Cheung Chung Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 126-137). / Abstracts in English and Chinese. / ABSTRACT (English version) --- p.iii / ABSTRACT (Chinese version) --- p.vi / ACKNOWLEDGMENTS --- p.viii / TABLE OF CONTENTS --- p.ix / LIST OF FIGURES --- p.xiii / LIST OF TABLES --- p.xvii / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter 1.1 --- Molecular Structure Determination --- p.1 / Chapter 1.2 --- Methods for Structure Determination --- p.1 / Chapter 1.2.1 --- Infrared (IR) Spectroscopy --- p.1 / Chapter 1.2.2 --- Electron Microscopy (EM) --- p.2 / Chapter 1.2.3 --- X-ray Diffraction (XRD) --- p.2 / Chapter 1.2.4 --- Nuclear Magnetic Resonance (NMR) Spectroscopy --- p.3 / Chapter 1.3 --- Solid State NMR Spectroscopy 一 Chemical Shielding Tensor --- p.4 / Chapter 1.4 --- Scope of This Thesis --- p.6 / Chapter CHAPTER TWO: --- PRINCIPLE AND THEORY --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Chemical Shielding Tensor (CST) --- p.7 / Chapter 2.2.1 --- Basis of Nuclear Magnetic Resonance --- p.7 / Chapter 2.2.2 --- Theoretical Description of CST --- p.8 / Chapter 2.3 --- CST Calculation --- p.11 / Chapter 2.3.1 --- Ramsey's Theory --- p.11 / Chapter 2.3.2 --- Gauge-including Atomic Orbitals (GIAO) Method --- p.13 / Chapter 2.4 --- Density Functional Theory (DFT) --- p.14 / Chapter 2.4.1 --- KS Theorem --- p.14 / Chapter 2.4.2 --- B3LYP - Hybrid DFT Functional --- p.16 / Chapter 2.5 --- Molecular Mechanic (MM) --- p.16 / Chapter 2.5.1 --- Basis Principle 一 Ball and Spring Model --- p.16 / Chapter 2.5.2 --- MM+ --- p.18 / Chapter 2.5.2.1 --- Bond Stretching --- p.18 / Chapter 2.5.2.2 --- Bond Bending --- p.19 / Chapter 2.5.2.3 --- Torsional Motion --- p.19 / Chapter 2.5.2.4 --- van der Waals Interaction --- p.19 / Chapter 2.5.2.5 --- Electrostatic Interaction --- p.20 / Chapter 2.5.2.6 --- Stretching-bending Interaction --- p.21 / Chapter 2.6 --- Isodesmic Reaction --- p.21 / Chapter CHAPTER THREE: --- METHODOLOGY AND EVALUATION --- p.23 / Chapter 3.1 --- Introduction --- p.23 / Chapter 3.2 --- Computational Method --- p.24 / Chapter 3.2.1 --- Evaluation of Different NMR Computation Level --- p.24 / Chapter 3.2.2 --- Computational Error 一 Round Off Error --- p.32 / Chapter 3.3 --- Local Structure Determination and Evaluation --- p.34 / Chapter 3.3.1 --- Methodology --- p.34 / Chapter 3.3.2 --- Definition of Local Structure --- p.37 / Chapter 3.3.3 --- Models used in Local Structure Determination --- p.37 / Chapter 3.3.3.1 --- Model without CST Modification (Mod-1) --- p.38 / Chapter 3.3.3.2 --- Models with CST Modification --- p.39 / Chapter 3.3.3.2.1 --- Model Using Correction Factors (Mod-2) --- p.39 / Chapter 3.3.3.2.2 --- Model Using Linear Equation (Mod-3) --- p.40 / Chapter 3.3.4 --- Evaluation - Me2P(S)C(OH)R1R2 --- p.41 / Chapter 3.4 --- Determination of Possible Conformation in Powder and Evaluation --- p.53 / Chapter 3.4.1 --- Introduction --- p.53 / Chapter 3.4.2 --- Methodology --- p.54 / Chapter 3.4.2.1 --- Preparation of Calibration Curve --- p.54 / Chapter 3.4.2.2 --- Determination of Possible Conformation Contributing to the Observed CST --- p.57 / Chapter 3.4.3 --- Evaluation --- p.59 / Chapter 3.5 --- Discussion --- p.72 / Chapter 3.5.1 --- Factors Affecting CST --- p.72 / Chapter 3.5.1.1 --- Inter-molecular Interaction --- p.72 / Chapter 3.5.1.1.1 --- O-H----S --- p.73 / Chapter 3.5.1.1.2 --- C-H----S --- p.78 / Chapter 3.5.1.1.3 --- van der Waals Forces --- p.80 / Chapter 3.5.1.2 --- Conformation --- p.81 / Chapter 3.5.2 --- Effect of Experimental Error on the Calculated Structure --- p.82 / Chapter 3.6 --- Summary --- p.84 / Chapter CHAPTER FOUR: --- APPLICATIONS --- p.86 / Chapter 4.1 --- Introduction --- p.86 / Chapter 4.2 --- Tetramethyldiphoshine Disulfide (TMPS) --- p.86 / Chapter 4.2.1 --- Local Structure --- p.87 / Chapter 4.2.2 --- Conformation --- p.92 / Chapter 4.3 --- "Carbon Compounds : 1,3,5-Trimethoxybenzene (1,3,5-TMB) and 1,4-Dimethoxybenzene (1,4-DMB)" --- p.97 / Chapter 4.3.1 --- Local Structure --- p.98 / Chapter 4.3.2 --- Conformation --- p.103 / Chapter 4.4 --- Conclusion --- p.110 / Chapter CHAPTER FIVE: --- CONCLUSIONS --- p.111 / APPENDIX --- p.114 / REFERENCES --- p.126

Hu Hong Bing. / "May 2004." / "13" in title is superscript. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Orientador: Carlile Campos Lavor / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica / Made available in DSpace on 2018-09-24T19:32:19Z (GMT). No. of bitstreams: 1 Alves_RafaelSantosdeOliveira_D.pdf: 2213205 bytes, checksum: 67a1681eb02b103974e57e3047edc755 (MD5) Previous issue date: 2013 / Resumo: O Problema de Geometria de Distâncias Moleculares (PGDM) consiste em encontrar uma imersão tridimensional de um grafo simples, não orientado, de forma que o peso nas arestas corresponda às distâncias inter-atômicas de uma molécula. Este é um problema de busca em um espaço contínuo, mas que pode ser discretizado sob algumas exigências, dando origem ao PGDM discretizado (PGDMD), que é solucionado usando informações sobre distâncias entre alguns átomos da molécula através de um algoritmo Branch and Prune (BP). Caso as distâncias sejam dadas por um conjunto de limites inferiores e superiores, temos um novo problema: o PGDMD intervalar (iPGDMD). A partir da interpretação geométrica deste último, propomos uma nova abordagem utilizando a Álgebra de Clifford a fim de tornar o algoritmo BP mais eficiente e de poder tratar algebricamente os problemas relacionados ao tratamento das distâncias intervalares / Abstract: The Molecular Distance Geometry Problem (MDGP) consists in finding a three dimensional embedding of simple, weighted, undirected graph such that the weight in the edges correspond to the inter-atomic distances of a molecule. This is a continuous search problem which can be discretized under some assumptions, yielding the Discretized MDGP (DMDGP), which is solved by a Branch and Prune (BP) algorithm using information about the distances among some atoms of the molecule. If the distances are given by a set of lower and upper bounds, a new problem arises: the interval DMDGP (iDMDGP). From a geometric interpretation of this problem, we propose a new approach, using Clifford Algebras, in order to improve the BP efficiency and treat algebraically the issues related to interval distances / Doutorado / Matematica Aplicada / Doutor em Matemática Aplicada

