Neutral gas-phase metal-carbide clusters are generated by laser ablation and are detected in the constructed time-of-flight mass-spectrometer by laser ionisation. Photo-ionisation efficiency (PIE) experiments are performed on the metal-carbide clusters to determine their ionisation potentials (IPs). Complimentary density functional theory (DFT) calculations are performed on the energetically favorable structural isomers of the metalcarbide clusters. Comparison between the calculated IPs of the isomers and the experimental IP allows the carrier of the observed ionisation onset for a metal-carbide cluster to be assigned. The niobium-carbide clusters Nb₃Cy (y = 0–4), Nb₄Cy (y = 0–6) and Nb₅Cy (y = 0–6) are examined by PIE experiments and DFT calculations. The IPs of the niobium-carbide clusters are found to be either left reasonably unchanged from the IPs of the bare metal clusters or moderately reduced. The clusters Nb₃C₂, Nb₄C₄, Nb₅C₂ and Nb₅C₃ display the largest IP reductions for their corresponding cluster series. The structures assigned to the IPs of the Nb₃Cy (y = 1–3) clusters are based on the carbon atoms attaching to the niobium faces and/or niobium-niobium edges of the triangular Nb₃ cluster. However, for Nb₃C₄ the ionisation onset is assigned to a low-lying isomer, which contains a molecular C₂ unit, rather than the lowest energy isomer, a niobium atom deficient 2×2×2 face-centred cubic (fcc) nanocrystal structure. The structures assigned to the IPs of the Nb₄Cy (y = 1–4) clusters are based on the carbon atoms attaching in turn to the niobium faces of the tetrahedral Nb₄ cluster, developing a 2×2×2 fcc nanocrystal structure for Nb₄C₄. For Nb₄C₃ two ionisation onsets are observed; one weak onset at low energy and another more intense onset at high energy. It is proposed that the two onsets are due to ionisation from both a metastable ³A₁ state and the ground ¹A₁ state of the lowest energy isomer. The ionisation onsets of Nb₄C₅ and Nb₄C₆ are also proposed to originate from metastable triplet states of the lowest energy isomers, with the transitions from the ground singlet states calculated to be greater than the highest achievable photon energy in the laboratory. The structures of Nb₄C₅ and Nb₄C₆ have one and two carbon atoms in a 2×2×2 fcc nanocrystal substituted with molecular C₂ units, respectively. The structures assigned to the IPs of the Nb₅Cy (y = 1–6) clusters are based on the underlying Nb₅ cluster being in either a “prolate” or “oblate” trigonal bipyramid geometry; the former has six niobium faces available for carbon addition, while the latter has two niobium butterfly motifs and two niobium faces available for carbon addition. Both the structures of Nb₅C₅ and Nb₅C₆ have the underlying Nb₅ cluster in the oblate trigonal bipyramid geometry and contain one and two molecular C₂ units, respectively. The tantalum-carbide clusters Ta₃Cy (y = 0–3), Ta₄Cy (y = 0–4) and Ta₅Cy (y = 0–6) are examined by PIE experiments and DFT calculations. The IPs of the tantalum-carbide clusters in each series show trends that are very similar to the corresponding iso-valent niobium-carbide cluster series, although the IP reductions upon carbon addition are smaller for the former. For the vast majority of tantalum-carbide clusters, the same structural isomer is assigned to the ionisation onset as that assigned for the corresponding niobium-carbide cluster. Bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta₃ZrCy (y = 0–4) clusters are examined by PIE experiments and DFT calculations. The IP trend for the Ta₃ZrCy cluster series is reasonably similar to that of the Ta₄Cy cluster series, although the IP reductions upon carbon addition are greater for the former. The structures assigned to the IPs of the Ta₃ZrCy (y = 1–4) clusters are based on the carbon atoms attaching in turn to the metal faces of the tetrahedral Ta₃Zr cluster. In summary, the work presented in this thesis demonstrates that the structures of metalcarbide clusters can be inferred by the determination of their IPs through PIE experiments in combination with DFT calculations on candidate structural isomers. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1347219 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2008

