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.

Presented thesis focuses on the study of transport properties of two intermetallic compounds, CeRhSi3 and CeCuAl3, under high external pressure. High-pressure dependence of previously reported pressure induced superconductivity in CeRhSi3 is studied closely up to 4.6 GPa, focusing on the, so-far-unstudied, pressure region above 3 GPa. After reaching maximal value at 2.9 GPa, the critical temperature of superconducting transition is gradually suppressed by further pressure application. Extensive search for possible pressure induced superconductivity in CeCuAl3 is conducted, employing solid-pressure-medium Bridgman anvil cells with theoretical pressure limit of 12 GPa. No pressure induced superconductivity is observed up to 4.5 GPa and down to 8 mK. Additionally, a calibration study of three liquid pressure exchange media from Daphne Oil 7000 series is carried out in order to advance high pressure experimental techniques. Comprehensive results about hydrostaticity, solidification, pressure drop and compressibility of individual pressure media are presented.

This thesis is focused on study of the vibron state in Ce intermetallics. The presence of a vibron state is a consequence of an enhanced magneto-elastic interaction, between phonons and 4f electrons of the Ce ion. The magneto-elastic interaction is usually weak and can be neglected, but here in CeAl2, CePd2Al2, CeCuAl3 and CeAuAl3 is considered to be strong enough, which leads to a bound state called the vibron state. A well determined crystal structure of these compounds is a necessary prerequisite to discuss this unique behaviour. Therefore our investigation is performed on the following levels: A crystal structure study of (Ce,La)Pd2Al2-xGax and CePt2Al2, by low temperature and high temperature X-ray powder diffraction; Investigation of bulk and transport properties of a CePt2Al2 single crystal using the specific heat, magnetisation and electrical resistivity measurements; Symmetry analysis of phonon modes and angular momentum operators in the model Hamiltonian, based on group theory; And finally the study of phonon dispersion curves in CePd2Al2 and LaPd2Al2 single crystals using inelastic X-ray scattering. All these results and preformed analyses lead to the following conclusions: The CePd2Al2 and LaPd2Al2 are incongruently melting phases. We found and described the way which has allowed us to...