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Yu, Youliang. "Computationally exploring ultrafast molecular ionization". Diss., Kansas State University, 2017. http://hdl.handle.net/2097/38548.
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Doctor of PhilosophyDepartment of Physics
Brett D. Esry
Strong-field ionization plays a central role in molecules interacting with an intense laser field since it is an essential step in high-order harmonic generation thus in attosecond pulse generation and serving as a probe for molecular dynamics through either the sensitivity of ionization to the internuclear separation or the laser-induced electron scattering. Strong-field molecular ionization has been studied both theoretically and experimentally, dominantly through the Born-Oppenheimer approximation and at equilibrium or small reaction distances. We have extended the theoretical studies of molecular ionization to a much broader extent. Specifically, due to the difficulty of treating ionization in Born-Oppenheimer representation especially for molecular dynamics involving strongly-correlated electron-nuclear motion, we have investigated an alternative time-independent--adiabatic hyperspherical--picture for a one-dimensional model of the hydrogen molecule. In the adiabatic hyperspherical representation, all the reaction channels--including ionization--for the hydrogen molecule have been identified in a single set of potential curves, showing the advantage of studying molecular dynamics involving multiple breakup channels coupled with each other. We have thus proposed a good candidate to study strongly-correlated molecular dynamics, such as autoionization and dissociative recombination. Moving to a time-dependent picture by numerically solving the time-dependent Schrödinger equation (TDSE), we have explored two extreme classes of strong-field ionization of hydrogen molecule ion: at large internuclear distances (R>30 a.u.) and for long-wavelength laser fields. Remarkably, we have found strong-field two-center effects in molecular ionization beyond the long-standing one-photon two-center interference as a manifestation of the double-slit interference. In particular, the total ionization probability at large internuclear distances shows strongly symmetry-dependent two-center dynamics in homonuclear diatomic molecules and two-center induced carrier-envelope phase effect in heteronuclear diatomic molecules. Such two-center effects are expected to generalize to other diatomic systems and could potentially be used to explain phenomena in multi-center strong-field physics. Moreover, we have theoretically confirmed, for the first time, the existence of low energy structure in molecular ionization in long-wavelength laser fields by solving the three-dimensional TDSE. Finally, we have performed a pump-probe study of the hydrogen molecular ion where a pump pulse first dissociates the molecule followed by a probe pulse which ionizes the dissociating wave packet, and surprisingly found a pronounced broad ionization peak at large R or large pump-probe delay (~150 fs). Numerically, we have developed and implemented new theoretical frameworks to more accurately and efficiently calculate quantum mechanical processes for small molecules--hydrogen molecule and its ion--which could readily be adapted to heavier diatomic systems.
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Erbsen, Wes Corbin. "Non-dissociative single-electron ionization of diatomic molecules". Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/15740.
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Master of ScienceDepartment of Physics
Carlos Trallero
Over the past four decades, the single-electron ionization of atoms has been a subject of great interest within the ultra-fast community. While contemporary atomic ionization models tend to agree well with experiment across a wide range of intensities (10[superscript]13-10[superscript]15 W/cm[superscript]2), analogous models for the ionization of molecules are currently lacking in accuracy. The deficiencies present in molecular ionization models constitute a formidable barrier for experimentalists, who wish to model the single-electron ionization dynamics of molecules in intense laser fields. The primary motivation for the work presented in this thesis is to provide a comprehensive data set which can be used to improve existing models for the strong-field ionization of molecules. Our approach is to simultaneously measure the singly-charged ion yield of a diatomic molecule paired with a noble gas atom, both having commensurate ionization potentials. These measurements are taken as a function of the laser intensity, typically spanning two orders of magnitude (10[superscript]13-10[superscript]15 W/cm[superscript]2). By taking the ratio of the molecular to atomic yields as a function of laser intensity, it is possible to "cancel out" systematic errors which are common to both species, e.g. from laser instability, or temperature fluctuations. This technique is very powerful in our ionization studies, as it alludes to the distinct mechanisms leading to the ionization of both molecular and atomic species at the same intensity which are not a function of the experimental conditions. By using the accurate treatments of atomic ionization in tandem with existing molecular ionization models as a benchmark, we can use our experimental ratios to modify existing molecular ionization theories. We hope that the data procured in this thesis will be used in the development of more accurate treatments describing the strong-field ionization of molecules.
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Schug, Kevin Albert. "Pseudo-Molecular Ion Formation by Aromatic Acids in Negative Ionization Mode Electrospray Ionization Mass Spectrometry". Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29886.
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Pseudo-molecular ion formation is an artifact common to most analyses performed by electrospray ionization mass spectrometry. These species are non-covalent complexes formed between an analyte of interest and any other components (such as mobile phase, additives, and impurities) present in the ionized sample band. Published literature addresses pseudo-molecular ion formation in routine analyses as well as in complicated molecular recognition processes. The majority of these works are directed towards the formation of complexes in the positive ionization mode. Consequently, investigation of pseudo-molecular ion formation in the negative ionization mode is a logical extension of work in this area.
Experiments presented here detail the work performed on elucidation of factors controlling ionization efficiency of aromatic acid pseudo-molecular ions by electrospray ionization in the negative ionization mode. Sets of tested acidic analytes, including ibuprofen derivatives and benzoic acid derivatives, were analyzed in the presence of various solution systems by flow injection analysis to determine the effect of pH, concentration, injection volume, and instrumental parameters on dominant ion forms observed in the mass spectra. These ion forms correspond to a deprotonated molecular ion ([M-H]-), a hydrogen-bound dimer ion ([2M-H]-), and a sodium-bridged dimer ion ([2M-2H+Na]-). Report of the latter ion form is unique to this work.
Response of these ion forms were found to vary greatly with changing solution parameters, particularly in the presence of common LC-MS modifiers, such as triethylamine, acetic acid, formic acid, and ammonium formate. Results point to the formation of the sodium-bridged dimer ion during gas-phase processes following the release of ions from disintegrated droplets. Ab initio theoretical calculations and correlations with calculated solution phenomena (such as pKa and log P) were used to elucidate structural arrangements and dominant factors controlling pseudo-molecular ion formation by aromatic acids in the negative ionization mode.Ph. D.
4
Gritschneder, Matthias. "Ionization and Triggered Star Formation in Turbulent Molecular Clouds". Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-104903.
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Vanne, Yulian V. "Ionization of molecular hydrogen in ultrashort intense laser pulses". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16107.
