Made available in DSpace on 2016-12-12T20:15:50Z (GMT). No. of bitstreams: 1 Iara Maite Campestrini.pdf: 1744610 bytes, checksum: 71e01f191ae9fa061c877988b0114787 (MD5) Previous issue date: 2013-07-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In order to increase the efficiency of magneto-optical traps, yielding a greater number of trapped atoms and long lifetimes, the effect of lightinduced desorption atom source emerges as an adjuvant and no thermal atoms. A prior experimental investigation (FRITSCH, 2011) showed that the number of rubidium atoms trapped increases when a light desorption focuses on the inner walls of the chamber imprisonment, whose material is stainless steel. The light desorption is applied from an incandescent lamp with power equal to 60 mW. The experimental data are adjusted and parameters are determined from the trap, in case of absence of light. Thus, the theoretical model proposed by Zhang et al. (2009) is applied, describing the increase of the number of atoms in the magneto-optical trap when the light desorption is triggered. In this setting, the rate of desorption and adsorption coefficient is estimated at 5x1017 atoms per second and 55 s-1. The combination of this model with that proposed by Monroe et al. (1990), in case of absence of light, perfectly describes the experimental curve generated when the mechanism for obtaining the magneto-optical trap and light desorption are actuated simultaneously. Furthermore, a theoretical prediction for the desorption rate, the rate of charging of magneto-optical trap and maximum number of atoms trapped on the basis of light desorption power is shown graphically. / Com o intuito de aumentar a eficiência das armadilhas magnéto-ópticas, obtendo-se um número maior de átomos aprisionados e longos tempos de vida, o efeito de dessorção atômica induzida por luz surge como uma fonte coadjuvante e não térmica de átomos. Uma investigação experimental prévia (FRITSCH, 2011) comprovou que o número de átomos de rubídio armadilhados aumenta quando uma luz de dessorção incide sobre as paredes internas da câmara de aprisionamento, cujo material é de aço inoxidável. A luz de dessorção aplicada é proveniente de uma lâmpada incandescente com potência igual a 60 mW. Os dados experimentais são fitados e os parâmetros da armadilha são determinados, para o caso sem luz. Com isso, o modelo teórico proposto por Zhang et al. (2009) é aplicado, descrevendo muito bem o incremento do número de átomos presentes na armadilha magnéto-óptica quando a luz de dessorção é acionada. Desse ajuste, a taxa de dessorção e o coeficiente de adsorção são estimados em 5x1017 átomos por segundo e 55 s-1. A união desse modelo com o proposto por Monroe et al. (1990), para o caso sem luz, descreve perfeitamente a curva experimental gerada quando o mecanismo para a obtenção da armadilha magnéto-óptica e a luz de dessorção são acionados simultaneamente. Além disso, uma previsão teórica para a taxa de dessorção, a taxa de carregamento da armadilha magnéto-óptica e o número máximo de átomos aprisionados em função da potência da luz de dessorção é mostrada graficamente.

<p dir="ltr">Laser-induced acoustic desorption (LIAD) is an evaporation technique that allows for thermally labile, nonvolatile neutral compounds to be vaporized without the need for derivatization or excessive heating. After a thin coating of a sample is applied to a titanium foil, the opposite side of the foil is subjected to laser irradiation to desorb neutral compounds from the opposite side into the gas phase. LIAD shows great potential for facilitating the analysis of a wide variety of compounds when coupled with molecular rotational resonance (MRR) spectroscopy. In this work, a few model compounds were chosen based on previous research to optimize the sample preparation and foil deposition methods for LIAD/MRR spectroscopy. One possible strategy to maximize the MRR signal is attempting to generate amorphous samples on the foils instead of ordered, crystalline samples. Changing the solvents used for dissolution of the compounds and freeze-drying the sample before deposition were also investigated.</p>

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<p>  </p> <p>Mass spectrometry (MS) is a powerful tool for the molecular-level characterization of complex mixtures. It is susceptible, selective, versatile, and fast. MS provides molecular weight information for the ionized analytes based on their mass-to-charge (<em>m/z</em>) ratios. Elemental compositions of the ionized analytes can be provided by MS operated at high resolution. In addition, MS provides invaluable information through tandem mass spectrometric approaches. Tandem mass spectrometry (MSn, n ≥ 2, where n is the number of ion-separation steps) utilizing collision-activated dissociation (CAD) has proven especially effective for elucidating the structures of individual compounds in complex mixtures. MS can be coupled with various external desorption/ionization methods. Laser-induced acoustic desorption (LIAD) is a technique that enables the evaporation of nonvolatile and thermally labile compounds into a mass spectrometer from the surface of the metal foil. LIAD is a soft evaporation technique that is a great companion for MS because it causes minimal fragmentation to the desorbed neutral molecules. LIAD can also be coupled with instruments other than mass spectrometers, such as molecular rotational resonance (MRR) spectrophotometer as a versatile evaporation technique. </p> <p>This dissertation focuses on research using high-resolution tandem mass spectrometric methods for the structural characterization of isomeric cations of asphaltene model compounds. The fragmentation behaviors of seven isomeric n-pentylquinoline radical cations are studied. Mechanisms for the formation of several fragment ions are also discussed based on quantum chemical calculations. Additionally, a novel suspension spin coating method is reported to improve LIAD performance. Further discussed in the dissertation is the endeavor of expanding the field of LIAD applications to MRR spectroscopy.</p>