Lau Kai-Chi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.iii / Table of Contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Gaussian´ؤ3 Method --- p.1 / Chapter 1.2 --- The G3 Method with Reduced MΦ ller-Plesset Order and Basis Set --- p.2 / Chapter 1.3 --- The Gaussian-3X Method --- p.2 / Chapter 1.4 --- The Modified G2 Method --- p.3 / Chapter 1.5 --- Calculation of Thermodynamical Data --- p.3 / Chapter 1.6 --- Remark on the Location of Transition Structures --- p.4 / Chapter 1.7 --- Scope of the Thesis --- p.4 / Chapter 1.8 --- References --- p.4 / Chapter Chapter 2 --- "A Gaussian-2 and Gaussian-3 Study of Alkoxide Anion Decompositions. I. H2 and CH4 Eliminations of the Methoxide, Ethoxide, i-Propoxide, and t-Butoxide Anions" --- p.6 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.2 --- Methods of Calcuations --- p.7 / Chapter 2.3 --- Results and Discussion --- p.8 / Chapter 2.3.1 --- Nature of ion-neutral complex --- p.8 / Chapter 2.3.2 --- Initial bond cleavage of alkoxide anions --- p.9 / Chapter 2.3.3 --- Dissociation of alkoxide anions --- p.10 / Chapter 2.4 --- Conclusions --- p.23 / Chapter 2.5 --- Publication Note --- p.25 / Chapter 2.6 --- References --- p.25 / Chapter Chapter 3 --- A Gaussian-2 and Gaussian-3 Study of Alkoxide Anion Decompositions. II. Alkane Eliminations of (CH3)2(C2H5)CO- and (i-Pr)(C2H5)2CO- --- p.28 / Chapter 3.1 --- Introduction --- p.28 / Chapter 3.2 --- Methods of Calculations --- p.29 / Chapter 3.3 --- Results and Discussion --- p.29 / Chapter 3.3.1 --- Initial bond cleavage of alkoxide anions --- p.30 / Chapter 3.3.2 --- Dissociation of alkoxde anions --- p.31 / Chapter 3.3.3 --- General dissociation mechanism of alkoxide anions --- p.35 / Chapter 3.4 --- Conclusions --- p.37 / Chapter 3.5 --- References --- p.37 / Chapter Chapter 4 --- A Gaussian-3 Study of the Photoionization and Dissociative Photoionization Channels of Dimethyl Disulfide --- p.40 / Chapter 4.1 --- Introduction --- p.40 / Chapter 4.2 --- Methods of Calculations --- p.41 / Chapter 4.3 --- Results and Discussion --- p.41 / Chapter 4.3.1 --- Bond cleavage reactions --- p.44 / Chapter 4.3.2 --- Dissociation channels involving transition structures --- p.45 / Chapter 4.4 --- Conclusions --- p.48 / Chapter 4.5 --- References --- p.48 / Chapter Chapter 5 --- A Gaussian´ؤ3 Study of the Photodissociation Channels of Propylene Sulfide --- p.50 / Chapter 5.1 --- Introduction --- p.50 / Chapter 5.2 --- Methods of Calculations --- p.51 / Chapter 5.3 --- Results and Discussion --- p.51 / Chapter 5.3.1 --- The dissociation channels involving transition structures --- p.53 / Chapter 5.3.2 --- The dissociations of sulfur atom --- p.56 / Chapter 5.4 --- Conclusions --- p.58 / Chapter 5.5 --- References --- p.59 / Chapter Chapter 6 --- Thermochemistry of Phosphorus Fluorides: A Gaussian´ؤ3 and Gaussian´ؤ3X Study --- p.60 / Chapter 6.1 --- Introduction --- p.60 / Chapter 6.2 --- Methods of Calculations --- p.62 / Chapter 6.3 --- Results and Discussion --- p.62 / Chapter 6.3.1 --- Comparison of the G3 and G3X methods --- p.62 / Chapter 6.3.2 --- Assessments of the experimental results --- p.65 / Chapter 6.4 --- Conclusions --- p.71 / Chapter 6.5 --- References --- p.71 / Chapter Chapter 7 --- Conclusions --- p.74 / Appendix A --- p.75 / Appendix B --- p.78

