding document are analised and filtered to make a running simulation of a train composition throught a specific software. Finally, one application of this method is presented in a graphical form containing kinematic and electrical calculations of the behavior that power system will perform, showing that system meets the requiriments of bidding document.

A presente tese trata da síntese, análise conformacional e estudo das interações eletrônicas dos 2-etilsulfinil-tioacetatos de fenila 4\'-substituídos (I) e dos tioacetatos de fenila 4\'-substituídos (II) (compostos de referência). O estudo conformacional foi realizado por intermédio da espectroscopia infravermelho (IV) apoiada por cálculos teóricos HF, DFT e NBO (Natural Bond Orbital). A análise no IV de vco da série (I) se correlaciona relativamente bem com os cálculos HF e B3LYP. Estes cálculos indicaram a existência de quatro conformações estáveis [q-c2-sin (q-g-sin), g3-sin, g1-anti e q-g2-sin], sendo somente as três primeiras conformações, de população significativa, presentes em solução. Conforme esperado nos α-sulfinil-tioésteres, no cálculo DFT, obtém-se a conformação q-g-sin que corresponde à conformação q-c2-sin, obtida no HF. Tanto no HF como no B3LYP as conformações q-c2-sin (q-g-sin) e g3-sin apresentam freqüências de vCO degeneradas e correspondem ao componente de maior freqüência e de maior intensidade do dubleto, e a conformação g1-anti corresponde ao componente de menor freqüência e de menor intensidade do dubleto no IV. Os cálculos HF e B3LYP reproduzem o resultado experimental. A população relativa do componente de maior freqüência de vCO, que corresponde à somatória das populações das conformações [q-c2-sin (HF) ou q-g-sin (DFT) e g3-sin (HF e DFT)], em relação ao componente de menor freqüência, que corresponde à conformação g1-anti (HF e DFT), varia de (100%, CCl4; 100%, CHCl3) no 4\'-nitro derivado (1) a (90%, CCl4; 83%; CHCl3) no 4\'-metóxi derivado(6). Enquanto a conformação q-c2-sin (HF) é estabilizada pelas interações eletrostática Oδ-(CO)...Sδ+(SO) e de transferência de carga nO(CO)/σ*S-O, as conformações q-g-sin, g3-sin e g1-anti (HF e DFT) são estabilizadas pelas interações σC4-S5/π*C1-O2 (forte), πC1-O2/σ*C4-S5, nS/π*C1-O2, nO(SO)/π*C1-O2, nO(CO)/σ*C6-H6 (fracas) e π*Cl 02/σ*C4-S5. Todas as conformações são fortemente estabilizadas pelas interações: n(S3)/π*C1-O2 (conjugativa), nO2(CO)/σ*C1-S3 e nO2(CO)/σ*C1-C2 (através das ligações), sendo mais fortes para as conformações q-c2-sin (HF), q-g-sin, g3-sin (HF e DFT) em relação à conformação g1-anti (HF e DFT). Adicionalmente, as conformações sin [q-c2 (HF), q-g (DFT) e g3 (HF e DFT)] são também estabilizadas pela interação nO(CO)/π*Ph e a conformação g1-anti é estabilizada, no HF e DFT, pelas interações: n2(SO)/σ*C11-H11 e πC9-C10/σ*C4-H4. Nos tioacetatos de fenila de referência (II) as interações orbitalares n(S3)/π*C1-O2, nO2(CO)/σ*C1-S3, nO2(CO)/σ*C1-C2 (fortes) e nO(CO)/π*Ph (fraca) são responsáveis pela maior estabilização da conformação sin (de maior freqüência calculada de vCO) em relação à conformação anti (de menor freqüência calculada de vCO), que é estabilizada pelas interações n(S3)/π*C1-O2, nO2(CO)/σ*C1-S3, n02(CO)/σ*C1-C2 (fortes) e πC9-C1O/σ*C4-H4 (fraca). Os valores negativos dos deslocamentos da freqüência teóricos da carbonila das conformações [q-c2-sin (HF), q-g-sin (DFT)], g1-anti (HF e DFT) e g3-sin (HF e DFT) dos compostos da série (I) em relação às freqüências de vCO (HF e DFT) dos confôrmeros sin e anti da série (II) estão de acordo com a somatória das interações eletrônicas acima mencionadas. A análise de difração de raio-X do 4\'-bromo derivado (I) indica que este composto é estabilizado no estado sólido numa conformação cuja geometria é semelhante à conformação q-g-sin de maior energia (na fase gasosa) / This thesis reports the synthesis, conformational analysis and electronic interaction study of 4\'-substituted 2-ethylsulfinyl-phenylthioacetates (I) and 4\'-substituted phenylthioacetates (II) (reference compounds). The conformational analysis was performed through IR spectroscopy supported by theoretical calculations HF, B3LYP and NBO (Natural Bond Orbital). The vCO analysis for series (I) in general matches welI with the HF and B3LYP computations. These data indicate