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The electronegativities of -SF���, -CF���SO���, and -SO���F have been measured with gas phase X-ray photoelectron spectroscopy. Of these three groups previously measured values were found only for -SF���. The electronegativities of -Cl, -Br, -CF���, and -CF���, were concurrently measured to determine how the findings of this research compare with other experimental values found in the literature. Our experimental electronegativities for -SF���, -CF���SO���, and -SO���F are 2.81 �� 0.12, 2.49 �� 0.09, and 2.92 �� 0.12 respectively. The electronegativity of -CF���, currently measured (2.78 �� 0.08) is significantly lower than other experimental values. The electronegativity of -SF��� is in agreement with other experimental values. The experimental electronegativities are compared with theoretical values calculated based on the assumption of Electronegativity Equalization and based on Mulliken's definition of electronegativity. It is found that the electronegativities calculated with Electronegativity Equalization are higher than the experimental values currently measured, and those calculated with Mulliken's definition are lower than the experimental values. / Graduation date: 1999

<p> This thesis presents a study of the roles of ligands on silicon in two parts.</p> <p> In Part A, the relationship between the β-effect - the ability of a silyl group to stabilize a carbocation β to silicon, and the electron-withdrawing ability of the ligands on silicon was examined. The bromination of a series of (E)-β-silylstyrenes was chosen as a way to quantify the β-stabilization. The degree of syn-addition of bromine to (E)-β-silylstyrene was used as a measure of the stabilizing ability of the silyl group.</p> <p> The bromination of a series of four (E)-β-silylstyrenes was investigated [ligands on silicon: (SiMe3O)3; (CH3COO)3; (CCl3COO)3; (CF3COO)3]. It was found that the degree of syn-addition decreases as the silyl group electronegativity increases. Combined with the results previously obtained in our lab, two linear relationships between the degree of syn-addition and the silyl group electronegativity were observed in two groups of (E)-β-silylstyrenes [Group A, ligands on silicon: Me3-nXn, n = 1-3, X= Cl, F and (MeO)3; (Me3SiO)3 and Group B, (CH3COO)3; (CCl3COO)3; (CF3COO)3; (p-MeOPhO)3; (PhO)3; (p-ClPhO)3]. The degree of syn-addition was found to be more sensitive towards the group electronegativity for compounds in Group B. It was also found that, as the group electronegativity increases, the α-SiCH 1H and 29Si NMR chemical shifts of compounds in Group A decrease. In contrast, the α-SiCH 1H and 29Si NMR chemical shifts of compounds in Group B tend to increase.</p> <p> In Part B, a series of hydrosilanes were studied and their reactivities in iodination were found to be in the order: CH3SiH(OEt)2 > PMHS > CH3SiHCl2.</p> <p> The behavior of these organosilicon compounds is discussed in terms of the structural features of the silyl groups - the ligands on silicon.</p> / Thesis / Master of Science (MSc)

Hexagonal boron nitride (h-BN) thin films are deposited by plasma enhanced chemical vapor deposition (PECVD). Effects of heat treatment and source gases on the structure and physical properties are investigated. Chemical bonding is analyzed in comparison with the better understood isoelectronic carbon compound, graphite. It seems that the basic difference between h-BN and graphite arises from the different electronegativities of boron and nitrogen atoms. Optical absorptions in UV-visible range for crystalline and amorphous structures are outlined. The expressions used for the evaluation of mechanical stress induced in thin films are derived. The deposited films are considered to be turbostratic as they do not exhibit the characteristic optical absorption spectra of a crystal. A new system, stylus profilometer, is implemented and installed for thin film thickness and mechanical stress measurements. Hydrogen atom density within the films, estimated from FTIR spectroscopy, is found to be a major factor affecting the order and mechanical stress of the films. Heat treatment of the films reduces the hydrogen content, does not affect the optical gap and slightly increases the Urbach energy probably due to an increased disorder. Increasing the nitrogen gas flow rate in the source gas results in more ordered films. The virtual crystal of these films is detected to be unique. Relative bond concentrations of the constituent elements indicate a ternary boron-oxygen-nitrogen structure. The physical properties of h-BN such as high resistivity and wide band gap seem suitable for optoelectronic applications such as gate dielectrics in thin film transistors and light emitting devices in the blue region.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18098号 / 理博第3976号 / 新制||理||1573(附属図書館) / 30956 / 京都大学大学院理学研究科化学専攻 / (主査)教授 吉村 一良, 教授 北川 宏, 教授 寺西 利治 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