Lee Ho-Lam. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 71-72). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Tables --- p.vi / List of Figures --- p.vii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Gaussian´ؤ3 Method --- p.1 / Chapter 1.2 --- "The G2++, a Modified Gaussian-2 Method" --- p.2 / Chapter 1.3 --- Density Functional Theory (DFT) --- p.2 / Chapter 1.4 --- Calculation of Thermodynamical Data --- p.3 / Chapter 1.5 --- Remark on the Location of Equilibrium and Transition Structures --- p.3 / Chapter 1.6 --- Natural Bond Orbital (NBO) Analysis --- p.3 / Chapter 1.7 --- Scope of the Thesis --- p.4 / Chapter 1.8 --- References --- p.4 / Chapter Chapter 2 --- Structures and Energetics of C3H6S+´Ø Isomers: A Gaussian-3 ab initio Study --- p.6 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Methods of Calculation --- p.8 / Chapter 2.3 --- Results and Discussion --- p.8 / Chapter 2.4 --- Conclusion --- p.21 / Chapter 2.5 --- Publication Note --- p.21 / Chapter 2.6 --- References --- p.22 / Chapter Chapter 3 --- A Gaussian-3 Study of the C3H6S Isomers and the Dissociation Channels of Diradical ´ØCH2CH2SCH2´Ø and Its Radical Cation ´ØCH2CH2SCH2+ --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Methods of Calculation --- p.25 / Chapter 3.3 --- Results and Discussion --- p.26 / Chapter 3.3.1 --- Structures and Energetics of C3H6S Isomers --- p.26 / Chapter 3.3.2 --- Dissociation Channels of ´ØCH2CH2SCH2´Ø and ´ØCH2CH2SCH2+ --- p.34 / Chapter 3.4 --- Conclusion --- p.40 / Chapter 3.5 --- Publication Note --- p.41 / Chapter 3.6 --- References --- p.41 / Chapter Chapter 4 --- Computational Study on the Electrocyclic Reactions of [16]Annulene --- p.43 / Chapter 4.1 --- Introduction --- p.43 / Chapter 4.2 --- Methods of Calculation --- p.45 / Chapter 4.3 --- Results and Discussion --- p.45 / Chapter 4.3.1 --- Reaction (1) --- p.49 / Chapter 4.3.2 --- Reaction (2) --- p.50 / Chapter 4.3.3 --- Reaction (3) --- p.52 / Chapter 4.3.4 --- Overall Reaction --- p.53 / Chapter 4.4 --- Conclusion --- p.54 / Chapter 4.5 --- Publication Note --- p.55 / Chapter 4.6 --- References --- p.55 / Chapter Chapter 5 --- Computational Study on the Structures and Stabilities of Some Hypothetical Silicon Nanotubes --- p.57 / Chapter 5.1 --- Introduction --- p.57 / Chapter 5.2 --- Model Design and Methods of Calculation --- p.59 / Chapter 5.3 --- Results and Discussion --- p.59 / Chapter 5.3.1 --- "Armchair (n,n) SiNTs" --- p.60 / Chapter 5.3.2 --- "Zigzag (n,0) SiNTs" --- p.61 / Chapter 5.3.3 --- "Chiral (n,m) SiNTs" --- p.65 / Chapter 5.3.4 --- Stabilities of SiNTs at Elevated Temperature --- p.69 / Chapter 5.4 --- Conclusion --- p.70 / Chapter 5.5 --- References --- p.71 / Chapter Chapter 6 --- Conclusion --- p.73 / Appendix A --- p.74 / Appendix B --- p.76 / Appendix C --- p.77

