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Author: Jordan Tyler O'Neal Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The motion of electrons in molecular superposition states happens on the attosecond timescale, roughly three orders of magnitude faster than nuclear motion. To study the first steps in a photochemical reaction, then, we must study the electron dynamics in early times before the nuclei have a chance to move. These purely electronic dynamics, uncoupled from nuclear motion, are dubbed charge migration (CM). CM can be described as a coherent superposition of delocalized electronic states evolving in time, which appears as a time-dependent oscillation in charge density across the molecule. On longer timescales, thought to be tens of femtoseconds, nuclear motion couples to the pure electronic CM. This tends to average out the CM, and there is evidence that this process can influence the nuclear reaction pathways. One can further envision using sequences of laser pulses to prepare CM states as a method of coherent control directing photochemical reaction pathways. However, understanding the loss of electronic coherence as nuclear motion occurs is difficult. Theoretical modeling of CM is computationally challenging, and there are open questions about the effects of nuclear motion. Experimental measurements can guide us towards better, more efficient approximations to help answer these outstanding questions. To this end, I present two experiments towards developing two separate methods for measuring CM. Both methods rely on the recently developed attosecond X-ray free-electron laser source at the LCLS free-electron laser facility. These two methods for measuring CM serve as early implementations of this new attosecond X-ray source. The first method to study CM, impulsive ionization, prepares a CM state by ionizing with an attosecond X-ray pulse which has coherent bandwidth large enough to populate multiple cationic states. The final state is then measured with X-ray absorption spectroscopy. I present preliminary results showing signatures of CM and nuclear motion damping the time-dependent charge density. The second method, nonlinear X-ray spectroscopy, is a sophisticated toolset using sequences of X-ray pulses to prepare and measure CM states. I present a measurement of a basic building block of nonlinear X-ray spectroscopy, impulsive stimulated X-ray Raman scattering, and use this result to show the feasibility in the near future of measuring valence CM states in a neutral molecule.
Author: Jordan Tyler O'Neal Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The motion of electrons in molecular superposition states happens on the attosecond timescale, roughly three orders of magnitude faster than nuclear motion. To study the first steps in a photochemical reaction, then, we must study the electron dynamics in early times before the nuclei have a chance to move. These purely electronic dynamics, uncoupled from nuclear motion, are dubbed charge migration (CM). CM can be described as a coherent superposition of delocalized electronic states evolving in time, which appears as a time-dependent oscillation in charge density across the molecule. On longer timescales, thought to be tens of femtoseconds, nuclear motion couples to the pure electronic CM. This tends to average out the CM, and there is evidence that this process can influence the nuclear reaction pathways. One can further envision using sequences of laser pulses to prepare CM states as a method of coherent control directing photochemical reaction pathways. However, understanding the loss of electronic coherence as nuclear motion occurs is difficult. Theoretical modeling of CM is computationally challenging, and there are open questions about the effects of nuclear motion. Experimental measurements can guide us towards better, more efficient approximations to help answer these outstanding questions. To this end, I present two experiments towards developing two separate methods for measuring CM. Both methods rely on the recently developed attosecond X-ray free-electron laser source at the LCLS free-electron laser facility. These two methods for measuring CM serve as early implementations of this new attosecond X-ray source. The first method to study CM, impulsive ionization, prepares a CM state by ionizing with an attosecond X-ray pulse which has coherent bandwidth large enough to populate multiple cationic states. The final state is then measured with X-ray absorption spectroscopy. I present preliminary results showing signatures of CM and nuclear motion damping the time-dependent charge density. The second method, nonlinear X-ray spectroscopy, is a sophisticated toolset using sequences of X-ray pulses to prepare and measure CM states. I present a measurement of a basic building block of nonlinear X-ray spectroscopy, impulsive stimulated X-ray Raman scattering, and use this result to show the feasibility in the near future of measuring valence CM states in a neutral molecule.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In the last few years laboratory-scale femtosecond laser-based research using XUV light has developed dramatically following the successful development of attosecond laser pulses by means of high-harmonic generation. Using attosecond laser pulses, studies of electron dynamics on the natural timescale that electronic processes occur in atoms, molecules and solids can be contemplated, providing unprecedented insight into the fundamental role that electrons play in photo-induced processes. In my talk I will briefly review the present status of the attosecond science research field in terms of present and foreseen capabilities, and discuss a few recent applications, including a first example of the use of attosecond laser pulses in molecular science. In addition, I will discuss very recent results of experiments where photoionization of dynamically aligned molecules is investigated using a high-harmonics XUV source. Photoionization of aligned molecules becomes all the more interesting if the experiment is performed using x-ray photons. Following the absorption of x-rays, ejected photoelectrons can be used as a probe of the (time-evolving) molecular structure, making use of intra-molecular electron diffraction. This amounts, as some have stated, to "illuminating the molecule from within". I will present the present status of our experiments on this topic making use of the FLASH free electron laser in Hamburg. Future progress in this research field not only depends on the availability of better and more powerful light sources, but also requires sophisticated detector strategies. In my talk I will explain how we are trying to meet some of the experimental challenges by using the Medipix family of detectors, which we have already used for time- and space-resolved imaging of electrons and ions.
