Ultrafast Molecular Dynamics Induced by FEW-femtosecond Ultraviolet Excitation PDF Download
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Author: Lorenzo Colaizzi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Lorenzo Colaizzi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Rebeca de Nalda
Publisher: Springer Science & Business Media
ISBN: 331902051X
Category : Science
Languages : en
Pages : 298
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Book Description
This book presents the latest developments in Femtosecond Chemistry and Physics for the study of ultrafast photo-induced molecular processes. Molecular systems, from the simplest H2 molecule to polymers or biological macromolecules, constitute central objects of interest for Physics, Chemistry and Biology, and despite the broad range of phenomena that they exhibit, they share some common behaviors. One of the most significant of those is that many of the processes involving chemical transformation (nuclear reorganization, bond breaking, bond making) take place in an extraordinarily short time, in or around the femtosecond temporal scale (1 fs = 10-15 s). A number of experimental approaches - very particularly the developments in the generation and manipulation of ultrashort laser pulses - coupled with theoretical progress, provide the ultrafast scientist with powerful tools to understand matter and its interaction with light, at this spatial and temporal scale. This book is an attempt to reunite some of the state-of-the-art research that is being carried out in the field of ultrafast molecular science, from theoretical developments, through new phenomena induced by intense laser fields, to the latest techniques applied to the study of molecular dynamics.
Author: Ming-Fu Lin
Publisher:
ISBN:
Category :
Languages : en
Pages : 104
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Book Description
Ultrafast femtosecond (10−15 s) dynamics of atomic xenon, vinyl bromide and carbon disulfide molecules are studied using a newly developed method of extreme ultraviolet (XUV) transient absorption spectroscopy. This research work is devoted to a deeper understanding of the fundamental electronic and nuclear dynamics using XUV light pulses from a high-order harmonic generation source. The produced XUV light pulses are utilized to selectively probe the chemical reaction coordinate with femtosecond temporal resolution. The experimental apparatus for transient absorption pump-probe spectroscopy is described in detail. The research described in this thesis contains four different gaseous atomic and molecular systems. The first system in the study is motivated by a goal to gain a better understanding of the core-excited state couplings of atomic xenon near zero delay between an intense NIR pump pulse (780 nm) and an XUV probe pulse. Secondly, the ionization and dissociation dynamics of molecular vinyl bromide (C2H3Br) under the influence of strong-field ionization are investigated. Finally, an ongoing research project of CS2 and thiophene molecules is presented for future studies of spin-orbit wavepacket and ring-opening dynamics, respectively. The NIR induced core-excited state coupling of atomic xenon is studied using femtosecond XUV transient absorption spectroscopy with photon energies between 50 eV to 70 eV. Coupling of the core-excited states 4d−1(2D5/2)6p(2P3/2) (65.1 eV) and 4d−1(2D3/2)6p(2P1/2) (67.0 eV) to neighboring states by the NIR field results in a threefold enhancement of XUV transmission. The induced transmission at 65.1 eV (67.0 eV) changes from 3.2 ± 0.4% (5.9 ± 0.5%) without the coupling laser to 9 ± 2% (22 ± 5%) at the maximum of the NIR field. A NIR field induced broad XUV absorption feature ranging from 60 eV to 65 eV is explained by the splitting of the field free absorption lines into multiplets when the Rabi frequencies of the coupling transitions higher than the NIR frequency. This assignment is supported by a numerical integration of the von Neumann equation for a few level quantum system. The dissociative ionization dynamics of vinyl bromide, C2H3Br, initiated by a strong laser field ionization are investigated. XUV light pulses with photon energy between 50 eV and 72 eV are utilized to detect the subsequent dynamics. Several dynamic features are observed including the neutral C2H3Br depletion, the formation of C2H3Br ions (X and A states), the production of C2H3Br dications, and the emergence of neutral Br (2P3/2) atoms from dissociative ionization. Free Br (2P3/2) atoms appear on a timescale of 330±150 fs. The singly charged ionic A state displays a time-dependent XUV absorption energy shift of ~0.4 eV during the first 300 fs after strong-filed ionization. The signal intensity from Br atoms correlates with the signal intensity from singly charged parent ions in the A state as a function of NIR laser peak intensity. The experimental observations suggest that vibrationally excited C2H3Br+ (A) ions possibly undergo ultrafast intramolecular vibrational energy redistribution concurrent with the C-Br bond dissociation within a time scale of 330±150 fs. The C2H3Br+ (X) and C2H3Br++ ions are relatively stable as a consequence of deeper potential wells and a high dissociation barrier, respectively. Two ongoing experiments of sulfur-containing molecules are presented that are aimed at future studies of a molecular spin-orbit wavepacket in CS2+ ions and ultrafast ring-opening dynamics of thiophene. Strong-field ionization can coherently populate two spin-orbit states in CS2+ ions. The spin-orbit splitting originates from the atomic sulfur (~60 meV). The small splitting offers the possibility to probe a coherent beating on a time scale of 69 fs, well beyond our temporal resolution of 25 fs. For thiophene, an ultrafast ring-opening process initiated by one-photon excitation at 193 nm is studied through multiphoton ionization at 780 nm. The parent ion population exhibits a fast decay on a time scale of 200±30 fs. This offers a reference for the future XUV transient absorption experiments using one-photon excitation at 193 nm and sulfur (2p) L-edge detection at 165 eV.
