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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

PFI-ZEKE SPECTROSCOPY AND THEORETICAL CALCULATIONS OF TRANSITION METAL-AROMATIC HYDROCARBON COMPLEXES

Sohnlein, Bradford Raymond 01 January 2007 (has links)
Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their electronic states and corresponding molecular structures were determined by comparing the experimental spectra to quantum chemical calculations and Franck-Condon simulations. In this dissertation, the metal complexes of four different aromatic hydrocarbon ligands were studied: benzene (bz), naphthalene (np), biphenyl (bp) and 1-phenyl naphthalene (phnp). In these complexes, the metal atom or ion was determined to bind to either one or two -rings. Three different bonding schemes were observed in these complexes. A twofold bonding scheme was observed in M+/M-np (M = Sc, Y, Ti, Zr, Hf), while a sixfold bonding scheme was observed in Sc+/Sc-bz and M+/M-bz2 (M = Sc, Ti, V, Cr, Mo, W). In the metal-polyphenyl complexes (i.e. Sc-, La-, and Ti-bp and Sc-phnp), twelve-fold metal-ligand bonding occurred, sixfold to two -rings of the ligand. This twelve-fold bonding mechanism requires rotation of the -rings by ~ 42 o and bending of the -rings by 40 to 57 o to clamp the metal atom or ion between the two -surfaces. Although the ground state spin multiplicities of the bare metal atoms and ions varied quite extensively, the multiplicities of the metal complexes were determined to be either singlet or doublet, except for Sc+/Sc-bz, V+-bz2, Ti-np, and Zr-np, where the triplet or quartet spin multiplicities were favored. The low spin and relatively narrower range of electron-spin multiplicities in the complexes were the result of d orbital splitting, where the degeneracy of the d orbitals was broken. Thus, the valence electrons were paired in each metal d-based molecular orbital of the complex to form low-spin singlet or doublet spin states. Some complexes favored triplet and quartet multiplicities, because the energy difference between the two highest occupied molecular orbitals was smaller than the electron pairing energy.
72

Single photon double valence ionization of methyl monohalides

Roos, Andreas January 2014 (has links)
This thesis is based on experimental results from measurements on methyl halides at a photon energy corresponding to the He IIβ emission line. Double ionization processes involving the valence electrons of the molecules CH3F, CH3Cl and CH3I are studied by means of a magnetic bottle TOF-PEPECO spectrometer. Resulting double ionization data of these molecules suggest that mainly direct double photoionization is observed as a continuous energy sharing between the ejected electron pairs. As a mean to further understand the double ionization processes, a "rule of thumb", for double ionization in molecules, is applied to the data presented in the double ionization spectra. This is done in order to quantify the effective distance between the two vacancies created in the dications. It is found that the distance between the vacancies may be related to the bond distance between the carbon and halogen atoms. Further investigations call for quantum chemical calculations to scrutinize this hypothesis. / Det här examensarbetet är baserat på experimentella fotojonisations studier av metyl halider vid en fotonenergi motsvarande He IIβ emissionslinjen. Valenselektronerna i dubbeljonisations processerna för CH3F, CH3Cl och CH3I har studerats under användning av en så-kallad magnetisk flask TOF-PEPECO spektrometer. Resultaten av dessa mätningar visar att mestadels direkt dubbeljonisation processer före- kommer, där elektronerna delar kontinuerligt på energin som friges vid jonisationen. Den dubbla jonisa- tions processen är ytterligare studerad genom att tillämpa en tumregel för dubbeljonisation i molekyler, vilket ger en indikation av hur stort avståndet är mellan de två vakanserna som skapades när molekylerna joniserade. Resultaten från tumregeln visar att avståndet mellan vakanserna kan vara relaterade till bind- ningsavståndet mellan kol-atomen och halogen-atomen, i respektive metyl halogen. För att ytterligare bekräfta dubbeljonisations processerna i dessa molekyler, krävs kvantmekaniska beräkningar.
73

Multiphoton detachment of negative alkaline ions

Vinci, Natalia January 2001 (has links)
No description available.
74

The dissociative single and double ionization of some simple molecules by fast ion and VUV photons

