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Dissertations / Theses on the topic 'Ionic clusters'

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Published: 4 June 2021
Last updated: 20 February 2023

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1

Bieske, Evan John, and n/a. "The Electronic Spectroscopy of Neutral and Ionic Clusters." Griffith University. School of Science, 1989. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051109.112502.

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This thesis is concerned with weakly bound neutral and ionic clusters. Spectra of the region near the S1fS0 electronic origin of four neutral van der Waals molecules - aniline-argon, phenol-argon, chlorobenzene-argon and fluorobenzene-argon - were obtained using resonance enhanced multiphoton ionization (REMPI). These spectra indicate that Fermi resonances between van der Waals stretching and bending motions are important in these molecules. Effective Hamiltonians are constructed that describe well the low frequency vibrations. In order to better discuss the low frequency van der Waals motions of aromatics bound to one and two rare gas atoms a simple model for the vibrations is developed. The model enables expression of van der Waals frequencies in terms of fundamental molecular properties and enables facile comparison of effective force constants in a variety of van der Waals molecules. The model is successfully employed to explain van der Waals vibrational structure associated with the origin region of aniline-(argon)2 using van der Waals potential parameters derived from the aniline-(argon)1 spectrum. REMPI and emission spectra of larger clusters of aniline and argon are also reported and discussed. Using atom-atom potentials, equilibrium structures for aniline-(argon)n (n=l, 2, 3) are calculated. The calculations prove useful in the analysis of the spectra.The BfX transitions of the cation complexes fluorobenzene+-argon and chlorobenzene+-argon have been investigated. The cations were prepared by resonance enhanced multiphoton ionization of the neutral van der Waals molecules. A time delayed tunable dye laser was then used to dissociate the cations, loss of an argon atom being the dominant process. When the second laser was tuned to a cation resonance the dissociation cross section increased markedly, allowing characterization of BfX transition. The resulting spectra are presented and discussed.
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2

Bieske, Evan John. "The Electronic Spectroscopy of Neutral and Ionic Clusters." Thesis, Griffith University, 1989. http://hdl.handle.net/10072/367202.

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This thesis is concerned with weakly bound neutral and ionic clusters. Spectra of the region near the S1fS0 electronic origin of four neutral van der Waals molecules - aniline-argon, phenol-argon, chlorobenzene-argon and fluorobenzene-argon - were obtained using resonance enhanced multiphoton ionization (REMPI). These spectra indicate that Fermi resonances between van der Waals stretching and bending motions are important in these molecules. Effective Hamiltonians are constructed that describe well the low frequency vibrations. In order to better discuss the low frequency van der Waals motions of aromatics bound to one and two rare gas atoms a simple model for the vibrations is developed. The model enables expression of van der Waals frequencies in terms of fundamental molecular properties and enables facile comparison of effective force constants in a variety of van der Waals molecules. The model is successfully employed to explain van der Waals vibrational structure associated with the origin region of aniline-(argon)2 using van der Waals potential parameters derived from the aniline-(argon)1 spectrum. REMPI and emission spectra of larger clusters of aniline and argon are also reported and discussed. Using atom-atom potentials, equilibrium structures for aniline-(argon)n (n=l, 2, 3) are calculated. The calculations prove useful in the analysis of the spectra.The BfX transitions of the cation complexes fluorobenzene+-argon and chlorobenzene+-argon have been investigated. The cations were prepared by resonance enhanced multiphoton ionization of the neutral van der Waals molecules. A time delayed tunable dye laser was then used to dissociate the cations, loss of an argon atom being the dominant process. When the second laser was tuned to a cation resonance the dissociation cross section increased markedly, allowing characterization of BfX transition. The resulting spectra are presented and discussed.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Science
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3

Tang, Chi Ming. "Structure and dynamics of doped ionic clusters : a computational study." HKBU Institutional Repository, 1991. https://repository.hkbu.edu.hk/etd_ra/5.

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4

Bruzzi, Eleonora. "Binding energies in large ionic clusters from kinetic energy release measurements." Thesis, University of Nottingham, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.717020.

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The determination of binding energy is a very important piece of information that an experiment can provide. We have devised a new experimental procedure to measure binding energies for unimolecular (metastable) decay of multiply charged metal-ligand cluster ions in gas phase. The new technique consists in preparing clusters by supersonic expansion, and in generating metal-ligand clusters by pick-up technique. A high resolution double-focusing mass spectrometer having reversed sector geometry is used to obtain mass-analysed ion kinetic energy spectra. The evaporative ensemble sta­tistical model by C. E. Klots is used to analyse the kinetic energy releases and to obtain the corresponding binding energies. Our new experimental method has been applied to measure the binding energy for the loss of one neutral molecule in a unimolecular (metastable) dissociation in H+ (H2O)n, H+ (H2O)n, and H+ (CH3OH)n for n < 30.
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5

Kung, Chung-Yi. "A laser-induced fluorescence-time of flight study of ionic clusters /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687115927182.

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6

Ubadigbo, Linda N. "CATHODIC DEPOSITION OF TRIANGULAR TUNGSTEN CLUSTERS FROM IONIC LIQUIDS: AN EXPLORATIVE STUDY." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1363352351.

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7

Ahmed, Ejaz. "Room-Temperature Synthesis of Transition Metal Clusters and Main Group Polycations from Ionic Liquids." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-80124.

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Main group polycations and transition metal clusters had traditionally been synthesized via high-temperature routes by performing reactions in melts or by CTR, at room-temperature or lower temperature by using so-called superacid solvents, and at room-temperature in benzene–GaX3 media. Considering the major problems associated with higher temperature routes (e.g. long annealing time, risk of product decomposition, and low yield) and taking into account the toxicity of benzene and liquid SO2 in room-temperature or lower temperature synthesis, a soft and sustainable chemical approach has been developed, employing a Lewis-acidic IL [bmim]Cl/AlCl3. This new alternative reaction medium has proven to be an excellent solvent system for the single–step synthesis of main group polycations and transition metal clusters. X-ray diffraction and Raman spectroscopy have been used for the structural characterization of the isolated compounds. Physical properties and quantum chemical calculations of some of the compounds have also been carried out.
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8

Harris, Tracey Lynn. "Electrochemistry of trinuclear metal clusters of molybdenum and tungsten in 1-ethyl-3- methylimidazolium tetrafluoroborate." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1222435098.

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9

D'Auria, Raffaella. "A study of ionic clusters in the lower atmosphere and their role in aerosol formation." Diss., Restricted to subscribing institutions, 2005. http://proquest.umi.com/pqdweb?did=888854191&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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10

Saheb, Amir Hossein. "Sensing materials based on ionic liquids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24789.

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Thesis (Ph.D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Janata, Jiri; Committee Member: Bunz, Uwe; Committee Member: Collard, David; Committee Member: Josowicz, Mira; Committee Member: Kohl, Paul.
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11

Navea, Juan G. Manzanares Carlos E. "Studies on the application of laser photoionization in supersonic-jets for the generation of intense ionic clusters." Waco, Tex. : Baylor University, 2006. http://hdl.handle.net/2104/4878.

