Дисертації з теми "Laser Induced Molecular Dissociation"
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1
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.
Повний текст джерелаАнотація:
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.
2
Ray, Dipanwita. "Photo-electron momentum distribution and electron localization studies from laser-induced atomic and molecular dissociations." Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/3901.
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3
Fischer, Andreas [Verfasser], and Robert [Akademischer Betreuer] Moshammer. "Dissociative Photoionization of Molecular Hydrogen - A Joint Experimental and Theoretical Study of the Electron-Electron Correlations induced by XUV Photoionization and Nuclear Dynamics on IR-Laser Dressed Transition States / Andreas Fischer ; Betreuer: Robert Moshammer." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180301552/34.
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4
Folkerts, Hein Otto. "Molecular dissociation induced by electron transfer to multicharged ions." [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1996. http://irs.ub.rug.nl/ppn/14544757X.
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5
Purcell, S. M. "Laser induced molecular motion in strong nonresonant laser fields." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19225/.
Повний текст джерелаАнотація:
The optical dipole force from a singe focussed laser beam was used to study the role of laser-induced molecular alignment on the centre-of-mass motion of carbon disulphide molecules in a molecular beam. The translational, rotational and vibrational temperatures of the carbon disulphide molecules were measured to be 3.4\pm0.2 K, 35\pm10 K and 250\pm14 K respectively. The velocity of the beam was measured to be 542\pm22 m s ^{-1}. Time-of-flight mass spectroscopy was used to measure the acceleration and deceleration of the molecules. Maximum velocity changes of 7.5 m s ^{-1} and 10 m s ^{-1} were recorded for linearly and circularly polarised light respectively. These results showed that the dipole force, \digamma \alpha \bigtriangledown [\alpha_e_f_f(I)I(r)], where \alpha_e_f_f is the effective polarisability and determined through laser-induced alignment, can be modified by changing the laser polarisation. For linearly and circularly polarised light, a 12% difference in effective polarisability was measured to produce a 20% difference in dipole force. The dipole force from a single focussed laser beam produces a molecular optical lens and the downstream density of the molecular focus was probed by measuring the ion signal for both laser polarisations. The focal lengths for linearly and circularly polarised light were found to be separated by \approx 100 \mu m. By altering the laser polarisation from linearly through elliptically to circularly polarised light, the focal length of the molecular optical lens could be smoothly altered over the \approx 100 \mu m focal range. The role of the effective polarisability of each rotational state was also studied numerically. Separate rotational states were found to significantly alter the focal properties of a molecular optical lens. In carbon disulphide, higher rotational states (J > 10), exhibit less molecular alignment and when occupied, the focal length of the molecular optical lens for these states was increased by 60 % compared to the ground state.
6
McKendrick, Colin Bruce. "UV laser multiphoton dissociation studies of H2O, NO2 and H2O2." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/12630.
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7
Zohrabi, Mohammad. "Quantum control of molecular fragmentation in strong laser field." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18401.
Повний текст джерелаАнотація:
Doctor of PhilosophyDepartment of Physics
Itzhak Ben-Itzhak
Present advances in laser technology allow the production of ultrashort (≲5 fs, approaching single cycle at 800 nm), intense tabletop laser pulses. At these high intensities laser-matter interactions cannot be described with perturbation theory since multiphoton processes are involved. This is in contrast to photodissociation by the absorption of a single photon, which is well described by perturbation theory. For example, at high intensities (≳5×10[superscript]13 W/cm[superscript]2) the fragmentation of molecular hydrogen ions has been observed via the absorption of three or more photons. In another example, an intriguing dissociation mechanism has been observed where molecular hydrogen ions seem to fragment by apparently absorbing no photons. This is actually a two photon process, photoabsorption followed by stimulated emission, resulting in low energy fragments. We are interested in exploring these kinds of multiphoton processes. Our research group has studied the dynamics and control of fragmentation induced by strong laser fields in a variety of molecular targets. The main goal is to provide a basic understanding of fragmentation mechanisms and possible control schemes of benchmark systems such as H[subscript]2[superscript]+. This knowledge is further extended to more complex systems like the benchmark H[subscript]3[superscript]+ polyatomic and other molecules. In this dissertation, we report research based on two types of experiments. In the first part, we describe laser-induced fragmentation of molecular ion-beam targets. In the latter part, we discuss the formation of highly-excited neutral fragments from hydrogen molecules using ultrashort laser pulses. In carrying out these experiments, we have also extended experimental techniques beyond their previous capabilities. We have performed a few experiments to advance our understanding of laser-induced fragmentation of molecular-ion beams. For instance, we explored vibrationally resolved spectra of O[subscript]2[superscript]+ dissociation using various wavelengths. We observed a vibrational suppression effect in the dissociation spectra due to the small magnitude of the dipole transition moment, which depends on the photon energy --- a phenomenon known as Cooper minima. By changing the laser wavelength, the Cooper minima shift, a fact that was used to identify the dissociation pathways. In another project, we studied the carrier-envelope phase (CEP) dependences of highly-excited fragments from hydrogen molecules. General CEP theory predicts a CEP dependence in the total dissociation yield due to the interference of dissociation pathways differing by an even net number of photons, and our measurements are consistent with this prediction. Moreover, we were able to extract the difference in the net number of photons involved in the interfering pathways by using a Fourier analysis. In terms of our experimental method, we have implemented a pump-probe style technique on a thin molecular ion-beam target and explored the feasibility of such experiments. The results presented in this work should lead to a better understanding of the dynamics and control in molecular fragmentation induced by intense laser fields.
8
Ablikim, Utuq. "Fragmentation of molecular ions in ultrafast laser pulses." Kansas State University, 2015. http://hdl.handle.net/2097/18962.
Повний текст джерелаАнотація:
Master of ScienceDepartment of Physics
Itzhak Ben-Itzhak
Imaging the interaction of molecular ion beams with ultrafast intense laser fields is a very powerful method to understand the fragmentation dynamics of molecules. Femtosecond laser pulses with different wavelengths and intensities are applied to dissociate and ionize molecular ions, and each resulting fragmentation channel can be studied separately by implementing a coincidence three-dimensional (3D) momentum imaging method. The work presented in this master’s report can be separated into two parts. First, the interaction between molecular ion beams and femtosecond laser pulses, in particular, the dissociation of CO[superscript]+ into C[superscript]++O, is studied. For that purpose, measurements are conducted at different laser intensities and wavelengths to investigate the possible pathways of dissociation into C[superscript]++O. The study reveals that CO[superscript]+ starts to dissociate from the quartet electronic state at low laser intensities. Higher laser intensity measurements, in which a larger number of photons can be absorbed by the molecule, show that the doublet electronic states with deeper potential wells, e.g. A [superscript]2Π, contribute to the dissociation of the molecule. In addition, the three-body fragmentation of CO[subscript]2[superscript]+ into C[superscript]++O[superscript]++O[superscript]+ is studied, and two breakup scenarios are separated using the angle between the sum and difference of the momentum vectors of two O[superscript]+ fragments. In the second part, improvements in experimental techniques are discussed. Development of a reflective telescope setup intended to increase the conversion efficiency of ultraviolet (UV) laser pulse generation is described, and the setup is used in the studies of CO[superscript]+ dissociation described in this report. The other technical study presented here is the measurement of the position dependence of timing signals picked off of a microchannel plate (MCP) surface. The experimental method is presented and significant time spread over the surface of the MCP detector is reported [1].