Browne, Clive R. H. January 1998 (has links)
No description available.
75

Energies of rare-earth ion states relative to host bands in optical materials from electron photoemission spectroscopy

Thiel, Charles Warren. January 2003 (has links) (PDF)
Thesis (Ph. D.)--Montana State University--Bozeman, 2003. / Typescript. Chairperson, Graduate Committee: Rufus L. Cone. Includes bibliographical references (p. 361-380).
76

Intense field electron excitation in transparent materials

Modoran, Georgia C. January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 121-127).
77

Photoelectron spectroscopy of transition metal complexes

Cooper, Glyn January 1986 (has links)
No description available.
78

Absorção cooperativa de dois fótons em átomos frios / Cooperative absorption of two-photon in cold atoms

Edwin Eduardo Pedrozo Peñafiel 27 July 2011 (has links)
Neste trabalho estudamos a absorção cooperativa de dois fótons em processos de colisão entre átomos frios de sódio aprisionados. Efeitos não-lineares exigem amostras de alta densidade para ser observados. Redesenhamos nosso sistema experimental para conseguir amostras de 1012 átomos/cm3. As principais alterações foram a construção de um desacelerador Zeeman em configuração spin-flip, a implementação de bombeamento diferencial entre o forno e a câmara principal, assim como redesenhar o forno. A fim de compreender e melhorar os processos de medição utilizamos a técnica de fotoionização nos estados 32P1/2 e 32P3/2. Com esses dados conseguimos calcular a seção transversal de ionização para cada um desses estados, que está de acordo com valores reportados na literatura. Estes resultados mostram que o novo desenho do sistema permite um grande ponto de partida para a medição da absorção de dois fótons. Uma tentativa de medir a absorção de dois fótons foi feita. Um pequeno aumento no número de íons produzidos por unidade de tempo foi observada em uma região deslocada para o vermelho de cerca de 4,5 GHz de onde inicialmente se esperava ocorrer a transição. Isto motiva a aprofundar o estudo da absorção de dois fótons, já que provavelmente essa medida seja um indício da ocorrência desse fenômeno. Assim, tanto a medição da seção de choque dos estados 32P1/2 e 32P3/2 e a tentativa de medir a absorção de dois fótons, fornecem uma base sólida para conhecer qual é a melhor maneira de obter resultados mais decisivos no que diz respeito à absorção cooperativa de dois fótons, e as vantagens do nosso sistema em futuros experimentos. / In this work we study the cooperative two-photon absorption in collisional processes between cold trapped sodium atoms. Nonlinear effects require high density samples to be observed. We redesign our experimental system to achieve samples up to 1012 atoms/ cm3 .The key changes were building a spin-flip Zeeman slower, implementing differential pumping between the oven and the chamber and changing the oven´s design. In order to understand and improve the measurement processes we did photoionization from the states 32P1/2 e 32P3/2. With this data we could calculate the ionization cross section for each of these states, which is in agreement with values reported in the literature. These results show that the new design of the system allows a great starting point for measuring of two-photon absorption. An attempt to measure the absorption of two-photon was made. A small increase in the number of ions produced per unit time was observed in a region shifted to the red of about 4.5 GHz from where we initially expected the transition to occur. This probably indicates two-photon absorption. Thus, both the measurement of cross section of states and the attempt to measure the absorption of two photons, provide a solid foundation for understanding what is the best way to obtain more decisive results with regard to cooperative absorption, and the advantages of performance of our system in future experiments.
79

Experimental spectroscopic studies of metals with electron, ion, and optical techniques

Mäkinen, A. . (Ari ) 14 January 2014 (has links)
Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented.
80

Electron spectroscopy of atoms and molecules using synchrotron radiation, UV radiation and electron impact

Caló, A. (Antonio) 14 December 2007 (has links)
Abstract The present thesis investigates the electronic structure of selected atoms and molecules in vapor phase. Electron spectroscopy is applied for studying the electronic transitions following excitation and ionization with electron and photon bombardment. The work focuses on the photoionization and Auger decay of selected noble gasses, and on the photoionization and Auger decay of core ionized or resonant excited alkali halide molecules. The experimental results are compared with theoretical predictions.

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