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Ein neuer numerischer ab initio Ansatz wurde entwickelt und zur Lösung der zeitabhängigen Schrödingergleichung für zweiatomig Moleküle mit zwei Elektronen (z.B. molekularer Wasserstoff), welche einem intensiven kurzen Laserpuls ausgesetzt sind, angewandt. Die Methode basiert auf der Näherung fester Kernabstände und der nicht-relativistischen Dipolnäherung und beabsichtigt die genaue Beschreibung der beiden korrelierten Elektronen in voller Dimensionalität. Die Methode ist anwendbar für eine große Bandbreite von Laserpulsparamtern und ist in der Lage, Einfachionisationsprozesse sowohl mit wenigen als auch mit vielen Photonen zu beschreiben, sogar im nicht-störungstheoretischen Bereich. Ein entscheidender Vorteil der Methode ist ihre Fähigkeit, die Reaktion von Molekülen mit beliebiger Orientierung der molekularen Achse im Bezug auf das linear polarisierte Laserfeld in starken Feldern zu beschreiben. Dementsprechend berichtet diese Arbeit von der ersten erfolgreichen orientierungsabhängigen Analyse der Multiphotonenionisation von H2, welche mit Hilfe einer numerischen Behandlung in voller Dimensionalität durchgeführt wurde. Neben der Erforschung des Bereichs weniger Photonen wurde eine ausführliche numerische Untersuchung der Ionisation durch ultrakurze frequenzverdoppelte Titan:Saphir-Laserpulse (400 nm) präsentiert. Mit Hilfe einer Serie von Rechnungen für verschiedene Kernabstände wurden die totalen Ionisationsausbeuten für H2 und D2 in ihren Vibrationsgrundzuständen sowohl für parallele als auch für senkrechte Ausrichtung erhalten. Eine weitere Serie von Rechnungen für 800nm Laserpulse wurde benutzt, um ein weitverbreitetes einfaches Interferenzmodel zu falsifizieren. Neben der Diskussion der numerischen ab initio Methode werden in dieser Arbeit verschiedene Aspekte im Bezug auf die Anwendung der Starkfeldnäherung für die Erforschung der Reaktion eines atomaren oder molekularen Systems auf ein intensives Laserfeld betrachtet.A novel ab initio numerical approach is developed and applied that solves the time-dependent Schrödinger equation describing two-electron diatomic molecules (e.g. molecular hydrogen) exposed to an intense ultrashort laser pulse. The method is based on the fixed-nuclei and the non-relativistic dipole approximations and aims to accurately describe both correlated electrons in full dimensionality. The method is applicable for a wide range of the laser pulse parameters and is able to describe both few-photon and many-photon single ionization processes, also in a non-perturbative regime. A key advantage of the method is its ability to treat the strong-field response of the molecules with arbitrary orientation of the molecular axis with respect to the linear-polarized laser field. Thus, this work reports on the first successful orientation-dependent analysis of the multiphoton ionization of H2 performed by means of a full-dimensional numerical treatment. Besides the investigation of few-photon regime, an extensive numerical study of the ionization by ultrashort frequency-doubled Ti:sapphire laser pulses (400 nm) is presented. Performing a series of calculations for different internuclear separations, the total ionization yields of H2 and D2 in their ground vibrational states are obtained for both parallel and perpendicular orientations. A series of calculations for 800nm laser pulses are used to test a popular simple interference model. Besides the discussion of the ab initio numerical method, this work considers different aspects related to the application of the strong-field approximation (SFA) for investigation of a strong-field response of an atomic and molecular system. Thus, a deep analysis of the gauge problem of SFA is performed and the quasistatic limit of the velocity-gauge SFA ionization rates is derived. The applications of the length gauge SFA are examined and a recently proposed generalized Keldysh theory is criticized.
6
McCartney, Mark. "Ionization processes in multielectron ion-atom collisions". Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359106.
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Purvis, John. "R-matrix-Floquet Theory of multiphoton ionization". Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239216.
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Trachy, Marc Lawrence. "Photoassociative ionization in cold rubidium". Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/695.
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Underwood, Jonathan. "Vector properties in molecular photodissociation". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311835.
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Hayton, S. J. T. "Single and double ionization of ions by energy-resolved electrons". Thesis, University of Newcastle Upon Tyne, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387406.
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Cross, Gillian M. "The multiphoton multiple ionization of molecules in intense laser fields". Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283758.
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Blease, Trevor Graham. "Laser multiphoton ionization spectroscopy and analysis of the xylene isomers". Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/14139.
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Gallimore, Peter James. "Molecular characterisation of organic aerosols using soft ionisation mass spectrometry". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709386.
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Arnberg, Elise. "Investigation of molecular probes for pH determination with electrospray ionization mass spectrometry". Thesis, Uppsala universitet, Institutionen för kemi - BMC, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-381962.
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Tremblin, Pascal. "Ionization impact on molecular clouds and star formation : numerical simulations and observations". Paris 7, 2012. http://www.theses.fr/2012PA077217.
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À toutes les échelles de l'Astrophysique, l'impact de l'ionisation venant des étoiles massives est une question cruciale. Quels sont les mécanismes de formation des piliers et des globules ? La formation des coeurs pré-stellaires est-elle déclenchée par l'ionisation ou préexistante ? Les étoiles massives ont-elles un impact sur la distribution en densité du gaz environnant? Ont-elles un impact sur la distribution des étoiles en fonction de leur masse (la fonction de masse initiale, IMF) ? Cette thèse vise à apporter des éléments de réponse à ces questions, en se concentrant en particulier sur la compréhension de la formation des structures entre le gaz froid et ionisé. Nous présentons l'état de l'art des travaux théoriques et des observations des régions ionisées (régions Hii) et nous introduisons les outils numériques qui ont été développés pour modéliser l'ionisation dans les simulations d'hydrodynamique turbulente effectuées avec le code HERACLES. Nous présentons un nouveau modèle pour la formation des piliers basés sur la courbure et l'effondrement de la coquille dense sur elle-même et un nouveau modèle pour la formation de globules basé sur la turbulence du gaz froid. Plusieurs diagnostics ont été développés pour tester ces nouveaux modèles sur les observations de RCW 120, RCW 36, Cygnus X, la Nébuleuse de la Rosette et de l'Aigle grâce aux cartes de colonne densité du télescope Herschel et aux données de raies moléculaires. En annexe, nous présentons également des travaux réalisés en parallèle de cette thèse : l'échange de charge dans la collision entre vents planétaires et stellaires et le test de site en sub-millimétrique sur la station Concordia en AntarctiqueAt all the scales of Astrophysics, the impact of the ionization from massive stars is a crucial issue. What are the formation mechanisms of pillars and globules? Are the formation of the young stellar objects triggered or would have they formed anyway? Do massive stars have an impact on the distribution of the surrounding gas? Do they have an impact on the mass distribution of stars (the initial mass function, IMF)? This thesis aims at shedding some light on these questions, by focusing especially on the formation of the structures between the cold and the ionized gas. We present the state of the art of the theoretical and observational works on ionized regions (Hii regions) and we introduce the numerical tools that have been developed to model the ionization in the hydrodynamic simulations with turbulence performed with the HERACLES code. Thanks to the simulations, we present a new model for the formation of pillars based on the curvature and collapse of the dense shell on itself and a new model for the formations of cometary globules based on the turbulence of the cold gas. Several diagnostics have been developed to test these new models in the observations of RCW 120, RCW 36, Cygnus X, the Rosette and Eagle Nebulae thanks to Herschel column density maps and molecular-line data. We also present in appendix other works that have been done in parallel of this thesis: the charge exchange in colliding planetary and stellar winds and the sub-millimeter site testing at the Concordia station in Antarctica
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Lindsay, Bernard Gregory. "State selected studies of some charge transfer and dissociative ionization collisions". Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317102.
