Vacuum Ultraviolet Time-Resolved Photoelectron Spectroscopy Using Velocity Map Imaging PDF Download
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Author: Michael Hemsworth
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This thesis covers two separate but related projects. The first project covers the design and simulation of a new angle-resolved photoelectron-photoion coincidence (PEPICO) spectrometer. The spectrometer utilizes velocity map imaging (VMI) to measure the photoelectron kinetic energy and angular distributions in coincidence or covariance with the photoion mass spectrum using a Wiley-McLaren time-of-flight mass spectrometer. The instrument was also designed for 3D VMI, a technique that measures the full three dimensional photoelectron velocity distribution. Simulations were performed to measure the spectrometer performance with respect to photoelectron kinetic energy resolution, mass resolution and photoelectron time spread resolution, the latter being important for 3D VMI. The second project covers a time-resolved velocity map imaging photoelectron spectroscopy study of nonadiabatic excited state dynamics in carbonyl sulfide (OCS). An ultrafast tunable vacuum ultraviolet light source was tuned to two different vibrational states of the singlet sigma plus excited state. A direct measurement of the excited state lifetimes was made. The photoelectron kinetic energy and angular distributions were used to determine three different ionization mechanisms: we found evidence for direct ionization, superexcited OCS* molecular autoionization and superexcited photofragment S* autoionization. In the future, definitive evidence of our assignments could be made with a coincidence measurement, thus the results from this experiment will be used as a benchmark for the new spectrometer described above.
Author: Michael Hemsworth
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This thesis covers two separate but related projects. The first project covers the design and simulation of a new angle-resolved photoelectron-photoion coincidence (PEPICO) spectrometer. The spectrometer utilizes velocity map imaging (VMI) to measure the photoelectron kinetic energy and angular distributions in coincidence or covariance with the photoion mass spectrum using a Wiley-McLaren time-of-flight mass spectrometer. The instrument was also designed for 3D VMI, a technique that measures the full three dimensional photoelectron velocity distribution. Simulations were performed to measure the spectrometer performance with respect to photoelectron kinetic energy resolution, mass resolution and photoelectron time spread resolution, the latter being important for 3D VMI. The second project covers a time-resolved velocity map imaging photoelectron spectroscopy study of nonadiabatic excited state dynamics in carbonyl sulfide (OCS). An ultrafast tunable vacuum ultraviolet light source was tuned to two different vibrational states of the singlet sigma plus excited state. A direct measurement of the excited state lifetimes was made. The photoelectron kinetic energy and angular distributions were used to determine three different ionization mechanisms: we found evidence for direct ionization, superexcited OCS* molecular autoionization and superexcited photofragment S* autoionization. In the future, definitive evidence of our assignments could be made with a coincidence measurement, thus the results from this experiment will be used as a benchmark for the new spectrometer described above.
Author: M. N. Gale
Publisher:
ISBN:
Category : Anions
Languages : en
Pages : 212
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Book Description
Author: Oliver Schalk
Publisher: American Chemical Society
ISBN: 0841299072
Category : Science
Languages : en
Pages : 201
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Book Description
Photochemistry is an important part of both chemistry and biology and is of great practical significance for the development of sustainable sources of energy. The mechanisms of photochemistry are far from trivial and far from understood. There are limits to how well theory can describe the processes and how well experiments can resolve them. This book aims to provide an overview of state-of-the-art methods for both theoretical development and experimental techniques, with a focus on ultrafast molecular processes and electronic excitation of organic molecules. These fields are active and progress is being made, carried by the increasing speed of computation and the development of new light sources, most notably X-ray sources at large facilities. Alongside these two layers of theoretical development and experimental techniques is a third layer—model building. In this layer, model building tries to find similarities in seemingly unrelated experimental results and deepen our general knowledge of photoinduced processes. Often, progress is made not by cutting-edge techniques but rather by using well-established techniques with a great variety of molecules—this approach promises less glory but is just as important as the first two layers. Examples mentioned in the text are the Woodward–Hoffman rules and the dynamophore concept. All three layers are crucial to push our knowledge further and, eventually, to use it for developing new and more advanced optical devices.
Author: Travis William Wright
Publisher:
ISBN: 9781339544151
Category :
Languages : en
Pages :
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Book Description
Studying the ultrafast dynamics of small molecules can serve as the first step in understanding the dynamics in larger chemically and biologically relevant molecules. To make direct comparisons with existing computational techniques, the photons used in pump-probe spectroscopy must make perturbative transitions between the electronic states of isolated small molecules. In this dissertation experimental investigations of ultrafast dynamics in electronic excitations of neutral ethylene and carbon dioxide are discussed. These experiments are performed using VUV/XUV femtosecond pulses as pump and probe. To make photons with sufficient energy for single photon transitions, VUV and XUV light is generated by high harmonic generation (HHG) using a high pulse energy ([approximately] 30 - 40 mJ) Ti:sapphire femtosecond laser. Sufficient flux must be generated to enable splitting of the HHG light into pump and probe arms. The system produces > 1010 photons per shot, corresponding to nearly 10 MW of peak power in the XUV. Using a high flux of high energy photons creates a unique set of challenges when designing a detector capable of performing pump-probe experiments. A velocity map imaging (VMI) detector has been designed to address these challenges, and has become a successful tool facilitating studies into molecular dynamics that were not possible before its implementation. The emphasis on using high energy, single photon transitions allowed theoretical calculations to be directly compared to experimental yields for the first time. This comparison resolved a long standing issue in the excited state lifetime of ethylene, and provided a confirmation of the branching ratio between the two nonadiabatic relaxation pathways that return ethylene back to its ground state from the [pi]*. The participation of the 3s Rydberg state has also been measured by collecting the time resolved photoelectron spectrum during the dynamics on ethylene [pi]* excited state, confirming calculations predicting the effect of the 3s. In carbon dioxide the first time resolved measurement in the lowest electronic excitation of carbon dioxide has been performed. A high kinetic energy release channel shows the signature of wavepacket dynamics within the excited state manifold. Deviation from the direct dissociation predicted for the pumped state provides experimental evidence confirming theoretical predictions of nonadiabatic transitions within the lowest lying electronically excited states.