Neutral gas-phase metal-carbide clusters are generated by laser ablation and are detected in the constructed time-of-flight mass-spectrometer by laser ionisation. Photo-ionisation efficiency (PIE) experiments are performed on the metal-carbide clusters to determine their ionisation potentials (IPs). Complimentary density functional theory (DFT) calculations are performed on the energetically favorable structural isomers of the metalcarbide clusters. Comparison between the calculated IPs of the isomers and the experimental IP allows the carrier of the observed ionisation onset for a metal-carbide cluster to be assigned. The niobium-carbide clusters Nb₃Cy (y = 0–4), Nb₄Cy (y = 0–6) and Nb₅Cy (y = 0–6) are examined by PIE experiments and DFT calculations. The IPs of the niobium-carbide clusters are found to be either left reasonably unchanged from the IPs of the bare metal clusters or moderately reduced. The clusters Nb₃C₂, Nb₄C₄, Nb₅C₂ and Nb₅C₃ display the largest IP reductions for their corresponding cluster series. The structures assigned to the IPs of the Nb₃Cy (y = 1–3) clusters are based on the carbon atoms attaching to the niobium faces and/or niobium-niobium edges of the triangular Nb₃ cluster. However, for Nb₃C₄ the ionisation onset is assigned to a low-lying isomer, which contains a molecular C₂ unit, rather than the lowest energy isomer, a niobium atom deficient 2×2×2 face-centred cubic (fcc) nanocrystal structure. The structures assigned to the IPs of the Nb₄Cy (y = 1–4) clusters are based on the carbon atoms attaching in turn to the niobium faces of the tetrahedral Nb₄ cluster, developing a 2×2×2 fcc nanocrystal structure for Nb₄C₄. For Nb₄C₃ two ionisation onsets are observed; one weak onset at low energy and another more intense onset at high energy. It is proposed that the two onsets are due to ionisation from both a metastable ³A₁ state and the ground ¹A₁ state of the lowest energy isomer. The ionisation onsets of Nb₄C₅ and Nb₄C₆ are also proposed to originate from metastable triplet states of the lowest energy isomers, with the transitions from the ground singlet states calculated to be greater than the highest achievable photon energy in the laboratory. The structures of Nb₄C₅ and Nb₄C₆ have one and two carbon atoms in a 2×2×2 fcc nanocrystal substituted with molecular C₂ units, respectively. The structures assigned to the IPs of the Nb₅Cy (y = 1–6) clusters are based on the underlying Nb₅ cluster being in either a “prolate” or “oblate” trigonal bipyramid geometry; the former has six niobium faces available for carbon addition, while the latter has two niobium butterfly motifs and two niobium faces available for carbon addition. Both the structures of Nb₅C₅ and Nb₅C₆ have the underlying Nb₅ cluster in the oblate trigonal bipyramid geometry and contain one and two molecular C₂ units, respectively. The tantalum-carbide clusters Ta₃Cy (y = 0–3), Ta₄Cy (y = 0–4) and Ta₅Cy (y = 0–6) are examined by PIE experiments and DFT calculations. The IPs of the tantalum-carbide clusters in each series show trends that are very similar to the corresponding iso-valent niobium-carbide cluster series, although the IP reductions upon carbon addition are smaller for the former. For the vast majority of tantalum-carbide clusters, the same structural isomer is assigned to the ionisation onset as that assigned for the corresponding niobium-carbide cluster. Bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta₃ZrCy (y = 0–4) clusters are examined by PIE experiments and DFT calculations. The IP trend for the Ta₃ZrCy cluster series is reasonably similar to that of the Ta₄Cy cluster series, although the IP reductions upon carbon addition are greater for the former. The structures assigned to the IPs of the Ta₃ZrCy (y = 1–4) clusters are based on the carbon atoms attaching in turn to the metal faces of the tetrahedral Ta₃Zr cluster. In summary, the work presented in this thesis demonstrates that the structures of metalcarbide clusters can be inferred by the determination of their IPs through PIE experiments in combination with DFT calculations on candidate structural isomers. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1347219 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2008

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 440-459).

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 156-168).

