Development and Construction of a New Photoelectron Imaging Spectrometer for Studying the Spectroscopy and Ultrafast Dynamics of Molecular Anions PDF Download
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Author: Gareth Michael Roberts
Publisher:
ISBN:
Category : Anions
Languages : en
Pages :
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Book Description
We present a detailed account of the development, construction, and commissioning of a new experiment for studying the spectroscopy and ultrafast dynamics of molecular anions in the gas phase. The new instrument incorporates: an electrospray ionisation source, which is capable of generating a vast class of molecular anions; a Wiley-McLaren time-of-flight mass spectrometer; and a compact photoelectron imaging arrangement for anions, which negates the use of pulsed high voltages. We use this instrument in conjunction with a femtosecond laser system to perform the first ultrafast time-resolved photoelectron imaging experiments on molecular anions generated through electrospray ionisation. A method for reconstructing three dimensional charged particle distributions from their associated two dimensional projections on an imaging detector plane is described. This new method utilises: (1) onion-peeling in polar co-ordinates (POP) to perform the reconstruction; and (2) basis set concepts to significantly enhance the algorithms computational speed. We compare this new POP algorithm with other reconstruction algorithms, which shows that the method is as good as the benchmark pBASEX method in terms of accuracy. Importantly, we show that it is also computationally fast, allowing images to be reconstructed as they are acquired in a typical imaging experiment. Original work is presented which investigates the spectroscopy and ultrafast excited dynamics of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion. The photoelectron spectrum of TCNQ? is measured at 3.1 eV, which is used to gain insight into the electronic structure and geometries of both the anion and neutral states. Time-resolved photoelectron imaging experiments explore the relaxation dynamics of its first excited 1 2B3u state, which we show undergoes internal conversion back to the 2B2g ground state on a timescale of 650 fs. Results also provide evidence of a wave packet motion on the excited state, which exhibits a characteristic frequency of 30 cm?1. Finally, we describe, for the first time, a formulism which allows ultrafast relaxation timescales to be extracted from the photoelectron angular distributions of isoenergetic photoelectron features. As an example, we use the time-resolved photoelectron angular distributions of a nearly isoenergetic feature in the photoelectron images of TCNQ?. From this model we extract a relaxation time for the 1 2B3u state, which quantitatively agrees with those extracted from fits to the features in the photoelectron spectra derived from the images.
Author: Gareth Michael Roberts
Publisher:
ISBN:
Category : Anions
Languages : en
Pages :
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Book Description
We present a detailed account of the development, construction, and commissioning of a new experiment for studying the spectroscopy and ultrafast dynamics of molecular anions in the gas phase. The new instrument incorporates: an electrospray ionisation source, which is capable of generating a vast class of molecular anions; a Wiley-McLaren time-of-flight mass spectrometer; and a compact photoelectron imaging arrangement for anions, which negates the use of pulsed high voltages. We use this instrument in conjunction with a femtosecond laser system to perform the first ultrafast time-resolved photoelectron imaging experiments on molecular anions generated through electrospray ionisation. A method for reconstructing three dimensional charged particle distributions from their associated two dimensional projections on an imaging detector plane is described. This new method utilises: (1) onion-peeling in polar co-ordinates (POP) to perform the reconstruction; and (2) basis set concepts to significantly enhance the algorithms computational speed. We compare this new POP algorithm with other reconstruction algorithms, which shows that the method is as good as the benchmark pBASEX method in terms of accuracy. Importantly, we show that it is also computationally fast, allowing images to be reconstructed as they are acquired in a typical imaging experiment. Original work is presented which investigates the spectroscopy and ultrafast excited dynamics of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion. The photoelectron spectrum of TCNQ? is measured at 3.1 eV, which is used to gain insight into the electronic structure and geometries of both the anion and neutral states. Time-resolved photoelectron imaging experiments explore the relaxation dynamics of its first excited 1 2B3u state, which we show undergoes internal conversion back to the 2B2g ground state on a timescale of 650 fs. Results also provide evidence of a wave packet motion on the excited state, which exhibits a characteristic frequency of 30 cm?1. Finally, we describe, for the first time, a formulism which allows ultrafast relaxation timescales to be extracted from the photoelectron angular distributions of isoenergetic photoelectron features. As an example, we use the time-resolved photoelectron angular distributions of a nearly isoenergetic feature in the photoelectron images of TCNQ?. From this model we extract a relaxation time for the 1 2B3u state, which quantitatively agrees with those extracted from fits to the features in the photoelectron spectra derived from the images.
Author: Alison Virginia Davis
Publisher:
ISBN:
Category :
Languages : en
Pages : 362
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Author: Steven John Kregel
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The electronic structure of molecular systems is responsible for a wide range of phenomena including fluorescence, phosphorescence, and many effects in semiconductors. One of the most remarkable is singlet fission, in which a singlet excitation on one molecule is split into two triplet excitations on neighboring molecules. These two triplets relax independently, and if integrated into a solar cell, singlet fission would raise the theoretical efficiency of solar cells from 30% to 44%. Singlet fission is difficult to study due to its dependence on the interplay of singlet and triplet states, between which transitions are strongly forbidden. This work details the construction of an instrument capable of performing anion photoelectron spectroscopy, one of the few techniques with access to singlet and triplet states on equal footing. The spectrometer is a new design, capable of providing constant resolution over its entire range, and was used to observe the ground and first excited states of the polyaromatic hydrocarbons anthracene and fluoranthene, along with the simple aromatic oxide radicals phenoxy, 1-naphthoxy, and 2-naphthoxy. The spectra provide highly precise values for these species electron affinities and excited state term energies, along with vibrational frequencies for the Franck-Condon active modes. Presented here is the first anion photoelectron study of the fluoranthene molecule, and the highest-resolution study to date of the anthracene molecule. Results show the clear presence of vibronic coupling in the singlet and triplet manifolds of both molecules, and we determine the electron affinities and T1 term energies of these species with great precision. The aromatic oxide radicals contain an oxygen atom bonded to the aromatic ring, which imparts a significant dipole moment to the neutral system. This dipole moment is strong enough to weakly bind an electron and produces photoelectron spectra which are strongly dependent on photon energy. While interesting, we acquired spectra at wavelengths designed to minimize this effect, and assign the active vibrational modes, some of which have been predicted but unseen until now due to their low intensity. We also determine the electron affinities for the 1-naphthoxy and 2-naphthoxy radicals.