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Paquette, Jay Paul. "The effect of realistic focal conditions on strong -field double ionization". W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539623545.
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In recent years, a great deal of progress has been made in understanding the ionization processes that result from the interaction of an intense laser pulse with multielectron atoms. However, due to experimental limitations, the effect of the laser field's spatial dependence on strong-field processes has rarely been investigated. Presented in this work is a theoretical analysis of this spatial dependence including a proposal for an experimentally observable result of the phenomenon. We begin by outlining the elements of the laser field that will vary as a function of position and show their effects on simple free electron trajectories. We then develop a classical, three-dimensional simulation of the entire process of double ionization of helium in an intense laser field using realistic, non-paraxial focal conditions. The existence of an out-of-phase electric field component in the laser propagation direction is determined, which produces an effective longitudinal ellipticity, resulting in a reduction in the double ion yields as a function of position in the laser focus. It is found that under conditions of tight focusing, the effective focal volume for non-sequential double ionization is significantly reduced.
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Magrakvelidze, Maia. "Nuclear dynamics and ionization of diatomic molecules in intense laser fields". Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2283.
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Cameron, Brett Russell. "Investigations of the flow dynamics of supersonic molecular beams and the ionization of molecular clusters by electron impact". Thesis, University of Canterbury. Chemistry, 1993. http://hdl.handle.net/10092/8506.
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A pulsed supersonic molecular beam apparatus has been constructed for the investigation of atomic and molecular van der Waals clusters. The apparatus was characterized by investigating supersonic beam intensities as a function of reservoir pressure and nozzle to skimmer separation, and by measuring supersonic beam speed distributions for various monatomic and diatomic gases and binary monatomic gas mixtures using time-of-flight methods. A new technique for deconvolving badly convoluted time-of-flight data was developed and successfully applied to the deconvolution of time-of-flight waveforms measured for unchopped pulsed supersonic beams of argon, krypton, CHCl₃ and CH₃Cl. Size distributions of van der Waals cluster species were investigated for supersonic expansions of pure argon and for seeded helium expansions containing 8O₂, N₂O and H₂O, NO and NO₂ and NH₃. Appearance potentials of the cluster ions (CO₂)n⁺, (N₂O) n⁺ (2 ≤ n ≤ 4) and (NH₃)nH⁺ (1 ≤ n ≤ 8), and the cluster ion fragments (N₂O∙O)+ and (N₂O∙NO)+ have been determined by electron impact ionization of neutral clusters formed in the supersonic beam. The measured appearance potential data were used to estimate cluster ion binding energies, and possible mechanisms for the formation of the cluster fragment ions (N₂O∙O)+ and (N₂O∙NO)+ are discussed.
Computational procedures have been developed for the calculation of supersonic beam properties as a function of distance along the expansion axis. Collision frequency, flow velocity, particle density, mean free path, and axial and radial temperatures in supersonic atomic and homonuclear diatomic beams have been calculated for various species using realistic interaction potentials and collision cross sections obtained from scattering theory. A simple approach to the estimation of rotational relaxation times and collision numbers in supersonic expansions was developed and used to calculate rotational relaxation times and rotational collision numbers for H₂, N ₂, O ₂ and Cl₂. A sophisticated direct simulation Monte Carlo procedure was devised for the investigation of rotational relaxation in small molecules. The devised relaxation model has been used to calculate rotational relaxation data for the homonuclear diatomic molecules H₂, N₂, O ₂ and Cl₂, and for the polyatomic species CO₂, OCS, NH₃, CH₄, CH₃Cl and C₂H₄. Results obtained using the Monte Carlo procedure were used to investigate the breakdown of translational and rotational equilibrium in supersonic expansions of CO₂, OCS and CH₃Cl.
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Watson, R. Craig Jr. "Laser-Ionization Time-of-Flight Mass Spectrometry of High Molecular Mass Inorganic Complexes". Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35554.
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Laser-Ionization Time-of-Flight Mass Spectrometry (LI-TOF-MS) is a sophisticated tool for the molecular-weight determination and structural characterization of a variety of molecules. Advances in instrumentation and ionization methods have recently expanded its role in the analysis of high-mass analytes. Large multimetallic complexes, which are efficient solar-energy converters, rely heavily on their chemical structure for optimum operation. Molecular mass determinations of these multimetallic complexes have been problematic due to their lability and high molecular weights.
This thesis describes the characterization of a LI-TOF-MS instrument and confirmation of theoretical time-of-flight mass-separation principles. Several test cases demonstrate the instrument's proper operation and calibration for a wide mass range of analytes. Mass spectral results of three organometallic compounds: i. [Ir(dpp)2Cl2](PF6), ii. {[(bpy)2Ru(dpp)]2IrCl2}(PF6)5, and iii. {[(bpy)2Ru(dpp)]2RuCl2}(PF6)5 under a variety of laser ionization and sample preparation conditions are compared. A complete structural characterization of the monometallic complex, [Ir(dpp)2Cl2](PF6), is presented. The two trimetallic analytes fragmented easily, but significant components of the molecules are successfully identified. After optimizing the ionization and analytical procedure, LI-TOF-MS proved useful in the analysis of high molecular mass metal complexes.
Master of Science
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Thomason, J. W. G. "Direct and indirect ionization of Zn'+ and Mg'+ by energy-resolved electrons". Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316232.
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Dashtiev, Maxim. "Fluorescence spectroscopy of trapped molecular ions produced with matrix-assisted laser desorption/ionization /". Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16949.
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Finch, Jeffrey William. "Selective mass spectrometry by single-photon ionization from a molecular hydrogen laser source". Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185895.
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A molecular hydrogen laser, with an output of 7.8 eV photons in the vacuum ultraviolet, is evaluated as a selective source for photoionization mass spectrometry. Types of compounds ionized by the laser include a variety of amines, nitrogen heterocycles, drugs of abuse, pharmaceuticals, and polynuclear aromatic hydrocarbons (PAHS). The laser is coupled to a time-of-flight mass analyzer, which allows a spectrum to be recorded with each laser pulse. The laser is a "soft" ionization source and mass spectra of nearly all of the compounds studied yield single ion peaks due to the parent molecule with no fragments. This results in simplified mass spectra with a one-to-one correspondence of photoactive molecules with molecular ion peaks. Since the photoionization threshold of the laser is relatively low, selectivity of the photoactive species is high in the presence of a complex sample matrix. The performance of the laser source is improved with a few changes in the original design. In addition, the previous method of recording mass spectra with a photographic emulsion is replaced with a digital oscilloscope, which averages spectra over many laser pulses. As a result, a true assessment of the technique's sensitivity is finally achieved. The time-of-flight mass spectrometer is modified with a new microchannel plate ion detector and preamplifier. As a result, detection limits for PAH's improve by nearly three orders of magnitude, from the 100 ng range to the 100 pg range. Selectivity of the laser photoionization source in complex mixture analysis is demonstrated with the ability to detect PAH's in a drinking water sample at concentrations below 100 parts-per-trillion, using a simple solid-phase extraction technique. Application of the technique for rapid screening of drugs of abuse in urine is demonstrated where solid-phase extraction columns are utilized for sample pretreatment. Urine samples spiked with drugs such as cocaine, codeine, morphine, phencyclidine, and methadone, yield photoionization mass spectra consisting of parent molecular ions for the drugs with a few noninterfering ion signals from the matrix. The technique is evaluated and compared to other drug screening techniques such as enzyme-multiplied immunoassay.