the existence of four stable conformations q-c2-sin (q-g-sin), g3-sin, g1-anti and q-g2-sin, being the first three conformations the only ones of reasonable populations and present in solution. As expected for the sulfinyl thioesters, in the DFT method the q-g-sin conformation is obtained instead of the q-c2-sin conformation of the HF method. Both in the HF and B3LYP the (q-c2-sin, q-g-sin) and g3-sin conformations show degenerated vCO frequencies and they correspond in the IR spectrum (solution) to the doublet higher frequency component of larger intensity. The g1-anti conformation corresponds to the doublet lower frequency component of smalIer intensity. In general, HF and DFT calculations reproduce well the experimental results. The relative population of the higher vCO doublet frequency component, which corresponds to the summing up of [(q-c2-sin (HF), q-g-sin (DFT) and g3-sin (HF and DFT)] conformation populations, with respect to the lower frequency component, which corresponds to g1-anti conformation population (HF and DFT), varies from (100%, CCl4; 100%, CHCl3) in the 4\'-nitro derivative (1) to (90%, CCl4; 83%; CHCl3) in the 4\'-metoxi derivative (6). While the q-c2-sin (HF) conformation is stabilized by the Oδ-(CO)....Sδ+(SO) electrostatic and nO(CO)/σ*S-O, nO(CO)/σ*C6-H6 orbital interactions, the q-g-sin, g3-sin e g1-anti (HF and DFT) conformations are stabilized by the σC4-S5/π*C1-O2 (strong), πC1-O2/σ*C4-S5, nS/π*C1-O2, nO(SO)/&#960*C1-02, nO(CO)/σ*C6-H6 (weak) and π*C1-O2/σ*C4-S5 interactions. All the conformations are strongly stabilized by: the n(S3)/π*C1-O2 and nO2(CO)/σ*C1-S3 e n02(CO)/σ*C1-C2 interactions, being stronger for the q-c2-sin (HF), q-g-sin, g3-sin (HF e DFT) conformations and weaker for the g1-anti conformation (HF and DFT). Furthermore, the sin [q-c2 (HF), q-g (DFT) and g3 (HF and DFT)] conformations are also stabilized through nO(CO)/&#960*Ph interaction and the g1-anti conformation is stabilized in the HF e DFT by the n2(SO)/σ*C11-H11 and πC9-C10/σ*C4-H4 interactions. This trend is in line with the higher the vCO frequency of [q-c2-sin (HF), q-g-sin (DFT)] and g3-sin (HF e DFT) conformations relative to the frequency of g1-anti (HF e DFT) conformation. As for the reference 4\'-substituted phenylthioacetates (II) the NBO method (HF and DFT) revealed that the n(S3)/π*C1-O2, nO2(CO)/&#963*C1-S3, nO2(CO)/σ*C1-C2 and nO(CO)/π*Ph (weak) interactions are responsible for the larger stabilization of the sin conformation (the higher computed vCO frequency) with respect to the anti conformation (the lower computed vCO frequency) which is stabilized by the N(S3)/π*C1-O2, nO2(CO)/σ*C1-S3 and nO2(CO)/σ*C1-C2 along with the weak πC9-C1O/σ*C4-H4 interactions. The negative carbonyl frequency shiftS (Δv) for the [q-c2-sin (HF), q-g-sin (DFT)], g1-anti (HF e DFT) e g3-sin (HF e DFT) conformers of compounds of series (I) relative to the vCO frequencies (HF e DFT) of sin e anti conformers of series (II) are in good agreement with the summing up of the above mentioned electronic interactions. The X-ray diffraction analysis of the 4\'-bromo derivative (I) shows that this compound assumes in the solid state a geometry similar to that of the less stable q-g2-sin conformation

Depuis quelques années, les codes de calculs Monte Carlo évoluant qui couplent un code Monte Carlo, pour simuler le transport des neutrons, à un solveur déterministe, qui traite l'évolution des milieux dû à l'irradiation sous le flux neutronique, sont apparus. Ces codes permettent de résoudre les équations de Boltzmann et de Bateman dans des configurations complexes en trois dimensions et de s'affranchir des hypothèses multi-groupes utilisées par les solveurs déterministes. En contrepartie, l'utilisation du code Monte Carlo à chaque pas de temps requiert un temps de calcul prohibitif.Dans ce manuscrit, nous présentons une méthodologie originale évitant la répétition des simulations Monte Carlo coûteuses en temps et en les remplaçant par des perturbations. En effet, les différentes simulations Monte Carlo successives peuvent être vues comme des perturbations des concentrations isotopiques de la première simulation. Dans une première partie, nous présenterons donc cette méthode, ainsi que la méthode de perturbation utilisée: l'échantillonnage corrélé. Dans