9
Chen, Hongxin. "Electromagnetically induced transparency in laser-cooled rubidium." Thesis, Open University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265348.
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10
Makhija, Varun. "Laser-induced rotational dynamics as a route to molecular frame measurements." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18522.
Повний текст джерелаАнотація:
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.
11
Klinkusch, Stefan. "Simulations of laser-induced correlated many-electron dynamics in molecular systems." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5544/.
Повний текст джерелаАнотація:
In this thesis, simulations of laser-driven many-electron dynamics in molecules are presented, i.e., the interaction between molecules and an electromagnetic field is demonstrated. When a laser field is applied to a molecular system, a population of higher electronic states takes place as well as other processes, e.g. photoionization, which is described by an appropriate model. Also, a finite lifetime of an excited state can be described by such a model.
In the second part, a method is postulated that is capable of describing electron correlation in a time-dependent scheme. This is done by introducing a single-electron entropy that is at least temporarily minimized in a further step.Im Rahmen dieser Doktorarbeit werden Simulationen lasergetriebener Vielelektronendynamik in Molekülen präsentiert, d.h., die Wechselwirkung zwischen Molekülen und einem elektromagnetischen Feld wird demonstriert. Bei Laseranregungen finden nicht nur elektronische Übergänge statt, sondern auch weitere Prozesse wie die Photoionisation, die mit einem geeigneten Modell beschrieben wird. Auch die endliche Lebensdauer angeregter Zustände kann mit einem solchen Modell beschrieben werden. Im zweiten Teil wird eine Methode postuliert, die fähig ist, die Elektronenkorrelation zeitabhängig zu beschreiben. Dies wird durch die Einführung einer Einelektronenentropie erreicht, die in einem weiteren Schritt zumindest kurzzeitig minimiert wird.
12
Li, Guangqi [Verfasser]. "Laser-induced electron transport through molecular junctions and DNA / Guangqi Li." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2008. http://d-nb.info/1034984772/34.
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13
Procino, I. "Laser induced molecular axis alignment : measurement and applications in attosecond science." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333960/.
Повний текст джерелаАнотація:
This thesis reports the measurement and applications of molecular axis alignment induced by strong non-resonant linearly polarised laser fields. The spatial alignment of gas phase molecules overcomes the loss of information that results from averaging angle-dependent quantities over all the possible orientations of an isotropic sample. Therefore, laser-induced molecular alignment techniques are an essential component in new experiments aimed at measuring the structure of molecules with attosecond time resolution. In the first part of this thesis an experiment to measure molecular axis alignment is described. This experiment is based on the velocity map imaging technique in conjunction with time-resolved femtosecond laser Coulomb explosion of the molecular sample by an intense circularly polarised laser beam. A circularly polarised beam is needed to ensure a uniform detection efficiency for each possible orientation of the molecular axis in the polarisation plane. However, such a polarisation produces ion distributions that are not cylindrically symmetric, preventing the use of the standard Abel inversion technique to retrieve the three-dimensional ion distributions from the detected two-dimensional images. A new inversion algorithm is presented that allows the retrieval of molecular axis distributions from angular distributions of ions without cylindrical symmetry. The second part of the thesis focuses on the application of laser-induced molecular alignment to retrieve molecular structure and dynamics from high-order harmonic generation (HHG) experiments. HHG with a mid-infrared laser source (1300 nm) from aligned molecular samples of CO2, N2, C2H2, and N2O are presented. The use of a laser source with a wavelength longer than that used in previous experiments (800 nm) has increased the amount of information obtainable from such experiments. These experiments have provided insight into the hole dynamics of CO2 following ionisation, and reveal for the first time structural features in the HHG spectra of molecules with low ionisation potentials such as C2H2.
14
Sayler, A. Max. "Measurements of ultrashort intense laser-induced fragmentation of simple molecular ions." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/2611.
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15
Law, D. W. "The laser induced isomerisation and photoacoustic spectroscopy of small molecules." Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234897.
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16
Graham, Leigh. "Quantum control of laser induced dynamics of diatomic molecular ions using shaped intense ultrafast laser pulses." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602512.
Повний текст джерелаАнотація:
The beauty of ultrafast science lies inherently in the ability to induce and image dynamics on a timescale comparable to the fastest nuclear motion, In recent years, a plethora of rich and fascinating phenomena involving the interaction of diatomic molecules with intense femtosecond laser pulse has been unveiled, Such research is motivated by the ambition to understand and optically drive chemical reactions to the highest degree of specificity, In this work, the strategy employed toward achieving this goal relies ., on the interaction of Hydrogenic ions and analytically shaped and well characterized pulses, The ability to manipulate photodissociation dynamics using the instantaneous frequency and temporal profile of pulses shaped with quadratic (ψ") and cubic (ψ’") spectral phase functions was studied, A three-dimensional (3D) momentum imaging technique was used to measure the kinetic energy release (KER) and angular distribution of the dissociation fragments, A significant enhancement in the dissociation probability of non-resonant transitions from the low lying vibrational levels using the sign and magnitude of the applied phase function as a control tool was demonstrated, Furthermore, the tractability of Hydrogenic ions means a mechanistic explanation for these observations can be theoretically determined, Investigating the behavior of ions more complex than H+2 in strong laser fields can present many theoretical and experimental challenges, Laser-induced fragmentation of CD+ was explored using the 3D momentum imaging technique in the longitudinal field imaging mode, The high mass ratio (12:2) hinders the simultaneous measurement of the two constituents, at all angles and kinetic energies, Alternatively, the recently developed longitudinal and transverse field imaging technique was used to perform a piecewise dissociation measurement, This allowed the branching ratio of the dissociation channels to be obtained, Furthermore, the fragmentation channels of CD+ were identified and studied as a function of laser intensity and wavelength,
17
Madden, Colette Sarah. "An investigation of InXe interaction potentials using laser induced fluorescence techniques." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334482.
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18
Meissner, Alexander Blacque. "Molecular dynamics simulations of laser induced shock response in reactive Ni/Al nanolaminates." College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/9985.
Повний текст джерелаАнотація:
Thesis (M.S.) -- University of Maryland, College Park, 2009.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
19
Bakry, A. H. A. "Tunable UV laser-induced photo-fragmentation of selected alkali halides in molecular beams." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636022.
