35 research outputs found
Recommended from our members
Ultrafast X-ray Studies of Structural Dynamics at SLAC
The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements demonstrate that the initial stage of crystal disordering results from inertial motion on a laser softened potential energy surface. These inertial dynamics dominate for the first half picosecond following laser excitation, indicating that interatomic forces minimally influence atomic excursions from the equilibrium lattice positions, even for motions in excess of an {angstrom}. This also indicates that the atoms disorder initially without losing memory of their lattice reference
Atomistic characterization of the active-site solvation dynamics of a model photocatalyst
The interactions between the reactive excited state of molecular photocatalysts and surrounding solvent dictate reaction mechanisms and pathways, but are not readily accessible to conventional optical spectroscopic techniques. Here we report an investigation of the structural and solvation dynamics following excitation of a model photocatalytic molecular system [Ir 2 (dimen) 4 ] 2+, where dimen is para-diisocyanomenthane. The time-dependent structural changes in this model photocatalyst, as well as the changes in the solvation shell structure, have been measured with ultrafast diffuse X-ray scattering and simulated with Born-Oppenheimer Molecular Dynamics. Both methods provide direct access to the solute-solvent pair distribution function, enabling the solvation dynamics around the catalytically active iridium sites to be robustly characterized. Our results provide evidence for the coordination of the iridium atoms by the acetonitrile solvent and demonstrate the viability of using diffuse X-ray scattering at free-electron laser sources for studying the dynamics of photocatalysis. © The Author(s) 201617111sciescopu
Recommended from our members
LCLS Ultrafast Science Instruments:Conceptual Design Report
The Stanford Linear Accelerator Center (SLAC), along with Argonne National Laboratory (ANL), Lawrence Livermore National Laboratory (LLNL), and the University of California at Los Angeles (UCLA), is constructing a Free-Electron Laser (FEL) facility, which will operate in the wavelength range 1.5 nm - 0.15 nm. This FEL, the Linac Coherent Light Source (LCLS), utilizes the SLAC linac and will produce sub-picosecond pulses of short wavelength X-rays with very high peak brightness and almost complete transverse coherence. The final one-third of the SLAC linac will be used as the source of electrons for the LCLS. The high energy electrons will be transported across the SLAC Research Yard, into a tunnel which will house a long undulator. In passing through the undulator, the electrons will be bunched by the force of their own synchrotron radiation and produce an intense, monochromatic, spatially coherent beam of X-rays. By varying the electron energy, the FEL X-ray wavelength will be tunable from 1.5 nm to 0.15 nm. The LCLS will include two experimental halls as well as X-ray optics and infrastructure necessary to create a facility that can be developed for research in a variety of disciplines such as atomic physics, materials science, plasma physics and biosciences. This Conceptual Design Report, the authors believe, confirms the feasibility of designing and constructing three X-ray instruments in order to exploit the unique scientific capability of this new LCLS facility. The technical objective of the LCLS Ultrafast Science Instruments (LUSI) project is to design, build, and install at the LCLS three hard X-ray instruments that will complement the initial instrument included in the LCLS construction. As the science programs advance and new technological challenges appear, instrumentation needs to be developed and ready to conquer these new opportunities. The LCLS instrument concepts have been developed in close consultation with the scientific community through a series of workshops team meetings and focused reviews. In particular, the LUSI project instruments have been identified as meeting the most urgent needs of the scientific community based on the advice of the LCLS Scientific Advisory Committee (SAC) in response to an open call for letters of intent (LOI) from the breadth of the scientific community
Anti Stokes resonant x ray Raman scattering for atom specific and excited state selective dynamics
Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x rays have been poor at picking up excited state moieties from the unexcited ones. With time resolved anti Stokes resonant x ray Raman scattering AS RXRS performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe CO 5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS RXRS with transform limited x ray pulses is given which will be covered experimentally by upcoming transform limited x ray source
Anti Stokes resonant x ray Raman scattering for atom specific and excited state selective dynamics
Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x rays have been poor at picking up excited state moieties from the unexcited ones. With time resolved anti Stokes resonant x ray Raman scattering AS RXRS performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe CO 5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS RXRS with transform limited x ray pulses is given which will be covered experimentally by upcoming transform limited x ray source
Ultrafast laser-induced melting and ablation studied by time-resolved diffuse X-ray scattering
Time-resolved diffuse X-ray scattering with 50 fs, 9.5 keV X-ray pulses from the Linear Coherent Light Source was used to study the structural dynamics in materials undergoing rapid melting and ablation after fs laser excitation
Carrier density dependant lattice stability in InSb
The ultrafast decay of the x-ray diffraction intensity following laser excitation of an InSb crystal has been utilized to observe carrier dependent changes in the potential energy surface. For the first time, an abrupt carrier dependent onset for potential energy surface softening and the appearance of accelerated atomic disordering for a very high average carrier density have been observed. Inertial dynamics dominate the early stages of crystal disordering for a wide range of carrier densities between the onset of crystal softening and the appearance of accelerated atomic disordering