Download or read book Photofragment Translational Spectroscopy of Propargyl Radicals at 248 Nm written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The photodissociation of propargyl radical, C3H3, and its perdeuterated isotopolog was investigated using photofragment translational spectroscopy. Propargyl radicals were produced by 193 nm photolysis of allene entrained in a molecular beam expansion, and then photodissociated at 248 nm. photofragment time-of-flight spectra were measured at a series of laboratory angles using electron impact ionization coupled to a mass spectrometer. Data for ion masses corresponding to C3H2, C3H, C3+, and the analogous deuterated species show that both H and H2 loss occur. The translational energy distributions for these processes have average values E{sub T} = 5.7 and 15.9 kcal/mol, respectively, and are consistent with dissociation on the ground state following internal conversion, with no exit barrier for H loss but a tight transition state for H2 loss. The translational energy distribution for H atom loss is similar to that in previous work on propargyl in which the H atom, rather than the heavy fragment, was detected. The branching ratio for H loss/H2 loss was determined to be 97.6/2.4 ± 1.2, in good agreement with RRKM results.

Download or read book Photodissociation of the Propargyl C3D3 Radicals at 248 Nm and 193 Nm written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The photodissociation of perdeuterated propargyl (D2CCCD) and propynyl (D3CCC) radicals was investigated using fast beam photofragment translational spectroscopy. Radicals were produced from their respective anions by photodetachment at 540 nm and 450 nm (below and above the electron affinity of propynyl). The radicals were then photodissociated by 248 nm or 193 nm light. The recoiling photofragments were detected in coincidence with a time- and position-sensitive detector. Three channels were observed: D2 loss, CD + C2D2, and CD3 + C2. Obervation of the D loss channel was incompatible with this experiment and was not attempted. Our translational energy distributions for D2 loss peaked at nonzero translational energy, consistent with ground state dissociation over small (

Download or read book Studies of Photofragment Translational Spectroscopy written by Scott Johnathan Goncher and published by . This book was released on 2008 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Production and Photodissociation of Neutral Free Radicals written by Neil Charles Cole-Filipiak and published by . This book was released on 2015 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary photochemistry of several combustion-relevant free radicals have been in- vestigated via photofragment translational spectroscopy. The relevance of radical photo- chemistry will be discussed, along with methodologies and details of each experiment. The experimental apparatus will also be described, especially with regard to the recent installa- tion of a tunable energy electron ionizer. The upgraded ionizer has been a significant advance, allowing for more detailed characterization of the radical source employed in this thesis. The photochemistry of the phenyl radical (c-C6H5), a combustion intermediate and pre- cursor to polycyclic aromatic hydrocarbons, was investigated at 248 and 193 nm. At 248 nm, an H-atom loss pathway was found, while at 193 nm both H-atom loss and C2H2 loss pathways were observed. For both wavelengths, P(ET) distributions suggested internal con- version to the ground electronic state followed by energy randomization and dissociation. The branching ratio between the two 193 nm dissociation pathways was found to be 0.2 ± 0.1 in favor of H-atom loss, in good agreement with statistical Rice-Rampsperger-Kassel-Marcus (RRKM) theory. An initial investigation of the methyl perthiyl radical (CH3SS) at 248 nm suggested the surprising results of both CH3 + SS and CH2S + SH dissociation channels with no evidence for S-atom loss. In both cases, the translational energy distributions were inconsistent with the expected energetics. Upon reinvestigation, the assumption of radical production--and there- fore radical photodissociation--was shown to be incorrect. The new results demonstrated S-loss and CH3 loss pathways, with the former appearing to involve a repulsive electronic excited state.