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Hussien, Abdou Mekky Mousa. "Ionization of diatomic molecules in intense laser fields". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17323.
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In dieser Arbeit wurde die Ionisation einiger zweiatomiger Moleküle (H2, N2 und O2) in intensiven Laserfeldern untersucht. Hierbei wurden verschiedene Modelle zur Beschreibung der Tunnelionisation sowohl untereinander als auch mit der Lösung der zeitabhängigen Schrödingergleichung (TDSE) verglichen. Die kernabstandsabhängige Ionisationswahrscheinlichkeit wurde für verschiedene Intensitäten betrachtet und die Gültigkeit modifizierter atomarer bzw. Molekularer Modelle zur Beschreibung der Tunnelionisation analysiert. Es wurde herausgefunden, dass Modelle, die auf der quasistatischen Näherung beruhen (wo die Ionisation unabhängig von der Frequenz des Laserfeldes ist), nur in einem kleinem Frequenz- und Intensitätsbereich hinreichend genaue Ergebnisse liefern, dem Tunnelregime. Modelle mit einem frequenzabhängigen Faktor stimmen hingegen sowohl im Tunnel- als auch im Mehrphotonenregime mit den genaueren TDSE Ergebnissen überein. Weiterhin wird auch die Abweichung zur Franck-Condon Näherung verdeutlicht. Es wurde ein kleiner Einfluss auf die Revival-Zeit des im Wasserstoffmolekül-Ion gestarteten Wellenpakets gefunden. Die Berücksichtigung von Bond-Softening führt weiterhin zu einer Verringerung der Revival-Zeit mit steigender Spitzenintensität des Lasers. Außerdem wird die Anisotropie der Ionisation von H2 als Funktion der Laserintensität in linear und zirkular polarisiertem Licht mit dem molekularen Tunnelmodell MO-ADK untersucht. Gute Übereinstimmung mit den experimentellen Beobachtungen wurde gefunden, insbesondere wenn der Effekt des Fokusvolumens des Laserfeldes berücksichtigt wird. Die Anwendbarkeit des Zwei-Zentren-Modells auf größere Moleküle, N2 und O2, wird ebenfalls getestet. Es wird beobachtet, dass dies für N2 (symmetrisches HOMO) funktioniert, für O2 (asymmetrisches HOMO) jedoch nicht.The ionization of some diatomic molecules, H2, N2, and O2, exposed to intense laser fields has been studied by comparing various molecular tunneling–ionization models with each other and with the numerical solution of the time-dependent Schrödinger equation (TDSE). The internuclear-distance dependent ionization yields over a wide range of laser peak intensities are investigated and the validity of the modified atomic and molecular tunneling models is examined. It is found that those models that depend on the quasi-static approximation, where ionization is independent on the oscillation frequency of the applied laser field, are useful for laser-induced ionization processes in only a very small region of the frequency and intensity domain of laser fields, i.e. in the tunneling regime. The models that include a frequency dependent factor are in a good agreement with the accurate TDSE calculations in both the multiphoton and the tunneling ionization regimes. Furthermore, the deviation from Franck-Condon-like distribution is also clarified. A small effect on the revival time of the vibrational wavepacket of hydrogen molecular ion, due to this deviation, has been found. Consideration of the bond-softening effect leads to a decrease in the revival time with increasing laser-peak intensity. The anisotropy of H2 as a function of laser intensity in linear and circular polarized fields using molecular tunneling model (MO-ADK) are also studied and a good agreement with the experimental observations, especially if the focal volume of the laser field is considered, has been obtained. The applicability of the two-center model for larger molecules, N2 and O2, is tested. It is found that it works with N2 (symmetric HOMO) but fails in O2 (ansymmetric HOMO).
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Attah, Isaac Kwame. "BINDING ENERGIES AND SOLVATION OF ORGANIC MOLECULAR IONS, REACTIONS OF TRANSITION METAL IONS WITH, AND PLASMA DISCHARGE IONIZATION OF MOLECULAR CLUSTERS". VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/525.
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In this dissertation, different approaches have been employed to address the quest of understanding the formation and growth mechanisms of carbon-containing molecular ions with relevance to astrochemistry. Ion mobility mass spectrometry and DFT computations were used to investigate how a second nitrogen in the pyrimidine ring will affect the formation of a covalent bond between the benzene radical cation and the neutral pyrimidine molecule, after it was shown that a stable covalent adduct can be formed between benzene radical cation and the neutral pyridine. Evidence for the formation of a more stable covalent adduct between the benzene radical cation and the pyrimidine is reported here. The effect of substituents on substituted-benzene cations on their solvation by an HCN solvent was also investigated using ion mobility mass spectrometry and DFT computations were also investigated. We looked at the effect of the presence of electron-withdrawing substituents in fluorobenzene, 1,4 di- fluorobenzene, and benzonitrile on their solvation by up to four HCN ligands, and compared it to previous work done to determine the solvation chemistry of benzene and phenylacetylene by HCN. We report here the observed increase in the binding of the HCN molecule to the aromatic ring as the electronegativity of the substituent increased. We also show in this dissertation, DFT calculations that reveal the formation of both hydrogen-bonded and electrostatic isomers, of similar energies for each addition to the ions respectively. The catalytic activity of the 1st and 2nd row TM ions towards the polymerization of acetylene done using the reflectron time of flight mass spectrometry and DFT calculations is also reported in this dissertation. We explain the variation in the observed trend in C-H/C-C activity of these ions. We also report the formation of carbide complexes by Zr+, Nb+, and Mo+, with the acetylene ligands, and show the thermodynamic considerations that influence the formation of these dehydrogenated ion-ligand complexes. Finally, we show in this dissertation, a novel ionization technique that we employed to generate ions that could be relevant to the interstellar and circumstellar media using the reflectron time of flight mass spectrometry.
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Gaire, Bishwanath. "Imaging of slow dissociation of the laser induced fragmentation of molecular ions". Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8852.
