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Abstract This thesis deals with the rotation-vibration theory and high resolution infrared spectroscopy of semirigid C3 molecules. Semirigid molecules form a class of molecules which are strongly bound with one well defined structure, and without low frequency internal motions. The theory, as well as the experimental studies of semirigid molecules are of special importance in the field of rotation-vibration spectroscopy. They provide a good starting point for interpreting and analyzing the spectra of practically all types of molecules. In this work, the theory is reviewed fromthe standpoint of one particular molecule, 13CH3I, which is a prolate symmetric top with C3 symmetry. The origin and the properties of the rotation-vibration Hamiltonian are discussed in detail. Molecular symmetry plays an important role in these studies. The expansion of the Hamiltonian for nuclear motion in powers of the vibrational operators converges rapidly as numerical examples thoughout the treatment indicate. The molecule is thus a good subject for the perturbation calculations, also reviewed here in detail. 13CH3I can be considered as a model example of semirigid molecules. From the spectroscopic point of view, this thesis is a study of the six fundamental bands of 13CH3I. The rotational analysis of the vibrational ground state is first given. Special attention is paid to obtaining the axial rotational constants which are problematic for symmetric top molecules. The relatively high energy level density of 13CH3I leads to several resonances. The fundamental bands, especially the higher ones, must therefore be treated as parts of band systems. Care is paid to properly take into account the effects of the near-lying vibrational levels on the constants of the fundamentals. Certain ambiguities in the rotation-vibration Hamiltonian of 13CH3I are also discussed.

<p> This thesis examines the rotation-vibration spectra of systems of two and three particles (spin zero). The results in the two-particle case agree with many of the gross features of the spectra of deformed axially symmetric even-even nuclei. In the three-particle case, the set of basis functions used i n the expansions of the wavefunctions was too small to give accurate eigenvalues and eigenvectors, but nevertheless the spectrum clearly corresponds to that of an asymmetric even-even nucleus. </p> / Thesis / Master of Science (MSc)

Ce rapport d'habilitation présente une synthèse de mes travaux de recherche réalisés au cours de ces 14 dernières années. J'ai distingué mes activités expérimentales (partie III), mes travaux théoriques concernant la spectroscopie des toupies quasi-sphériques (partie IV), ainsi que ceux concernant la spectroscopie de molécules piégées dans des solides (partie V).

Reproduction de : Thèse doctorat : Physique : Reims : 2004. / Titre provenant de l'écran titre. Bibliogr. : 178ref.

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Para efeito de aplicação em cálculos de canais acoplados, potenciais calculados de maneira exata para sistemas envolvendo núcleos deformados não são adequados, pois resultariam em integrais multidimensionais muito difíceis de serem calculadas numericamente pelo tempo de cálculo computacional que isso implica. Nesta dissertação, apresentamos expressões para calcular de maneira aproximada os potenciais nuclear e coulombiano entre núcleos deformados, sendo essas expressões uma generalização de resultados obtidos em trabalhos anteriores. Os cálculos foram feitos no contexto do Modelo Generalizado de Rotação-Vibração (GRVM), que é um modelo de estrutura nuclear desenvolvido recentemente. Para obter essas expressões, as densidades nucleares foram expandidas até segunda ordem na deformação e foi levado em conta um valor finito para a difusividade nuclear nos cálculos de dupla convolução. Comparamos os correspondentes resultados obtidos com aqueles provenientes de algumas outras expressões, usualmente assumidas nesse tipo de cálculos, e também com os valores exatos (obtidos ao resolver numericamente a integral sextupla no cálculo de dupla convolução). As análises mostraram que a nossa aproximação -GRVM- é superior a essas outras de uma maneira geral, e, em particular, de forma muito melhor na região de pequenas distâncias de interação. As expressões analíticas do GRVM exprimem a dependência do potencial com as deformações de maneira explícita, sendo essa característica extremamente útil para a obtenção de potenciais de acoplamento de maneira analítica / For systems involving deformed nuclei, potentials calculated through an exact form are not appropriated for applications in coupled-channel (CC) calculations, because they result in multidimensional integrals impossible to be calculated numerically. In this work, we present equations for calculating the heavy-ion nuclear and Coulomb potentials, in an approximate form, that express the dependence of the potential on the deformations explicitly. This characteristic is extremely useful for obtaining coupling potentials analytically. The calculations were made in the context of the Generalized Rotation-Vibration Model (GRVM), which is a recently developed model of nuclear structure. To obtain these expressions, the nuclear densities were expanded up to second order in the deformation and a finite diffuseness value was taken into account in the calculation of the double-folding potential. We have compared the corresponding results with those obtained from other expressions usually assumed in such calculations, and also with the exact potential strength values (obtained by solving numerically the six dimensional integral of the double-folding calculation). The analyses show that our approach presents better results than the others, particularly so much better in the region of interaction of small distances.

Ce rapport d'habilitation présente une synthèse des activités de recherche que j'ai menées ces huit dernières années. J'ai distingué d'une part les recherches concernant la spectroscopie rovibrationnelle dans un état électronique singulet (Partie III) et d'autre part celles concernant la spectroscopie rovibronique dans un état électronique dégénéré (Partie IV).

Para efeito de aplicação em cálculos de canais acoplados, potenciais calculados de maneira exata para sistemas envolvendo núcleos deformados não são adequados, pois resultariam em integrais multidimensionais muito difíceis de serem calculadas numericamente pelo tempo de cálculo computacional que isso implica. Nesta dissertação, apresentamos expressões para calcular de maneira aproximada os potenciais nuclear e coulombiano entre núcleos deformados, sendo essas expressões uma generalização de resultados obtidos em trabalhos anteriores. Os cálculos foram feitos no contexto do Modelo Generalizado de Rotação-Vibração (GRVM), que é um modelo de estrutura nuclear desenvolvido recentemente. Para obter essas expressões, as densidades nucleares foram expandidas até segunda ordem na deformação e foi levado em conta um valor finito para a difusividade nuclear nos cálculos de dupla convolução. Comparamos os correspondentes resultados obtidos com aqueles provenientes de algumas outras expressões, usualmente assumidas nesse tipo de cálculos, e também com os valores exatos (obtidos ao resolver numericamente a integral sextupla no cálculo de dupla convolução). As análises mostraram que a nossa aproximação -GRVM- é superior a essas outras de uma maneira geral, e, em particular, de forma muito melhor na região de pequenas distâncias de interação. As expressões analíticas do GRVM exprimem a dependência do potencial com as deformações de maneira explícita, sendo essa característica extremamente útil para a obtenção de potenciais de acoplamento de maneira analítica / For systems involving deformed nuclei, potentials calculated through an exact form are not appropriated for applications in coupled-channel (CC) calculations, because they result in multidimensional integrals impossible to be calculated numerically. In this work, we present equations for calculating the heavy-ion nuclear and Coulomb potentials, in an approximate form, that express the dependence of the potential on the deformations explicitly. This characteristic is extremely useful for obtaining coupling potentials analytically. The calculations were made in the context of the Generalized Rotation-Vibration Model (GRVM), which is a recently developed model of nuclear structure. To obtain these expressions, the nuclear densities were expanded up to second order in the deformation and a finite diffuseness value was taken into account in the calculation of the double-folding potential. We have compared the corresponding results with those obtained from other expressions usually assumed in such calculations, and also with the exact potential strength values (obtained by solving numerically the six dimensional integral of the double-folding calculation). The analyses show that our approach presents better results than the others, particularly so much better in the region of interaction of small distances.