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12

Wende, Torsten [Verfasser]. "Gas phase infrared photodissociation spectroscopy of mass-selected ionic clusters : metal oxides and microhydrated anions / Torsten Wende." Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1030488509/34.

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13

Woods, Charles. "Electrochemical deposition of molybdenum and tungsten from trinuclear metal clusters (M3O2(OAC)6(H2O)3(CF3SO3)2) in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1279124132.

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14

Frock, Lynn Renee. "Synthesis and Electrodeposition of Mixed Metal Trinuclear Clusters of Molybdenum and Chromium in Ionic Liquid onto a Platinum Electrode." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1357925302.

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15

Eisermann, Jana [Verfasser], Dariush [Gutachter] Hinderberger, and Christopher [Gutachter] Kay. "Colloid-like ionic clusters : structure formation with small molecules through weak interactions in solution / Jana Eisermann ; Gutachter: Dariush Hinderberger, Christopher Kay." Halle (Saale) : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2019. http://d-nb.info/1210728575/34.

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16

Ahmed, Ejaz, and Michael Ruck. "Chemistry of polynuclear transition-metal complexes in ionic liquids." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138716.

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Transition-metal chemistry in ionic liquids (IL) has achieved intrinsic fascination in the last few years. The use of an IL as environmental friendly solvent, offers many advantages over traditional materials synthesis methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room-temperature IL have been found to be excellent media for stabilising transition-metal clusters in solution and to crystallise homo- and heteronuclear transition-metal complexes and clusters. Furthermore, the use of IL as solvent provides the option to replace high-temperature routes, such as crystallisation from the melt or gas-phase deposition, by convenient room- or low-temperature syntheses. Inorganic IL composed of alkali metal cations and polynuclear transition-metal cluster anions are also known. Each of these areas will be discussed briefly in this contribution
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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17

Ahmed, Ejaz, and Michael Ruck. "Chemistry of polynuclear transition-metal complexes in ionic liquids." Royal Society of Chemistry, 2011. https://tud.qucosa.de/id/qucosa%3A27774.

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Transition-metal chemistry in ionic liquids (IL) has achieved intrinsic fascination in the last few years. The use of an IL as environmental friendly solvent, offers many advantages over traditional materials synthesis methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room-temperature IL have been found to be excellent media for stabilising transition-metal clusters in solution and to crystallise homo- and heteronuclear transition-metal complexes and clusters. Furthermore, the use of IL as solvent provides the option to replace high-temperature routes, such as crystallisation from the melt or gas-phase deposition, by convenient room- or low-temperature syntheses. Inorganic IL composed of alkali metal cations and polynuclear transition-metal cluster anions are also known. Each of these areas will be discussed briefly in this contribution.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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18

Ahmed, Ejaz [Verfasser], Michael [Akademischer Betreuer] Ruck, and Johannes [Akademischer Betreuer] Beck. "Room-Temperature Synthesis of Transition Metal Clusters and Main Group Polycations from Ionic Liquids / Ejaz Ahmed. Gutachter: Johannes Beck. Betreuer: Michael Ruck." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://d-nb.info/1067729674/34.

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19

Boulanger, Clotilde. "Réactions redox topotactiques des chalcogénures à clusters de molybdène : Analyse par voie électrochimique et applications." Nancy 1, 1987. http://www.theses.fr/1987NAN10067.

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Étude des possibilités de désinsertion par voie électrochimique et chimique des différents chalcogénures à clusters de molybdène. Limite imposée par l'oxydation des structures hôtes. Synthèse de nouvelles phases métastables à clusters condensés : o et h Mo9Se11 à clusters uniques Mo9 Mo6 Te6. Étude de l'insertion par voie électrochimique. Influence des paramètres expérimentaux. Approche d'une modélisation des processus. Analyse des systèmes MoyXz/Mn+ = Cr3+, Mn²+, Co²+, Ni²+, Zn²+, Cd²+. Classification des systèmes redox
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20

Engemann, David Christopher [Verfasser], Heinz [Akademischer Betreuer] Hövel, and Thomas [Gutachter] Weis. "Silver clusters deposited into polymers, aerogels and ionic liquids studied with X-ray and optical spectroscopy / David Christopher Engemann. Betreuer: Heinz Hövel. Gutachter: Thomas Weis." Dortmund : Universitätsbibliothek Dortmund, 2014. http://d-nb.info/110828986X/34.

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21

Varga, János [Verfasser], and Armin [Akademischer Betreuer] Reller. "Application of Thermal Analysis: Single Photon Ionization Time-of-Flight Mass Spectrometry for Studies of Inorganic Clusters and Ionic Liquids / János Varga ; Betreuer: Armin Reller." Augsburg : Universität Augsburg, 2017. http://d-nb.info/114105390X/34.

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22

Roese, Stefanie [Verfasser], Heinz [Akademischer Betreuer] Hövel, and Manfred [Gutachter] Bayer. "Stabilization and aggregation of preformed silver clusters in room temperature ionic liquids: a UV/Vis and X-ray absorption spectroscopy study / Stefanie Roese ; Gutachter: Manfred Bayer ; Betreuer: Heinz Hövel." Dortmund : Universitätsbibliothek Dortmund, 2017. http://d-nb.info/1149920459/34.

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23

Jarvis, Vern Marshall. "Studies of molecular cluster ions." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30074.

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24

Miller, Catherine Elizabeth. "Characterization of ion Cluster fragmentation in ionic liquid ion sources." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122372.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 273-281).
Ion electrospray propulsion is a cutting-edge micropropulsion technology that could revolutionize the capabilities of microsatellites. Ion electrospray thrusters could also be used on large spacecraft for precision attitude control applications such as gravity wave detection and exoplanet imaging. Novel room temperature molten salts, called ionic liquids, are used as propellant, which are composed purely of positive and negative molecular ions. When exposed to strong electric fields, ions and metastable clusters of ions are evaporated from the bulk liquid surface. The free ions and ion clusters can be accelerated to high velocities, producing thrust at high specific impulse. The performance of ion electrospray thrusters is affected by the composition of the ion beam and the amount of ion clusters that break apart during the acceleration phase. To improve thruster performance, a better understanding of the fundamental physics of ion evaporation and cluster break-up is needed.
The break-up of ion clusters, also called fragmentation, is not a well understood phenomenon. It has been observed in past experiments, but the rates of break-up have not been measured. The focus of this work is to experimentally investigate fragmentation more deeply than ever before. To accomplish this, a specialized instrumentation suite has been designed, built, and tested to measure fragmentation characteristics in unprecedented detail. A full-beam, spherical geometry retarding potential analyzer is used to measure the rates of fragmentation of ion clusters both outside the thruster and within the acceleration region for the first time. A narrow-beam, high time-resolution time of flight mass spectrometer is used to measure the beam composition. Single emitters based on resorcinol formaldehyde carbon xerogels were used as ion sources. Four ionic liquids spanning a wide range of liquid properties were characterized: EMI-FAP, EMI-Im, EMI-BF4, and BMI-I.
Analytical models were also developed to enhance the interpretation of the experimental results. The experimental measurements show that the amount of fragmentation increases with distance from the thruster and follows a constant rate equation. The mean lifetimes of ion clusters outside of the thruster range from 1-6 [mu]s, indicating that these clusters are quite unstable. It is observed that the fragmentation throughout most of the acceleration region is linear with respect to electric potential, which can be understood using analytical models. Rapid fragmentation likely occurs immediately after evaporation due to the strong electric fields near the emission site, which has significant implications for thruster performance. It is also observed that clusters of complex molecular ions which consist of many atoms tend to be the most stable. The initial temperature of ion clusters, which range from 520 K - 790 K, were estimated using analytical methods.
The effect of liquid temperature on the rates of fragmentation was also investigated. In conclusion, the work in this thesis provides a greatly enhanced understanding of ion cluster fragmentation, particularly how it is affected by ionic liquid properties, liquid temperature, and electric fields.
This research was supported by a NASA Space Technology Research Fellowship
by Catherine Elizabeth Miller.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics
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25

