Van der Waals molecules are complexes of two or more atoms or molecules bound by weak intermolecular forces rather than a conventional chemical bond. This thesis contains a high resolution molecular beam study of the rotational spectra of two such species, ArNO and NeNO. A new hamiltonian is presented to account for the spectra of these open-shell complexes. The theory is similar to that already known for the uncomplexed diatom, nitric oxide, but is modified to an asymmetric top form appropriate for these non-linear species. Two novel interactions require inclusion. The first models a slight quenching of the NO orbital angular momentum by the rare gas atoms. The second is a large centrifugal distortion associated with the effects of the bending motion on the projection of the electronic angular momentum on the complex's a-inertial axis. A comparatively rich, though incomplete, spectrum is obtained for ArNO. Most of the transitions that originate from the lower rotational states are assigned and fitted to within a few MHz using the modified open-shell hamiltonian. Possible sources are suggested for the origins of the small residual errors between the observed and calculated transition frequencies. A vibrationally-averaged structure is derived from the fitted molecular parameters indicating an equilibrium geometry which is quite close to a T-shape. The hyperfine structure in the spectrum which is associated with the ¹⁴ N nucleus is well fitted by the hamiltonian; however, the magnetic hyperfine parameters are significantly perturbed from the values that best fit the lambda-doubling spectrum of the uncomplexed diatom. The implications of this with respect to the nature of the rare gas-nitric oxide intermolecular interaction are discussed. Greater experimental difficulties are encountered in trying to record the radiofrequency and microwave spectrum of NeNO and so fewer transitions have been measured than for ArNO. A partial analysis yields approximate values for the structural parameters. The complex exhibits a larger deviation from the T-shaped geometry than is observed for ArNO. The spectrum also provides an estimate of the magnitude of the quenching of the orbital angular momentum. The quenching interaction is somewhat larger in the neon complex.

Thesis (M.S.)--University of North Texas, Dec., 2007. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Rhode Island, 2004. / Typescript. Includes bibliographical references (leaves 90-92).

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (leaves 99-102).

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009. / Committee Chair: Loren D. Williams; Committee Member: Donald Doyle; Committee Member: Nicholas V. Hud; Committee Member: Roger Wartell; Committee Member: Stephen Harvey. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Techn. Universiẗat, Diss., 2004--Berlin.

Orientador: Leonardo Goldstein Jr / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-03T18:09:40Z (GMT). No. of bitstreams: 1 Lopes_MarcosDonizete_M.pdf: 5077011 bytes, checksum: c1b9066b877bcfe1af8be5b8a935e84d (MD5) Previous issue date: 2003 / Resumo: O emprego de modelos constitui uma solução prática para estudar a influência dos fatores operacionais no desempenho dos ciclones de porte industrial. A construção dos modelos deve obedecer a fatores de escala apropriados que determinam a existência de semelhança entre o modelo e o protótipo. Modelo e protótipo apresentarão comportamento fluidodinâmico semelhante se forem geometricamente semelhantes e se os valores dos números adimensionais correspondentes forem iguais. Um conjunto de números adimensionais representativo dos fenômenos envolvidos no escoamento gás-sólidos em ciclones deve levar em conta as forças interparticulares, como a de van der Waals e a eletrostática. A dificuldade para obedecer às condições de semelhança levando-as em conta seria, no entanto, muito grande. Assim sendo, desconsiderou-se a eventual participação das forças interparticulares na determinação do grupo de números adimensionais a partir dos quais se gerou as leis de escala. Estas leis simplificadas foram aplicadas para a construção de dois ciclones, modelo e protótipo, em escala, que foram testados para determinação da faixa de aplicação da simplificação introduzida. Adicionalmente abriu-se mão de operar com uma semelhança dinâmica completa entre modelo e protótipo, tendo-se a chamada Semelhança Incompleta, pois, por motivos práticos, operou-se o modelo com ar em condições ambientais, o que equivale a desprezar as forças viscosas em relação às forças de inércia, subtraindo-se o requisito da igualdade do número de Reynolds das relações de escala. O presente trabalho mostrou experimentalmente a existência de concentrações a partir das quais a simplificação proposta perde a validade, implicando que as forças desconsideradas são de magnitude tal que não podem deixar de ser consideradas na geração dos adimensionais. Verificouse que, abaixo destas concentrações limite houve semelhança quanto ao rendimento de coleta, como se constatou pela existência de igualdade dos rendimentos de coleta dos ciclones modelo e protótipo, quando em condições operacionais de velocidades correspondentes e com a mesma concentração de sólidos na entrada dos ciclones. Verificou-se também que a perda de pressão, Dp, adimensionalizada em relação à perda de pressão no ciclone vazio mostrou-se mais adequada que a razão Dp/romo2; para definição da semelhança quanto à perda de pressão, possivelmente porque a velocidade na entrada do ciclone, mo, não seja a velocidade mais adequada a ser utilizada na adimensionalização da perda de pressão / Abstract: The use of models in scale is a practical way of studying how the operational parameters influence the performance of industrial cyclones. The model and the prototype cyclones should be built according to a scaling law - given by a set of dimensionless parameters --, so that they are similar. It there will be fluid-dynamical similarity between the cyclones if they are geometrically similar and the sets of corresponding dimensionless parameters are equal. A group of dimensionless parameters which represent the gas-solid flow phenomenon in cyclones should consider interpartic1e forces, such as the van der Waals and the electrostatic forces. However, as it would be quite difficult to comply with a scaling law determined from taking into consideration these forces, it was decided not to include them and check the range of applicability of the simplified set. Moreover, during the tests, all the dimensionless parameters were made equal, with the exception of the Reynolds number, because, for practical reasons, atmospheric air was used in the tests for both prototype and model cyc1ones, what is equivalent to neglect the viscous forces as compared to the inertial forces. The present work showed that when the model and prototype cyclones were operating at the corresponding velocities and with the same solids concentration at the inlet, similarity was obtained between the collection efficiencies when the solids concentration was less than 1.0 kg/kg, meaning that the proposed methodology was appropriate, that is, that the forces not included were not significant and could be neglected. Concerning the pressure drop in the cyclones, it was observed that the ratio of the pressure drop, Dp, by the pressure drop in the cyclone with no solids, was more appropriate than the ratio Dp/romo2; for expressing similarity, maybe because the entrance velocity, mo, is not the best velocity to be used as a scaling parameter / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