un second temps, nous mettrons en place un modèle théorique permettant d'étudier les caractéristiques de la méthode des échantillons corrélés afin de comprendre ses effets durant les calculs en évolution. Enfin, dans la troisième partie nous discuterons de l'implémentation de cette méthode dans TRIPOLI-4® en apportant quelques précisions sur le schéma de calcul qui apportera une accélération importante aux calculs en évolution. Nous commencerons par valider et optimiser le schéma de perturbation à travers l'étude de l'évolution d'une cellule de combustible de type REP. Puis cette technique sera utilisée sur un calcul d'un assemblage de type REP en début de cycle. Après avoir validé la méthode avec un calcul de référence, nous montrerons qu'elle peut accélérer les codes Monte Carlo évoluant standard de presque un ordre de grandeur. / For several years, Monte Carlo burnup/depletion codes have appeared, which couple Monte Carlo codes to simulate the neutron transport to deterministic methods, which handle the medium depletion due to the neutron flux. Solving Boltzmann and Bateman equations in such a way allows to track fine 3-dimensional effects and to get rid of multi-group hypotheses done by deterministic solvers. The counterpart is the prohibitive calculation time due to the Monte Carlo solver called at each time step.In this document we present an original methodology to avoid the repetitive and time-expensive Monte Carlo simulations, and to replace them by perturbation calculations: indeed the different burnup steps may be seen as perturbations of the isotopic concentration of an initial Monte Carlo simulation. In a first time we will present this method, and provide details on the perturbative technique used, namely the correlated sampling. In a second time we develop a theoretical model to study the features of the correlated sampling method to understand its effects on depletion calculations. In a third time the implementation of this method in the TRIPOLI-4® code will be discussed, as well as the precise calculation scheme a meme to bring important speed-up of the depletion calculation. We will begin to validate and optimize the perturbed depletion scheme with the calculation of a REP-like fuel cell depletion. Then this technique will be used to calculate the depletion of a REP-like assembly, studied at beginning of its cycle. After having validated the method with a reference calculation we will show that it can speed-up by nearly an order of magnitude standard Monte-Carlo depletion codes.

A termodinâmica computacional é uma ferramenta capaz de fornecer informações básicas sobre soluções e concentração de seus constituintes, em um dado sistema complexo a uma certa temperatura e pressão. Nos últimos anos, a união entre a teoria do funcional da densidade e a termodinâmica computacional tem renovado o estudo dos materiais intermetálicos ordenados, uma vez que os cálculos de estrutura eletrônica de primeiros princípios são hoje capazes de proporcionar resultados extremamente precisos para as energias de formação de compostos estequiométricos. Dentro deste contexto, investigamos os diagramas de fases dos sistemas Fe-Al, Mo- Fe, Cr-Al, Fe-Cr, Fe-Cr-Al na estrutura cúbica de corpo centrado utilizando o método Full-Potential Linear Augmented Plane Waves(FP-LAPW) aliado ao Método Variacional de Clusters(CVM) na aproximação do tetraedro irregular. Através do método FP-LAPW determinamos a energia total de configurações cristalinas dos sistemas cúbicos de corpo centrado. Esses valores são utilizados como parâmetros de entrada do CVM para a determinação do potencial termodinâmico do sistema em suas diferentes fases e os correspondentes equilíbrios entre essas fases em função da composição e da temperatura (diagrama de fases). Embora o Fe-Al tenha grande interesse tecnológico, o seu comportamento magnético é bastante complicado. A inclusão de Cr na liga de Fe-Al tem um alto interesse industrial na utilização desta ligas em altas temperaturas, mas o banco de dados referentes as caracteristicas estruturais e eletrônicas são escassos. Neste contexto de aplicações procuramos investigar as características estruturais e eletrônicas buscando correlacionar as informações experimentais com as obtidas via cálculo de estrutura eletrônica