Sushko, Petr Valentinovich. "Development and application of embedded cluster methodologies for defects in ionic materials." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326037.

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26

Ahmed, Ejaz, Joachim Breternitz, Matthias Friedrich Groh, and Michael Ruck. "Ionic liquids as crystallisation media for inorganic materials." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138932.

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Ionic liquids (ILs) have made a great impact on materials science and are being explored for potential applications in several disciplines. In this article, we briefly highlight the current state-of-the-art techniques employing ILs as new crystallisation media, working as neutral solvent, template or charge compensating species. The use of an IL as environmental friendly solvent offers many advantages over traditional crystallisation methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room temperature ILs have been found to be excellent solvent systems for the crystallisation of a wide range of substances and morphologies ranging from nanoscopic crystals to micro- and even to macroscopic crystals. Moreover, high temperature routes, such as crystallisation from melts or gas phase deposition, have been replaced by convenient room or low temperature syntheses, employing ILs as reaction media
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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27

Ahmed, Ejaz, Joachim Breternitz, Matthias Friedrich Groh, and Michael Ruck. "Ionic liquids as crystallisation media for inorganic materials." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27794.

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Ionic liquids (ILs) have made a great impact on materials science and are being explored for potential applications in several disciplines. In this article, we briefly highlight the current state-of-the-art techniques employing ILs as new crystallisation media, working as neutral solvent, template or charge compensating species. The use of an IL as environmental friendly solvent offers many advantages over traditional crystallisation methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room temperature ILs have been found to be excellent solvent systems for the crystallisation of a wide range of substances and morphologies ranging from nanoscopic crystals to micro- and even to macroscopic crystals. Moreover, high temperature routes, such as crystallisation from melts or gas phase deposition, have been replaced by convenient room or low temperature syntheses, employing ILs as reaction media.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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28

Villanueva, Martha A. "Structures of small organic cluster ions computed using self-consistent field semiempirical molecular orbital methods." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/30323.

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29

Davis, Jessica Ann. "Synthesis of Mixed Metal Trinuclear Cluster of Molybdenum and Tungsten and Their Electrochemistry in Ionic Liquids." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1348094887.

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30

Åkerstedt, Josefin. "Subvalent Cluster Compounds and Synthesis in Alternative Reaction Media." Doctoral thesis, KTH, Tillämpad fysikalisk kemi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-107218.

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With the aim of finding alternative reaction media for the synthesis of subvalent main group and transition metal cluster compounds, traditionally made through solid state reactions or in superacidic media, different alternative reaction media have been explored in this work. Room-temperature ionic liquids are amongst the more unconventional reaction media used. The syntheses performed have been aimed at both anionic and cationic cluster and the main tools used for characterization have been different X-ray diffraction and spectroscopic techniques. Selected ionic liquids have along with dichloromethane been shown to work as alternative reaction media for room temperature synthesis of the Bi5[GaCl4]3 salt. The salt containing the subvalent naked bismuth polycation Bi5 3+ was isolated from reduction reactions of BiCl3 in Ga/GaCl3-dichloromethane respectively Ga/GaCl3-ioinc liquid media. Three different classes of ionic liquids based on phosphonium-, imidazolium- and pyrrolidinium- salts have been used in synthesis. Homopolyatomic clusters from the lighter Group 15 element arsenic have also been studied. Solutions from the oxidative and reductive reaction routes of arsenic and AsCl3 in Lewis acidic toluene media were studied by EXAFS spectroscopy. The results were evaluated using molecular dynamics simulations of arsenic clusters. A discussion on how the calculated As4 cluster model relates to the experimental data resulted from this study. In terms of homopolyatomic anionic clusters the [K+(2,2,2-crypt)]2Ge9 2- compound containing the naked Ge9 2- anionic cluster has been isolated. The crystallographic investigation of [K+(2,2,2-crypt)]2Ge9 2- shows Zintl cluster anion Ge9 2- to be tricapped trigonal-prismatic with a symmetry very close to D3h. A chemical bonding analysis reveals two local minima of D3h symmetry and the cluster interaction scheme to be based on highly delocalised bonding. Ligand supported transition metal clusters from tungsten and palladium have also been prepared. Reduction of WCl6 in a reaction mixture of ionic liquid and co-solvent toluene resulted in tritungsten decachloride; W3Cl10(MeCN)3, being formed. Furthermore, palladium sandwich compounds; [Pd2(Ga2Cl7)(C7H8)2], [Pd2(GaCl4)(C9H12)2]∙C9H12 and [Pd2(Ga2Cl7)(C6H5Cl)2] have been prepared using GaCl3-arene reaction media.

QC 20121212

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31

Sukhbaatar, Tamir. "Approche multi-échelle pour la compréhension de mécanismes d'extraction de l'uranium en utilisant des liquides ioniques." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2018. http://www.theses.fr/2018ENCM0002.

