The infrared spectra of gaseous oxalyl fluoride, oxalyl chloride, and oxalyl chloride fluoride, and the Raman spectra of liquid oxalyl fluoride and liquid oxalyl chloride have been measured. A satisfactory analysis of these spectra has been obtained for all three molecules on the basis of the trans isomer. An I.B.M. 7040 digital computer has been programmed to calculate the fundamental frequencies, normal coordinates, Urey-Bradley force constants, and potential energy distributions in Urey-Bradley space. The two electronic band systems of oxalyl fluoride whose origins are located at 3082 Å and 3340 Å have been photographed in absorption under low resolution. These band systems have been assigned ¹Aᵤ←¹A_g and ³Aᵤ←¹A_g transitions respectively, and have been partially analyzed in terms of the vibrational energy levels associated with the combining electronic states. / Thesis / Doctor of Philosophy (PhD)

Density functional theory (DFT) calculations (using Becke's exchange in conjunction with Lee-Yang-Parr's correlation functional (BLYP) and Becke's three-parameter hybrid DFT/HF method using Lee-Yang-Parr's correlation functional (B3LYP)) have been carried out to investigate the structure, dipole moment, and vibrational spectrum of azulene. Structural parameters obtained by both BLYP/6-31G* and B3LYP/6-31G* geometry optimization are in good agreement with available experimental data and show clearly the aromatic nature (bond equalization), a property the Hartree-Fock theory fails to describe correctly. The BLYP/6-31G* and B3LYP/6-31G* dipole moments are within experimental uncertainty and are in good agreement with results obtained from the much more expensive MP2 and MR-SDCI calculations. Most of the BLYP/6-31G* vibrational frequencies are in excellent agreement with available experimental assignments. On the basis of the calculated results, assignments of some missing frequencies in the experimental studies are proposed.

In this work we have investigated the electronic properties of several types of molecular systems involving a metallic element. Our motivation for such applications on metallic compounds was to obtain an accurate description of close lying electronic states, in which the relativistic effects of heavy atoms are known to be important. Thus various approaches and methods have been employed to treat these effects, including the multi-configurational method, with atomic pseudopotentials and large basis sets. In the first study, we have determined the properties of the low lying electronic states of the diatomic compounds MX, whose combinations in the solid phase produce ionic semi-conductor materials with piezoelectric properties. Based on highly correlated ab initio calculations, we have elucidated the common properties of the low lying electronic states of these diatomic compounds with eight valence electrons, which can be considered as precursors for piezoelectric effects in their solid phase. Based on our electronic structure calculations, we could identify among these diatomic compounds those who could lead to good candidates for piezoelectric effects. As the second application, we have determined the electronic structure and the spectroscopic constants for the ground state of the HZnF molecule and for the low lying electronic states of its diatomic fragments. This application was initiated and motivated by interesting and puzzling results on the close system HZnCl. Comforted by our experience with the previous studies, we used the pseudopotentials approach to obtain an accurate description of the low lying states of ZnH which could be satisfactorily compared with existing data. Next, the ZnF and ZnCl diatomic molecules have been studied with the same ansatz to reveal the properties of so far unknown electronic states. Finally, the potential energy surface of the ground state of HZnF has been determined, and several spectroscopic properties have been deduced