Повний текст джерелаАнотація:
This thesis is concerned with two sensitive and selective methods for detecting low concentrations of molecules and reactive atoms. The methods are described in detail, and in particular emphasis is given to the design, construction and operation of systems to implement Resonance Ionization Spectroscopy (RIS) and Laser Induced Fluorescence (LIF) for detecting photodissociated alkali atoms and alkali halide molecules. Alkali halide molecules are often treated as model cases by both theoreticians and experimenters because of their unique properties which distinguish them from other molecules such as the avoided crossing of their lowest two excited potential curves with the ground state potential curve. Molecular beams of sodium iodide, lithium iodide, and caesium iodide, representative for alkali halides, were used as a rich source to study the dissociation and the detection of these molecules. In the RIS experiments, a pulsed tunable UV laser was used to photodissociate NaI, LiI and CsI. Na, Li, and Cs atoms were detected by two-step RIS. This is the first time that RIS on alkali halides has been performed in a molecular beam. The photodissociation of NaI was studied as a function of the UV-wavelength. The result has shown that the dissociation cross section for NaI at the first UV maximum (325nm) is of the same magnitude as the absorption cross section determined by Davidovits et al, 1967. A variety of different experiments were conducted to establish the sensitivity of the technique, and detection limits of 5x106 Na-atoms cm-3, 10^6 Li-atoms cm^-3 and 3x106 Cs-atoms cm-3 were measured. To detect NaI molecules, a molecular beam of NaI was used to demonstrate the technique of LIF. However, no spectrally resolved molecular LIF was observed; explanations for the failure are provided, and in this context factors that affect the detection sensitivity of RIS and LIF are discussed.
20
Mondal, Ritwik. "Relativistic theory of laser-induced magnetization dynamics." Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-315247.
Повний текст джерелаАнотація:
Ultrafast dynamical processes in magnetic systems have become the subject of intense research during the last two decades, initiated by the pioneering discovery of femtosecond laser-induced demagnetization in nickel. In this thesis, we develop theory for fast and ultrafast magnetization dynamics. In particular, we build relativistic theory to explain the magnetization dynamics observed at short timescales in pump-probe magneto-optical experiments and compute from first-principles the coherent laser-induced magnetization. In the developed relativistic theory, we start from the fundamental Dirac-Kohn-Sham equation that includes all relativistic effects related to spin and orbital magnetism as well as the magnetic exchange interaction and any external electromagnetic field. As it describes both particle and antiparticle, a separation between them is sought because we focus on low-energy excitations within the particle system. Doing so, we derive the extended Pauli Hamiltonian that captures all relativistic contributions in first order; the most significant one is the full spin-orbit interaction (gauge invariant and Hermitian). Noteworthy, we find that this relativistic framework explains a wide range of dynamical magnetic phenomena. To mention, (i) we show that the phenomenological Landau-Lifshitz-Gilbert equation of spin dynamics can be rigorously obtained from the Dirac-Kohn-Sham equation and we derive an exact expression for the tensorial Gilbert damping. (ii) We derive, from the gauge-invariant part of the spin-orbit interaction, the existence of a relativistic interaction that linearly couples the angular momentum of the electromagnetic field and the electron spin. We show this spin-photon interaction to provide the previously unknown origin of the angular magneto-electric coupling, to explain coherent ultrafast magnetism, and to lead to a new torque, the optical spin-orbit torque. (iii) We derive a definite description of magnetic inertia (spin nutation) in ultrafast magnetization dynamics and show that it is a higher-order spin-orbit effect. (iv) We develop a unified theory of magnetization dynamics that includes spin currents and show that the nonrelativistic spin currents naturally lead to the current-induced spin-transfer torques, whereas the relativistic spin currents lead to spin-orbit torques. (v) Using the relativistic framework together with ab initio magneto-optical calculations we show that relativistic laser-induced spin-flip transitions do not explain the measured large laser-induced demagnetization. Employing the ab initio relativistic framework, we calculate the amount of magnetization that can be imparted in a material by means of circularly polarized light – the so-called inverse Faraday effect. We show the existence of both spin and orbital induced magnetizations, which surprisingly reveal a different behavior. We establish that the laser-induced magnetization is antisymmetric in the light’s helicity for nonmagnets, antiferromagnets and paramagnets; however, it is only asymmetric for ferromagnets.
21
Liu, Yuan. "Development of laser spectroscopy for elemental and molecular analysis." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5978.
Повний текст джерелаАнотація:
Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are still growing analytical and sensing spectroscopic techniques. They significantly reduce the time and labor cost in analysis with simplified instrumentation, and lead to minimal or no sample damage. In this dissertation, fundamental studies to improve LIBS analytical performance were performed and its fusion with Raman into one single sensor was explored.
On the fundamental side, Thomson scattering was reported for the first time to simultaneously measure the electron density and temperature of laser plasmas from a solid aluminum target at atmospheric pressure. Comparison between electron and excitation temperatures brought insights into the verification of local thermodynamic equilibrium condition in laser plasmas.
To enhance LIBS emission, Microwave-Assisted LIBS (MA-LIBS) was developed and characterized. In MA-LIBS, a microwave field extends the emission lifetime of the plasma and stronger time integrated signal is obtained. Experimental results showed sensitivity improvement (more than 20-fold) and extension of the analytical range (down to a few tens of ppm) for the detection of copper traces in soil samples.
Finally, laser spectroscopy systems that can perform both LIBS and Raman analysis were developed. Such systems provide two types of complimentary information – elemental composition from LIBS and structural information from Raman. Two novel approaches were reported for the first time for LIBS-Raman sensor fusion: (i) an Ultra-Violet system which combines Resonant Raman signal enhancement and high ablation efficiency from UV radiation, and (ii) a Ti:Sapphire laser based NIR system which reduces the fluorescence interference in Raman and takes advantage of femtosecond ablation for LIBS.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
22
Jans, Elijah R. "Laser Diagnostics for Kinetic Studies of Nonequilibrium Molecular Plasmas and High-Speed Flows." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618850427972453.
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Anis, Fatima. "Role of nuclear rotation in H[subscript]2[superscript]+ dissociation by ultra short laser pulses." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2181.
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24
Hua, Jianjun. "Isotopic effects in H[subscript]2+ dynamics in an intense laser field." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1538.
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25
Klinkusch, Stefan [Verfasser], and Peter [Akademischer Betreuer] Saalfrank. "Simulations of laser-induced correlated many-electron dynamics in molecular systems / Stefan Klinkusch. Betreuer: Peter Saalfrank." Potsdam : Universitätsbibliothek der Universität Potsdam, 2011. http://d-nb.info/1017198861/34.
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26
Webb, Matthew James. "Investigations into molecular dynamics induced by laser-pulsed heating : a low temperature scanning tunneling microscope study." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619587.
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27
Zuo, Li. "Molecular Mechanisms of Stress-induced Reactive Oxygen Species Formation in Skeletal Muscle." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1038853894.
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28
Mogni, Gabriele. "Simulations of shock-induced phase transitions in silicon." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:8f8d5f8f-941d-4167-9066-85389c4a3dd5.