Author: Alison Virginia Davis
Publisher:
ISBN:
Category :
Languages : en
Pages : 362
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Book Description
Author: Martin Alex Bjørnholst
Publisher: Springer Nature
ISBN: 3030536297
Category : Science
Languages : en
Pages : 155
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Book Description
This book explores how structure impacts the dynamics of organic molecules in an extensive and impressive range of femtosecond time-resolved experiments that are combined with state-of-the-art theoretical approaches. It explores an area of molecular dynamics that remains largely uncharted and provides an extraordinary overview, along with novel insights into the concept of the dynamophore – the functional group of ultrafast science. Divided into four parts, this book outlines both experimental and computational studies on the VUV photoinduced dynamics of four cyclic ketones and one linear ketone, the ring-opening and dissociative dynamics of cyclopropane, and the potential ultrafast intersystem crossing in three methylated benzene derivatives. Model systems for the disulfide bond and the peptide bond, both of which are related to the structure of proteins, are also investigated. This highly informative and carefully presented book offers a wealth of scientific insights for all scholars with an interest in molecular dynamics.
Author: Lei Yang
Publisher:
ISBN: 9781267663399
Category :
Languages : en
Pages :
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Book Description
By detecting the central signal of the photoelectron image as a function of vacuum ultraviolet (VUV) laser energy, we have obtained a high-resolution threshold photoelectron spectrum for the ground state of chlorobenzene cation (C6H5Cl) using the velocity-map imaging-photoelectron method. By employing the vacuum ultraviolet (VUV) laser velocity-map imaging (VMI) photoelectron scheme to discriminate energetic photoelectrons, we have measured the VUV-VMI-threshold photoelectrons (VUV-VMI-TPE) spectra of propargyl radical [C3H3 (X̃2B1)] near its ionization threshold at photoelectron energy bandwidths of 3 and 7 cm−1 (full-width at half-maximum, FWHM). The photoionization efficiency (PIE) and pulsed field ionization-photoion (PFI-PI) spectra for oxygen atoms O(3P2, 1, 0) resulting from the 193.3 nm photodissociation of SO2 have been measured using tunable vacuum ultraviolet (VUV) laser radiation in the frequency range of 109200 - 109900 cm−1. By coupling a tunable vacuum ultraviolet (VUV) laser system with the velocity-map imaging system, we have measured the photoionization efficiency (PIE) and the pulsed field ionization-photoion (PFI-PI) spectra for chlorine atoms Cl(2P[subscript 3/2, 1/2]) produced from the 193.3nm photodissociation of C6H5Cl in the VUV wavenumber range of 103,580 to 105,600 cm−1. The predissociation of N2 from the rotational levels in the o1[Pi subscript u] (v'=2) and b' 1[Sigma subscript u] (v'=8) bands have been studied in the wavelength range from 109,350 cm−1 (13.5577 eV) to 109,580 cm−1 (13.5862 eV) by time-sliced velocity-map imaging technique with VUV photoionization detection of the fragments.
Author: Darcy S. Peterka
Publisher:
ISBN:
Category :
Languages : en
Pages : 412
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Book Description
Author: Martin Quack
Publisher: John Wiley & Sons
ISBN: 0470066539
Category : Science
Languages : en
Pages : 2236
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Book Description
The field of High-Resolution Spectroscopy has been considerably extended and even redefined in some areas. Combining the knowledge of spectroscopy, laser technology, chemical computation, and experiments, Handbook of High-Resolution Spectroscopy provides a comprehensive survey of the whole field as it presents itself today, with emphasis on the recent developments. This essential handbook for advanced research students, graduate students, and researchers takes a systematic approach through the range of wavelengths and includes the latest advances in experiment and theory that will help and guide future applications. The first comprehensive survey in high-resolution molecular spectroscopy for over 15 years Brings together the knowledge of spectroscopy, laser technology, chemical computation and experiments Brings the reader up-to-date with the many advances that have been made in recent times Takes the reader through the range of wavelengths, covering all possible techniques such as Microwave Spectroscopy, Infrared Spectroscopy, Raman Spectroscopy, VIS, UV and VUV Combines theoretical, computational and experimental aspects Has numerous applications in a wide range of scientific domains Edited by two leaders in this field Provides an overview of rotational, vibration, electronic and photoelectron spectroscopy Volume 1 - Introduction: Fundamentals of Molecular Spectroscopy Volume 2 - High-Resolution Molecular Spectroscopy: Methods and Results Volume 3 - Special Methods & Applications
Author: Stuart A. Rice
Publisher: John Wiley & Sons
ISBN: 0470259485
Category : Science
Languages : en
Pages : 648
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Book Description
This series provides the chemical physics field with a forum for critical, authoritative evaluations of advances in every area of the discipline.