O método de equalização da eletronegatividade (Electronegativity Equalization Method, EEM), fundamentado em teoria do funcional da densidade eletrônica, foi combinado à aproximação de Born generalizada para moléculas (Generalized Born, GB), e denominado GBEEM (Dias et al., 2002). Os momentos de dipolo permanente no vácuo e em meio condensado (constante dielétrica ~ 80), e distribuições de cargas atômicas, mostraram boa concordância com modelo SM5.4 baseado em cargas CM1 em nível PM3 (12 moléculas, correspondendo a 29 cargas atômicas). Este resultado é interessante devido à simplicidade inerente do GBEEM e seu baixo custo computacional. Uma nova parametrização das durezas e eletronegatividades foi feita com o objetivo de melhorar a distribuição de cargas atômicas em moléculas isoladas em relação ao modelo CM1. Um conjunto de 250 estruturas/cargas PM3/CM1 de moléculas neutras pertencentes a 13 funções orgânicas foi utilizado como alvo na parametrização, utilizando uma metodologia Algoritmo Genético/Simplex de pesquisa de mínimos (Menegon et al., 2002). Boa concordância entre os modelos foi obtida. A validação da parametrização e do EEM foi efetuada usando moléculas bifuncionais (tetrapeptídeo e trisacarídeo) mostrando também boa concordância e robustez. Entretanto, a análise do momento de dipolo permanente das 250 moléculas mostrou uma séria limitação do EEM, e portanto do GBEEM, apesar da boa concordância entre as cargas EEM e CM1. O EEM superestimou os momentos de dipolo. Tal fato pode decorrer de vários fatores, dentre os quais, o truncamento da expansão nas cargas atômicas e ausência de tratamento explícito de interação de troca (exchange). Foi sugerida uma aproximação que restringe a transferência de carga entre grupos na molécula que contornou a limitação do método na predição de momentos de dipolo no vácuo e meio condensado (Shimizu et al., 2004). Com base nos recentes resultados, foi desenvolvido um modelo de solvatação baseado no GBEEM e no modelo de Floris-Tomasi. A calibração foi feita com um conjunto de 62 moléculas neutras (13 grupos funcionais) tendo como alvo as energias livres de hidratação experimentais. Os resultados apresentaram um desvio médio absoluto de 0,71 kcal/mol em relação aos valores experimentais. / The electronegativity equalization method (EEM), founded on density functional theory (DFT), has been combined to the generalized Born approximation (GB) for molecules, and called GBEEM (Dias et al., 2002). The permanent dipole moment in vacuum and condensed phase (dieletric constant ~ 80), and atomic charges distributions, have shown good agreement with SM5.4 solvation model based on CM1 charges at PM3 level (12 molecules, corresponding to 29 atomic charges). This result is interesting due the simplicity of GBEEM and its low computational cost. A new parameterization of the hardness and electronegativities was done with the aim to improve the atomic charges distribution on isolated molecules in comparison to CM1 model. The training set with 250 PM3/CM1 structures/charges of neutral molecules in 13 different organic functions was employed as target in the parameterization. A new optimization approach composed of Genetic and Simplex algorithms was used to fit parameters (Menegon et al., 2002). Good agreement between the models was found. The validation of parameterization and EEM was done using bifunctional molecules (tri-glucose and tetra-peptide) showing good agreement and robustness. However, analysis of permanent dipole moments of 250 molecules shown a serious caveat of EEM and GBEEM, beside the good agreement between EEM and CM1 charges. EEM has overestimated the dipole moments. Such result may be due to the truncated expansion in atomic charges and lacking of explicit treatment of exchange interaction. A new approximation was proposed constraining the charge transfer between groups within the molecule. This approximation corrected the caveat of EEM in the prediction of dipole moments in vacuum and condensed phase (Shimizu et al., 2004). Based on these results, a new solvation model was developed founded in GBEEM and Floris-Tomasi model. The parameterization was done with a training set of 62 neutral molecules (13 functional groups) and experimental hydration free energies as target. This new solvation model has produced a mean absolute deviation, MAD, of 0.71 kcal/mol comparing to experimental data.