e o CVM. / Thermodynamics is a computational tool capable of providing information basics solutions and concentrations of constituents in a given complex system at a given temperature and pressure. In recent years, the union between the density functional theory and computational thermodynamics has renewed study of ordered intermetallic materials, since the electronic structure calculations from first principles are now able to provide extremely accurate results for the energies of formation of stoichiometric compounds. in this context, we investigate the phase diagrams of the systems Fe-Al, Fe- Mo, Cr-Al, Fe-Cr, Fe-Cr-Al in the body-centered cubic structure using the method Full-Potential Linear Augmented Plane Waves (FP-LAPW) ally the clusters variational method(CVM) in approximation of the tetrahedron irregular. Through the FP-LAPW method determines the total energy of the crystal with configurations body centered cubic systems. These values are used as input parameters of the CVM for the determination of the thermodynamic potential of the system in its different phases and the corresponding equilibrium between these phases as a function of composition and temperature (phase diagram). Although the Fe-Al has a great interest technology, its magnetic behavior is quite complicated. The inclusion of Cr in Fe-Al alloy has a high industrial interest in using this alloy in high temperatures, but the database regarding the structural characteristics and electronics are scarce. In this context we seek to investigate the application structural and electronic characteristics correlate the information seeking experiments with those obtained via the electronic structure calculation and the CVM.

Com o aumento da consciência global sobre os riscos do Aquecimento do Planeta e de suas possíveis causas ficou claro que é necessário desenvolver ou adaptar processos industriais de maneira a aproveitar dejetos como o CO2. Dentre as formas de se aproveitar o CO2, destaca-se a ciclo-adição aos epóxidos, com a formação de ciclocarbonatos. A reação é tecnologicamente interessante, pois ciclocarbonatos possuem diversas aplicações como solventes polares apróticos, eletrólitos e matéria prima para compostos como purinas, carbamatos, glicóis, policarbonato e outros. Para que a reação ocorra em tempo e condições viáveis, há a necessidade de se trabalhar com catalisadores. Foram reportados muitos catalisadores ao longo dos anos. Dentre os catalisadores mais comumente utilizados, destacam-se os sais orgânicos. Porém o estudo sobre modelos cinéticos e mecanismo de reação ainda carecem de mais atenção. Desta forma este trabalho propõe-se a estudar esta parte, através de experimentos cinéticos, modelos teóricos e cálculos de química quântica. Para isto escolheu-se estudar a ação catalítica do brometo de 1-propil-4-azo-1-azôniobiciclo[2,2,2]octano (P-DABCO) frente a um catalisador bem descrito na literatura, o brometo de tetrapropilamônio (TPA). / Nowadays mankind are becoming more aware about Global Warming risks and its possible causes. With that in mind, it is necessary to develop or to adapt industrial processes to use some wastes like CO2. One of the best strategies to utilize CO2 is to convert it to cyclic carbonate through cyclic addition reaction to epoxides. This reaction is important because cyclic carbonates have other useful applications. For example, they can be used as polar aprotic solvents, electrolytes and as starting material for other compounds like purine, carbamates, glycols, polycarbonate, among others. However, the cyclic addition reaction must be catalyzed so as to get the desired product in short possible time and under soft conditions. Many catalysts have been reported in the literature that can be used for the cyclic addition reaction, with the organic salts being very common ones. Most of these reports focus on the efficiency of the catalyst and little attention has been paid to the reaction kinetics models and reaction mechanisms. Thus, we intend to study this part. For this purpose, we will do kinetics experiments, theoretical models and quantum chemistry calculation. The 1-alkyl-4-aza-1-azaniabicyclo[2.2.2]octyl bromide was chosen to this work and will be compared with tetrapropylammonium bromide that is known in the literature.