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Doctor of PhilosophyDepartment of Physics
Itzhak Ben-Itzhak
Lasers are being used widely for the study and manipulation of the dynamics of atomic and molecular targets, and advances in laser technology makes it possible to explore new areas of research — for example attosecond physics. In order to probe the fragmentation dynamics of molecular ions, we have developed a coincidence three-dimensional momentum imaging method that allows the kinematically complete study of all fragments except electrons. Recent upgrades to this method allow the measurement of slow dissociation fragments, down to nearly zero velocity, in intense ultrafast laser fields. Evidences for the low energy breakup are presented using the benchmark molecules diatomic H[subscript]2[superscript]+ and polyatomic H[subscript]3[superscript]+ . The low energy fragments in H[subscript]2[superscript]+ dissociation are due to the intriguing zero-photon dissociation phenomenon. This first experimental evidence for the zero-photon dissociation is further supported by sophisticated theoretical treatment. We have explored the laser pulse length, intensity, wavelength, and chirp dependence of zero-photon dissociation of H[subscript]2[superscript]+, and the results are well described by a two-photon process based on stimulated Raman scattering. Similar studies of the slow dissociation of H[subscript]3[superscript]+ reveal that two-body dissociation is dominant over three-body dissociation. The most likely pathways leading to low-energy breakup into H[superscript]++H[subscript]2, in contradiction to the assessments of the channels in at least one previous study, are explored by varying the laser pulse duration and the wavelength. In addition, we have investigated the dissociation and single ionization of N[subscript]2[superscript]+ , and an interesting high energy feature in addition to the low energy has been observed at higher intensities. Such high energy results from the breakup of molecules in excited states are accessible at higher intensities where their potential energy is changing rapidly with the internuclear distance. We have extended the intense field ionization studies to other molecular ions N[subscript]2[superscript]+ , CO[superscript]+, NO[superscript]+, and O[subscript]2[superscript]+ . The dissociative ionization of these molecules follow a general mechanism, a stairstep ionization mechanism. Utilizing the capability of the upgraded experimental method we have measured the non-dissociative and dissociative ionization of CO[superscript]+ using different pulse lengths. The results suggest that dissociative ionization can be manipulated by suppressing some ionization paths.
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Du, Meng Li. "The effect of closed classical orbits on quantum spectra: Ionization of atoms in a magnetic field". W&M ScholarWorks, 1987. https://scholarworks.wm.edu/etd/1539623773.
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A quantitative theory of oscillatory spectra for atoms in a magnetic field is developed. When an atom is placed in a magnetic field, and absorption spectrum into states close to the ionization threshold is measured, it is found that the absorption as a function of energy is a superposition of many sinusoidal oscillations. Such interesting and surprising phenomenon are fully explained and described by the theory.;The theory is based on three approximations: (1) Near the atomic nucleus, the diamagnetic field is negligible. (2) Far from the nucleus, the wave propagates semiclassically. (3) Waves returning to the nucleus are similar to (cylindrically-modified) Coulomb-Scattering waves. Using these approximations, together with the simple physical picture of absorption process, formula is derived for the transition rate as a function of final states energy.;The main result is that the transition rate is equal to the sum of two very different kinds of contributions. The first is the averaged transition rate in the absence of the magnetic field, which is a smooth function of energy; the second is itself a sum over many oscillations. Each oscillation is closely associated with a band of wave, initially going out from the nucleus, propagating along a family of trajectories, and finally returning to the vicinity of the nucleus. Because in the center of the family of trajectories is a closed orbit going from the nucleus and returning to the nucleus, we say "a closed orbit makes an oscillatory contribution to the absorption spectrum".;Formulas and algorithms are derived and specified for the calculations of the spectrum from the initial quantum state, dipole polarization, and the properties of the closed classical orbits. Good agreements with experiments were found. Very detailed interpretations are obtained.
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Makhija, Varun. "Laser-induced rotational dynamics as a route to molecular frame measurements". Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18522.
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Doctor of PhilosophyDepartment of Physics
Vinod Kumarappan
In general, molecules in the gas phase are free to rotate, and measurements made on such samples are averaged over a randomly oriented distribution of molecules. Any orientation dependent information is lost in such measurements. The goal of the work presented here is to a) mitigate or completely do away with orientational averaging, and b) make fully resolved orientation dependent measurements. In pursuance of similar goals, over the past 50 years chemists and physicists have developed techniques to align molecules, or to measure their orientation and tag other quantities of interest with the orientation. We focus on laser induced alignment of asymmetric top molecules. The first major contribution of our work is the development of an effective method to align all molecular axes under field-free conditions. The method employs a sequence of nonresonant, impulsive laser pulses with varied ellipticities. The efficacy of the method is first demonstrated by solution of the time dependent Schr\"{o}dinger equation for iodobenzene, and then experimentally implemented to three dimensionally align 3,5 difluoroiodobenzene. Measurement from molecules aligned in this manner greatly reduces orientational averaging. The technique was developed via a thorough understanding and extensive computations of the dynamics of rotationally excited asymmetric top molecules. The second, and perhaps more important, contribution of our work is the development of a new measurement technique to extract the complete orientation dependence of a variety of molecular processes initiated by ultrashort laser pulses. The technique involves pump-probe measurements of the process of interest from a rotational wavepacket generated by impulsive excitation of asymmetric top molecules. We apply it to make the first measurement of the single ionization probability of an asymmetric top molecule in a strong field as a function of all relevant alignment angles. The measurement and associated calculations help identify the orbital from which the electron is ionized. We expect that this technique will be widely applicable to ultrafast-laser driven processes in molecules and provide unique insight into molecular physics and chemistry.
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Johansson, Henrik. "Fragmentation of Amino Acids and Microsolvated Peptides and Nucleotides using Electrospray Ionization Tandem Mass Spectrometry". Licentiate thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-37202.
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This thesis presents three different series of high energy (keV) collision experiments as well as a brief scientific introduction to the field. In the first series, protonated glycine and leucine were collided with carbon dioxide and a beam attenuation method was applied to determine their total fragmentation cross sections. A technique was also presented for how to restore the resolution in mass spectra obtained with a hemispherical electrostatic analyzer followed by a position sensitive detector (micro-channel plate equipped with a resistive anode). In the second series of experiments, Collision Induced Dissociation (CID) and Electron Capture Induced Dissociation (ECID) studies were performed on the nucleotide adenosine 5'-monophosphate anion (AMP-) in water complexes. The two dissociation techniques revealed different fragmentation patterns and a numerical solvent evaporation model was used to interpret the spectra. It was then found that the CID and ECID processes were associated with different internal energy distributions. The third experiment concerned ECID of the protonated dipeptide glycine-alanine ([GA+H]+) in complexes with water, methanol, acetonitrile or crown ether. Depending on the attached molecular species, different ratios between the two competing channels ammonia loss and N-Cα bond cleavage were observed. Quantum chemical calculations revealed that a notable shift in the location of the captured electron occurred for the case of two acetonitriles and one crown ether compared to the bare ion and the ion in complexes with either water or methanol. Finally, this thesis will discuss developments of the electrospray ionization platform as well as the new Double ElectroStatic IonRing ExpEriment (DESIREE) facility.
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Atkins, Danielle S., i N/A. "Electron Coincidence Studies of Molecules". Griffith University. School of Biomolecular and Physical Sciences, 2007. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20070920.112918.