Dans cette étude, nous avons déterminé les propriétés électroniques de plusieurs types de composés moléculaires possédant un élément métallique. Notre motivation pour l'étude de tels systèmes était de montrer qu'il était possible d'obtenir une description précise d'états électroniques très proches en énergie, pour lesquels il est connu que les effets relativistes jouent un rôle important. Pour traiter ces effets nous avons mis en oeuvre différentes approches et méthodes, en particulier des méthodes multiconfigurationnelles, des pseudopotentiels atomiques et de grandes bases de fonctions. Dans une première étude nous avons déterminé les propriétés des états électroniques de plus basse énergie de composés diatomiques MX dont l'association en phase solide conduit à des composés semi-conducteurs présentant des propriétés piézoélectrique importantes. A l'aide de calculs électroniques incluant une large part de la corrélation électronique nous avons mis en évidence les propriétés communes à une famille de composés diatomiques possédant huit électrons de valence et qui peuvent être considérés comme précurseurs des solides piézoélectriques. Il a ainsi été possible d'identifier les couples diatomiques qui constituaient les meilleurs candidats pour une production d'effet piézoélectrique en phase solide. Dans la deuxième application, nous avons calculé la structure électronique et les constantes spectroscopiques de l'état fondamental de la molécule HZnF ainsi que les états de plus basse énergie des fragments diatomiques associés. Cette étude était motivée par une analogie avec un système voisin HZnCl dont les premiers états électroniques présentent des caractéristiques non complètement résolues. Après avoir validé notre approche sur l'étude de ZnH et comparé nos résultats à ceux d'études antérieures, nous avons entrepris la détermination de la structure électronique des molécules ZnF et ZnCl pour lesquelles nous avons pu identifier des états électroniques encore mal connus. Utilisant les résultats obtenus sur ZnH et ZnF, nous avons déterminé la surface d'énergie potentielle de l'état fondamental de HZnF et nous en avons déduit plusieurs grandeurs spectroscopiques caractérisant cet état / In this work we have investigated the electronic properties of several types of molecular systems involving a metallic element. Our motivation for such applications on metallic compounds was to obtain an accurate description of close lying electronic states, in which the relativistic effects of heavy atoms are known to be important. Thus various approaches and methods have been employed to treat these effects, including the multi-configurational method, with atomic pseudopotentials and large basis sets. In the first study, we have determined the properties of the low lying electronic states of the diatomic compounds MX, whose combinations in the solid phase produce ionic semi-conductor materials with piezoelectric properties. Based on highly correlated ab initio calculations, we have elucidated the common properties of the low lying electronic states of these diatomic compounds with eight valence electrons, which can be considered as precursors for piezoelectric effects in their solid phase. Based on our electronic structure calculations, we could identify among these diatomic compounds those who could lead to good candidates for piezoelectric effects. As the second application, we have determined the electronic structure and the spectroscopic constants for the ground state of the HZnF molecule and for the low lying electronic states of its diatomic fragments. This application was initiated and motivated by interesting and puzzling results on the close system HZnCl. Comforted by our experience with the previous studies, we used the pseudopotentials approach to obtain an accurate description of the low lying states of ZnH which could be satisfactorily compared with existing data. Next, the ZnF and ZnCl diatomic molecules have been studied with the same ansatz to reveal the properties of so far unknown electronic states. Finally, the potential energy surface of the ground state of HZnF has been determined, and several spectroscopic properties have been deduced

O espectro vibracional do monofluoracetileno (HCCF) e do monocloroacetileno (HCCCl) são calculados por meio de técnicas algébricas sob a hipótese de que eles resultam de uma simetria u(4) dada pela cadeia u(4) ⊃ so(4) ⊃ so(3). Os resultados são comparados com as 170 linhas vibracionais experimentais disponíveis para o HCCF e com as 23 disponíveis para o HCCCL. Os desvios médios encontrados de 7 cm-1 e 4 cm-1, respectivamente, estabelecem estes sistemas como os melhores exemplos de simetria dinâmica em Física Molecular até o momento. Numa outra aplicação de técnicas algébricas, tendo em mente aplicações que requerem a manipulação de diferentes representações irredutíveis, nós calculamos fórmulas fechadas e analíticas para os elementos de matriz dos geradores da álgebra simplética sp(4,C) atuando numa representação irredutível arbitrária da cadeia sp(4,C) ⊃ sp(2,C) ⊕sp(2, C), a qual está sendo utilizada no estudo do código genético. A base utilizada é ortogonal e é análoga à base de Gel\'fand- Tsetlin para as álgebras unitárias. / The vibrational spectrum of monofluoroacetylene (HCCF) and of monochloroacetylene (HCCCl) are calculated by means of algebraic techniques under the hypothesis that they result from a U(4) symmetry through the chain U(4) symmetry through the chain U(4) ⊃ O(4) ⊃ O(3). The results are compared with the 170 experimentally available vibrational lines for the HCCF and with the 23 experimentally available vibrational lines for the HCCCl. The mean square deviation is founded to be 7 cm-1 and 4 cm-1, respectivelly, establishing these spectra as the best examples of a dynamical symmetry reported in Molecular Physics so far. In another application of algebraic techniques, having in mind applications in which the algebraic handling of several different irreducible representations are necessary, we provide closed formulas for the matrix elements of the symplectic sp(4,C) Lie algebra on an arbitrary irreducible representation on the chain sp(4,C) ⊃ sp(2,C) ⊕ sp(2,C), which is being used in the study of the genetic code by Lie algebras. The used basis is orthogonal and analogous to the Gel\'fand- Tsetlin basis of unitary algebras.

