A5058193339- Methane Hydrates and Related Phenomena
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Seismic Waves and Analysis
- Advanced Chemical Physics Studies
- Spectroscopy and Quantum Chemical Studies
- Particle physics theoretical and experimental studies
- Quantum Chromodynamics and Particle Interactions
- Photochemistry and Electron Transfer Studies
- Laser-Matter Interactions and Applications
- Mass Spectrometry Techniques and Applications
- Nuclear physics research studies
- Atomic and Subatomic Physics Research
- Quantum, superfluid, helium dynamics
- X-ray Spectroscopy and Fluorescence Analysis
- Earthquake Detection and Analysis
- Dark Matter and Cosmic Phenomena
- Advanced X-ray Imaging Techniques
- Advanced Electron Microscopy Techniques and Applications
- High-Energy Particle Collisions Research
- Electron and X-Ray Spectroscopy Techniques
- Nuclear Physics and Applications
- Atomic and Molecular Physics
- Spectroscopy and Laser Applications
- Molecular Junctions and Nanostructures
University of Chicago
1985-2025
Brown University
2016-2025
Lawrence Livermore National Laboratory
2005-2024
University of Basel
1988-2024
Luxembourg Institute of Science and Technology
2024
University of Houston
2024
American Society For Engineering Education
2024
Zhejiang University
2024
North Carolina State University
2024
University of Nebraska–Lincoln
2023
Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet goal to watch evolve their geometrical structure in real remains challenging. By mapping nuclear motions femtosecond x-ray pulses, we created real-space representations evolving dynamics during a well-known chemical reaction and show series time-sorted structural snapshots...
The use of pump-probe experiments to study complex transient events has been an area significant interest in materials science, biology, and chemistry. While the emphasis on laser pump with probe x-ray experiments, there is a growing using electrons as probes. Early used for gas-phase diffraction photostimulated chemical reactions. More recently, scientists are beginning explore phenomena solid state such phase transformations, twinning, solid-state reactions, radiation damage, shock...
A rf photocathode electron gun is used as an source for ultrafast time-resolved pump-probe diffraction. The authors observed single-shot diffraction patterns from a 160nm Al foil using the 5.4MeV beam Gun Test Facility at Stanford Linear Accelerator. Excellent agreement with simulations suggests that experiments time resolution approaching 100fs are possible.
The photochemically induced electrocyclic ring-opening reaction of 1,3-cyclohexadiene to 1,3,5-hexatriene serves as a prototype for many important reactions in chemistry and biological systems. Based on experimental computational studies, detailed picture the has now emerged: Excitation Franck-Condon region places molecule steeply repulsive part 1B potential energy surface, which propels exactly conrotatory direction that conforms Woodward-Hoffmann rules orbital symmetry. Bypassing cusp...
Abstract The light-induced ultrafast switching between molecular isomers norbornadiene and quadricyclane can reversibly store release a substantial amount of chemical energy. Prior work observed signatures dynamics in both upon ultraviolet excitation but could not follow the electronic relaxation all way back to ground state experimentally. Here we study after exciting (201 nanometres) using time-resolved gas-phase extreme photoelectron spectroscopy combined with non-adiabatic simulations....
Changes in electron diffraction patterns are observed on ultrashort time scales upon irradiation of 1,3-cyclohexadiene with femtosecond laser pulses. 1,3- Cyclohexadiene is known to experience a ring opening reaction hexatriene excitation the 1B2 electronic state. Internal conversion brings molecule saddle point, from where one pathway leads back cyclohexadiene, while another path generates 1,3,5-hexatriene its isomeric forms. Structural observations made at picosecond delays using an pulse...
We describe a gas-phase x-ray scattering experiment capable of capturing molecular motions with atomic spatial resolution and femtosecond time resolution. X-ray free electron lasers can deliver intense pulses ultrashort duration, making them suitable to study ultrafast chemical reaction dynamics in an ultraviolet pump, probe scheme. A cell diffractometer balances sample flow gas density laser focusing conditions provide adequate vector high signal intensity near-uniform excitation...
Abstract We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of ICPEAC conference. In Roadmap I, we focus light–matter interaction. this area, studies ultrafast molecular dynamics have been rapidly growing, with advent new light sources such as attosecond lasers x-ray free electron lasers. parallel, experiments established synchrotron radiation femtosecond using cutting-edge detection schemes are revealing scientific...