Author: Travis William Wright
Publisher:
ISBN: 9781339544151
Category :
Languages : en
Pages :
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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: Oliver Kühn
Publisher: Springer Science & Business Media
ISBN: 3540680373
Category : Science
Languages : en
Pages : 855
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Book Description
This book summarizes several years of research carried out by a collaboration of many groups on ultrafast photochemical reactions. It emphasizes the analysis and characterization of the nuclear dynamics within molecular systems in various environments induced by optical excitations and the study of the resulting molecular dynamics by further interaction with an optical field.
Author: Rebeca de Nalda
Publisher: Springer
ISBN: 9783319020525
Category : Science
Languages : en
Pages : 287
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Book Description
This book presents the latest developments in Femtosecond Chemistry and Physics for the study of ultrafast photo-induced molecular processes. Molecular systems, from the simplest H2 molecule to polymers or biological macromolecules, constitute central objects of interest for Physics, Chemistry and Biology, and despite the broad range of phenomena that they exhibit, they share some common behaviors. One of the most significant of those is that many of the processes involving chemical transformation (nuclear reorganization, bond breaking, bond making) take place in an extraordinarily short time, in or around the femtosecond temporal scale (1 fs = 10-15 s). A number of experimental approaches - very particularly the developments in the generation and manipulation of ultrashort laser pulses - coupled with theoretical progress, provide the ultrafast scientist with powerful tools to understand matter and its interaction with light, at this spatial and temporal scale. This book is an attempt to reunite some of the state-of-the-art research that is being carried out in the field of ultrafast molecular science, from theoretical developments, through new phenomena induced by intense laser fields, to the latest techniques applied to the study of molecular dynamics.
Author: Ruth A. Livingstone
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Femtosecond time resolved photoelectron imaging spectroscopy equipment was designed, constructed, and used to reveal the non-adiabatic dynamics of model biological systems. Indole and phenol derivatives were studied as models for eumelanin, a pigment found in humans designed to protect the body from ultraviolet radiation. The photo-dynamics of these molecules was studied after excitation with ultraviolet radiation, with particular emphasis on the effect that the hydroxyl groups have on the p * dissociative state. It was found that adding a hydroxyl group onto indole to create 5-hydroxyindole had little significant effect on the photodynamics at the excitation wavelengths studied. Adding a second hydroxyl group to phenol had a strongly marked effect only when the hydroxyl groups were in close proximity to each other, in which case it dramatically increased the relaxation rate. An ultrafast optical system, imaging photoelectron spectrometer, and software to control the hardware, and collect and analyse photoelectron data were successfully implemented and used to collect and analyse data. This system will be of use for many more years and will be the basis of much future research.
Author: Marc J J Vrakking
Publisher: Royal Society of Chemistry
ISBN: 1788015134
Category : Science
Languages : en
Pages : 512
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Book Description
Attosecond science is a new and rapidly developing research area in which molecular dynamics are studied at the timescale of a few attoseconds. Within the past decade, attosecond pump–probe spectroscopy has emerged as a powerful experimental technique that permits electron dynamics to be followed on their natural timescales. With the development of this technology, physical chemists have been able to observe and control molecular dynamics on attosecond timescales. From these observations it has been suggested that attosecond to few-femtosecond timescale charge migration may induce what has been called “post-Born-Oppenheimer dynamics”, where the nuclei respond to rapidly time-dependent force fields resulting from transient localization of the electrons. These real-time observations have spurred exciting new advances in the theoretical work to both explain and predict these novel dynamics. This book presents an overview of current theoretical work relevant to attosecond science written by theoreticians who are presently at the forefront of its development. It is a valuable reference work for anyone working in the field of attosecond science as well as those studying the subject.