O espectro vibracional do monofluoracetileno (HCCF) e do monocloroacetileno (HCCCl) são calculados por meio de técnicas algébricas sob a hipótese de que eles resultam de uma simetria u(4) dada pela cadeia u(4) ⊃ so(4) ⊃ so(3). Os resultados são comparados com as 170 linhas vibracionais experimentais disponíveis para o HCCF e com as 23 disponíveis para o HCCCL. Os desvios médios encontrados de 7 cm-1 e 4 cm-1, respectivamente, estabelecem estes sistemas como os melhores exemplos de simetria dinâmica em Física Molecular até o momento. Numa outra aplicação de técnicas algébricas, tendo em mente aplicações que requerem a manipulação de diferentes representações irredutíveis, nós calculamos fórmulas fechadas e analíticas para os elementos de matriz dos geradores da álgebra simplética sp(4,C) atuando numa representação irredutível arbitrária da cadeia sp(4,C) ⊃ sp(2,C) ⊕sp(2, C), a qual está sendo utilizada no estudo do código genético. A base utilizada é ortogonal e é análoga à base de Gel\'fand- Tsetlin para as álgebras unitárias. / The vibrational spectrum of monofluoroacetylene (HCCF) and of monochloroacetylene (HCCCl) are calculated by means of algebraic techniques under the hypothesis that they result from a U(4) symmetry through the chain U(4) symmetry through the chain U(4) ⊃ O(4) ⊃ O(3). The results are compared with the 170 experimentally available vibrational lines for the HCCF and with the 23 experimentally available vibrational lines for the HCCCl. The mean square deviation is founded to be 7 cm-1 and 4 cm-1, respectivelly, establishing these spectra as the best examples of a dynamical symmetry reported in Molecular Physics so far. In another application of algebraic techniques, having in mind applications in which the algebraic handling of several different irreducible representations are necessary, we provide closed formulas for the matrix elements of the symplectic sp(4,C) Lie algebra on an arbitrary irreducible representation on the chain sp(4,C) ⊃ sp(2,C) ⊕ sp(2,C), which is being used in the study of the genetic code by Lie algebras. The used basis is orthogonal and analogous to the Gel\'fand- Tsetlin basis of unitary algebras.

Research Doctorate - Doctor of Philosophy (PhD) / (**Note: this abstract is a plain text version of the author's abstract, the original of which contains characters and symbols which cannot be accurately represented in this format. The properly formatted abstract can be viewed in the Abstract and Thesis files above.**) The electronic structure and rovibrational spectroscopy of MH2, MHn+2, HMHen+ and MHen+2 (M = Li, Be, Na, Mg, K, Ca; n = 1, 2) have been investigated using correlated ab initio ansatz. In order to determine the efficacy of various electronic structure methods with respect to Group-I and II hydrides and helides, atomic properties of Li, Be,Na, Mg, K and Ca were calculated. Relativistically-corrected UCCSD(T) and ICMRCI(+Q) were deemed to be the most suitable ansatz with respect to both efficiency and accuracy. The lowest 2A1 and 2Σ- states of MH2 were found to be purely repulsive, in agreement with previous predictions. The main factor determining the structure and stability of the excited states of MH2 was the relative orientations and occupations of the valence p atomic orbital of M and the H2 1Ou orbital. The ground states of MHn+2 were found to be the result of the charge-quadrupole interaction between Mn+ and the H2 molecular subunit. The structures of the ground states of HMHe+ were extremely uxional with respect to the central bond angle co-ordinate. The ground state PESs of MHe+2 were also extremely sensitive to the ab initio ansatz by which they are modelled. The respective bonding of the H and He in both HMHe+ and HMHe2+ appeared to be charge-dependent in the case of Be, Mg and Ca. Despite the weak bonding observed for the Group-II hydrohelide and helide monocations, the corresponding dications each exhibit thermodynamically stable equilibria. The solution algorithm of von Nagy-Felsobuki and co-workers was employed in the calculation of vibrational and rovibrational spectra. This algorithm employed an Eckart-Watson Hamiltonian in conjunction with rectilinear normal co-ordinates. Vibrational and rovibrational Hamiltonian matrices were diagonalised using variational methods. This algorithm was extended so that the vibration transition moment integrals, and hence vibrational radiative properties, of linear triatomic molecules could be calculated. A method by which vibration-averaged structures are calculated was also developed and implemented. Analytical potential energy functions (PEFs) and dipole moment functions (DMFs) of (1A1)LiH+2, (1A1)NaH+2, (1A1)BeH2+2,(1A1)MgH2+2, (1Σ+g )BeHe2+2, (2Σ+)HBeHe2+, (1Σ+g )MgHe2+2 and (2Σ+)HMgHe2+ were developed using leastsquare regression techniques in conjunction with discrete ab initio grids. Vibrational structures and spectra of these species were subsequently calculated. In addition, the rovibrational spectra of (1A1)LiH+2, (1A1)NaH+2, (1A1)BeH2+2 and (1A1)MgH2+2 were calculated. For (1A1)LiH+2 and (1A1)LiD+2 , calculated rovibrational transition frequencies for J ≤ 10 and 0 ≤ K ≤ 3 were within ca. 0.1-0.2% of experimental values.