En chimie quantique, le principe variationnel est largement utilisé pour calculer la limite supérieure de l'énergie exacte d'un système atomique ou moléculaire. Des méthodes pour calculer la valeur limite inférieure de l'énergie existent mais sont bien moins connues. Une méthode précise pour calculer une telle limite inférieure permettrait de fournir une barre d'erreur théorique pour toute méthode de chimie quantique. Nous avons appliqué des méthodes de type variance pour calculer différentes énergies limites inférieures de l'atome d'hydrogène en utilisant des fonctions de base gaussiennes. L'énergie limite supérieure se trouve être toujours plus précise que ces différentes limites inférieures, i.e. plus proche de l'énergie exacte. L'importance de points singuliers sur l'évaluation de valeurs moyennes d'opérateurs quantiques a également été soulignée.Nous avons étudié les réactions d'adsorption d'un atome de fluor et d'un ion fluorure sur de petits agrégats de lithium Li$_n$ (n=2-15), à l'aide de méthodes de chimie quantique précises. Pour le plus petit système, nous avons montré que la formation de complexes stables Li$_2$F et Li$_2$F$^-$ se produit par un transfert d'électrons sans barrière et à longue portée, de Li$_2$ vers F pour le système neutre et l'inverse pour le système anionique. De telles réactions pourraient être rapides à très basse température. De plus, les complexes formés présentent des caractéristiques uniques de "longue liaison". Pour les systèmes plus gros Li$_n$F/Li$_n$F$^-$ ($n\geqslant4$), nous avons montré que les énergies d'adsorption peuvent être aussi grandes que 6~eV selon le site d'adsorption et que plus d'un état électronique est impliqué dans le processus d'adsorption. Les complexes formés présentent des propriétés intéressantes de "super alcalins" et pourraient servir d'unités de base dans la synthèse de composés à transfert de charge avec des propriétés ajustables. / In quantum chemistry, the variational principle is widely used to calculate an upper bound to the true energy of an atomic or molecular system. Methods for calculating the lower bound value to the energy exist but are much less known. An accurate method to calculate such a lower bound would allow to provide a theoretical error bar for any quantum chemistry method. We have applied variance-like methods to calculate different lower bound energies of a hydrogen atom using Gaussian basis functions. The upper bound energy is found to be always more accurate than the lower bound energies, i.e. closer to the exact energy. The importance of singular points on mean value evaluation of quantum operators has also been brought to attention.The adsorption reactions of atomic fluorine (F) and fluoride (F$^-$) on small lithium clusters Li$_n$ (n=2-15) have been investigated using accurate quantum chemistry ab initio methods. For the smallest system, we have shown that the formation of the stable Li$_2$F and Li$_2$F$^-$ complexes proceeds via a barrierless long-range electron transfer, from the Li$_2$ to F for the neutral and conversely from F$^-$ to Li$_2$ for the anionic system. Such reactions could be fast at very low temperature. Furthermore, the formed complexes show unique long bond characteristics. For the bigger Li$_n$F/Li$_n$F$^-$ systems ($n\geqslant 4$), we have shown that the adsorption energies can be as large as 6~eV depending on the adsorption site and that more than one electronic state is implied in the adsorption process. The formed complexes show interesting "superalkali" properties and could serve as building blocks in the synthesis of charge-transfer compounds with tunable properties.

Lanthanum-mediated bond activation reactions of small hydrocarbon molecules, including alkenes, alkynes, and alkadienes, were carried out in a laser vaporization metal cluster beam source. Time-of-flight mass spectrometry and mass-analyzed threshold ionization (MATI) spectroscopy, in combination with quantum chemical and multi-dimensional Franck-Condon factor calculations, were utilized to identify the reaction products and investigate their geometries, electronic structures, and formation mechanisms. La-hydrocarbon association was only observed in the reaction of La with isoprene. C-H bond activation was observed in all reactions, hydrogen elimination was observed as the prominent reaction for the alkenes (2-butene, isobutene, 1-pentene, and 2-pentene), alkynes (1-butyne, 2-butyne, and 1-pentyne), and 1,4-pentadiene, and C-C bond activation was observed for the five-membered hydrocarbons (1-pentene, 2-pentene, 1-pentyne, isoprene, and 1,4-pentadiene). The La-hydrocarbon radicals formed in these reactions had lanthanacyclic structures in various sizes, and each of the La-hydrocarbon complexes had a doublet ground state with a 6s1 La-based electron configuration. Ionization removed the 6s electron, and the resultant ion was in a singlet state. Formations of dehydrogenated products were either through a concerted hydrogen elimination process or the dehydrogenation after ligand isomerization. The C-C bond activation proceeded through La-assisted hydrogen migration, followed by C-C bond cleavage, or vice versa.