Повний текст джерелаАнотація:
An understanding of the fundamental mechanism behind the relief of shear stress in single-crystal silicon subject to loading by shock-waves has to this day remained elusive. What is known is that this material undergoes a first-order pressure-induced polymorphic phase transition from its ambient pressure cubic-diamond (cd) crystal structure to its first stable high-pressure phase, known as β-Sn, at a pressure of about 120 kbar under hydrostatic compression. By investigating the evolution of the transition parameters for this phase transition as a function of increasing uniaxial shear stress representative of the effects of shock-compression via ab-initio Density Functional Theory computational techniques, we predict a significant lowering of the stress at which the phase transition occurs. This raises the question as to whether the onset of plastic response at the material's Hugoniot Elastic Limit (HEL) reported in experiments corresponds in fact to the phase transition itself, a very plausible possibility which has never been considered before. Furthermore, we present molecular dynamics simulations using a Tersoff-like potential of shock-compressed single crystals of silicon. We find an elastic response up to a critical stress, above which the shear stress is relieved by an inelastic response associated with a partial transformation to a new high-pressure phase, where both the new phase (Imma) and the original cubic diamond phase are under close to hydrostatic conditions. We note that these simulations are also consistent with shear stress relief provided directly by the shock-induced phase transition itself, without an intermediate state of plastic deformation of the cubic diamond phase.
29
Sen, Ananya. "Chiral recognition in neutral and ionic molecular complexes." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112163/document.
Повний текст джерелаАнотація:
L'objectif principal de cette thèse est l’étude spectroscopique de molécules ou de complexes portant plusieurs centres chiraux en phase gazeuse, pour comprendre les effets de la stéréochimie sur leurs propriétés structurales. Des alcaloïdes dérivés de la Cinchonine ont été introduits intacts en phase gazeuse par ablation laser. Ils ont été étudiés en combinant un jet supersonique avec de la spectroscopie laser. Les deux pseudo-énantiomères Quinine et Quinidine ont montré des spectres électroniques et vibrationnels similaires, en accord avec leur structure similaire. Leurs propriétés en solution diffèrent davantage, comme le montrent les expériences de dichroïsme circulaire vibrationnel (VCD). Cette différence est encore plus marquée dans l’Hydroquinine et l’Hydroquinidine. Enfin la reconnaissance chirale a été étudiée dans des complexes ioniques dans un piège à ions. La stabilité des complexes formés entre S-camphre et les R et S-Alanine protonées indique une préférence homochirale. Cependant, l'énergie d'interaction calculée ainsi que les spectres IRMPD dans la région des empreintes digitales sont identiques. Le rôle des conformères plus hauts en énergie dans la reconnaissance chirale a été discutéThe main objective of this thesis is a spectroscopic study of molecules or complexes bearing multiple chiral centres in the gas phase, to understand the effects of stereochemistry on their structural properties. Neutral cinchona alkaloids have been introduced intact in gas phase by laser-ablation. They have been studied by combining supersonic expansion with laser spectroscopy. The two pseudo-enantiomers Quinine and Quinidine show similar electronic and vibrational spectra, in line with similar structure. Their properties in solution differ more, as shown by Vibrational Circular Dichroism (VCD) experiments. This difference is further enhanced in Hydroquinine and Hydroquinidine. Lastly chiral recognition has been studied in ionic complexes in an ion trap. A homochiral preference has been shown in the stability of the complexes formed between S-Camphor and R and S protonated Alanine. However, the calculated interaction energy as well as the IRMPD spectrum in the fingerprint region are identical. The role of higher energy conformers in chiral recognition has been discussed
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Handt, Jan. "Ab-initio molecular dynamics studies of laser- and collision-induced processes in multielectron diatomics, organic molecules and fullerenes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-62279.
Повний текст джерелаАнотація:
This work presents applications of an ab-initio molecular dynamics method, the so-called nonadiabatic quantum molecular dynamics (NA-QMD), for various molecular systems with many electronic and nuclear degrees of freedom. Thereby, the nuclei will be treated classically and the electrons with time-dependent density functional theory (TD-DFT) in basis expansion. Depending on the actual system and physical process,
well suited basis sets for the Kohn-Sham orbitals has to be chosen. For the ionization process a novel absorber acting in the energy space as well as additional basis functions will be used depending on the laser frequency.
In the first part of the applications, a large variety of different laser-induced molecular processes will be investigated. This concerns, the orientation dependence of the ionization of multielectronic diatomics (N2, O2), the isomerization of organic molecules (N2H2) and the giant excitation of the breathing mode in fullerenes (C60).
In the second part, fullerene-fullerene collisions are investigated, for the first time in the whole range of relevant impact velocities concerning the vibrational and electronic energy transfer (\"stopping~power\").
For low energetic (adiabatic) collisions, it is surprisingly found, that a two-dimensional, phenomenological collision model can reproduce (even quantitatively) the basic features of fusion and scattering observed in the fully microscopic calculations as well as in the experiment.
For high energetic (nonadiabatic) collisions, the electronic and vibrational excitation regimes are predicted, leading to multifragmentation up to complete atomization.
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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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Fischer, Michael. "Non-adiabatic quantum molecular dynamics: - Benchmark systems in strong laser fields - Approximate electron-nuclear correlations." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-148848.
Повний текст джерелаАнотація:
The non-adiabatic quantum molecular dynamics (NA-QMD) method couples self-consistently classical nuclear motion with time-dependent density functional theory (TDDFT) in basis expansion for the electron dynamics. It has become a versatile approach to study the dynamics of atoms, molecules and clusters in a wide range of scenarios. This work presents applications of the NA-QMD method to important benchmark systems and its systematic extension to include quantum effects in the nuclear motion.
Regarding the first objective, a complete study of the strong-field ionization and dissociation dynamics of nature’s simplest molecule H2+ is performed. By including all electronic and nuclear degrees of freedom and all reaction channels, molecular rotation is shown to play an important role in the ionization process. In addition, strong orientation effects in the energy deposition process of the Buckminster fullerene C60 in short intense laser pulses are surprisingly found in full dimensional calculations. Their consequences on the subsequent nuclear relaxation dynamics shed new light on available experimental data and future experiments are proposed to confirm the detailed predictions.
Regarding the second objective, the NA-QMD formalism is basically extended to take electron-nuclear correlations into account. This extension is achieved by means of a trajectory surface hopping scheme in the adiabatic Kohn-Sham framework. First studied examples from collision physics and photochemistry illustrate the relevance and importance of quantum effects in the nuclear dynamics.
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Postell, David Jonathan. "Laser Induced Fluorescence Spectroscopy of molecular bromine: Observations of Emission to High Vibrational Levels in the Ground (X) State." Wright State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=wright1186777955.
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Liao, Chen-Ting, Xuan Li, Daniel J. Haxton, Thomas N. Rescigno, Robert R. Lucchese, C. William McCurdy, and Arvinder Sandhu. "Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modifications." AMER PHYSICAL SOC, 2017. http://hdl.handle.net/10150/624049.
Повний текст джерелаАнотація:
We used extreme ultraviolet (XUV) transient absorption spectroscopy to study the autoionizing Rydberg states of oxygen in an electronically- and vibrationally-resolved fashion. XUVpulse initiates molecular polarization and near-infrared pulse perturbs its evolution. Transient absorption spectra show positive optical-density (OD) change in the case of ns sigma(g) and nd pi(g) autoionizing states of oxygen and negative OD change for nd sigma(g) states. Multiconfiguration time-dependent Hartree-Fock (MCTDHF) calculations are used to simulate the transient absorption and the resulting spectra and temporal evolution agree with experimental observations. We model the effect of nearinfrared perturbation on molecular polarization and find that the laser-induced phase-shift model agrees with the experimental andMCTDHF results, while the laser-induced attenuation model does not. We relate the electronicstate- symmetry-dependent sign of the OD change to the Fano parameters of the static absorption line shapes.