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En raison de leurs propriétés intéressantes telles que faible tension de vapeur, non-inflammabilité et grande fenêtre électrochimique, les Liquides Ioniques sont considérés comme alternatifs aux solvants organiques volatils et font l’objet d’études dans diverses applications comme par exemple en extraction liquide-liquide qui est l’une des techniques de séparation la plus utilisée en hydrométallurgie. L’influence de ces nouveaux diluants sur les propriétés d’agrégation des molécules extractantes et sur leurs propriétés extractantes n’a jusqu’à aujourd’hui pas été appréhendée de façon générale, et encore moins, quant à l’extraction de l’uranium d’un lixiviat acide. Les travaux de cette thèse se focalisent donc sur l’étude de l’effet de l’agrégation des extractants usuels (mélange synergique HDEHP/TOPO et trioctylamine respectivement) et des nouveaux composés bifonctionnels issus des familles amidophosphonates et oxyde d’aminophosphines sur l’extraction de l’uranium i) des milieux phosphates et ii) des milieux sulfates. Les propriétés extractantes ont pour la première fois été comparées à leurs propriétés d’agrégation dans un liquide ionique sélectionné, par des mesures de diffusion des rayons X et des neutrons aux petits angles. Ces données en complément des mesures de tension de surface ont permis de déterminer pour chaque système, la Concentration d’Agrégation Critique, analogue de la Concentration de Micellisation Critique pour les tensioactifs, qui est reliée à l’énergie libre de micellisation. Les mécanismes d’extraction ainsi que la nature des espèces extraites ont également été recherchés afin de comparer les résultats du milieu liquide ionique à ceux du milieu classique
Due to their attractive properties such as negligible vapor pressure, non-flammability and large electrochemical window, Ionic Liquids are considered to be good substitutes to volatile organic compounds and have been main topic of many research studies for different applications including solvent extraction, which is one of the widely used techniques in hydrometallurgy. Despite a large number of reported mechanistic studies, effect of such diluents on both of extracting agents’ capacity and self-assembling feature has not been elucidated so far and even less concerning uranium extraction from a leachate produced by ore leaching. In this context, main focus of the present thesis has been uranium extraction from i) phosphate media and ii) sulfate media by using ionic liquid as a diluent of an extracting phase. First of all, a screening test of different ionic liquids has been performed with the reference extracting agents (HDEHP/TOPO mixture for extraction from phosphate media and trioctylamine from sulfate media) as well as with amidophosphonate and aminophosphine oxide bifunctional compounds. Then, uranium extraction mechanisms in a selected ionic liquid with these extractants have been investigated at molecular and supramolecular scales. As an analogy to the Critical Micellar Concentration which is related to the Gibbs free energy of Micellization in a case of surfactants, a Critical Aggregation Concentration has been determined by using results obtained by Small-Angle X ray, Neutron Scattering techniques and interfacial tension measurements. Finally, the results obtained in the ionic liquid have been compared to those obtained in a conventional molecular diluent
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32

Merkert, Christine [Verfasser], and Gereon [Akademischer Betreuer] Niedner-Schatteburg. "Metal cluster aggregates of the composition Fen+/, Con+/-, Nin+/- and [ConMm]+/- (M: Au, Rh and Pt) as model systems for catalytic C-H activation and structural determination of ionic dicarboxylic acids as model system for intramolecular hydrogen bonding / Christine Merkert. Betreuer: Gereon Niedner-Schatteburg." Kaiserslautern : Technische Universität Kaiserslautern, 2014. http://d-nb.info/1051310377/34.

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33

Pötschke, Markus. "Simulation of electric field-assisted nanowire growth from aqueous solutions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-194735.

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The present work is aimed at investigating the mechanisms of nanowire growth from aqueous solutions through a physical and chemical modeling. Based on this modeling, deriving an optimized process control is intended. The work considers two methods of nanowire growth. The first is the dielectrophoretic nanowire assembly from neutral molecules or metal clusters. Secondly, in the directed electrochemical nanowire assembly metal-containing ions are reduced in an AC electric field in the vicinity of the nanowire tip and afterwards deposited at the nanowire surface. To describe the transport and growth processes, continuum models are employed. Furthermore, it has been necessary to consider electro-kinetic fluid flows to match the experimental observations. The occurring partial differential equations are solved numerically by means of finite element method (FEM). The effect of the process parameters on the nanowire growth are analyzed by comparing experimental results to a parameter study. The evaluation has yielded that an AC electro-osmotic fluid flow has a major influence on the dielectrophoretic nanowire assembly regarding the growth velocity and morphology. In the case of directed electrochemical nanowire assembly, the nanowire morphology can be controlled by the applied AC signal shape. Based on the nanowire growth model, an optimized AC signal has been designed, whose parametrization allows to adjust to the chemical precursor and the desired nanowire diameter
Ziel der vorliegenden Arbeit ist es, mittels physikalischer und chemischer Modelle die Mechanismen des Nanodrahtwachstums aus wässrigen Lösungen zu erforschen und daraus eine optimierte Prozesskontrolle abzuleiten. Dabei werden zwei Verfahren des Nanodrahtwachstums näher betrachtet: Dies sind die dielektrophoretische Assemblierung von neutralen Molekülen oder Metallclustern sowie die gerichtete elektrochemische Nanodrahtabscheidung (engl. directed electrochemical nanowire assembly), bei der metallhaltige Ionen im elektrischen Wechselfeld an der Nanodrahtspitze zunächst reduziert und anschließend als Metallatome abgeschieden werden. Zur Beschreibung der Transport- und Wachstumsprozesse werden Kontinuumsmodelle eingesetzt. Darüber hinaus hat es sich als notwendig erwiesen, elektrokinetische Fluidströmungen zu berücksichtigen, um die experimentellen Beobachtungen zu reproduzieren. Die auftretenden partiellen Differenzialgleichungen werden mittels der Finiten Elemente Methode (FEM) numerisch gelöst. Die Auswirkungen der Prozessparameter auf das Nanodrahtwachstum werden durch den Vergleich von experimentellen Ergebnissen mit Parameterstudien analysiert. Die Auswertung hat ergeben, dass für das dielektrophoretische Wachstum ein durch Wechselfeldelektroosmose (engl. AC electro-osmosis) angetriebener Fluidstrom die Drahtwachstumsgeschwindigkeit und -morphologie maßgeblich beeinflusst. Im Falle der gerichteten elektrochemischen Nanodrahtabscheidung lässt sich die Drahtmorphologie über das angelegte elektrische Wechselsignal steuern. Unter Verwendung des Wachstumsmodells ist ein optimiertes Signal generiert worden, dessen Parametrisierung eine gezielte Anpassung auf den chemischen Ausgangsstoff und den gewünschten Drahtdurchmesser erlaubt
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34

Rocha, Marcelo de Queiroz. "Crescimento, fenologia e rendimento do tomateiro cereja em cultivo hidropônico." Universidade Federal de Pelotas, 2009. http://repositorio.ufpel.edu.br/handle/ri/2397.