Download or read book Photodissociation Dynamics Studies Via Photofragment Translational Spectroscopy written by Niels E. Sveum and published by . This book was released on 2006 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Photodissociaion Dynamics of Neutral Free Radicals written by Bogdan Negru and published by . This book was released on 2012 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photofragment translational spectroscopy was used to study the photodissociation dynamics of the phenyl and tert-butyl radicals. These radicals were produced in a collisionless environment from the flash pyrolysis of the appropriate precursor, nitrosobenzene for phenyl and azo-tert-butane for the tert-butyl radical. The photodissociation dynamics of the phenyl radical (C6H5) were investigated at 248 and 193 nm. At 248 nm, the only dissociation products observed were from hydrogen atom loss, attributed primarily to H + o-C6H4 (ortho-benzyne). The observed translational energy distribution was consistent with statistical decay on the ground state surface. At 193 nm, dissociation to H + C6H4 and C4H3 + C2H2 was observed. The C6H4 fragment can be either o-C6H4 or l-C6H4 resulting from opening of the phenyl ring. The C4H3 + C2H2 products dominate over the two H loss channels. Attempts to reproduce the observed branching ratio by assuming ground state dynamics were unsuccessful. This discord, between the experimentally observed branching ratio and the theoretically predicted branching ratio led us to reinvestigate the dissociation dynamics of the phenyl radical at 193 nm, while producing the radical under different source conditions. The photodissociation dynamics of the tert-butyl radical (t-C4H9) were investigated at 248 nm. Two distinct channels of approximately equal importance were identified: dissociation to H + 2-methylpropene (C4H8), and CH3 + dimethylcarbene (C3H6). Neither the translational energy distributions that describe these two channels nor the product branching ratio are consistent with statistical dissociation on the ground state, and instead favor a mechanism taking place on excited state surfaces. The studies presented in this dissertation show that although hydrogen atom loss is sometimes expected to be the only major dissociation pathway in the photodissociation of hydrocarbon radicals this is not always a justified assumption.

Download or read book Photodissociation Studies of Combustion Relevant Radical Molecules written by Mark Jeffrey Shapero and published by . This book was released on 2017 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt: The photodissociation of several combustion relevant radical molecules has been carried out. These species behave significantly different from closed shell species and the experiments presented here provide fundamental new insights into the chemical dynamics of free radicals. The experiments were carried out on a molecular beam photofragment translational spectroscopy instrument. Radicals were generated by flash pyrolysis of a suitable precursor and entrained in a pulsed molecular beam. The radicals were then photodissociated and the products were detected with a rotatable mass spectrometer based on electron impact ionization. The benzyl radical photodissociation and the cyclopentadienyl radical photodissociation were investigated at 248 nm. Two dissociation channels were observed for each radical. The benzyl radical dissociates into H + C7H6 and CH3 + C6H4 and the cyclopentadienyl radical dissociates to H + C5H4 and C3H3 + C2H2, where the C5H4 fragment was identified as ethynylallene by its ionization energy. The translational energy distribution determined for each channel suggests that every dissociation mechanism occurs via internal conversion to the ground state followed by intramolecular vibrational redistribution and dissociation. The branching ratio between the two competing channels for each radical was measured experimentally and compared to RRKM (Rice-Ramspberger-Kassel-Marcus) calculations. For both radicals, the dominant experimental channel was corroborated by RRKM calculations.