Orientador: Cláudio Cabello / Banca: Manoel Lima de Menezes / Banca: Ivo Mottin Demiate / Resumo: A fécula de mandioca (Manihot esculenta Crantz) contém aproximadamente 98 % de amido, em peso seco. Este amido é constituído por dois tipos de polissacarídeos: a amilose ( de 16 a 20 % ), com cadeias lineares de monômeros de glicose e peso molecular 1,5.105 a 1,0.106 Da; e amilopectina ( de 80 a 84 % ), com cadeias ramificadas e peso molecular 5,0.106 a 1,0.108 Da. A estrutura molecular desses polissacarídeos influi diretamente nas propriedades funcionais dos amidos, as quais são interessantes para diversos usos industriais. O principal objetivo desta pesquisa é avaliar e adaptar a técnica de separação de moléculas conhecida por cromatografia de permeação em gel, seguida da caracterização das frações coletadas na permeação e verificar as propriedades viscográficas do amido. Nesta principal técnica utilizada, conhecida também por cromatografia por exclusão de tamanho, as moléculas se separam de acordo com seus tamanhos e pesos moleculares. Sendo assim, moléculas maiores que os poros do gel, saem primeiro da coluna, enquanto moléculas de tamanhos intermediários aos dos poros do gel, saem no final da permeação. As amostras usadas neste trabalho foram féculas extraídas de sete etnovariedades de mandioca, que foram previamente tratadas e posteriormente solubilizadas em solventes adequados e injetadas na coluna de permeação contendo um gel de porosidade pré-determinada. Foi usado um sistema completo para permeação em gel, contendo colunas, géis, coletor automático das frações permeadas, bomba peristáltica, kit de proteínas e carboidrato padrão, dentre outros acessórios fornecidos pela Amersham Pharmacia Biotech. Empregou-se solventes P.A. e enzima pura (Sigma-Aldrich); equipamento analisador de carbono (TOC), marca Shimadzu e espectrofotômetro UV-visível com varredura de 190 a 1100 nm, marca Varian... / Abstract: Cassava starch ( Manihot esculenta Crantz ) contains approximately 98 % of starch in dry weight. This starch is constituted of two polysaccharide: amylose ( 16 to 20% ), with lineal chains of glucose monomers and molecular weight 1,5.105 to 1,0.106 Da; and amylopectin ( 80 to 84% ), with ramified chains and molecular weight from 5,0.106 to 1,0.108 Da. The molecular structure of these polysaccharides influences directly the functional properties of the starches, which are interesting for several industrial uses. The main objective of this research is to evaluate and to adapt the technique of separation of molecules known by gel permeation chromatography, followed by the characterization of the fractions collected in the permeation and to verify the viscographic properties of the starch. In this main used technique, also known by size exclusion chromatography, the molecules are separated in agreement with sizes and molecular weights. So, molecules larger than the pores of the gel, leave the column first, while molecules of intermediary sizes come out in the end of the permeation. The samples used in this work were starches extracted from seven cassava ethnovarieties, that were previously treated and then dissolved in appropriate solvents and injected in the permeation column that was filled with a gel of defined porosity. A complete system for gel permeation was used, constituted of columns, gels, automatic collector, peristaltic pump, kit of proteins and standard carbohydrate, among other accessories supplied by Amersham Pharmacia Biotech. Solvents (for analysis) and pure enzyme (Sigma-Aldrich) were used; equipment to analyze organic carbon (TOC), from Shimadzu and UV-visible spectrophotometer with scanning from 190 to 1100 nm, from Varian were employed... / Mestre