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Vogt, David Sebastian. "Laser-Induced Breakdown Spectroscopy for the Exploration of Mars: Analysis of Molecular Emissions and Spatial Characterization of the Plasma." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21016.
Повний текст джерелаАнотація:
Die Arbeit beschäftigt sich mit laser-induzierter Plasmaspektroskopie (LIBS) im Kontext der robotischen Mars-Erkundung. Bei LIBS wird Plasma analysiert, das durch Ablation von Probenmaterial gebildet wird. Die Methode wird seit 2012 von dem Instrument ChemCam des Mars-Rovers Curiosity eingesetzt, um das Gestein und den Boden der Marsoberfläche zu untersuchen. Sie wird auch in der NASA-Mission Mars 2020 und in der chinesischen Mission HX-1 eingesetzt werden, welche im Jahr 2020 zum Mars starten sollen.
Zwei Studien dieser Arbeit betrachten Emissionen von Molekülen, die sich im Plasma bilden. Diese können zur Detektion von Chlor und Fluor eingesetzt werden, die von geologischem Interesse für Mars sind. Emissionen von MgCl und CaCl werden in simulierten Marsbedingungen für die Bestimmung der Chlorkonzentration untersucht. Nur das CaCl-Signal wird als stark genug befunden. Dieses ist am stärksten bei vergleichsweise geringen Chlorkonzentrationen, was durch einen Nichtgleichgewichtszustand des Plasmas erklärt werden kann. In der zweiten Studie werden die Emissionen von CaCl und CaF verglichen. Beide können mit demselben Modell in Abhängigkeit der Konzentrationen der Reaktionspartner beschrieben werden. Allerdings werden auch starke Matrixeffekte beobachtet, die die Emissionen beeinträchtigen können.
Im letzten Teil der Arbeit wird der Plasma-Imaging-Aufbau beschrieben, der aufgebaut wurde. Der Aufbau ermöglicht räumlich aufgelöste Messungen der Emissionsspektren. Es werden erste Ergebnisse vorgestellt, die mit diesem Aufbau erzielt wurden. Diese zeigen, dass CaCl und CaF nur im Plasmazentrum emittieren, was mit einer Verdünnung und Ausbildung eines Niedertemperaturbereichs im Plasmazentrum erklärt werden kann. Atomare Emissionen von Wasserstoff, Kohlenstoff und Sauerstoff sind dagegen intensiver an der Plasmafront und zeigen Verwirbelungen auf, was auf komplexe Temperaturverteilungen und auf einen starken Einfluss von Strömungen im Plasma hinweist.In this thesis, laser-induced breakdown spectroscopy (LIBS) is investigated in the context of the robotic exploration of Mars. In LIBS, the plasma formed by laser-ablated sample material is analyzed spectroscopically. Since 2012, it is employed by the ChemCam instrument on board the Mars rover Curiosity to analyze rocks and soil on the Martian surface. The technique will also be used in NASA's Mars 2020 mission and in the Chinese HX-1 mission, which are both scheduled to launch to Mars in 2020. The first two studies are concerned with emissions of molecules that form in the laser-induced plasma. These can be used to detect chlorine and fluorine, which are of geological interest for Mars. In the first study, MgCl and CaCl emissions are investigated for the detection and quantification of chlorine in Martian atmospheric conditions. Only the CaCl signal is found to be intense enough for this purpose. The CaCl signal is found to be skewed towards low chlorine concentrations, which is explained by a non-equilibrium model of the laser-induced plasma. In the second study, the emissions of CaCl and CaF are compared. The same model is used to describe the dependence of both signals on the respective reactant concentrations. Strong matrix effects are observed that affect the observed intensities. In the final part of the thesis the plasma imaging setup that was developed in the context of this thesis is presented. It enables spatially resolved measurements of the plasma emission spectra. First results show that CaCl and CaF emissions are confined close to the plasma center, likely because rarefaction leads to a low-temperature center in which molecules can form. Atomic emissions of hydrogen, carbon, and oxygen are more stable at the plasma front and show signs of vorticity, indicating a complex temperature distribution and a strong influence of flows within the plasma.
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Forthomme, Damien. "High Resolution Laser Spectroscopy Of Selected Molecules In The Gas Phase." Thesis, Fredericton: University of New Brunswick, 2011. http://hdl.handle.net/1882/35387.
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Gu, Yuxing. "Measurements of temperature and density profiles of iodine vapor between parallel plates in the transition regime using laser induced fluorescence /." free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9974999.
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Adams, J. W. "Kinetic investigations of selected alkaline-earth atoms by time-resolved spectroscopic methods including laser-induced atomic fluorescence and molecular chemiluminescence." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595351.
Повний текст джерелаАнотація:
This thesis is concerned with the kinetic investigation of gaseous alkaline-earth atoms in specific electronic states by time-resolved spectroscopic methods. The first part of the thesis is directed towards a study of the collisional behaviour of ground state atoms, in particular, Sr[5s2(1S0)], generated by pulsed irradiation and monitored by time-resolved atomic resonance absorption spectroscopy. In broader terms, it was also envisaged that this would provide a framework for considering and comparing the behaviour of this atom in both ground and excited state reactions, especially that of Sr[5s5p(3PJ)], described later in the thesis, in order to investigate the relationship between collisional behaviour and electronic structure. Whilst this method did not yield data for Sr[5s2(1S0)], the investigation did provide a structure for considering alkaline-earth atom chemistry in general. The second part of the thesis describes the study of the collisional behaviour of the electronically excited strontium atom, Sr[5s5p(3PJ)], generated by pulsed laser excitation at elevated temperatures. The reactions of this optically metastable atomic state with the molecules CH3Cl, CF3Cl, CH3Br and CF3Br were studied by both time-resolved atomic emission from Sr[5s5p(3P1)] → Sr[5s2(1S0)] and time-resolved molecular chemiluminescence from SrX(A2Π1/2,3/2, B2Σ+ - X2Σ+), following halogen atom (X = Cl, Br) abstraction. Quantitative characterisation of the time-dependencies of the atomic and molecular emissions indicated direct halogen abstraction by Sr(53PJ). Branching ratios into these specific molecular electronic states were derived by computerised integration of the intensities of the atomic and molecular decay profiles and were shown to be statistical in nature.
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Geng, J. "Kinetic studies of alkaline-earth atoms in specific electronic states by resonance absorption spectroscopy and laser-induced atomic and molecular emission." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599351.