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The electron-electron coincidence (e,2e) technique yields complete kinematical information about the electron impact ionization process. The (e,2e) technique has been widely used to study dynamical effects in ionizing collisions with atomic targets, however studies of molecular ionization using this technique have been very limited. Recently further experimental studies of small molecules have been proposed, as the cross sections of small molecules are now computable using sophisticated theoretical approaches [77, 24]. This thesis presents dynamical investigations for the electron impact ionization of the molecular targets H2O and H2, employing the (e,2e) technique to experimentally measure the triple differential cross section (TDCS). The TDCS is defined as the probability that a bound electron will be ejected from the target atom or molecule (into a particular direction with a defined energy) and the initial electron will be scattered into a particular direction with a particular energy. All TDCSs presented within this thesis were performed using an electron coincidence spectrometer in the coplanar asymmetric geometry at intermediate incident electron energies. This thesis presents the electron impact ionization TDCSs of H2O. A series of measurements were performed using H2O in the vapour form. Measurements of the TDCS are presented for the 2a1 atomic-like orbital and the 1b2, 3a1 and 1b1 molecular orbitals at a common incident electron energy of 250eV, ejected electron energy of 10eV and scattering angle of -15o. The experimental TDCSs are compared with theoretical cross sections that were calculated by Champion et al [25, 26] using a distorted wave Born approach (DWBA). TDCS measurements for the single ionization of the hydrogen molecule, H2 were performed as in recent years there has been evidence that indicates the ejected electron angular distribution is perturbed due to Young-type interference effects. The oscillatory structure which is predicted in the cross section is due to the two-centred nature of the molecule [27, 29]. This thesis presents experimental TDCSs for the ionization of H2 which are compared to TDCSs of helium. A series of measurements for the TDCSs of H2 and He are presented at a common incident electron energy of 250eV and scattering angle of -15o, for a range of ejected electron energies between 10eV and 100eV. The experimental TDCSs are compared with two types of theoretical calculations.
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Atkins, Danielle S. "Electron Coincidence Studies of Molecules". Thesis, Griffith University, 2007. http://hdl.handle.net/10072/367729.
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The electron-electron coincidence (e,2e) technique yields complete kinematical information about the electron impact ionization process. The (e,2e) technique has been widely used to study dynamical effects in ionizing collisions with atomic targets, however studies of molecular ionization using this technique have been very limited. Recently further experimental studies of small molecules have been proposed, as the cross sections of small molecules are now computable using sophisticated theoretical approaches [77, 24]. This thesis presents dynamical investigations for the electron impact ionization of the molecular targets H2O and H2, employing the (e,2e) technique to experimentally measure the triple differential cross section (TDCS). The TDCS is defined as the probability that a bound electron will be ejected from the target atom or molecule (into a particular direction with a defined energy) and the initial electron will be scattered into a particular direction with a particular energy. All TDCSs presented within this thesis were performed using an electron coincidence spectrometer in the coplanar asymmetric geometry at intermediate incident electron energies. This thesis presents the electron impact ionization TDCSs of H2O. A series of measurements were performed using H2O in the vapour form. Measurements of the TDCS are presented for the 2a1 atomic-like orbital and the 1b2, 3a1 and 1b1 molecular orbitals at a common incident electron energy of 250eV, ejected electron energy of 10eV and scattering angle of -15o. The experimental TDCSs are compared with theoretical cross sections that were calculated by Champion et al [25, 26] using a distorted wave Born approach (DWBA). TDCS measurements for the single ionization of the hydrogen molecule, H2 were performed as in recent years there has been evidence that indicates the ejected electron angular distribution is perturbed due to Young-type interference effects. The oscillatory structure which is predicted in the cross section is due to the two-centred nature of the molecule [27, 29]. This thesis presents experimental TDCSs for the ionization of H2 which are compared to TDCSs of helium. A series of measurements for the TDCSs of H2 and He are presented at a common incident electron energy of 250eV and scattering angle of -15o, for a range of ejected electron energies between 10eV and 100eV. The experimental TDCSs are compared with two types of theoretical calculations.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
Faculty of Science, Environment, Engineering and Technology
Full Text
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Vajdi, Aram. "Experimental study of strong field ionization and high harmonic generation in molecules". Kansas State University, 2015. http://hdl.handle.net/2097/19161.
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Master of SciencePhysics
Vinod Kumarappan
This report includes the experimental details and results of two experiments. The first experiment addresses carrier envelope phase (CEP) effects in higher order harmonic generation (HHG), and the second experiment is a pump-probe experiment on CO₂ molecules using ultrashort laser pulses. Ultrashort laser pulses that are only a few optical cycles long are of interest for studying different atomic and molecular processes. The CEP of such a pulse is an important parameter that can affect the experimental results. Because the laser pulses we used in the HHG experiment have random CEP, we tagged a given harmonic spectrum with the CEP of the fundamental laser pulse that generated it by measuring both shot-by-shot. The first chapter of this report is about the experimental details and the results we got from our CEP-tagged HHG experiment that enabled us to observe the interference of different quantum pathways. In the second experiment, discussed in the second chapter of this report, we tried to study the structure of the CO₂⁺ ion created by strong field ionization in a pump-probe experiment. For this experiment, we used an ultrashort laser pulse to ionize CO₂ molecules, and after various time delays we probed the ionic wave packet by ionizing CO₂⁺ with another ultrashort laser pulse. By performing Fourier analysis on the delay-dependent CO₂⁺⁺ yield, we were able to identify the populated states of CO₂⁺.
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Shi, Fengjian. "LASER ELECTROSPRAY MASS SPECTROMETRY: INSTRUMENTATION AND APPLICATION FOR DIRECT ANALYSIS AND MOLECULAR IMAGING OF BIOLOGICAL TISSUE". Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/445496.
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ChemistryPh.D.
This dissertation elucidates the instrumentation and application of a hybrid ambient ionization source, laser electrospray mass spectrometry (LEMS), for the direct analysis and molecular imaging of biological tissue without matrix deposition. In LEMS, laser pulses from a Ti:Sapphire laser amplifier (60 fs, 800 nm, and 1 mJ) interact with surface analytes and transfer them from the condensed phase into the gas phase without the requirement of either exogenous matrix or endogenous water in the sample. The laser vaporized analytes are captured and ionized by an electrospray source, and finally detected by a mass analyzer. It was found that a turn-key, robust femtosecond fiber laser with longer wavelength, longer duration, and lower pulse energy at 1042 nm, 425 fs, and 50 µJ, respectively, provided comparable results with the Ti:Sapphire laser. Vaporization of intact, dried or aqueous cytochrome c and lysozyme samples was demonstrated by the fiber laser. A charge states distribution at lower charge states indicating folded conformation of proteins and the hemoglobin α subunit-heme complex from whole blood was observed. Endogenous anthocyanins, sugars, and other metabolites were detected and revealed the anticipated metabolite profile for the flower petal and leaf samples by the fiber laser. Phospholipids, especially phosphatidylcholine, were identified from a fresh mouse brain section sample. These lipid features were suppressed in both the fiber laser and Ti:Sapphire LEMS measurement in the presence of optimal cutting temperature compounds which are commonly used in animal tissue cryosectioning. This dissertation also details the design of an automated mass spectrometry imaging source based on the Ti:Sapphire LEMS. The laser, translation stage, and mass analyzer are synchronized and controlled using a customized user interface to enable step-by-step scanning of the area of interest on a given tissue sample. The imaging source is coupled with a high resolution accurate mass quadrupole time-of-flight (QTOF) mass analyzer with tandem mass analysis capability. A lateral resolution of 60 µm was demonstrated on a patterned ink film by LEMS imaging. Plant metabolites including sugar and anthocyanins were directly imaged from a leaf sample. Small metabolites, lipids and proteins were simultaneously imaged from a single tissue section of a pig liver sample. Biomarkers of blood-brain barrier damage and traumatic brain injury (TBI) that occurred during the injury were detected and imaged from a TBI mouse brain. The loading values from principal component analysis (PCA) were shown to be useful for identification of features of interest from the large LEMS imaging dataset.