Download or read book Photofragment Translational Spectroscopy of Simple Hydride Molecules and Radicals written by Steven Hardy Selig Wilson and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2007 with total page 960 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fast Beam Investigations of Two and Three Body Photodissociation by Time and Position Coincidence Imaging written by Paul Crider and published by . This book was released on 2010 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fast beam photofragment translational spectroscopy has been used to elucidate the photodissociation dynamics of small radicals and closed-shell anions. Imaging of photofragments in time- and position-coincidence allows the determination of mass distributions, translational energy distributions [P(ET) distributions], and in the case of three-body fragmentation channels, ternary Dalitz plots depicting the momentum disposal among the fragments. These data yield information about the potential energy surfaces responsible for dissociation as well dynamic and kinematic information about the decay mechanism itself. Chapter 1 presents a brief overview of photodissociation dynamics and photofragment translational spectroscopy and some recurring themes of the research presented in this Thesis are explored. The use of Dalitz plots in kinematic analysis of three-body dissociation is discussed in detail. Chapters 2 and 3 present, respectively, experimental and theoretical findings on the photodissociation of perdeuterated C3D3 isotopologs, propargyl (D2CCCD) and propynyl (CCCD3) at 248 and 193 nm. Mass distributions reveal D2 loss and three heavy mass channels: CD + C2D2, CD2 + C2D, and CD3 + C2. The D loss channel is present, but incompatible with our detection scheme and thus was not observed. P(ET) distributions indicate each dissociation proceeds by internal conversion followed by statistical dissociation on the ground state surface. In Chapter 3, results of high level ab initio calculations are presented and RRKM rate constants are determined. Chapter 4 presents results on two- and three-body photodissociation dynamics of I2Br & hibar; from 300 to 270 nm. Two- and three-body dissociation is observed throughout this wavelength range. Four distinct two-body channels are observed: Br- + I2, I- + IBr, Br + I2-, and I + IBr-. Dalitz plots indicate three-body dissociation occurs primarily by a concerted decay mechanism. A sequential dissociation mechanism, where Br- + I2(B) is followed by electronic predissociation of the metastable I2(B) fragment into ground state I atoms is reported. Chapter 5 presents preliminary results of two- and three-body photodissociation of ozone at 193 and 157 nm. Ozone is prepared by photodetachment of ozonide at 386 nm (about 1.1 eV above the detachment energy). Greater than expected kinetic energy release is observed for both wavelengths in the P(ET) distributions. The additional energy is attributed to two sources: extra energy available by photodetaching far above the electron affinity of ozone, and extra internal energy in the ozonide precursor. Three-body dissociation occurs at 193 nm as a 3.6% channel and at 157 nm as a 19.2% channel. Three-body dissociation proceeds at both wavelengths by a synchronous, concerted decay mechanism.

Download or read book Photochemistry written by A Gilbert and published by Royal Society of Chemistry. This book was released on 2007-10-31 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: The breadth of scientific and technological interests in the general topic of photochemistry is truly enormous and includes, for example, such diverse areas as microelectronics, atmospheric chemistry, organic synthesis, non-conventional photoimaging, photosynthesis, solar energy conversion, polymer technologies, and spectroscopy. This Specialist Periodical Report on Photochemistry aims to provide an annual review of photo-induced processes that have relevance to the above wide-ranging academic and commercial disciplines, and interests in chemistry, physics, biology and technology. In order to provide easy access to this vast and varied literature, each volume of Photochemistry comprises sections concerned with photophysical processes in condensed phases, organic aspects which are sub-divided by chromophore type, polymer photochemistry, and photochemical aspects of solar energy conversion. Volume 34 covers literature published from July 2001 to June 2002. Specialist Periodical Reports provide systematic and detailed review coverage in major areas of chemical research. Compiled by teams of leading authorities in the relevant subject areas, the series creates a unique service for the active research chemist, with regular, in-depth accounts of progress in particular fields of chemistry. Subject coverage within different volumes of a given title is similar and publication is on an annual or biennial basis.

Download or read book Electronic and Photoelectron Spectroscopy written by Andrew M. Ellis and published by Cambridge University Press. This book was released on 2005-01-13 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electronic and photoelectron spectroscopy can provide extraordinarily detailed information on the properties of molecules and are in widespread use in the physical and chemical sciences. Applications extend beyond spectroscopy into important areas such as chemical dynamics, kinetics and atmospheric chemistry. This book aims to provide the reader with a firm grounding of the basic principles and experimental techniques employed. The extensive use of case studies effectively illustrates how spectra are assigned and how information can be extracted, communicating the matter in a compelling and instructive manner. Topics covered include laser-induced fluorescence, resonance-enhanced multiphoton ionization, cavity ringdown and ZEKE spectroscopy. The volume is for advanced undergraduate and graduate students taking courses in spectroscopy and will also be useful to anyone encountering electronic and/or photoelectron spectroscopy during their research.

Download or read book Photoionization And Photodetachment In 2 Parts written by Cheuk-yiu Ng and published by World Scientific. This book was released on 2000-06-30 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt: Owing to the advances of vacuum ultraviolet and ultrafast lasers and third generation synchrotron sources, the research on photoionization, photoelectrons, and photodetachment has gained much vitality in recent years. These new light sources, together with ingenious experimental techniques, such as the coincidence imaging, molecular beam, pulsed field ionization photoelectron, mass-analyzed threshold ion, and pulsed field ion pair schemes, have allowed spectroscopic, dynamic, and energetic studies of gaseous species to a new level of detail and accuracy. Profitable applications of these methods to liquids are emerging.This invaluable two-volume review consists of twenty-two chapters, focusing on recent developments in photoionization and photodetachment studies of atoms; molecules, transient species, clusters, and liquids.

