<p> The ultraviolet absorption spectrum of oxalyl chloride-fluoride has been recorded under high resolution, and has been attributed to a superposition of the spectra of the cis isomer (which appears weakly) and the trans isomer. The ultraviolet spectra of the cis isomers of oxalyl bromide, oxalyl chloride and oxalyl fluoride have also been identified. With the help of theoretical calculations, discrete absorption in the ultraviolet spectrum of trans oxalyl chloride-fluoride has been attributed to the superposition of four systems: (a) the singlet-singlet and singlet-triplet transitions which involve promotion of an electron from the highest energy non-bonding orbital (n₁) to the lowest energy antibonding orbital (π₁*) and (b) the singlet-singlet and singlet-triplet transitions which involve promotion from n₁ to the second lowest energy antibonding π orbital (π₂*). The S-S and S-T, n₁ → π₁* transitions have been analyzed in detail. </p> <p> Theoretical calculations have been carried out which indicate that α,β diketones, promotion of an electron to the lowest energy antibonding skeletal orbital (σ₁*) produces states which have a tendency towards dissociation along the C-C bond. It has been postulated that the diffuseness of the high energy absorption spectrum results from such a molecular dissociation, the Aᵤ(π₁,π₁*) state being strongly predissociated by the Aᵤ(n₁,σ₁*) state while the Aᵤ(n₁,π₁*) state is strongly predissociated by the Aᵤ(π₁,σ₁*) state. </p> <p> It has been postulated that the fluid phases of glyoxal and biacetyl consist of an equilibrium mixture of these molecules in various degrees of aggregation (e.g., monomeric, dimeric, trimeric,...). An ultraviolet band system previously assigned to a second n → π* transitions of these molecules has been reassigned to the first n → π* transition of a polymeric species. Some evidence has been assembled which supports this hypothesis. </p> / Thesis / Doctor of Philosophy (PhD)

Orientador: Edison Bittencourt / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-15T12:07:07Z (GMT). No. of bitstreams: 1 Zangiacomi_MarcosHenrique_D.pdf: 1507466 bytes, checksum: 17472578194a52bea38f1fd549a47fb5 (MD5) Previous issue date: 2009 / Resumo: 0 mercado atual procura por materiais que apresentem boas propriedades ópticas, que satisfaçam os consumidores e os usuários em geral e que sejam de fácil manuseio e processabilidade. No geral, um polímero deve apresentar boas propriedades ópticas, resistência ao impacto e dureza, compatíveis com o seu uso como lentes oftálmicas. O processo de fabricação de lentes oftálmicas poliméricas por muito tempo foi feito por meio de processos térmicos (cura térmica, processo que ainda é usado), levando cerca de 20 horas ou mais na obtenção de lentes que não apresentassem problemas de trincas por diferença de propriedades no corpo da lente. Dessa forma a introdução da tecnologia de cura pela luz ultravioleta (UV) permitiu a obtenção de materiais com a mesma característica e até superiores aquelas obtidas através da cura térmica e com a vantagem da diminuição do tempo de processo, diminuindo de horas para minutos, resultando também em redução dos custos. Neste trabalho foram utilizados os monômeros e oligômeros listados a seguir: metil metacrilato de metila (MAM), 1,6-Hexanediol diacrilato (HDDMA), diacrilato uretano alifático tetrafuncional (Ebecryl 5129) e diacrilato epóxi bisfenol-A (Ebecryl 3700) e em cada formulação foi aplicado um sistema de fotoiniciadores (nomes comerciais) compostos por Darocur 1173, Irgacure 184, Irgacure 1300, Irgacure 2959 e Irgacure 250 e Irgacure 819. Os sistemas de fotoiniciadores foram formulados a base de 3% p/p sobre cada formulação, seguindo as orientações dos fornecedores e de resultados experimentais obtidos ao longo deste estudo, sendo o tempo de cura da formulação de 7 minutos. Foram analisadas as propriedades mecânicas relevantes que uma lente deve apresentar, entre elas, dureza e resistência ao impacto. Foram determinadas também as temperaturas de transição vítrea obtidas da formulação, e a resistência ao calor. Foram comparados com os diversos fotoiniciadores, e realizado um estudo inicial da cinética, bem como medidas as entalpias e conversões resultantes da polimerização na temperatura de trabalho de 100°C, utilizando-se um fotocalorímetro diferencial de varredura (DPC). / Abstract: The current market calls for materials presenting good optical properties which satisfy consumers and users in general and that can be easily handled and processed. Generally, a polymer must present good optical properties, impact resistance and hardness - all compatible in their use as ophthalmic lenses. For quite a long period of time, ophthalmic lenses manufacturing had been achieved by means of thermal processes (thermal curing), taking up to 20 hours to obtain lenses free of cracking and/or processing errors. In this manner, the introduction of ultraviolet light curing technology has allowed the production of materials with equal and even superior characteristics than those obtained through thermal curing, and with advantages in processing time (reduced from hours to minutes), as well as costs, which were also reduced. The following monomers and oligomers were utilized in this study: methyl methacrylate (MAM), 1,6-Hexanediol diacrylate (HDDMA), diacrylate tetra functional aliphatic urethane (Ebecryl 5129) and epoxy diacrylate bisphenol A (Ebecryl 3700-20 t). A system of photoinitiators composed by darocur 1173, Irgacure 184, Irgacure 1300, Irgacure 2959, Irgacure 250 and Irgacure 819 have been applied in each formulation. The photoinitiators systems have been formulated on a 3% p/p basis, following suppliers orientations and experimental results obtained throughout this study, with a 7-minute formulation curing time. The main mechanical properties a lens must present, such as acceptable harness and impact resistance, were analyzed in the study. Vitreous transition temperature, heat resistance and the evaluation of the photoinitiators in kinetics have been analyzed and studied, as well as the evolution of enthalpy during a 100°C polymerization process and formulation conversions by differential photocalorimetry distinguishing (DPC). / Doutorado / Ciencia e Tecnologia de Materiais / Doutor em Engenharia Química

The infrared, Raman and ultraviolet spectra of cyclopentanone, cyclopentanone -α,α,α',α'-d₄ and cyclopentanone-d₈ have been studied. The high resolution ultraviolet absorption spectra of the three isotopic species have been analysed in detail. The electronic transition has been identified as a single-singlet transition associated with ṉ→π* orbital electron promotion. The vibrational and rotational structures accompanying this electronic transition have been analysed and the results are in agreement with theoretical predictions. The geometry of the molecule in both ground and excited states has been calculated. In the excited state conformation, the oxygen atom is bent out of the plane of the three adjacent carbon atoms; there is a potential barrier of 705cm⁻¹ with respect to the oxygen out-of-plane bending vibration in the upper state. / Thesis / Doctor of Philosophy (PhD)