Temple University--Theses
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Herrwerth, Oliver. "Atomic and molecular ionization dynamics in strong IR and XUV fields probed by time-resolved coincidence spectroscopy". Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-137966.
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Kiontke, Andreas, Ariana Oliveira-Birkmeier, Andreas Opitz i Claudia Birkemeyer. "Electrospray ionization efficiency is dependent on different molecular descriptors with respect to solvent pH and instrumental configuration". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-216278.
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Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we
investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature.
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Bohinski, Timothy Blaise. "STRONG FIELD MOLECULAR IONIZATION: CONTROLLED DISSOCIATION IN RADICAL CATIONS WITH DYNAMIC RESONANCES AND ADIABATICALLY PREPARED LAUNCH STATES". Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/310686.
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ChemistryPh.D.
This dissertation investigates the electronic spectroscopy of a series of alkyl phenyl ketone radical cations and the dynamics of selective launch states in the strong field regime with tunable near infrared ultrashort laser pulses from 790 nm - 1550 nm coupled to mass spectrometric detection. Our method relies on tunable strong field laser pulses in the range from 1150 nm - 1550 nm to adiabatically ioinized gas phase molecules and prepare ions in the ground ionic state that serve as a launch state for future excitation and control. Adiabatic ionization is capable of transferring little energy to the molecule and producing a majority of a parent molecular ion in comparison to nonadiabatic ionization wherein multiple ionic states can be populated with an accompanying high degree of molecular fragmentation. We measure a dynamic resonance in the low lying electronic states of the acetopheone radical cation via preparation of a launch state with adiabatic ionization followed by a one photon transition within a single pulse duration which facilitates bond dissociation to produce the benzoyl ion. Experiments on acetophenone homologues and derivatives elucidate the structural dependence of the electronic resonance and supporting ab initio calculations identify the dynamic resonance along the molecular torsional coordinate between the ground ionic state, D0, and second excited state, D2. Post ionization excitation within the pulse duration transfers the ground state wavepacket to the D2 surface where the wavepacket encounters a three state conical intersection that facilitates the preferred bond dissociation. Time resolved photodissociation experiments measure the dynamics of the launch state, large amplitude oscillations and extended coherence times support the notion that adiabatic ionization populates a majority of the ground ionic surface. Control of the dissociation products is initiated from the launch state by varying the pump wavelength and probe intensity. Elimination of the D0 wavepacket with a 1370 nm reveals additional secondary dynamics that are attributed to wavepacket motion on the D2 surface. Finally, the effect of para substitution on the acetophenone radical cation is explored as a strategy to control the launch state wavepacket dynamics. Suppresion of the wavepacket dynamics are observed with the addition of alkoxy groups whereas extended coherence of the launch state dynamics approaching ~5 ps is observed upon trifluoromethyl substitution. A possible mechanism for the extended coherenece based on coupled torsional rotors is proposed.
Temple University--Theses
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Fröbel, Friedrich Georg [Verfasser], Stefanie [Gutachter] Gräfe i Ulf [Gutachter] Peschel. "Attosecond ionization dynamics in a molecular charge-transfer system / Friedrich Georg Fröbel ; Gutachter: Stefanie Gräfe, Ulf Peschel". Jena : Friedrich-Schiller-Universität Jena, 2019. http://d-nb.info/1207273090/34.
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CHO, HYUCK. "COINCIDENCE DETECTION OF PROTONS AND METASTABLE HYDROGEN ATOMS FROM DISSOCIATIVE IONIZATION OF MOLECULAR HYDROGEN BY ELECTRON IMPACT (TIME-OF-FLIGHT)". Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188027.
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A coincidence has been observed between H(2S) and H⁺ fragments resulting from the bombardment of H₂ with 100 eV electrons. A significant source of this coincidence is believed to be the 2sσ(g) state of H₂⁺. The time-of-flight (TOF) distribution of H(2S) fragments from the 2sσ(g) state was measured and converted to the kinetic energy distribution from which the potential energy of the 2sσ(g) state in the Franck-Condon region was constructed. The result is in good agreement with a published calculation.
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Li, Chengjun. "Experimental study on electron impact double ionization dynamics for atomic and small molecular targets at intermediate incident energy". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00867037.
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In this work, different double ionization (DI) mechanisms of various atomic and molecular targets by electron impact at different intermediate incident energies have been studied by so-called (e, 3-1e) and (e, 3e) experiments. Four and five fold differential cross sections in angle and in energy have been measured and analyzed in a coplanar geometry. The experimental measurements are compared with both first order and second order theoretical model calculations. The results shows that the theories including second order mechanism (such as Two Step 2, TS2) are generally in better agreement with the experimental data than these only including first order mechanisms (such as Shake Off and Two Step 1). This demonstrates that under present kinematics, second order mechanism plays an important role or even dominates over first order mechanisms. Besides, all DI results are compared with the predictions of TS2 kinematical analysis developed by Lahmam-Bennani et al (2010). Most of the structures shown in the measured angular distribution can be correctly explained by the TS2 kinematical analysis predictions. Besides, we extend this model by including the recoil contribution in each step. Some structures which cannot be explained by the previous model are well explained by the extended TS2 kinematical model. The isoelectronic target structure influence in DI is investigated preliminarily. The (e, 3-1e) results on Ne and CH₄ indicate the differences under same kinematics. The data analysis is underway.
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Edgü-Fry, Erge. "Single electron capture and ionization involving atomic (and molecular) H and He at low to intermediate impact energies /". Search for this dissertation online, 2003. http://wwwlib.umi.com/cr/ksu/main.
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Savage, Owen Gerard. "The energy and angular distribution of fragment ions produced in the single and double ionization of simple molecules by fast ions". Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334641.
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O'Connor, Caroline Sophie Scott. "The properties of molecular ions". Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314259.
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Alexander, Jason S. "Interference effects due to projective-target nucleus scattering in single ionization of molecular hydrogen by 75 keV proton impact". Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Alexander_09007dcc8064b51f.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 27, 2009) Includes bibliographical references (p. 70-74).
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Callahan, Damien Lee. "The coordination of nickel in hyperaccumulating plants /". Connect to thesis, 2007. http://eprints.unimelb.edu.au/archive/00003773.
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Phan, Vo Hong Minh. "Cosmic ray interaction in molecular environment". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7070.
