We report an experimental and numerical study of the propagation of free-electron laser pulses (wavelength 24.3 nm) through helium gas. Ionization and excitation populates the He^{+} 4p state. ...Strong, directional emission was observed at wavelengths of 469, 164, 30.4, and 25.6 nm. We interpret the emissions at 469 and 164 nm as 4p-3s-2p cascade superfluorescence, that at 30.4 nm as yoked superfluorescence on the 2p-1s transition, and that at 25.6 nm as free-induction decay of the 3p state.
Resolving the structural dynamics of bond breaking, bond formation, and solvation is required for a deeper understanding of solution-phase chemical reactions. In this work, we investigate the ...photodissociation of triiodide in four solvents using femtosecond time-resolved X-ray solution scattering following 400 nm photoexcitation. Structural analysis of the scattering data resolves the solvent-dependent structural evolution during the bond cleavage, internal rearrangements, solvent-cage escape, and bond reformation in real time. The nature and structure of the reaction intermediates during the recombination are determined, elucidating the full mechanism of photodissociation and recombination on ultrafast time scales. We resolve the structure of the precursor state for recombination as a geminate pair. Further, we determine the size of the solvent cages from the refined structures of the radical pair. The observed structural dynamics present a comprehensive picture of the solvent influence on structure and dynamics of dissociation reactions.
Optimization of focusing conditions is important in free-electron laser applications. A time-of-flight mass analyzer has been designed and constructed for this purpose. The time-of-flight spectra of ...ionic species evolved from laser ablation of gold were measured. The yields of ionic species showed strong correlations with free-electron-laser intensity. This method conveniently allows for direct estimation of laser intensity on sample and determination of focusing position.
Serial crystallography is a rapidly growing method that can yield structural insights from microcrystals that were previously considered to be too small to be useful in conventional X‐ray ...crystallography. Here, conditions for growing microcrystals of the photosynthetic reaction centre of Blastochloris viridis within a lipidic cubic phase (LCP) crystallization matrix that employ a seeding protocol utilizing detergent‐grown crystals with a different crystal packing are described. LCP microcrystals diffracted to 2.25 Å resolution when exposed to XFEL radiation, which is an improvement of 0.15 Å over previous microcrystal forms. Ubiquinone was incorporated into the LCP crystallization media and the resulting electron density within the mobile QB pocket is comparable to that of other cofactors within the structure. As such, LCP microcrystallization conditions will facilitate time‐resolved diffraction studies of electron‐transfer reactions to the mobile quinone, potentially allowing the observation of structural changes associated with the two electron‐transfer reactions leading to complete reduction of the ubiquinone ligand.
Serial crystallography relies upon the growth of microcrystals at high concentration. An LCP crystallization protocol for the Blastochloris viridis photosynthetic reaction centre that utilizes seeding from detergent‐grown crystals is reported.
We study the photoelectron angular distribution (PAD) from the two-photon ionization (TPI) of He by femtosecond EUV pulses. The calculation with the time-dependent Schrödinger equation (TDSE) and the ...measurement at the SPring-8 EUV-FEL show reasonable agreement. The extracted relative phase δ between the s and d wave packets are distinct from that between the corresponding eigenstates, due to the competition between sequential and direct ionization paths. When the pulse is resonant with an excited level, the sequential and direct TPI compete with each other, and δ and the PAD depend on the pulse width. On the other hand, when the Ry-dberg manifold is coherently excited, δ does not vary with the pulse width.
Multiple photoionization processes of giant rare-gas clusters are investigated in the wavelength region of 51 to 61nm at Spring8. We report here some latest results of our investigation; the ...frustration of photoionization for giant xenon clusters and the charge transfer in Ar-core Ne-shell clusters.
We have successfully determined the internuclear distance of I
molecules in an alignment laser field by applying our molecular structure determination methodology to an I 2p X-ray photoelectron ...diffraction profile observed with femtosecond X-ray free electron laser pulses. Using this methodology, we have found that the internuclear distance of the sample I
molecules in an alignment Nd:YAG laser field of 6 × 10
W/cm
is elongated by from 0.18 to 0.30 Å "in average" relatively to the equilibrium internuclear distance of 2.666 Å. Thus, the present experiment constitutes a critical step towards the goal of femtosecond imaging of chemical reactions and opens a new direction for the study of ultrafast chemical reaction in the gas phase.
Polarization control using an X-ray phase retarder in combination with an arrival timing diagnostic on BL3 of SACLA is reported.
Control of the polarization of an X-ray free-electron laser (XFEL) has ...been performed using an X-ray phase retarder (XPR) in combination with an arrival timing diagnostic on BL3 of the SPring-8 Angstrom Compact free-electron LAser (SACLA). To combine with the timing diagnostic, a pink beam was incident on the XPR crystal and then monochromated in the vicinity of samples. A high degree of circular polarization of ∼97% was obtained experimentally at 11.567 keV, which agreed with calculations based on the dynamical theory of X-ray diffraction. This system enables pump–probe experiments to be operated using circular polarization with a time resolution of 40 fs to investigate ultrafast magnetic phenomena.
PDF