Dissertation (PhD)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Made available in DSpace on 2014-10-09T12:55:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:00Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:55:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:00Z (GMT). No. of bitstreams: 0 / Neste trabalho foi desenvolvida a t¶ecnica de Espectroscopia de Plasma Induzido por Laser aplicada µa an¶alise de patrim^onio hist¶orico atrav¶es do estudo das moedas de Um Cruzeiro de 1945 e Mil R¶eis de 1939, utilizando um laser de Nd:YAG operando em modo de chaveamento Q. Foram determinadas as melhores condi»c~oes de energia do pulso laser e tempos de atraso entre o pulso e a aquisi»c~ao dos espectros e de integra»c~ao do sinal espectrosc¶opico para aplica»c~ao da t¶ecnica em patrim^onio hist¶orico. Para garantir a reprodutibilidade da t¶ecnica, a temperatura de excita»c~ao eletr^onica, a temperatura de ioniza»c~ao e a densidade eletr^onica do plasma foram determinadas. O dano causado µas moedas foi avaliado utilizando a t¶ecnica de Tomogra¯a por Coer^encia ¶ Optica. Utilizando o m¶etodo livre de calibra»c~ao, as concentra»c~oes elementares foram determinadas, por¶em a concentra»c~ao determinada para o Alum¶³nio, presente no material de forja, estava abaixo de seu valor nominal e do valor determinado atrav¶es da t¶ecnica de An¶alise por Ativa»c~ao Neutr^onica. Uma investiga»c~ao da fra»c~ao de ioniza»c~ao revelou que a fra»c~ao de ioniza»c~ao presente no plasma estava acima do valor esperado por ioniza»c~ao t¶ermica para as temperaturas atingidas, indicando a presen»ca de processos de ioniza»c~ao n~ao t¶ermicos, que in°uenciavam nas medidas do Alum¶³nio. Foi realizada uma corre»c~ao na concentra»c~ao do elemento, utilizando a fra»c~ao de ioniza»c~ao devido aos processos de ioniza»c~ao n~ao t¶ermicos, e os novos valores de concentra»c~ao determinados obtiveram uma grande concord^ancia com os valores nominal e determinados por An¶alise por Ativa»c~ao Neutr^onica. ii / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Cette thèse décrit le travail expérimental sur différentes techniques visant l'obtention du contrôle de l'état quantique d'atomes et de molécules, pour application dans l'informatique quantique, la métrologie et l'astrophysique. Le contrôle cohérent exige des conditions précises de fonctionnement d'un système où la décohérence est minimisée. La construction d'une machine à jet atomique de calcium est présentée comme l'élément de base d'expériences où des schémas d'excitation laser choisis permettront de préparer de façon robuste un état quantique au moyen d'impulsions composites. La deuxième section décrit ma contribution pour améliorer la stabilité de fréquence relative de l'horloge à fontaine de cesium CSF2, à l'institut allemand de métrologie. Un piège magnéto-optique modifié produit un faisceau d'atomes de césium lents. Ils sont préparés dans un état noir spécifique puis sont efficacement transférés à la mélasse optique de la fontaine. L'augmentation du nombre d'atomes participant ainsi au cycle d'horloge améliore sa stabilité d'un facteur 6. La troisième section concerne les spectres de molécules NiH et FeH. Plusieurs sources pour leur production en laboratoire ont été développées et testées. Une expérience d'absorption laser différentielle et une technique de spectroscopie intra-cavité sont appliquées aux molécules faiblement absorbantes NiH, afin d'obtenir leurs coefficients d'absorption dans le rouge. La réponse Zeeman de la molécule FeH (une sonde du champ magnétique des étoiles froides) dans le proche infrarouge est étudiée par spectroscopie laser de précision afin d'établir des facteurs Landé pour 33 niveaux rovibrationnelles de l'état électronique F 4? / This thesis describes experimental work on different techniques aiming to achieve control of the quantum state of atoms and molecules, envisaging applications in quantum computing, metrology and astrophysics.Successful coherent control requires careful design of operating conditions for a system where decoherence is minimized. The construction of a calcium atomic beam is presented as a necessary element in experiments with laser excitation schemes chosen to provide high-fidelity preparation of a quantum satate by means of composite pulses. The second section describes my contribution to the improvement of the relative frequency stability of the Cs fountain clock CSF2 at the German institute of metrology. A modified magneto-optical trap is employed to form a beam of slow cesium atoms. They are prepared in a specific dark state and subsequently are efficiently transferred to the optical molasses of the fountain. Increasing number of atoms participating in the clock cycle in this way improves the stability of the clock by a factor of 6.The third section is concerned with spectra of metal hydride molecules NiH and FeH. Several sources for production of these molecules in laboratories were developed and tested. A differential laser absorption experiment and a cavity-enhanced spectroscopy technique are applied on the w??kly absorbing NiH molecules, to obtain absorption coefficients for the red bands of NiH. The Zeeman response of the FeH molecule (a probe for magnetic fields in cool stars) in the near-IR is investigated by precision laser spectroscopy establishing Landé factors for 33 rovibrational levels of the F 4? electronic state

Dual-comb spectroscopy (DCS) has widespread applications. It has become a more prominent spectroscopic tool because it has broad spectral coverage with high frequency resolution. We demonstrate the broadband and high resolution of DCS to probe transient events, showing the rst use of DCS of laser-induced plasmas (LIPs). Our measurements span absorption features 7 THz wide, simultaneously detecting Rb D2, K D1 and D2 absorption lines with the ability to resolve the isotope ratios in the Rb D2 line. This technique is more broadband and faster than tunable laser absorption spectroscopy because it eliminates the requirement to scan across transitions. Additionally, DCS makes higher resolution measurements than laser-induced break- down spectroscopy. Our ultimate goal is to use DCS as a technique to ascertain the chemical composition of unknown samples. Our rst demonstration of this technique illustrates that DCS makes broadband, high-resolution measurements with the ability to measure isotope ratios, which is necessary for determining sample composition.