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Made available in DSpace on 2014-08-20T14:33:07Z (GMT). No. of bitstreams: 1 Dissertacao_Marcelo_ de_ Queiroz_ Rocha.pdf: 725823 bytes, checksum: baf6fa097603da126ae27ec658aca762 (MD5) Previous issue date: 2009-03-27
The use of a new production system demand to know the behavior of cultures and establish the most appropriate management. It is necessary to understand the relationships that control the operation of the plant, and then understand the way in which these relations are dazzling together to result in final income. The growth dynamic, the fenological characterization and yield components of the red cherry tomato crop (Lycopersicon esculentum var. cerasiforme), cultivated in hydroponic system during summer-autumn 2008 crop season, were studied through two experiments conducted in plastic greenhouse, in the Campus of the Universidade Federal de Pelotas, RS. The first experiment was carried out to study the effect of different levels of ionic concentration of the nutrient solution on growth and yield components of cherry tomato (number of fruits, fruit mean weight and fruit yield). This experimental factor was assessed in four different levels: standard nutrient solution, containing 100% of the concentration of nutrients recommended by "Japan Horticultural Experimental Station", corresponding to an initial electrical conductivity (ECi) of 2,3 dS m-1, nutrient solution with reductions of 25 and 50% and with increment of 25% in the concentration of nutrients in relation to the standard solution, corresponding to ECis of 1,3; 1,8 and 2,8 dS m-1, respectively. Another experimental factor in this study was the position of flower cluster and its influence on the yield components. The second experiment was conducted to verify the effect of low sink demand on the vegetative growth in plants cultivated with standard nutrient solution. Two treatments were established: low sink demand (no fruit on the plant by removing 11 all inflorescences) and high sink demand (by maintaining of inflorescences and allowing the fruit to the plant). In both experiments, from the data of dry matter and leaf area accumulated during the experimental period, the production and distribution of dry matter among the different organs of the plant and growth index were determined. The results obtained in the first experiment allow to concluded that: the vegetative stage comprised 30,9% of the crop cycle and the number of the flowers is not dependent on the inflorescence position on the main stem; the position of floral cluster in the plant does not affect the yield components number and weight of the fruit, with little influence on the production of fruits per cluster of cherry tomato; the change of the ion concentration of the nutrient solution (in a range from 1,3 to 2,8 dS m-1) does not affect the number of fruits per plant, but an EC higher than 2,3 dS m-1 causes a reduction in mean weight of the fruits; the leaf expansion, the fruit growth and yield of cherry tomato decrease when the ionic concentration of the nutrient solution increases in the range from 1,8 to 2,8 dS m-1 and when it is reduced from 1,8 to 1,3 dS m-1; the nutrient solution of 1,8 dS m-1 EC can be recommended to increase the fruit yield of cherry tomato in hydroponic system in the summer-autumn crop season. The results observed in the second experiment showed that the fruits corresponded to approximately 26% of the total dry matter of plants in which the fruits are allowed. Thus, in red cherry tomato plants, fruits were not the biggest sink of photoassimilates, since the leaves represented approximately 39% of total dry matter of plants which the fruits are allowed. Thus, the leaf fraction was characterized as the largest source and at the same time as the largest sink of photoassimilates. The fruits has competed more strongly with the leaves than the stems by photoassimilates, indicating that stem and leaves are not characterized as a single compartment for storage of photoassimilates.
O emprego de um novo sistema de produção demanda conhecer o comportamento das culturas e definir o manejo mais adequado. É necessário, portanto, conhecer as relações que regem o funcionamento da planta e, em seguida, compreender a forma segundo a qual todas essas relações se encandeiam entre si para resultar no rendimento final. A dinâmica do crescimento, a caracterização fenológica e os componentes do rendimento da cultura do tomate cereja vermelho (Lycopersicon esculentum var. cerasiforme), cultivado em sistema hidropônico durante o ciclo de verão-outono de 2008, foram estudados através de dois experimentos conduzidos em estufa plástica, no Campus da Universidade Federal de Pelotas, RS. O primeiro experimento foi realizado objetivando-se estudar o efeito de diferentes níveis de concentração iônica da solução nutritiva sobre o crescimento e os componentes do rendimento do tomateiro cereja (número de frutos, peso médio do fruto e produção de frutos). Este fator experimental foi avaliado em quatro diferentes níveis: solução nutritiva padrão, contendo 100% da concentração de nutrientes recomendada pela Japan Horticultural Experimental Station , correspondendo a uma condutividade elétrica inicial (CEi) de 2,3 dS m-1; soluções nutritivas com reduções de 25% e 50% e com incremento de 25% da concentração de nutrientes em relação à solução padrão, correspondendo a CEi de 1,3; 1,8 e 2,8 dS m-1, respectivamente. Outro fator experimental estudado neste experimento foi a posição do cacho floral e sua influência sobre os componentes do rendimento. As avaliações fenológicas foram realizadas em plantas conduzidas na solução padrão. O segundo experimento foi conduzido a fim de verificar o efeito da baixa demanda de drenos sobre o crescimento vegetativo em plantas cultivadas com solução 9 nutritiva padrão. Dois tratamentos foram estabelecidos: baixa demanda de drenos (ausência de frutos na planta através da remoção de todas as inflorescências) e alta demanda de drenos (através da permanência das inflorescências e permitindo-se a frutificação na planta). Em ambos os experimentos, a partir dos dados de matéria seca e da área foliar acumuladas ao longo do período experimental, determinou-se a produção e distribuição de matéria seca entre os diferentes órgãos aéreos da planta e os índices de crescimento. Através dos resultados obtidos no primeiro experimento conclui-se que: a fase vegetativa corresponde a 30,9% do ciclo de cultivo e o número de flores emitidas independe da posição da inflorescência na haste principal; a posição do cacho floral na planta não afeta os componentes do rendimento número e peso médio do fruto, exercendo pouca influência sobre a produção de frutos por cacho do tomateiro cereja; a variação da concentração iônica da solução nutritiva (na faixa entre 1,3 e 2,8 dS m-1) não afeta o número de frutos colhidos por planta mas uma CE superior a 2,3 dS m-1 provoca uma redução no peso médio do fruto; a expansão foliar, o crescimento de frutos e a produtividade do tomateiro cereja diminuem quando a concentração iônica da solução nutritiva aumenta no intervalo entre 1,8 e 2,8 dS m-1 e quando é reduzida de 1,8 para 1,3 dS m-1; a solução nutritiva com CE de 1,8 dS m-1 pode ser recomendada para aumentar a produtividade do tomateiro cereja em sistema hidropônico no ciclo de verão-outono. Os resultados observados no segundo experimento mostram que os frutos corresponderam à aproximadamente 26% da matéria seca total das plantas nas quais se permitiu a frutificação. Desta forma, no tomateiro cereja vermelho, os frutos não foram os maiores drenos de fotoassimilados, uma vez que as folhas representaram aproximadamente 39% da matéria seca total das plantas que frutificaram. Assim, a fração folhas caracterizou-se como a maior fonte e, ao mesmo tempo, como o maior dreno de fotoassimilados. Os frutos competem mais fortemente com as folhas do que com o caule pelos assimilados, indicando que caule e folhas não se caracterizam como um compartimento único de estocagem de fotoassimilados.
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35

Bindi, Chiara. "Emissione di Bremsstrahlung ed applicazioni astrofisiche." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018.

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L'elaborato è costituito da due capitoli principali. Il primo capitolo è incentrato prevalentemente sulla trattazione fisica del processo di emissione di Bremsstrahlung: nella prima parte si procede trattando il caso di singolo elettrone per poi passare al caso generale di emissione termica, si conclude affrontando il caso relativistico. Nel secondo capitolo vengono trattate le principali applicazioni astrofisiche del fenomeno. L'emissione per Bremsstrahlung implica una zona di gas altamente ionizzato: in tal senso viene studiata la regione HII caratterizzata dalla presenza di stelle calde e massive di tipo O/B che tramite la radiazione UV ionizzano il gas che le circonda. Nello spettro si osserva emissione Bremsstrahlung che va dall'ottico al radio. Altra applicazione riguarda le galassie ellittiche dove vi è gas altamente ionizzato situato attorno al nucleo. La fase del mezzo interstellare in questo tipo di galassie è l'HIM e vi è emissione di Bremsstrahlung. Infine si parla dell'emissione X causata dal processo di accrescimento tra un oggetto compatto ed una stella compagna.
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36

Chandezon, Frédéric. "Étude expérimentale de la stabilité d'agrégats de sodium multichargés produits par collision d'agrégats neutres avec des ions." Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10201.