Abstract When a molecule interacts with light, its electrons can absorb energy from the electromagnetic field by rapidly rearranging their positions. This constitutes first step of photochemical and photophysical processes that include primary events in human vision photosynthesis. Here, we report direct measurement initial redistribution electron density when 1,3-cyclohexadiene (CHD) is optically excited. Our experiments exploit intense, ultrashort hard x-ray pulses Linac Coherent Light...
Multicomponent reactions enable the synthesis of large molecular libraries from relatively few inputs. This scalability has led to broad adoption these by pharmaceutical industry. Here, we employ four-component Ugi reaction demonstrate that multicomponent can provide a basis for large-scale data storage. Using this combinatorial chemistry encode more than 1.8 million bits art historical images, including Cubist drawing Picasso. Digital is written using robotically synthesized products, and...
Dynamics of a ground-state chemical reaction are revealed by ultrafast x-ray scattering.
Evidence for a three-nucleon absorption mechanism has been observed in $^{3}\mathrm{He}$ positive and negative pions of 220 MeV/c. The effect shows pure phase-space behavior with integrated cross sections 3.9\ifmmode\pm\else\textpm\fi{}0.5 mb ${\ensuremath{\pi}}^{+}$ 3.7\ifmmode\pm\else\textpm\fi{}0.6 ${\ensuremath{\pi}}^{\ensuremath{-}}$ absorption.
Rydberg spectra are shown to provide a spectral fingerprint that is sensitive molecular structure in unique ways. The concepts demonstrated using set of isomeric fluorophenols and sequence aliphatic diamines. In the fluorophenols, sensitivity extends placement single hydrogen atom can be traced charge distributions associated with locations atoms functional groups respect center. Experiments on tetramethyl diamines demonstrate structural encompasses extended structure, including parts...
All stages of the electrocyclic ring-opening 1,3-cyclohexadiene (CHD) were observed by time-resolved photoionization-photoelectron spectroscopy. Spectra 1B state, previously unobserved using methods, obtained upon optical excitation ultrashort laser pulses at 4.60 or 4.65 eV, followed ionization with 3.81, 3.85, and 4.10 revealing a lifetime 30 fs. In an experiment 3.07 eV probe photons 4.69 pump, we time-sequenced progression Rydberg states that includes s, p, d series n = 3 to 6. The...
We aim to observe a chemical reaction in real time using gas-phase X-ray diffraction. In our initial experiment at the Linac Coherent Light Source (LCLS), we investigated model system 1,3-cyclohexadiene (CHD) very low vapor pressures. This serves as benchmark for numerous transformations organic synthesis and natural product biology. Excitation of CHD by an ultraviolet optical pulse initiates electrocyclic that transforms closed ring into open-chain structure 1,3,5-hexatriene. describe...
Identification of the initially prepared, optically active state remains a challenging problem in many studies ultrafast photoinduced processes. We show that excited electronic can be determined using anisotropic component time-resolved X-ray scattering signals. The concept is demonstrated time-dependent N-methyl morpholine gas phase upon excitation by 200 nm linearly polarized optical pulse. Analysis angular dependence signal near time zero renders orientation transition dipole moment...
Resolving gas phase molecular motions with simultaneous spatial and temporal resolution is rapidly coming within the reach of x-ray Free Electron Lasers (XFELs) Mega-electron-Volt (MeV) electron beams. These two methods enable scattering experiments that have yielded fascinating new results, while both are important for determining transient structures in photochemical reactions, it to understand their relative merits. In present study, we evaluate respective cross sections simulate ability...
Significance Charge transfer plays a fundamental role in many areas of chemistry, physics, biology, and materials science. The spatial redistribution electrons is typically associated with changes the molecular geometry. A comprehensive understanding this process requires atomic resolution femtosecond temporal resolution. Here, we exploit an X-ray free-electron laser to determine excited-state structures during charge sub-Ångström Important behaviors such as bond elongation contraction...
Disulfide bonds are ubiquitous molecular motifs that influence the tertiary structure and biological functions of many proteins. Yet, it is well known disulfide bond photolabile when exposed to ultraviolet C (UVC) radiation. The deep-UV–induced S─S fragmentation kinetics on very fast timescales especially pivotal fully understand photostability photodamage repair mechanisms in In 1,2-dithiane, smallest saturated cyclic molecule mimics biologically active species with bonds, we investigate...
This article contains two cases with accompanying surgical videos, illustrating the use of a Tutoplast plug to create watertight seal in corneoscleral fistula formed after tube shunt removal. These demonstrate that can be cut into strategic geometric shape both at entry site and reinforce adjacent areas scleral thinning during removal or repositioning surgery. Specifically, piece dehydrated was shaped small rectangle an attached larger rectangle. The smaller "head" would fistula, while...