Parâmetros teóricos obtidos pela otimização de geometria da estrutura molecular em fase gasosa com o método quântico semi-empírico PM3, foram usados para correlacionar constantes de partição (log Poct; log Pc16 e log Pcic) para uma série de 700 solutos, considerando como referência as LSER obtidas com os parâmetros experimentais dos solutos: acidez (Σα2), basicidade (Σβ2), e dipolaridade/polarizabilidade (π2) de ligação de hidrogênio; refração molar de excesso (R2) e volume característico (Vx). Os parâmetros avaliados foram: as energias HOMO e LUMO; o momento de dipolo elétrico e as cargas atômicas parciais do hidrogênio mais positivo e do átomo mais negativo (classe IV - modelo CM1 ); e o índice de polarizabilidade como proposto por Famini e col.. Estes parâmetros teóricos, juntamente com Vx, são adequadas para serem utilizados em LSER na correlação dos valores de log P. Para a maioria dos solutos considerados, as quantidades eletrostáticas q+ , Ιq-Ι e µ descrevem adequadamente os termos de acidez, basicidade e dipolaridade de ligação de hidrogênio, o que não ocorre para solutos com mais de um polo positivo ou negativo relevante, como hidroquinona, nem para solutos como 2-nitrofenol com capacidade de formar ligação de hidrogênio intramolecular. As LSER para log Poct; log Pc16 e log Pcic com estes parâmetros teóricos são quimicamente consistentes. Cargas atômicas parciais, largamente usadas qualitativamente para descrever a reatividade de compostos e de grupos funcionais, podem ser usadas como descritor quantitativo de interações moleculares em estudos de solubilização, o primeiro estágio, que governa muitas reações químicas. / Semiempirical quantum theoretical parameters, obtained from PM3 geometry optimization method in gas-phase for a wide range of 700 solutes, were used to correlate experimental partition coeficients (log Poct; log Pc16 and log Pcyc), bearing as reference the LSER with experimentally derived parameters: Hydrogen bond acidity (Σα2), basicity (Σβ2) , and dipolarity/polarizability (π2); excess molar refraction and characteristic volume (Vx). Theoretical quantities tested includes: HOMO and LUMO energies; class IV, CM1 model atomic partial charges (q+ and Ιq-Ι) and dipole moment (µ); Famini\'s polarizability index (πF); and Vx. Those quantum derived quantities can successfully be used, jointly with Vx, to correlate log P values in the LSER approach. For most of the considered solutes, electrostatic quantities q+, Ιq-Ι and µ describes fairly well Hydrogen bond acidity, basicity and dipolarity terms, but do not describe hydrogen bond terms for solutes with more than one relevant positive or negative centers, like hydroquinone, nor solutes like 2-nitrophenol wich forms intramolecular hydrogen bond when in condensed phases. LSER with those theoretical parameters for log Poct, log Pc16 and log Pcic are chemically consistent. Atomic partial charges, widelly used to describe compounds and functional group reactivity in a qualitative way, can be used as a quantitative descriptor of molecular interactions in solubility, the first step wich drive a lot of chemical reactions.