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Le but de cette these est d'etudier la stabilite d'un agregat de sodium vis-a-vis d'un exces de charge positive. Dans un premier temps, nous avons procede a la construction de l'experience. La source utilisee pour la formation des agregats est du type thermalisation gazeuse. Avec cette source, nous avons obtenu des agregats froids de quelques atomes jusqu'a environ un millier. Le spectrometre de masse a temps de vol construit pour l'experience utilise un systeme d'acceleration a deux etages type wiley-mclaren, mais avec une focalisation amelioree. Une resolution en masse superieure a 2000 est obtenue vers la masse 1100 uma, et les agregats de sodium monocharges ayant jusqu'a 700 atomes peuvent etre separes. Dans un deuxieme temps, nous avons etudie la production et la stabilite d'agregats de sodium multicharges. L'ionisation sequentielle d'agregats neutres par une impulsion laser permet d'obtenir des agregats multicharges chauds, c'est-a-dire evaporant des atomes. La charge maximale des agregats est limitee par l'energie des photons. L'interaction d'agregats neutres avec des ions montre la coexistence de deux processus d'ionisation: la capture a distance d'electrons par le champ coulombien de l'ion et l'emission statistique d'electrons suite a l'excitation electronique de l'agregat quand un ion le traverse. Lorsque la charge de l'ion augmente, le premier processus devient predominant. Ceci implique une diminution de la temperature des agregats multicharges obtenus qui se traduit experimentalement par une diminution de la taille critique. En conclusion, l'interaction d'agregats neutres avec des ions permet de produire des agregats multicharges, de charge, de taille et de temperature variables. Elle apparait comme une methode de choix pour l'etude de la fragmentation lorsque ces edifices sont instables
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37

Amarouche, Mohand. "Modelisation des agregats de gaz rares et dynamique d'ar : :(3)**(+)." Toulouse 3, 1988. http://www.theses.fr/1988TOU30135.

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Calcul de la structure d'equilibre et de l'energie d'agregats ioniques positifs de xe et ar a l'aide d'un hamiltonien de type excitonique, extrait des courbes de potentiel des diatomiques correspondants, en incluant le couplage spin-orbite et les interactions a 3 corps entre dipoles induits instantanement. Emploi de ce modele pour calculer les barrieres de potentiel entre divers isomeres, les diverses possibilites de fragmentation apres photoionisation verticale et les echanges de masse lors de collisions entre agregats; observation d'une stabilite remarquable des agregats a 13 et 19 atomes, formes de couronnes pleines autour de coeurs ionises a 3 ou 4 atomes. Couplage du modele excitonique a la methode de dynamique "hemiquantique" pour etudier la photodissociation de ar::(3)**(+), dont on calcule la section efficace a partir du moment de transition de l'espece diatomique obtenu par des calculs ab initio
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38

Habassi, Chefik. "Mise en evidence du phenomene d'agregation ionique dans les resines polyester neutralisees par des ions metalliques." Paris 6, 1988. http://www.theses.fr/1988PA066282.

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Etude de composes modeles, molecules de faible masse et oligomeres difonctionnels, neutralises et gonfles ou non par des solvants; diminution de la mobilite des chaines au voisinage des groupes -coomg et existence de plusieurs conformations dans les produits neutralises. Mise en evidence par saxs d'agregats ioniques de 5 a 10 a disperses dans la matrice constituee du polymere et du solvant de gonflement
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39

Cao, Yi-Bin. "Vibrational predissociation spectroscopy of mass-selected ionic clusters." Thesis, 1994. https://thesis.library.caltech.edu/7650/2/Cao%201994.pdf.

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This thesis presents structural investigations of molecular ions and ionic clusters using vibrational predissociation spectroscopy. Experimentally, a pulsed beam of the mass-selected ion is crossed by a tunable infrared laser beam generated by a Nd:YAG pumped LiNbO_3 optical parametric oscillator. The resulting fragment ion is mass-analyzed and detected, with its intensity as a function of the laser wavelength being the "action" spectrum of the parent ion. In the case of SiH_7^+, we observed a vibrational band centered at 3866 cm^(-1) with clear P, Q, R branches, which is assigned as a perturbed H_2 stretch. The absence of a second H_2 band suggests that the ion forms a symmetric complex with a structure H_2•SiH_3^+•H_2 , in contrast to the species CH_7^+, which has the structure CH_5^+•H_2. The infrared spectra of NO_2^+(H_2O)_n clusters exhibit a marked change with cluster size, indicating that an intracluster reaction occurs with sufficient solvation. Specifically, in NO_2^+(H_2O)_n clusters where n≤3, H_2O binds to a nitronium ion core; but at n=4 the NO_2^+ reacts, transforming the cluster to a new structure of H_3O^+•(H_2O)_(n_2)•HNO_3. For protonated chlorine nitrate, we have observed two distinct isomers previously predicted by ab initio calculations: NO_2^+•(HOC1), the lowest energy isomer, and (ClO)(HO)NO^+, a covalently bonded isomer about 20 kcal/mol higher in energy. Both isomers decompose to NO_2^+ and HOCl upon photo-excitation. These results for HClONO_2^+ lend strong support to the involvement of an ionic mechanism in the reaction of ClONO_2 on polar stratospheric cloud surfaces, a critical step in the dramatic springtime depletion of ozone over Antarctica. Current research activities on halide-solvent clusters and metal-ligand complexes as well as technological improvements of the apparatus are also discussed.
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40

Wu, Chih-Che, and 吳志哲. "Investigations of Mixed Ionic Clusters using Vibrational Predissociation Spectroscopy." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/48694436399736110003.