O método de equalização da eletronegatividade (Electronegativity Equalization Method, EEM), fundamentado em teoria do funcional da densidade eletrônica, foi combinado à aproximação de Born generalizada para moléculas (Generalized Born, GB), e denominado GBEEM (Dias et al., 2002). Os momentos de dipolo permanente no vácuo e em meio condensado (constante dielétrica ~ 80), e distribuições de cargas atômicas, mostraram boa concordância com modelo SM5.4 baseado em cargas CM1 em nível PM3 (12 moléculas, correspondendo a 29 cargas atômicas). Este resultado é interessante devido à simplicidade inerente do GBEEM e seu baixo custo computacional. Uma nova parametrização das durezas e eletronegatividades foi feita com o objetivo de melhorar a distribuição de cargas atômicas em moléculas isoladas em relação ao modelo CM1. Um conjunto de 250 estruturas/cargas PM3/CM1 de moléculas neutras pertencentes a 13 funções orgânicas foi utilizado como alvo na parametrização, utilizando uma metodologia Algoritmo Genético/Simplex de pesquisa de mínimos (Menegon et al., 2002). Boa concordância entre os modelos foi obtida. A validação da parametrização e do EEM foi efetuada usando moléculas bifuncionais (tetrapeptídeo e trisacarídeo) mostrando também boa concordância e robustez. Entretanto, a análise do momento de dipolo permanente das 250 moléculas mostrou uma séria limitação do EEM, e portanto do GBEEM, apesar da boa concordância entre as cargas EEM e CM1. O EEM superestimou os momentos de dipolo. Tal fato pode decorrer de vários fatores, dentre os quais, o truncamento da expansão nas cargas atômicas e ausência de tratamento explícito de interação de troca (exchange). Foi sugerida uma aproximação que restringe a transferência de carga entre grupos na molécula que contornou a limitação do método na predição de momentos de dipolo no vácuo e meio condensado (Shimizu et al., 2004). Com base nos recentes resultados, foi desenvolvido um modelo de solvatação baseado no GBEEM e no modelo de Floris-Tomasi. A calibração foi feita com um conjunto de 62 moléculas neutras (13 grupos funcionais) tendo como alvo as energias livres de hidratação experimentais. Os resultados apresentaram um desvio médio absoluto de 0,71 kcal/mol em relação aos valores experimentais. / The electronegativity equalization method (EEM), founded on density functional theory (DFT), has been combined to the generalized Born approximation (GB) for molecules, and called GBEEM (Dias et al., 2002). The permanent dipole moment in vacuum and condensed phase (dieletric constant ~ 80), and atomic charges distributions, have shown good agreement with SM5.4 solvation model based on CM1 charges at PM3 level (12 molecules, corresponding to 29 atomic charges). This result is interesting due the simplicity of GBEEM and its low computational cost. A new parameterization of the hardness and electronegativities was done with the aim to improve the atomic charges distribution on isolated molecules in comparison to CM1 model. The training set with 250 PM3/CM1 structures/charges of neutral molecules in 13 different organic functions was employed as target in the parameterization. A new optimization approach composed of Genetic and Simplex algorithms was used to fit parameters (Menegon et al., 2002). Good agreement between the models was found. The validation of parameterization and EEM was done using bifunctional molecules (tri-glucose and tetra-peptide) showing good agreement and robustness. However, analysis of permanent dipole moments of 250 molecules shown a serious caveat of EEM and GBEEM, beside the good agreement between EEM and CM1 charges. EEM has overestimated the dipole moments. Such result may be due to the truncated expansion in atomic charges and lacking of explicit treatment of exchange interaction. A new approximation was proposed constraining the charge transfer between groups within the molecule. This approximation corrected the caveat of EEM in the prediction of dipole moments in vacuum and condensed phase (Shimizu et al., 2004). Based on these results, a new solvation model was developed founded in GBEEM and Floris-Tomasi model. The parameterization was done with a training set of 62 neutral molecules (13 functional groups) and experimental hydration free energies as target. This new solvation model has produced a mean absolute deviation, MAD, of 0.71 kcal/mol comparing to experimental data.