Author: J. Hastings Publisher: IOS Press ISBN: 1643681338 Category : Science Languages : en Pages : 272
Book Description
Many X-Ray Free-Electron Lasers (X-FELs) have been designed, built and commissioned since the first lasing of the Linac Coherent Light Source in the hard and soft X-ray regions, and great progress has been made in improving their performance and extending their capabilities. Meanwhile, experimental techniques to exploit the unique properties of X-FELs to explore atomic and molecular systems of interest to physics, chemistry, biology and the material sciences have also been developed. As a result, our knowledge of atomic and molecular science has been greatly extended. Nevertheless, there is still much to be accomplished, and the potential for discovery with X-FELs is still largely unexplored. The next generation of scientists will need to be well versed in both particle beams/FEL physics and X-ray photon science. This book presents material from the Enrico Fermi summer school: Physics of and Science with X-Ray Free-Electron Lasers, held at the Enrico Fermi International School of Physics in Varenna, Italy, from 26 June - 1 July 2017. The lectures presented at the school were aimed at introducing graduate students and young scientists to this fast growing and exciting scientific area, and subjects covered include basic accelerator and FEL physics, as well as an introduction to the main research topics in X-FEL-based biology, atomic molecular optical science, material sciences, high-energy density physics and chemistry. Bridging the gap between accelerator/FEL physicists and scientists from other disciplines, the book will be of interest to all those working in the field.
Author: E.L. Saldin Publisher: Springer Science & Business Media ISBN: 3662040662 Category : Technology & Engineering Languages : en Pages : 470
Book Description
The Free Electron Laser (FEL) will be a crucial tool for research and industrial applications. This book describes the physical fundamentals of FELs on the basis of classical mechanics, electrodynamics, and the kinetic theory of charged particle beams, and will be suitable for graduate students and scientists alike. After a short introduction, the book discusses the theory of the FEL amplifier and oscillator, diffraction effects in the amplifier, and waveguide FEL.
Author: Ahmed Zewail Publisher: Elsevier ISBN: 008092669X Category : Science Languages : en Pages : 333
Book Description
This inspired book by some of the most influential scientists of our time--including six Nobel laureates--chronicles our emerging understanding of the chemical bond through the last nine decades and into the future. From Pauling's early structural work using x-ray and electron diffraction to Zewail's femtosecond lasers that probe molecular dynamics in real time; from Crick's molecular biology to Rich's molecular recognition, this book explores a rich tradition of scientific heritage and accomplishment. The perspectives given by Pauling, Perutz, Rich, Crick, Porter, Polanyi, Herschbach, Zewail, and Bernstein celebrate major scientific achievements in chemistry and biology with the chemical bond playing a fundamental role. In a unique presentation that also provides some lively insights into the very nature of scientific thought and discovery, The Chemical Bond: Structure and Dynamics will be of general interest to scientists, science historians, and the scientifically inclined populous.
Author: Eberhard J. Jaeschke Publisher: Springer ISBN: 9783319143934 Category : Science Languages : en Pages : 0
Book Description
Hardly any other discovery of the nineteenth century did have such an impact on science and technology as Wilhelm Conrad Röntgen’s seminal find of the X-rays. X-ray tubes soon made their way as excellent instruments for numerous applications in medicine, biology, materials science and testing, chemistry and public security. Developing new radiation sources with higher brilliance and much extended spectral range resulted in stunning developments like the electron synchrotron and electron storage ring and the freeelectron laser. This handbook highlights these developments in fifty chapters. The reader is given not only an inside view of exciting science areas but also of design concepts for the most advanced light sources. The theory of synchrotron radiation and of the freeelectron laser, design examples and the technology basis are presented. The handbook presents advanced concepts like seeding and harmonic generation, the booming field of Terahertz radiation sources and upcoming brilliant light sources driven by laser-plasma accelerators. The applications of the most advanced light sources and the advent of nanobeams and fully coherent x-rays allow experiments from which scientists in the past could not even dream. Examples are the diffraction with nanometer resolution, imaging with a full 3D reconstruction of the object from a diffraction pattern, measuring the disorder in liquids with high spatial and temporal resolution. The 20th century was dedicated to the development and improvement of synchrotron light sources with an ever ongoing increase of brilliance. With ultrahigh brilliance sources, the 21st century will be the century of x-ray lasers and their applications. Thus, we are already close to the dream of condensed matter and biophysics: imaging single (macro)molecules and measuring their dynamics on the femtosecond timescale to produce movies with atomic resolution.
Author: Jordan Tyler O'Neal
Author: Jordan Tyler O'Neal
Author: 
Author: J. Hastings
Author: E.L. Saldin
Author: Joyce Alvin Bearden
Author: Ahmed Zewail
Author: Michael R. Berman
Author: Eberhard J. Jaeschke
Author: Reginald William Blake Pearse