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博士
國立臺灣大學
化學研究所
91
This thesis depicts new experimental investigations of mass-selected mixed cluster ions, produced under supersonic expansion conditions of using a vibrational predissociation ion trap spectrometer equipped with a corona discharge ion source and coupled with an infrared laser system. Density functional theory calculations are performed at B3LYP/6-31+G* level to assist interpretation of the spectra. The combined investigation provides information on structure and proton transfer dynamics of ionic clusters in the gas phase. Subjects studied include hydrophobic interactions, competitive proton solvation by solvents, hydrolysis/hydration of the peptide analogue, and the first overtone spectroscopy of ionic clusters. The experimental layout of the vibrational predissociation ion trap (VPIT) spectrometer and involved parameters in the calculations using density functional theory (DFT) are described in Chapter One. A description of the notations used throughout this work is given therein. Chapter Two illustrates proton assisted hydrophobic interactions in the gas phase. Four modeling coumpounds, (CH3)2O dimer, (CH3)(C2H5)O dimer, CH3C(O)CH3 dimer, and CH3C(O)H dimer, with single protonated water molecule are investigated by infrared spectroscopy under various beam conditions. In Chapter Three, the behavior of the excess proton (H+) in binary solvent is closely examined. Proton competition between methanol and water sheds insight into anomalous high proton conductivity in solution. Chapter Four characterizes the hydration/hydrolysis of peptide-containing molecule (formamide) by both infrared and mass spectroscopy. First infrared spectroscopic evidence of O-protonation rather than N-protonation of protonated mixed formamide clusters is found, which is in line with the prediction from the amide resonance model. Acid-assisted hydration of CH3C(O)CH2C(O)CH3 , the peptide chain analogue, is inspected in Chapter Five. Water-bridged conformation, either H3O+-bridged or H5O2+-bridged structure, is produced under various supersonic beam conditions. In all the mixed water cluster ions, both the sample-centered and the H3O+-centered isomers are identified on the basis of both experimental observations and theoretical calculations. Proton pulling effects have been discussed in these modeling systems. The first overtone spectroscopy of protonated water and methanol complexes is demonstrated in Chapter Six. Although there have been a number of publications for overtone spectroscopy of single molecule and neutral complexes, there are only few investigations on overtone spectroscopy of ionic clusters. We present in this chapter the first spectroscopic identifications and derive harmonic frequencies and anharmonic coefficients of the OH stretches in H+(H2O)3-5, and H+(CH3OH)4 from their first overtone and combination bands in the near infrared region using a tunable optical parametric oscillator (OPO) laser system.
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41

Kuwata, KeithTadao. "Spectroscopic and Computational Studies of Ionic Clusters as Models of Solvation and Atmospheric Reactions." Thesis, 1998. https://thesis.library.caltech.edu/14280/1/Kuwata_Keith_1998_Thesis_Scan.pdf.

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Ionic clusters are useful as model systems for the study of fundamental processes in solution and in the atmosphere. Their structure and reactivity can be studied in detail using vibrational predissociation spectroscopy, in conjunction with high level ab initio calculations. This thesis presents the applications of infrared spectroscopy and computation to a variety of gas-phase cluster systems.

A crucial component of the process of stratospheric ozone depletion is the action of polar stratospheric clouds (PS Cs) to convert the reservoir species HCl and chlorine nitrate (CIONO₂) to photochemically labile compounds. Quantum chemistry was used to explore one possible mechanism by which this activation is effected:
CI⁻ + CIONO₂ → CI₂ + NO₃⁻ (1)
Correlated ab initio calculations predicted that the direct reaction of chloride ion with CIONO₂ is facile, which was confirmed in an experimental kinetics study. In the reaction a weakly bound intermediate Cl₂--NO₃⁻ is formed, with ~70% of the charge localized on the nitrate moiety. This enables the Cl₂--NO₃⁻ cluster to be well solvated even in bulk solution, allowing (1) to be facile on PSCs.

Quantum chemistry was also applied to the hydration of nitrosonium ion (NO⁺), an important process in the ionosphere. The calculations, in conjunction with an infrared spectroscopy experiment, revealed the structure of the gas-phase clusters NO⁺(H₂O)ₙ. The large degree of covalent interaction between NO⁺ and the lone pairs of the H₂O ligands is contrasted with the weak electrostatic bonding between iodide ion and H₂O.

Finally, the competition between ion solvation and solvent self-association is explored for the gas-phase clusters CI⁻(H₂O)ₙ, and CI⁻(NH₃)ₙ. For the case of water, vibrational predissociation spectroscopy reveals less hydrogen bonding among H₂O ligands than predicted by ab initio calculations. Nevertheless, for n≥5, cluster structure is dominated by water-water interactions, with CI⁻ only partially solvated by the water cluster. Preliminary infrared spectra and computations on CI⁻(NH₃)ₙ indicate that NH₃ preferentially binds to CI⁻ ion instead of forming inter-solvent networks.

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42

Kuwata, Keith Tadao. "Spectroscopic and Computational Studies of Ionic Clusters as Models of Solvation and Atmospheric Reactions." Thesis, 1998. https://thesis.library.caltech.edu/14280/1/Kuwata_Keith_1998_Thesis_Scan.pdf.

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Abstract:

Ionic clusters are useful as model systems for the study of fundamental processes in solution and in the atmosphere. Their structure and reactivity can be studied in detail using vibrational predissociation spectroscopy, in conjunction with high level ab initio calculations. This thesis presents the applications of infrared spectroscopy and computation to a variety of gas-phase cluster systems.

A crucial component of the process of stratospheric ozone depletion is the action of polar stratospheric clouds (PS Cs) to convert the reservoir species HCl and chlorine nitrate (CIONO₂) to photochemically labile compounds. Quantum chemistry was used to explore one possible mechanism by which this activation is effected:
CI⁻ + CIONO₂ → CI₂ + NO₃⁻ (1)
Correlated ab initio calculations predicted that the direct reaction of chloride ion with CIONO₂ is facile, which was confirmed in an experimental kinetics study. In the reaction a weakly bound intermediate Cl₂--NO₃⁻ is formed, with ~70% of the charge localized on the nitrate moiety. This enables the Cl₂--NO₃⁻ cluster to be well solvated even in bulk solution, allowing (1) to be facile on PSCs.

Quantum chemistry was also applied to the hydration of nitrosonium ion (NO⁺), an important process in the ionosphere. The calculations, in conjunction with an infrared spectroscopy experiment, revealed the structure of the gas-phase clusters NO⁺(H₂O)ₙ. The large degree of covalent interaction between NO⁺ and the lone pairs of the H₂O ligands is contrasted with the weak electrostatic bonding between iodide ion and H₂O.

Finally, the competition between ion solvation and solvent self-association is explored for the gas-phase clusters CI⁻(H₂O)ₙ, and CI⁻(NH₃)ₙ. For the case of water, vibrational predissociation spectroscopy reveals less hydrogen bonding among H₂O ligands than predicted by ab initio calculations. Nevertheless, for n≥5, cluster structure is dominated by water-water interactions, with CI⁻ only partially solvated by the water cluster. Preliminary infrared spectra and computations on CI⁻(NH₃)ₙ indicate that NH₃ preferentially binds to CI⁻ ion instead of forming inter-solvent networks.

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43

Perera, Kanchana Manori. "Electronic Spectroscopy and Dissociation Dynamics of Gas-Phase Transition Metal Containing Cations and Dications." 2009. http://scholarworks.umass.edu/open_access_dissertations/22.