Ligações de hidrogênio é um tema que tem despertado o interesse da comunidade científica desde o final do século XIX. Sua importância é enorme nos processos ligados à vida, como por exemplo na estabilização das estruturas de DNA e na manutenção da água em seu estado líquido. Várias metodologias teóricas foram desenvolvidas para o estudo de sistemas moleculares e das ligaçõas de hidrogênio, entre elas está o emprego de cálculos de teoria de perturbação de muitos corpos (MBPT). Uma alternativa aos cálculos moleculares com MBPT, que tem crescido em termos de aplicação e confiança, é o emprego da teoria do funcional da densidade (DFT). Nesta tese, calculamos propriedades de sistemas hidrogênio-ligados em clusters e líquidos, usando ambas as metodologias DFT e MBPT. Entre as propriedades consideradas estão constantes rotacionais, momentos de dipolo, energias de ligação, deslocamentos espectroscópicos quando da formação do complexo e espalhamento de luz. Parte desta tese é dedicada a salientar as diferenças entre as propriedades de um cluster otimizado e a estrutura de um líquido gerada por simulação de Monte Carlo. Comparamos os resultados obtidos para o complexo uréia-água nestas duas situações e reforçamos o fato de que líquido e cluster são situações físicas distintas, cujas propriedades também são diferentes. Os sistemas estudados foram HCN, CH IND. 3CN, HC IND. 3N, HC IND. 2NC, HCN...H IND. 2O, CH IND. 3CN...H IND.2O, (CH IND. 3) IND.3CCN...H IND. 2O e (NH IND. 2) IND. 2CO...H IND. 2O. Dos resultados obtidos nesta fase, verificamos que DFT é de fato uma alternativa completamente viável para a obtenção de propriedades de moléculas e biomoléculas hidrogênio-ligadas. / Hydrogen bonding is a topic of interest in the scientific community since the end of the XIX century. Its importance is enormous in processes related to life as, for example, the stabilization of DNA structures and the maintenance of water in its liquid state. Several theoretical methodologies were developed to study molecular systems and hydrogen bonds, among them is the use of many-body perturbation theory (MBPT). An alternative to MBPT, that has gained confidence, is the employment of the density functional theory (DFT). In the present thesis we calculate properties of hydrogen-bonded systems in clusters and liquids using both methodologies, DFT and MBPT. Among the properties considered are rotational constants, dipole moments, biding energies, spectroscopic shifts upon complex formation and light scattering. Part of this thesis is dedicated also to point out the difference between the properties of an optimized cluster and a liquid structure generated by Monte Carlo simulation. We compare the results obtained for the urea-water complex in these two situations and reinforce the fact that liquid and cluster are different physical situations, whose properties are also different. The systems studied were HCN, CH IND.3CN, HC IND.3N, HC IND.2NC, HCN H IND.2O and (NH IND.2)IND.2CO H IND.2O. from the results obtained in this thesis, we verify that DFT is indeed feasible to obtain properties of hydrogen bonded molecules and biomolecules.

O objetivo deste trabalho é descrever a estrutura eletrônica da espécie diatôrnica BeMg, utilizando métodos ab initio multiconfiguracionais. A primeira descrição teórica da espécie BeMg foi feita por Chiles e Dykstra em 1982, empregando os métodos SCF, CCD e CEPA. Naquele trabalho, os autores propuseram que a estrutura eletrônica do BeMg seria intermediária entre a apresentada pelas espécies Be2 e Mg2. Em 1994, Boldyrev et al. empregaram o método QCISD e conjuntos de bases atômicas do tipo 6 - 311 + G* para calcular a distância de equilíbrio do BeMg. Até onde sabemos, não existe nenhum outro estudo téorico, nem experimental, sobre esta espécie. Apesar dos esforços anteriores, devido à natureza dos átomos envolvidos, para descrever com maiores detalhes e precisão não somente o estado fundamental, mas também diferentes estados eletrônicos excitados, é necessário empregar métodos ab initio multiconfiguracionais, fato explicitamente reconhecido por Boldyrev et al. Em 1994. No presente trabalho, as curvas de energia potencial para os estados eletrônicos energeticamente mais baixos, que correlacionam com os primeiros quatro canais de dissociação, da espécie BeMg foram descritas teoricamente empregando conjunto de bases atômicas do tipo cc-pVQZ e funções de onda do tipo CASSCF/MRCI. Todos os orbitais de valência, além de um conjunto adicional de funções de correlação do tipo s e p foram