Author: Seyyed Javad Robatjazi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Photoelectron spectroscopy employing X-ray and extreme ultraviolet (XUV) radiation is one of the most important experimental methods to study the electronic structure of atoms, molecules, and solids. Recent developments of XUV and X-ray sources with ultrashort pulse durations, like free-electron lasers (FELs) and high-order harmonics of infrared lasers, enabled combining this approach with a concept of a time-resolved measurement, where a pair of synchronized short light pulses is used to initiate and observe a physical or chemical process of interest. Among other advances, such combination turned out to be particularly useful for atomic physics and gas-phase femtochemistry, where femtosecond or even sub-femtosecond short-wavelength radiation can be used to trigger the dynamics in high-lying states previously inaccessible for time-resolved measurements and offers a variety of novel schemes to probe light-induced electronic and nuclear motion. One of the key challenges for time-domain studies employing short-pulsed radiation sources is that they are necessarily broadband and, thus, typically populate a broad range of atomic of molecular states. The main goal of this thesis is to develop an experimental approach that enables state-selective analysis of the dynamics induced by such broadband femtosecond pulses in the XUV domain, and to apply it to study several exemplary reactions in photoionized molecules. Since reducing the bandwidth of the XUV pulse would ultimately limit the achievable temporal resolution, in this work the challenge of state selectivity is addressed by employing photoelectron-photoion and photoion-photoion coincident measurements. In the experimental apparatus developed as a part of this thesis, a double-sided velocity map imaging (VMI) spectrometer for coincident detection of electrons and ions is combined with a femtosecond pump-probe setup that includes a near-infrared (NIR) laser and a fiber-based XUV source based on high-order harmonics generation. This instrument has been commissioned, characterized, and applied to several time-resolved experiments on atomic and molecular targets. More specifically, this thesis describes three different sets of experiments. First, a brief overview of several XUV-NIR pump-probe measurements addressing two-color single, double or triple ionization of atoms is presented. Here, the main focus is set on capturing generic characteristic features of the corresponding two-color signals, and on revealing physical mechanisms determining their "transient" or "steady" behavior with respect to the time delay between the XUV and NIR pulses. The second series of experiments focuses on exploring coupled electronic and nuclear dynamics in XUV-ionized CO2 molecule probed by the synchronized NIR pulse. This study, which constitutes the central part of the thesis, relies on the detection of the photoelectron that reveals which electronic state is initially populated, in coincidence with ionic fragments, which provide information on the specific dissociation channel of the molecular ion after the interaction with both pulses. Here, we observe signatures of an electron-hole wave packet motion near a conical intersection of two low-lying cationic states, trace rotational dynamics determined by the dependence of the state-specific XUV photoionization cross section on molecular orientation, and disentangle the contributions of individual states to different dissociation pathways. The third series of experiments aims at studying nuclear dynamics in XUV-ionized alcohol molecules, focusing on the channels involving ultrafast hydrogen motion. Here, ion mass spectrometry measurements on methanol and its deuterated isotopologue CH3OH and CD3OH show that, depending on a specific XUV wavelength, the formation of molecular hydrogen or trihydrogen cations can be either dominated by the channels combining the hydrogen from the oxygen site with one or two hydrogens from the methyl carbon, or by the ejections of all hydrogen atoms from the methyl group. Coincident electron spectra for specific ionic fragments enable linking these channels to the calculated dissociation pathways leading to H2+ or H3+ formation. Finally, we present the results of XUV-NIR pump-probe experiments on ethanol, where a transient enhancement of particular dissociation channels has been observed. The experimental methodology presented in this work can be readily extended to a broad range of molecular systems, including both, molecular ions and high-lying excited states of the neutral molecules. At the same time, highly-differential data on small polyatomic molecules like CO2, methanol, and ethanol presented here, can be used to benchmark theoretical models for XUV ionization of these prototypical systems, improving our general understanding of light-induced molecular dynamics.
Author: Lai Chung Liu
Publisher: Springer Nature
ISBN: 3030548511
Category : Science
Languages : en
Pages : 249
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Book Description
The thesis provides the necessary experimental and analytical tools to unambiguously observe the atomically resolved chemical reactions. A great challenge of modern science has been to directly observe atomic motions during structural transitions, and while this was first achieved through a major advance in electron source brightness, the information content was still limited and new methods for image reconstruction using femtosecond electron diffraction methods were needed. One particular challenge lay in reconciling the innumerable possible nuclear configurations with the observation of chemical reaction mechanisms that reproducibly give the same kind of chemistry for large classes of molecules. The author shows that there is a simple solution that occurs during barrier crossing in which the highly anharmonic potential at that point in nuclear rearrangements couples high- and low-frequency vibrational modes to give highly localized nuclear motions, reducing hundreds of potential degrees of freedom to just a few key modes. Specific examples are given in this thesis, including two photoinduced phase transitions in an organic system, a ring closure reaction, and two direct observations of nuclear reorganization driven by spin transitions. The emerging field of structural dynamics promises to change the way we think about the physics of chemistry and this thesis provides tools to make it happen.