Author: Benjamin Jefferys Greenblatt
Publisher:
ISBN:
Category :
Languages : en
Pages : 554
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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A new experimental technique for the time-resolved study of anion reactions is presented. Using femtosecond laser pulses, which provide extremely fast ([approx] 100 fs) time resolution, in conjunction with photoelectron spectroscopy, which reveals differences between anion and neutral potential energy surfaces, a complex anion reaction can be followed from its inception through the formation of asymptotic products. Experimental data can be modeled quantitatively using established theoretical approaches, allowing for the refinement of potential energy surfaces as well as dynamical models. After a brief overview, a detailed account of the construction of the experimental apparatus is presented. Documentation of the data acquisition program is contained in the Appendix. The first experimental demonstration of the technique is then presented for I[sub 2][sup -] photodissociation, modeled using a simulation program which is also detailed in the Appendix. The investigation of I[sub 2][sup -] photodissociation in several size-selected I[sub 2][sup -](Ar)[sub n] (n= 6-20) and I[sub 2][sup -](CO[sub 2])[sub n] (n= 4-16) clusters forms the heart of the dissertation. In a series of chapters, the numerous effects of solvation on this fundamental bond-breaking reaction are explored, the most notable of which is the recombination of I[sub 2][sup -] on the ground[tilde X]([sup 2][Sigma][sub u][sup+]) state in sufficiently large clusters. Recombination and trapping of I[sub 2][sup -] on the excited[tilde A]([sup 2][Pi][sub 3/2,g]) state is also observed in both types of clusters. The studies have revealed electronic state transitions, the first step in recombination, on a[approx]500 fs to[approx]10 ps timescale. Accompanying the changes in electronic state is solvent reorganization, which occurs on a similar timescale. Over longer periods ([approx]1 ps to & gt;200 ps), energy is transferred from vibrationally excite d I[sub 2][sup -] to modes of the solvent, which in turn leads to solvent evaporation. These effects become more important as cluster size increases. In addition, differences in timescale and mechanism are observed between clusters of Ar, which binds to I[sup -] and I[sub 2][sup -] rather weakly, and CO[sub 2], whose large quadruple moment allows substantially stronger binding to these anions.
Author: J. H. D. Eland
Publisher: Elsevier
ISBN: 1483103218
Category : Science
Languages : en
Pages : 286
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Book Description
Photoelectron Spectroscopy: An Introduction to Ultraviolet Photoelectronspectroscopy in the Gas Phase, Second Edition Photoelectron Spectroscopy: An Introduction to Ultraviolet PhotoelectronSpectroscopy in the Gas Phase, Second Edition aims to give practical approach on the subject of photoelectron spectroscopy, as well as provide knowledge on the interpretation of the photoelectron spectrum. The book covers topics such as the principles and literature of photoelectron microscopy; the main features and analysis of photoelectron spectra; ionization techniques; and energies from the photoelectron spectra. Also covered in the book are topics suc as photoelectron band structure and the applications of photoelectron spectroscopy in chemistry. The text is recommended for students and practitioners of chemistry who would like to be familiarized with the concepts of photoelectron spectroscopy and its importance in the field.
Author: Shigemasa Suga
Publisher: Springer Nature
ISBN: 3030640736
Category : Science
Languages : en
Pages : 511
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Book Description
This book presents photoelectron spectroscopy as a valuable method for studying the electronic structures of various solid materials in the bulk state, on surfaces, and at buried interfaces. This second edition introduces the advanced technique of high-resolution and high-efficiency spin- and momentum-resolved photoelectron spectroscopy using a novel momentum microscope, enabling high-precision measurements down to a length scale of some tens of nanometers. The book also deals with fundamental concepts and approaches to applying this and other complementary techniques, such as inverse photoemission, photoelectron diffraction, scanning tunneling spectroscopy, as well as photon spectroscopy based on (soft) x-ray absorption and resonance inelastic (soft) x-ray scattering. This book is the ideal tool to expand readers’ understanding of this marvelously versatile experimental method, as well as the electronic structures of metals and insulators.
Author: Michael Hemsworth
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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: A. D. Baker
Publisher: Elsevier
ISBN: 1483152367
Category : Science
Languages : en
Pages : 193
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Book Description
Photoelectron Spectroscopy provides an introduction to the principles of photoelectron spectroscopy, including its applications in structural and analytical chemistry. It deals with both X-ray and UV-photoelectron spectroscopy. This book begins with the basic principles of electron spectroscopy and describes the UV photoelectron spectrometers and X-ray photoelectron spectrometers. It then lists several factors influencing the appearance of the photoelectron spectra. This book concludes by describing other forms of electron spectroscopy and photoelectron techniques. Students and chemists who are looking for a readable introduction to photoelectron spectroscopy will find this book useful.
Author: 岡崎国立共同研究機構分子科学研究所
Publisher:
ISBN:
Category : Molecular structure
Languages : en
Pages : 286
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Book Description