Research Doctorate - Doctor of Philosophy (PhD) / (**Note: this abstract is a plain text version of the author's abstract, the original of which contains characters and symbols which cannot be accurately represented in this format. The properly formatted abstract can be viewed in the Abstract and Thesis files above.**) The electronic structure and rovibrational spectroscopy of MH2, MHn+2, HMHen+ and MHen+2 (M = Li, Be, Na, Mg, K, Ca; n = 1, 2) have been investigated using correlated ab initio ansatz. In order to determine the efficacy of various electronic structure methods with respect to Group-I and II hydrides and helides, atomic properties of Li, Be,Na, Mg, K and Ca were calculated. Relativistically-corrected UCCSD(T) and ICMRCI(+Q) were deemed to be the most suitable ansatz with respect to both efficiency and accuracy. The lowest 2A1 and 2Σ- states of MH2 were found to be purely repulsive, in agreement with previous predictions. The main factor determining the structure and stability of the excited states of MH2 was the relative orientations and occupations of the valence p atomic orbital of M and the H2 1Ou orbital. The ground states of MHn+2 were found to be the result of the charge-quadrupole interaction between Mn+ and the H2 molecular subunit. The structures of the ground states of HMHe+ were extremely uxional with respect to the central bond angle co-ordinate. The ground state PESs of MHe+2 were also extremely sensitive to the ab initio ansatz by which they are modelled. The respective bonding of the H and He in both HMHe+ and HMHe2+ appeared to be charge-dependent in the case of Be, Mg and Ca. Despite the weak bonding observed for the Group-II hydrohelide and helide monocations, the corresponding dications each exhibit thermodynamically stable equilibria. The solution algorithm of von Nagy-Felsobuki and co-workers was employed in the calculation of vibrational and rovibrational spectra. This algorithm employed an Eckart-Watson Hamiltonian in conjunction with rectilinear normal co-ordinates. Vibrational and rovibrational Hamiltonian matrices were diagonalised using variational methods. This algorithm was extended so that the vibration transition moment integrals, and hence vibrational radiative properties, of linear triatomic molecules could be calculated. A method by which vibration-averaged structures are calculated was also developed and implemented. Analytical potential energy functions (PEFs) and dipole moment functions (DMFs) of (1A1)LiH+2, (1A1)NaH+2, (1A1)BeH2+2,(1A1)MgH2+2, (1Σ+g )BeHe2+2, (2Σ+)HBeHe2+, (1Σ+g )MgHe2+2 and (2Σ+)HMgHe2+ were developed using leastsquare regression techniques in conjunction with discrete ab initio grids. Vibrational structures and spectra of these species were subsequently calculated. In addition, the rovibrational spectra of (1A1)LiH+2, (1A1)NaH+2, (1A1)BeH2+2 and (1A1)MgH2+2 were calculated. For (1A1)LiH+2 and (1A1)LiD+2 , calculated rovibrational transition frequencies for J ≤ 10 and 0 ≤ K ≤ 3 were within ca. 0.1-0.2% of experimental values.