Повний текст джерелаАнотація:
Investigations of the kinetics and dynamics of elementary gas-phase collisional processes and reactions have proved to be of major significance in many areas of both pure and applied physics and chemistry. A thorough understanding, both experimental and theoretical, of the collisional processes of defined quantum states of atoms and molecules is required. This includes physical processes such as energy transfer, collisional quenching, diffusion, charge transfer and ionisation, and chemical processes such as reaction rates, mechanism branching ratios and reaction potential energy surfaces. These topics have long been important in a variety of systems, including atmospheric chemistry, gaseous plasmas, combustion science and developing novel chemical laser systems. The primary motivation for the present work is to extend our knowledge about the collisional behaviour and reaction kinetics of alkaline-earth atoms in specific electronic states. The first part of this thesis (chapters 1-5) is directed towards a kinetic investigation of ground state atoms, in particular, Ca[4s2(1S0)], generated by flash photolysis of gaseous iodide molecules and whose decay is monitored by time-resolved atomic resonance absorption spectroscopy in the 'single-shot mode'. A new body of data for the absolute rate constants for the F, Cl, Br and I-atom abstraction reactions of Ca[4s2(1S0)] with a range of halide molecules are reported. The diffusional behaviour of this atom in noble gases, He, Kr and Xe and also N2, is also investigated in this work and the diffusion coefficients are consequently presented here. It is envisaged in broader terms that these studies have not only provided some new kinetic data for use in related areas but also contribute to form a framework for theoretical considerations and comparisons between the ground state and excited state reactions involving this atom. It is also considered that this type of research can be helpful in the area of exploring the relationship between reaction rate constants and the atomic or molecular electronic structures. In this work, the influence of molecular structure on the reaction rate when increasing the number of carbon atoms in the alkyl-halide chains is also investigated. Some measurements of the absorption cross-sections of gaseous MI2 (M = Ca, Sr, Ba) molecules by UV radiation as a function of wavelength are also made in this work but are presented in the appendices of this thesis.
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Jacquot, Mickael. "Mesure par radiomètres ICOTOM et validation des flux radiométriques dans un plasma de CO2 pur simulant des conditions d'entrée de type EXOMARS." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR121.
Повний текст джерелаАнотація:
Lors de l’entrée dans l’atmosphère de Mars d’un objet à vitesse hypersonique, il se crée une onde de choc détachée en amont de l’objet ainsi qu’un plasma hors équilibre à enthalpie importante et à haute intensité radiative. Si de nombreuses études ont été menées sur la protection nécessaire à apporter à l’objet pour résister à ces conditions physico-chimiques, les phénomènes chimiques liés à la recombinaison du CO2 en arrière de l’objet sont moins bien maîtrisés ; les quantités prévues de rayonnement découlant de cette recombinaison disposent donc de larges marges d’erreur. C’est en particulier le cas dans l’infrarouge, et la raison pour laquelle le CNES a développé deux radiomètres destinés à la mesure de ces flux émis par CO et CO2 en vol martien. Il convient donc d’étalonner ces capteurs pour la mesure des flux radiatifs en vol et d’étudier cette recombinaison sur un jet libre de plasma de CO2 pur en laboratoire. L’étalonnage des radiomètres est fait devant une source de type corps noir ; concernant l’état du plasma de laboratoire issu d’une torche à plasma inductive, l’étude de la diffusion Raman spontanée induite par laser sur CO et de la fluorescence à deux photons induite par laser sur O permettent d’estimer les températures et densités des espèces respectivement soudées, et ainsi de jauger de l’état de recombinaison du plasmaWhen an object is entering the atmosphere of Mars at hypersonic speeds, a detached shock layer is forming in front of the said object accompanied by a high-enthalpy non-equilibrium plasma with high radiative intensity. Several studies have already been conducted about the necessary protective layer for the object to withstand such physico-chemical conditions, however the chemical phenomena concerning CO2 recombination around the back of the object are not too well known ; the radiative quantities coming from this recombination are often given with large error margins because of this. It is particularly the case in the infrared, that is why the French Space Agency developed two radiometers designed for mesuring radiative heat fluxes emitted by CO and CO2 during a martian flight. It seems relevant to calibrate these sensors for quantitative measurements of radiative heat fluxes in flight conditions and to study the recombination of a pure CO2 plasma in laboratory conditions. The radiometers have been calibrated in front of a blackbody source ; concerning the state of the laboratory plasma created by an inductive plasma torch, a study of the laser-induced spontaneous Raman scattering on CO and of two-photon absorption laser-induced fluorescence on O have been conducted, enabling evaluation of both temperatures and densities of the probed species, and so give an estimate on the plasma recombination state
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Watanabe, Yuji Nascimento. "Cinética e dinâmica molecular do processo de dispersão bidimensional em sistemas de injeção em fluxo (FI):construção e validação de um aparato experimental." Programa de Pós-Graduação em Química da UFBA, 2002. http://www.repositorio.ufba.br/ri/handle/ri/10021.
Повний текст джерелаАнотація:
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Yuji Watanabe.pdf: 3696013 bytes, checksum: 64d732d452c08c675e78db3f991bf851 (MD5)Made available in DSpace on 2013-04-23T14:35:12Z (GMT). No. of bitstreams: 1 Yuji Watanabe.pdf: 3696013 bytes, checksum: 64d732d452c08c675e78db3f991bf851 (MD5) Previous issue date: 2002
Este trabalho é constituído de três etapas, a saber: · planejamento e construção de um aparato experimental para medidas de fluorescência total (LIF) e depolarização fluorescente (PLF) em sistema de injeção em fluxo (FI); testes operacionais visando otimizar parâmetros experimentais; avaliação fotoquímica/fotofísica da cinética e dinâmica molecular duma reação química em FI. O aparato experimental automatizado é constituído de um sistema de detecção de fluorescência, um sistema FI e um sistema ótico. Permite a aquisição com alta resolução espacial (20mm) de perfis de distribuição de concentração (LIF) e de orientação molecular vertical e horizontal (PLF) em função do tempo de transporte do fluxo. Os perfis interpolados em mapas bidimensionais fornecem informações sobre a cinética e a dinâmica molecular dos processos de dispersão axial e radial de amostras em fluxo carregador. Foram medidas tensões interfaciais estáticas, pelo método do ângulo de contato, para escolher a constituição química do percurso analítico e minimizar a sua influência na cinética e na dinâmica molecular de dispersão. Foi determinada a influência da aceleração gravitacional e do número de injeções por período de amostragem, dentre outros parâmetros usuais, no processo de dispersão.Observou-se a existência de padrões de dispersão diferenciados para a Rodamina B (RB) a depender da sua orientação espacial. Isto foi atribuído ao grupo benzóico perpendicular ao grupo xantênico e comprovado pela utilização da Rodamina 6G (R6G) sob as mesmas condições. A contribuição da cinética e da dinâmica moleculares de dispersão no rendimento de uma reaçãoquímica em fluxo foi avaliado com adição de Ca(II), um agente supressor da fluorescência da RB.
Salvador
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Gautier, Pierre. "Dosage des polluants NO et CO par imagerie de fluorescence induite par laser dans les écoulements réactifs." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR26/document.