Les études de mélanges binaires sous conditions extrêmes ont mené à la découverte de solides appelés composés van der Waals. La découverte d’un composé van der Waals dans un mélange de deux gaz nobles par Loubeyre et al. (1993) permet de supposer que différentes combinaisons de gaz nobles formeront, aux conditions pression-température-concentration appropriées, de tels solides. Des échantillons de gaz nobles (néon + argon) et (hélium + argon) furent étudiés sous hautes pressions par diffraction de rayons X issus du rayonnement synchrotron dans le but de former et caractériser un composé inédit. Une faible miscibilité des espèces étudiées est observée via la présence de démixtions et de solutions solides dans les échantillons. Parallèlement, une étude du composé binaire (azote + méthane) a été poursuivie par l’affinement des positions moléculaires d’un composé van der Waals connu pour ce système. Des solutions potentielles pour la structure cristalline sont proposées et discutées.

In this work, the phase behavior of binary systems comprising nitrogen and a noble element (nitrogen + argon and nitrogen + krypton) was studied at high density in the condensed state. Following the work of Lotz et al.[2001], the main goal of this work was to further investigate the pressure-concentration phase diagram as well as to look for the possible formation of van der Waals compounds at elevated pressures and room temperature and study their physical properties, using both vibrational spectroscopy and X-ray diffraction. The observed phases, formed by single atoms and/or simple molecules in the binary systems were solved and modeled for their corresponding crystalline structures. From experimental results, lattice parameters for all crystalline structures and phase transitions, if detected, have been observed to shift with respect to that of the pure substances. The analyses and characterization of these binary systems are discussed in detail.

One of the fastest growing fields in condensed matter physics is that of two-dimensional materials; compounds that promise to revolutionize nanotechnology due to the ability to easily isolate clean atomically thin sheets of conducting material for use in atomic-scale circuits. Since the initial demonstration of the electric-field effect in nanocircuits fabricated from mechanically exfoliated graphene, the number of available compounds that can be isolated and used in atomically thin circuits has exponentially grown to include diverse electrical properties from metals and insulators to superconductors and magnets. The bulk compounds from which flakes are isolated are known as van der Waals materials named for their intrinsic structural anisotropy resulting in weak van der Waals chemical bonds in one dimension. Since this field is relatively young, there are a multitude of branching opportunities for experimental advancement. In this work, we begin by addressing a significant technical challenge within the two-dimensional community; contacting and measuring air-sensitive two-dimensional materials. We developed a novel technique for embedding metal electrodes in atomically thin insulating flakes used to simultaneously contact and preserve a wide-array of air-sensitive two-dimensional materials. Using this technique, we proceed to explore the properties of a diverse set of van der Waals compounds in both three dimensions and two dimensions. We investigate the nature of superconductivity in the two-dimensional limit by quantifying the fragility of the superconducting state in a single atomic sheet of NbSe2. In combination with theoretical time-dependent Ginzburg-Landau simulations, we show that the dissipation in two-dimensional NbSe2 can be accurately described by vortex dynamics, including the poorly understood low-temperature metallic-like state. We examine how superconductors proximitize with normal metals through measurements on atomic-scale normal metal/insulator/superconductor tunnel junctions fabricated from van der Waals materials, demonstrating agreement with Blonder- Tinkham-Klapwijk theory. In addition, in junctions fabricated from graphene and NbN, a high-critical- field superconductor, we gain an understanding of Andreev processes in graphene under large magnetic fields. Finally, we provide a detailed characterization Re6Se8Cl2 and CrSBr, two new van der Waals compounds. In Re6Se8Cl2, we develop a novel strategy for doping in van der Waals compounds with labile ligands, demonstrating a semiconducting to superconducting transition upon electron doping. In CrSBr, we discover a well-developed semiconducting gap along with strong coupling between magnetic order and transport properties, unique among van der Waals magnets. Further, we find the semiconducting and magnetic properties persist down to 2 layers of CrSBr, with the observation of air-stability, establishing it as a promising material platform for increasing the applicability of van der Waals magnets.