incluídos no espaço ativo. Diversas constantes espectroscópicas também foram calculadas para os estados eletrônicos selecionados. O estado fundamental foi caracterizado como de simetria 1Σ+ e fracamente ligado (De = 0,05 eV), possuindo consequentemente uma distância internuclear de equihbrio relativamente longa (3, 30 Å, ωe = 44, 2 cm-1). É interessante notar que nos trabalhos anteriores a distância internuclear de equilíbrio do estado fundamental foi calculada com sendo 4, 5 Å e 5,1 Å, por Chiles e Dykstra e Boldyrev et al., respectivamente. Os dois primeiros estados excitados são o a3II (Re = 2,416 Å, Te = 11029 cm-1) e o b3 Σ+ (Re = 2,578 Å, Te = 11058 cm-1), ambos com energia de dissociação igual a 1,28 eV. / The first theoretical description of BeMg (using the SCF, CCD, and CEPA methods) was done by Chiles and Dykstra in 1982, when it was proposed that its electronic structure would be intermediate to Be2 and Mg2. In 1994, Boldyrev et al., using the QCISD method and 6 - 311+G* basis sets, presented other results on this diatomic species. To the best of our knowledge, there are no other study about this diatomic species. However, due to the nature of the atoms involved, it is necessary to employ more sophisticated theoretical methods to describe BeMg accurately. In this study, potential energy curves for the lowest-lying electronic states correlating with the first four dissociation channels were determined using the cc-p VQZ basis sets and CASSCF /MRCI wave functions. All valence orbitals plus one set of s and p correlating functions were included in the active space. A whole set of spectroscopic constants completes the characterization of each state. In its ground state (X1Σ+) BeMg is weakly bond (De = 0.05 eV), and consequently has a long internuclear equilibrium distance (Re = 3.30 Å, we = 44.2cm-1). It is interesting to note that in previous theoretical works, the internuclear equilibrium distance was calculated to be around 4.5 Å and 5.1 Å. The first two excited states are an a3II (Re = 2.416 Å, Te= 11029 cm-1) and a b3Σ+ (Re = 2.578 Å, Te= 11058 cm-1), with the same dissociation energy, 1.28 eV.

The vibrational potential energy surfaces in electronic ground and excited states of several ring molecules were investigated using several different spectroscopic methods, including far-infrared (IR), Raman, ultraviolet (UV) absorption, fluorescence excitation (FES), and single vibronic level fluorescence (SVLF) spectroscopies. Based on new information obtained from SVLF and millimeter wave spectra, the far-IR spectra of coumaran were reassigned and the one-dimensional ring-puckering potential energy functions for several vibrational states in the S0 ground state were determined. The barrier was found to be 154 cm-1 and the puckering angles to be ± 25°, in good agreement with the millimeter wave barrier of 152 cm-1 and puckering angles of ± 23°. Moreover, the UV absorption and FES spectra of coumaran allowed the one-dimensional ring-puckering potential energy functions in the S1 excited state to be determined. The puckering barrier is 34 cm-1 for the excited state and the puckering angles are ± 14°. Several calculations with different basis sets have been carried out to better understand the unusual vibrational frequencies of cyclopropenone. It was shown that there is strong interaction between the C=O and symmetric C-C stretching vibrations. These results differ quantitatively from a previous normal coordinate calculation and interpretation. The vapor-phase Raman spectrum of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene was analyzed and compared to the predicted spectrum from DFT calculations. The spectrum further shows it has D2h symmetry, in which the skeletons of both rings are planar. The infrared and Raman spectra of vapor-phase and liquid-phase 1,4-benzodioxan and 1,2,3,4-tetrahydronaphthalene were collected and the complete vibrational assignments for both molecules were made. Theoretical calculations predicted the barriers to planarity to be 4809 cm-1 for 1,2,3,4-tetrahydonaphthalene and 4095 cm-1 for 1,4-benzodioxan. The UV absorption, FES, and SVLF spectra of both molecules were recorded and assigned. Both one and two-dimensional potential energy functions of 1,4-benzodioxan for the ring-twisting and ring-bending vibrations were carried out for the S0 and S1(π,π*) states, and these were consistent with the high barriers calculated for both states. The low-frequency spectra of 1,2,3,4-tetrahydronaphthalene in both S0 and S1(π,π*) states were also analyzed.