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Studies of gas-phase ionic clusters have become an integral component in understanding microsolvation and catalysis by transition metal cations. Further interest in this field is due to the possibility of bridging the gap between the condensed and gas phases by developing our understanding of clusters and the possibility that small clusters can have unique chemical and catalytic properties. Most gas phase studies have focused on singly charged ions. Electrospray allows for the production of multiply charged ions solvated by a few solvent molecules. Understanding smaller reactive species such as metal centered clusters with well-defined, gas phase conditions also allows for detailed comparison between theory and experiments. In these studies the main focus is to understand bond activation by transition metal cations and solvation of transition metal dications. The gas phase ions of interest are studied using an electrospray-ionization or laser-ablation dual time-of-flight mass spectrometer and are characterized using photofragment spectroscopy in the visible and ultraviolet regions of the spectrum. Photofragment spectroscopy is a powerful method that can be used in gas phase studies to gather a wealth of information on the ions' bond strengths, spectroscopic constants, and dissociation kinetics and dynamics. The study of TiO + (CO 2 ) spectroscopy (Chapter 3) was a result of study of CO 2 bond activation by Ti + that went on to provide a wealth of information on the spectroscopy and dissociation kinetics of this molecule. An electronic transition of the TiO + chromophore was observed, 2 Π[arrow left] 2 Δ, revealing new information about the excited state and the effect of TiO + electronic state on the metal- CO 2 ligand interaction. The photodissociation spectrum of this molecule is well resolved and shows progressions in the covalent Ti-O stretch and metal-ligand stretch and rock. The lifetime of electronically excited TiO + (CO 2 ) was measured, and depends strongly on vibrational energy. Calculations on TiO + and TiO + (CO 2 ) were combined with experimental results on TiO + (CO 2 ) to predict spectroscopic transitions of TiO + , an astrophysically interesting molecule. The photodissociation dynamics of M 2+ (CH 3 CN)n(H 2 O)m where M = Co and Ni, (Chapter 4) is important in understanding the gas phase microsolvation of metal dications. The coordination number and type of solvent affect the dissociation pathways. M 2+ (CH 3 CN)n (n>2) primarily lose a solvent molecule. Electron transfer is a minor channel for n=3 and is the only channel observed for n=2. Mixed clusters M 2+ (CH 3 CN)n(H 2 O)m preferentially lose water. Loss of acetonitrile is a minor channel, as is proton transfer. Water is the proton donor. Replacing acetonitrile with water increases the proton transfer channel. Nickel and cobalt complexes show similar dissociation dynamics, with proton transfer more likely for nickel complexes. Methane activation by transition metal catalysts is industrially important as it can be used to produce gasoline from natural gas. We studied the products and intermediates of the reaction of laser-ablated platinum atoms with methane (Chapter 5). Photoionization efficiency curves were measured for PtCH 2 and the [H-Pt-CH 3 ] insertion intermediate using tunable vacuum ultraviolet light. The resulting ionization energies were combined with bond strengths for the cations to derive bond strengths for the neutrals. These were used to construct a potential energy surface for methane activation by platinum atoms.
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44

Lin, Yih-Tyng, and 林奕廷. "A. Aza-crown ether functionalized silicon quantum dots as metal ion sensors B. Functionalized MoS2 quantum dots as metal ion sensors C. Theoretical study of Bn clusters in ionic liquids." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7kr4mb.

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碩士
國立東華大學
化學系
107
A. Aza-crown ether functionalized silicon quantum dots as metal ion sensors The B3LYP/LanL2DZ method was employed to calculate the binding energy between metal ions and aza-crown ether (C12H23O5N, C14H27O6N, and C14H28O5N2). The magnitudes of binding energies are found to correlate with the capability of aza-crown ether functionalized silicon quantum dots used as metal ion (K+, Na+, Mg2+,Ca2+, Sr2+, Ba2+, Mn2+) sensors. B. Functionalized MoS2 quantum dots as metal ion sensors B3LYP with LanL2DZ and QZVP were used to study the capability of three functionalized (-COOH, -NH2, and -SH) MoS2 quantum dots to detect Co2+, Cd2+and Pb2+ ion. The binding energy between the ions and MoS2 clusters was investigated to assess the sensing mechanism. C. Theoretical study of Bn clusters in ionic liquids The interactions between Boron clusters (Bn, n=6) and ionic liquid were investigated using the B3LYP/cc-pVTZ level of calculations. The likely structures and their IR and Raman spectra are obtained.
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45

Pötschke, Markus. "Simulation of electric field-assisted nanowire growth from aqueous solutions." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A29190.

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Abstract:
The present work is aimed at investigating the mechanisms of nanowire growth from aqueous solutions through a physical and chemical modeling. Based on this modeling, deriving an optimized process control is intended. The work considers two methods of nanowire growth. The first is the dielectrophoretic nanowire assembly from neutral molecules or metal clusters. Secondly, in the directed electrochemical nanowire assembly metal-containing ions are reduced in an AC electric field in the vicinity of the nanowire tip and afterwards deposited at the nanowire surface. To describe the transport and growth processes, continuum models are employed. Furthermore, it has been necessary to consider electro-kinetic fluid flows to match the experimental observations. The occurring partial differential equations are solved numerically by means of finite element method (FEM). The effect of the process parameters on the nanowire growth are analyzed by comparing experimental results to a parameter study. The evaluation has yielded that an AC electro-osmotic fluid flow has a major influence on the dielectrophoretic nanowire assembly regarding the growth velocity and morphology. In the case of directed electrochemical nanowire assembly, the nanowire morphology can be controlled by the applied AC signal shape. Based on the nanowire growth model, an optimized AC signal has been designed, whose parametrization allows to adjust to the chemical precursor and the desired nanowire diameter.
Ziel der vorliegenden Arbeit ist es, mittels physikalischer und chemischer Modelle die Mechanismen des Nanodrahtwachstums aus wässrigen Lösungen zu erforschen und daraus eine optimierte Prozesskontrolle abzuleiten. Dabei werden zwei Verfahren des Nanodrahtwachstums näher betrachtet: Dies sind die dielektrophoretische Assemblierung von neutralen Molekülen oder Metallclustern sowie die gerichtete elektrochemische Nanodrahtabscheidung (engl. directed electrochemical nanowire assembly), bei der metallhaltige Ionen im elektrischen Wechselfeld an der Nanodrahtspitze zunächst reduziert und anschließend als Metallatome abgeschieden werden. Zur Beschreibung der Transport- und Wachstumsprozesse werden Kontinuumsmodelle eingesetzt. Darüber hinaus hat es sich als notwendig erwiesen, elektrokinetische Fluidströmungen zu berücksichtigen, um die experimentellen Beobachtungen zu reproduzieren. Die auftretenden partiellen Differenzialgleichungen werden mittels der Finiten Elemente Methode (FEM) numerisch gelöst. Die Auswirkungen der Prozessparameter auf das Nanodrahtwachstum werden durch den Vergleich von experimentellen Ergebnissen mit Parameterstudien analysiert. Die Auswertung hat ergeben, dass für das dielektrophoretische Wachstum ein durch Wechselfeldelektroosmose (engl. AC electro-osmosis) angetriebener Fluidstrom die Drahtwachstumsgeschwindigkeit und -morphologie maßgeblich beeinflusst. Im Falle der gerichteten elektrochemischen Nanodrahtabscheidung lässt sich die Drahtmorphologie über das angelegte elektrische Wechselsignal steuern. Unter Verwendung des Wachstumsmodells ist ein optimiertes Signal generiert worden, dessen Parametrisierung eine gezielte Anpassung auf den chemischen Ausgangsstoff und den gewünschten Drahtdurchmesser erlaubt.
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