Повний текст джерелаАнотація:
La thèse consiste à développer une technique d'imagerie quantitative de concentration de polluants dans les écoulements réactifs. Il s'agit d'une part de développer l'imagerie de fluorescence sur NO. Un modèle de fluorescence à n niveaux a été développé pour calculer l'évolution de la fluorescence avec la température, concentration des espèces et pression. Ce modèle a été validé avec des mesures de fluorescence et d'absorption obtenues dans une cellule optique fonctionnant jusqu'à 800 K et 20 bar puis dans un brûleur laminaire haute-pression. De ce modèle a été définie une stratégie permettant la mesure de la distribution instantanée de NO dans une flamme stratifiée. Une étude similaire pour détecter CO a été ensuite initiée. Des mesures de fluorescence à deux photons ont été obtenues dans la cellule et dans une flamme plate atmosphérique. Les résultats montrent que cet outil est opérationnel, répondant à un besoin pour l'amélioration des performances des systèmes de propulsionThis PhD work is to develop a quantitative imaging technique for measurements of the concentration of pollutants in reactive flows. On one hand, the concern was to develop the NO fluorescence imaging technique. For this purpose, an n-level fluorescence model was first developed to calculate the behavior of fluorescence signals with temperature, species concentration, and pressure. Then this model was validated with fluorescence and absorption measurements acquired in an optical cell up to 800 K and to 20 bar and in a high-pressure laminar burner. From this model, a strategy used to measure the instantaneous NO distribution in a stratified flame was defined. Then, a similar study to detect CO with fluorescence was then investigated. Two-photon fluorescence measurements were performed in the optical cell and in a flame. The results make clear that the spectroscopic diagnostic becomes operational with the need to improve the performances of propulsion systems
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Wiederschein, Frank [Verfasser], Helmut [Akademischer Betreuer] Grubmüller, Bernd [Akademischer Betreuer] Abel, and Marcus [Akademischer Betreuer] Müller. "Investigation of Laser-Induced-Liquid-Beam-Ion-Desorption (LILBID) with Molecular Dynamics Simulations / Frank Wiederschein. Gutachter: Helmut Grubmüller ; Bernd Abel ; Marcus Müller. Betreuer: Helmut Grubmüller." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2010. http://d-nb.info/1043610707/34.
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Porterfield, Veronica Marie. "The Transcriptome of the Suprachiasmatic Nucleus and its Response to Photic Stimuli." Kent State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=kent1228167654.
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Vogt, David Sebastian [Verfasser], Heinz-Wilhelm [Gutachter] Hübers, Reinhard [Gutachter] Noll, and Olivier [Gutachter] Forni. "Laser-Induced Breakdown Spectroscopy for the Exploration of Mars: Analysis of Molecular Emissions and Spatial Characterization of the Plasma / David Sebastian Vogt ; Gutachter: Heinz-Wilhelm Hübers, Reinhard Noll, Olivier Forni." Berlin : Humboldt-Universität zu Berlin, 2020. http://d-nb.info/1203126808/34.
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Gregoire, Sylvain. "Etude et optimisation de la méthode LIBS (Laser Induced Breakdown Spectroscopy) pour l'identification de matériaux organiques appliquée au recyclage des plastiques et à la conservation du patrimoine." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01062281.
Повний текст джерелаАнотація:
La LIBS est une technique d'analyse élémentaire dont la rapidité d'exécution et la portabilité en font une technique idéale pour l'analyse des matériaux sur site. Elle a déjà largement fait ses preuves dans le cadre de l'analyse de matériaux inorganiques. Mais les molécules organiques usuelles présentent des compositions atomiques similaires (C, O, H, N), rendant leur identification en LIBS difficile. L'utilisation de traitements de données tels que les rapports de raies ou la chimiométrie est donc inéluctable pour séparer efficacement plusieurs types de molécules organiques en LIBS. Malgré le caractère élémentaire de cette technique, les spectres obtenus lors de l'analyse de matériaux organiques montrent la signature spectrale de molécules diatomiques C2 et CN. Longtemps considéré comme des recombinaisons aléatoires des atomes présents dans le plasma, le signal de ces molécules s'avère d'dépendant de la nature des liaisons moléculaires de la molécule d'origine. Ce travail de thèse s'oriente autour de trois grands axes d'études - L'utilisation de traitements de données tels que la chimiométrie pour établir un protocole de traitements optimal visant à la discrimination des polymères dans le cadre du tri des plastiques. Un protocole optimisé a pu être avancé en UV et en IR. - L'identification des matières organiques utilisées en peinture murale (liants, adhésifs et consolidants) a pu être réalisée sur des échantillons de peinture de référence. Les traitements de données utilisés précédemment ont pu être appliqués sur ces échantillons présentant une matrice majoritairement inorganique. - La compréhension des procédés de formation des molécules diatomiques dans le plasma pour améliorer leur utilisation et ainsi optimiser la discrimination des matériaux organiques sur la base du signal moléculaire en LIBS. Le développement d'un système d'imagerie a permis de suivre le comportement spatio-temporel des espèces atomiques et moléculaires dans le plasma sous régimes UV et IR. Une hypothèse de formation des molécules sous ablation UV et IR a pu être établie.
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Mauger, François. "Double ionisation d' atomes soumis à des impulsions laser intenses : vue de l' espace des phases." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4031.
Повний текст джерелаАнотація:
Lorsqu'ils sont soumis à des pulses laser courts et intenses, des atomes peuvent perdre des électrons. Plusieurs canaux sont impliqués dans la double ionisation, comme la NSDI et le scénario associé de la recollision. La recollision est maintenant vue comme la “pierre d'angle de la physique en champ fort” pour les éclairages qu'elle donne dans l'organisation de la matière et en ce qu'elle constitue l'une des manifestations les plus flagrantes de la corrélation électron-électron dans la nature. Dans ce manuscrit, une analyse théorique des mécanismes de double ionisation est menée en utilisant la mécanique classique. Cette description complémente les modèles quantiques en observant la dynamique depuis un cadre de travail différent et avec l'éclairage de la dynamique nonlinéaire. L'analyse, menée dans l'espace des phases, permet l'identification des structures organisatrices qui régulent les différents mécanismes d'ionisation. Pour des champs laser polarisés linéairement, le mécanisme de la recollision est complété par l'image de l'électron interne. L'électron interne donne accès à une description fine de la dynamique de recollision et explique les différentes routes pour la double ionisation. Il permet également de faire des prédictions telles que l'intensité du coude dans la probabilité de double ionisation et explique complètement la RESI. En polarisation circulaire, il est communément cru que la recollision n'est pas possible, en dépit de résultats expérimentaux contradictoires. En fait, l'analyse de l'espace des phases montre que la recollision est possible mais pas accessible à tous les atomes, réconciliant par conséquent les contradictions expérimentales précédentesWhen subjected to strong and short laser pulses, atoms may lose electrons. Several ionization channels are involved in such double ionization events, like nonsequential double ionization (NSDI) and its associated recollision scenario. Recollision is now seen as the “keystone of strong field physics”, for its insights into the organization of matter, and is one of the most dramatic manifestations of electron-electron correlation in nature. In this manuscript a theoretical analysis of the double ionization mechanisms is carried out using classical mechanics. This description complements quantum treatments by observing the dynamics from a different framework, with the light of nonlinear dynamics, as both frameworks exhibit the main ingredient, i.e., strong electron-electron correlation. The analysis, carried out in phase space (e.g., through reduced models) enables the identification of the organizing structures that regulate the ionization channels. For linearly polarized lasers, the recollision mechanism is completed by the picture of the “inner” electron. The inner electron gives access to a fine description of the recollision dynamics and explains the routes to double ionization. It also enables verifiable predictions such as the location of the characteristic knee shape in the double ionization yield versus laser intensity and fully explains delayed ionizations like RESI. For circular polarization, it is commonly believed that recollision is not possible, despite apparently contradictory experimental results. In fact, the phase space analysis shows that recollision is possible but not accessible to all atoms, thus reconciling the previous experimental results
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Louvradoux, Thomas. "Spectroscopie à haute résolution de H2+ : production et refroidissement sympathique d'ions piégés." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7168.