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De nombreuses évidences observationnelles parvenues de différentes expériences au début du 20e siècle ont révélé que la Terre est constamment bombardée par des rayons cosmiques, des particules de haute énergie d'origine extraterrestre. Étant donné que ces particules sont très énergétiques, on pense qu'elles pourraient pénétrer profondément dans les nuages moléculaires et ioniser les parties les plus denses de ces objets, où naissent de nouvelles étoiles. Cela signifie que les rayons cosmiques règlent le niveau d'ionisation qui contrôle non seulement la chimie des nuages moléculaires mais également le couplage entre le gaz et le champ magnétique qui soutient le nuage en contrastant la gravité pendant le processus de formation des étoiles. On remarque que les taux d'ionisation déduits des observations infrarouges et radio sont beaucoup plus importants que la valeur communément citée dans la littérature. Ce désaccord doit mener à une réévaluation du taux d'ionisation dans les nuages, d'un point de vue théorique. Cette tâche nécessite une meilleure compréhension du transport des rayons cosmiques dans les nuages et, plus important encore, la connaissance de la quantité de rayons cosmiques de basse énergie à différentes positions dans notre Galaxie. Le premier sujet a été étudié dans des documents pionniers des années 70 et 80, mais il pourrait y avoir de la place pour d'ultérieures améliorations. En ce qui concerne le deuxième, on a des connaissances récentes, du moins pour le milieu interstellaire local, grâce aux données des sondes Voyager. Il n'est cependant pas très clair si ces données pourraient être considérées comme des valeurs de référence pour la densité des rayons cosmiques de basse énergie dans l'ensemble de la Galaxie. L'objectif de ce travail est donc d'étudier la propagation des rayons cosmiques de basse énergie dans des environnements neutres et aussi de mieux interpréter les données d'observation du taux d'ionisation dans les nuages moléculaires isolés et ceux au voisinage des accélérateurs cosmiques, tels que les restes de supernovaIt has been revealed by observational evidences from various experiments at the beginning of the 20th century that the Earth is constantly bombarded by cosmic rays, high-energy particles of extraterrestrial origin. Since these particles are very energetic, it is believed that they could penetrate deep into molecular clouds and ionize the densest parts of these objects where new stars are born. This means that cosmic rays regulate the level of ionization that controls not only the chemistry of molecular clouds but also the coupling between the gas and the magnetic field which support the cloud against gravity during the process of star formation. Interestingly, the ionization rates inferred from infrared and radio observations are much larger than the commonly quoted value in the literature. This calls for a reassessment from a theoretical point of view of the ionization rate in clouds. This task requires a better understanding of the transport of cosmic rays into clouds and, more importantly, the knowledge of the amount of low energy cosmic rays at different positions in our Galaxy. The former has been investigated in some of the pioneering papers in the seventies and eighties but there might be room for some improvements. The latter is known not too long ago at least for the local interstellar medium thanks to the data from the Voyager probes. It is, however, not very clear whether or not these data could be considered as reference values for the density of low energy cosmic rays in the entire Galaxy. The aim of this work is, therefore, to study the propagation of low energy cosmic rays in neutral environments and also to better interpret the observational data of the ionization rate in both isolated molecular clouds and the ones in the vicinity of cosmic accelerators like supernova remnants
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Tate, Wendy Rose. "Surface-enhanced laser desorption/ionization time-of-flight mass spectroscopy (SELDI-TOF-MS) as a tool for molecular endpoint analysis of PX-12, a thioredoxin-1 inhibitor". Thesis, The University of Arizona, 2005. http://hdl.handle.net/10150/291852.
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Thioredoxin-1 is a redox protein upregulated in many cancers. Its functions include inhibition of apoptosis, increasing cellular growth and proliferation. It has been shown that cells displaying increased levels of Trx-1 have increased drug resistance. PX-12 is a Trx-1 inhibitor that shows anti-proloferative and cytotoxic activity in vitro and in vivo. We used surface enhanced laser desorption/ionization time-of-flight mass spectroscopy (SELDI-TOF-MS) to measure plasma Trx-1 levels of patients treated with PX-12 as a side study of a phase-I trial. SELDI-TOF-MS was able to measure a decrease in plasma Trx-1 after PX-12 treatment semi-quantitatively. In addition, SELDI measured 57 other protein peaks in plasma; seven which were found in all plasma samples analyzed. One of these peaks was located at 13.86kDa and identified through LC-MS/MS sequencing to be a variant of Transthyretin. Further studies into these additional peaks are necessary to determine their biological importance in relation to Trx-1 and PX-12.
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Zhang, Kaikai. "Atomic and Molecular dynamics in intense mid-infrared fields". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440204616.
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Wilbois, Timo Eduard Karl [Verfasser], i Hanspeter [Akademischer Betreuer] Helm. "Single ionization of molecular hydrogen in strong laser fields : : experimental imaging and analysis = Einfachionisation von molekularem Wasserstoff in starken Laserfeldern". Freiburg : Universität, 2011. http://d-nb.info/1123458669/34.
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Tejwani, Ravindra Wadhumal. "EXPERIMENTAL AND MOLECULAR DYNAMICS SIMULATION STUDIES OF PARTITIONING AND TRANSPORT ACROSS LIPID BILAYER MEMBRANES". UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/738.
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Most drugs undergo passive transport during absorption and distribution in the body. It is desirable to predict passive permeation of future drug candidates in order to increase the productivity of the drug discovery process. Unlike drug-receptor interactions, there is no receptor map for passive permeability because the process of transport across the lipid bilayer involves multiple mechanisms. This work intends to increase the understanding of permeation of drug-like molecules through lipid bilayers.
Drug molecules in solution typically form various species due to ionization, complexation, etc. Therefore, species specific properties must be obtained to bridge the experiment and simulations. Due to the volume contrast between intra- and extravesicular compartments of liposomes, minor perturbations in ionic and binding equilibria become significant contributors to transport rates. Using tyramine as a model amine, quantitative numerical models were developed to determine intrinsic permeability coefficients. The microscopic ionization and binding constants needed for this were independently measured. The partition coefficient in 1,9-decadiene was measured for a series of compounds as a quantitative surrogate for the partitioning into the hydrocarbon region of the bilayer. These studies uncovered an apparent long-range interaction between the two polar substituents that caused deviations in the microscopic pKa values and partition coefficient of tyramine from the expected values. Additionally the partition coefficients in the preferred binding region of the bilayer were also measured by equilibrium uptake into liposomes.
All-atom molecular dynamics simulations of lipid bilayers containing tyramine, 4- ethylphenol, or phenylethylamine provided free energies of transfer of these solutes from water to various locations on the transport path. The experimentally measured partition coefficients were consistent with the free energy profiles in showing the barrier in the hydrocarbon region and preferred binding region near the interface. The substituent contributions to these free energies were also quantitatively consistent between the experiments and simulations. Specific interactions between solutes and the bilayer suggest that amphiphiles are likely to show preferred binding in the head group region and that the most of hydrogen bonds involving solutes located inside the bilayer are with water molecules. Solute re-orientation inside the bilayer lowers the partitioning barrier by allowing favorable interactions.
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Hill, Jacob A. Hill. "SURFACE LAYER MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME OF FLIGHT MASS SPECTROMETRY (SL-MALDI-TOF MS) ANALYSIS OF POLYMER BLEND SURFACE COMPOSITION". University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1514479406062149.
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