Download or read book Femtochemistry and Femtobiology written by Monique M. Martin and published by Elsevier Science Limited. This book was released on 2004 with total page 569 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reflects the heights of knowledge of ultrafast chemical processes attained in these early years of the 21st century : the latest research in femtosecond and picosecond molecular processes in Chemistry and Biology, carried out around the world, is described here in more than 110 articles. The results were presented and discussed at the VIth International Conference on Femtochemistry, in Paris, France, from July 6 to July 10, 2003. The articles published here were reviewed by referees selected from specialists in the Femtochemistry community, guaranteeing a collective responsability for the quality of the research reported in the next 564 pages. Femtochemistry is an ever-growing field, where new research areas are constantly opening up, and one which both stimulates and accompanies the development of ultrafast technologies. The increasing interest in femtobiology and chemistry at the frontier with biology is an obvious indicator of the present impact of life sciences in our society. New materials and reactions at surfaces are also some of the relatively new topics that promise rapid developments. New methodologies and technologies for probing and following in real time molecular dynamical phenomena have appeared within the last ten years or so. These methods, based on multidimensional IR spectroscopies, ultrafast X-ray and electron diffraction techniques, are well represented in this book. Of ever-improving performance, they are now applied to the characterization of structural dynamics of an increasing number of chemical and biological systems. This book reports the state of research in Femtochemistry and Femtobiology presented at Paris, at the Maison de la Chimie, in July 2003, representing the tenth anniversary of the conference. * Overview of the most recent research on ultrafast events * Application of new methodologies on chemical and biological systems * Contributions by key players in the field

Download or read book Molecular Reaction Dynamics written by Raphael D. Levine and published by Cambridge University Press. This book was released on 2009-06-04 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular reaction dynamics is the study of chemical and physical transformations of matter at the molecular level. The understanding of how chemical reactions occur and how to control them is fundamental to chemists and interdisciplinary areas such as materials and nanoscience, rational drug design, environmental and astrochemistry. This book provides a thorough foundation to this area. The first half is introductory, detailing experimental techniques for initiating and probing reaction dynamics and the essential insights that have been gained. The second part explores key areas including photoselective chemistry, stereochemistry, chemical reactions in real time and chemical reaction dynamics in solutions and interfaces. Typical of the new challenges are molecular machines, enzyme action and molecular control. With problem sets included, this book is suitable for advanced undergraduate and graduate students, as well as being supplementary to chemical kinetics, physical chemistry, biophysics and materials science courses, and as a primer for practising scientists.

Download or read book Tunnelling in Molecules written by Johannes Kästner and published by Royal Society of Chemistry. This book was released on 2020-09-22 with total page 453 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum tunnelling is one of the strangest phenomena in chemistry, where we see the wave nature of atoms acting in “impossible” ways. By letting molecules pass through the kinetic barrier instead of over it, this effect can lead to chemical reactions even close to the absolute zero, to atypical spectroscopic observations, to bizarre selectivity, or to colossal isotopic effects. Quantum mechanical tunnelling observations might be infrequent in chemistry, but it permeates through all its disciplines producing remarkable chemical outcomes. For that reason, the 21st century has seen a great increase in theoretical and experimental findings involving molecular tunnelling effects, as well as in novel techniques that permit their accurate predictions and analysis. Including experimental, computational and theoretical chapters, from the physical and organic to the biochemistry fields, from the applied to the academic arenas, this new book provides a broad and conceptual perspective on tunnelling reactions and how to study them. Quantum Tunnelling in Molecules is the obligatory stop for both the specialist and those new to this world.

Download or read book Emerging Trends in Chemical Applications of Lasers written by Michael R. Berman and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This book is about Emerging Trends in Chemical Applications of Lasers"--