Simulações de sais de carbonato fundidos pelo método de Dinâmica Molecular (MD) foram efetuadas com o modelo polarizável de cargas flutuantes (FC). O modelo de cargas flutuantes implementa os efeitos de polarização pelo método de Lagrangiano estendido, onde as variáveis extras são as próprias cargas parciais do íon poliatômico. O modelo FC foi parametrizado por meio de cálculos ab inito, aplicado ao ânion carbonato. Cálculos de Química Quântica ab initio foram utilizados para corroborar o modelo proposto para o ânion carbonato. Os sistemas investigados consistem em misturas de carbonatos alcalinos fundidos, Li2CO3/K2CO3, os quais são utilizados como eletrólitos em células a combustível. As simulações MD foram utilizadas para verificar o efeito da polarização dos ânions sobre a estrutura e dinâmica do líquido. Estudamos o efeito da inclusão de polarização sobre a condutividade do eletrólito. / Simulations of molten carbonate salts by the method of Molecular Dynamics (MD) have been performed with the fluctuanting charge (FC) model. The FC model implements the effect of polarization by using method of extended Lagrangian, where the extra variables are the partial charges of the poliatomic ion. The FC model was parametrized by ab inito calculations os a single carbonate anion. Quantum Chemistry calculations bave been used to corroborate the model for the carbonate anion. The investigated systems consist of alkaline carbonate mixtures, Li2CO3/K2CO3, which are used as electrolytes in fuel cells. MD simulations have been used to verify polarization effects on structure and dynamics of the liquid. We study the effect of including anion polarization on the condutivity of the electrolyte.

Simulações de sais de carbonato fundidos pelo método de Dinâmica Molecular (MD) foram efetuadas com o modelo polarizável de cargas flutuantes (FC). O modelo de cargas flutuantes implementa os efeitos de polarização pelo método de Lagrangiano estendido, onde as variáveis extras são as próprias cargas parciais do íon poliatômico. O modelo FC foi parametrizado por meio de cálculos ab inito, aplicado ao ânion carbonato. Cálculos de Química Quântica ab initio foram utilizados para corroborar o modelo proposto para o ânion carbonato. Os sistemas investigados consistem em misturas de carbonatos alcalinos fundidos, Li2CO3/K2CO3, os quais são utilizados como eletrólitos em células a combustível. As simulações MD foram utilizadas para verificar o efeito da polarização dos ânions sobre a estrutura e dinâmica do líquido. Estudamos o efeito da inclusão de polarização sobre a condutividade do eletrólito. / Simulations of molten carbonate salts by the method of Molecular Dynamics (MD) have been performed with the fluctuanting charge (FC) model. The FC model implements the effect of polarization by using method of extended Lagrangian, where the extra variables are the partial charges of the poliatomic ion. The FC model was parametrized by ab inito calculations os a single carbonate anion. Quantum Chemistry calculations bave been used to corroborate the model for the carbonate anion. The investigated systems consist of alkaline carbonate mixtures, Li2CO3/K2CO3, which are used as electrolytes in fuel cells. MD simulations have been used to verify polarization effects on structure and dynamics of the liquid. We study the effect of including anion polarization on the condutivity of the electrolyte.