Повний текст джерелаАнотація:
L'objectif du projet est de réaliser la spectroscopie vibrationnelle à deux photons sans effet Doppler de haute résolution sur l'ion moléculaire H2+ afin d'obtenir une mesure optique directe du rapport de la masse du proton à celle de l'électron. Les ions H2+ doivent être piégés et refroidis, mais ne peuvent être refroidis que par refroidissement sympathique par l'intermédiaire d'ions Be+ refroidis par laser. Après une introduction générale, la deuxième partie de ce manuscrit décrit le piégeage d'ions et présente le piège linéaire que nous utilisons afin de piéger les ions H2+ et Be+, ainsi que les méthodes qui permettent de créer les ions Be+ soit par impact électronique, soit par photo-ionisation d'un jet d'atome de Be. Dans la troisième partie nous présentons la source d'ions H2+ sélective en état interne utilisant la photo-ionisation multiphotonique résonante d'H2 à l'aide d'un laser en impulsion à 303 nm puis nous présentons les ions moléculaires froids sélectionnés en état interne obtenus. Dans la quatrième partie nous présentons le modèle de la spectroscopie par photo-dissociation photonique résonante (REMPD) qui nous permet d'observer la transition dans H2+. Dans la cinquième partie nous présentons la conception et la réalisation de la source laser à 313 nm permettant de refroidir les ions Be+ par refroidissement Doppler. La sixième partie présente l'observation de cristaux de Coulomb de Be+ ainsi que des cristaux mixtes de Be+ et H2+, elle présente aussi les différentes techniques expérimentales qui nous permettent d'obtenir et d'observer ces cristaux. La septième partie décrit la source de spectroscopie à 9,17 µmThe objective of the project is to perform high-resolution Doppler-free two-photon vibrational spectroscopy on the H2+ molecular ions in order to obtain a direct optical measurement of the electron to proton mass ratio. The H2+ ions must be trapped and cooled but can only be cooled by sympathetic cooling using Be+ laser cooled ions. After a general introduction, the second part of this manuscrit describes ion trapping and presents the linear trap we use to trap H2+ and Be+ ions, as well as the methods used to create Be+ ions either by electronic impact or by photo-ionization of a stream of Be atoms. In the third part we present the state selective H2+ ion source using resonance enhanced multiphoton ionisation (REMPI) with a 303 nm pulsed laser, then we present the state-selected cold molecular ions obtained. In the fourth part we present a model for the resonance enhanced multiphoton dissociation spectroscopy technique that we use in order to detect the transition in H2+. In the fifth part we present the design and realization of the 313 nm laser source for Doppler cooling of Be+ ions. The sixth part presents the observation of Coulomb crystals of Be+ as well as mixed crystals of Be+ and H2+, it also presents the different experimental techniques that allow us to obtain and observe these crystals. The seventh part describes the spectroscopy source at 9,17 µm
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Buridon, Victor. "Application de la spectrométrie de masse COINTOF à l'étude de la dissociation de petits agrégats d'eau protonés par collision sur un atome d'argon : développement d'une cible de nano-gouttes de gaz rare." Phd thesis, Université Claude Bernard - Lyon I, 2013. http://tel.archives-ouvertes.fr/tel-00994146.
Повний текст джерелаАнотація:
L'étude de l'irradiation dans le système moléculaire à l'échelle du nanomètre est un domaine d'investigation innovant des sciences des radiations. Le Dispositif d'Irradiation d'Agrégats Moléculaires (DIAM) est conçu en vue les conséquences de l'irradiation dans des petits systèmes moléculaires modèles comme les agrégats d'eau protonés. L'irradiation provoque la fragmentation en plusieurs fragments neutres ou chargés. La technique de spectrométrie de masse COINTOF (Correlated Ion and Neutral Time of Flight) permet la détection corrélées des fragments neutres et chargés issus de la dissociation d'un système moléculaire préalablement sélectionné en masse et en vitesse. Les données collectées sont traitées et structurées pour permettre l'analyse statistique des corrélations sur un grand nombre d'événements de fragmentation. Parallèlement à l'identification des canaux de fragmentation, la technique COINTOF permet la mesure de leur rapport de branchement et de leur section efficace. La méthode est présentée pour la dissociation induite par collision sur un atome d'argon, d'agrégats d'eau protonés H+(H2O)n:[2;7], accélérés à 8keV. L'efficacité de détection, information déterminante pour la production de données quantitatives, est mesurée à partir des données et étudiée en fonction de la distribution l'amplitude des signaux de détection. Enfin, un nouveau système de cible constituée de nanogouttes de gaz rares a été développé
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Teyssier, Cécile. "Spectrométrie de masse COINTOF : Conception et d'un analyseur à temps de vol et développement de la méthode d'analyse." Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00744850.
Повний текст джерелаАнотація:
Le Dispositif d'Irradiation d'Agrégats Moléculaires (DIAM) est conçu pour l'étude de mécanismes de dissociation résultant de l'interaction de nanosystèmes moléculaires avec des protons de 20-150 keV. Une technique originale de spectrométrie de masse appelée COINTOF (Correlated Ion and Neutral Time Of Flight) permet la mesure corrélée du temps de vol des fragments neutres et chargés issus de la dissociation d'un système moléculaire sélectionné en masse. Une stratégie de traitement des signaux a été développée afin de pouvoir distinguer des fragments proches en temps (< 1ns). Les données collectées sont structurées dans le logiciel ROOT® pour l'analyse statistique des corrélations. Le fonctionnement de la technique COINTOF est illustré par des expériences de dissociation induite par collision d'agrégats d'eau protonés sur une cible gazeuse. La méthodologie d'analyse des données est exposée à travers l'étude du canal de dissociation du trimère d'eau protoné produisant l'ion chargé H3O+ et deux molécules d'eau. La distribution de la différence de temps de vol entre les deux fragments neutres est mesurée, mettant en évidence une énergie libérée de quelques eV. En parallèle, un second spectromètre de masse à temps de vol adapté à l'évolution du dispositif a été développé. Il associe un temps de vol linéaire et un temps de vol orthogonal et intègre un détecteur à position (ligne à retard). Des simulations ont démontré les potentialités du nouvel analyseur. Enfin, des travaux ont été menés au laboratoire R.-J. A. Lévesque (Université de Montréal) portant sur les capacités d'imagerie de détecteurs à position multi-pixel de la collaboration MPX-ATLAS.