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Dynamic Complex-to-Complex Transformations of Heterobimetallic Systems Influence the Cage Structure or Spin State of Iron(II) Ions
No full textTwo new heterobimetallic cages, a trigonal‐bipyramidal and a cubic one, were assembled from the same mononuclear metalloligand by adopting the molecular library approach, using iron(II) and palladium(II) building blocks. The ligand system was designed to readily assemble through subcomponent self‐assembly. It allowed the introduction of steric strain at the iron(II) centres, which stabilizes its paramagnetic high‐spin state. This steric strain was utilized to drive dynamic complex‐to‐complex transformations with both the metalloligand and heterobimetallic cages. Addition of sterically less crowded subcomponents as a chemical stimulus transformed all complexes to their previously reported low‐spin analogues. The metalloligand and bipyramid incorporated the new building block more readily than the cubic cage, probably because the geometric structure of the sterically crowded metalloligand favours the cube formation. Furthermore it was possible to provoke structural transformations upon addition of more favourable chelating ligands, converting the cubic structures into bipyramidal ones
Multiple Photodetachment of Carbon Anions via Single and Double Core-Hole Creation
No full textWe report on new measurements of m-fold photodetachment (m = 2 − 5) of carbon anions via K-shellexcitation and ionization. The experiments were carried out employing the photon-ion merged-beamstechnique at a synchrotron light source. While previous measurements were restricted to doubledetachment (m = 2) and to just the lowest-energy K-shell resonance at about 282 eV, our absoluteexperimental m-fold detachment cross sections at photon energies of up to 1000 eV exhibit a wealth of newthresholds and resonances. We tentatively identify these features with the aid of detailed atomic-structurecalculations. In particular, we find unambiguous evidence for fivefold detachment via double K-holeproduction
Collapse of layer dimerization in the photo-induced hidden state of
No full textPhoto-induced switching between collective quantum states of matter is a fascinating rising field with exciting opportunities for novel technologies. Presently, very intensively studied examples in this regard are nanometer-thick single crystals of the layered material 1T-TaS2, where picosecond laser pulses can trigger a fully reversible insulator-to-metal transition (IMT). This IMT is believed to be connected to the switching between metastable collective quantum states, but the microscopic nature of this so-called hidden quantum state remained largely elusive up to now. Here, we characterize the hidden quantum state of 1T-TaS2 by means of state-of-the-art x-ray diffraction and show that the laser-driven IMT involves a marked rearrangement of the charge and orbital order in the direction perpendicular to the TaS2-layers. More specifically, we identify the collapse of interlayer molecular orbital dimers as a key mechanism for this non-thermal collective transition between two truly long-range ordered electronic crystals
Spatial separation of 2-propanol monomer and its ionization-fragmentation pathways
No full textThe spatial separation of 2-propanol monomer from its clusters in a molecular beam by an electrostatic deflector was demonstrated. Samples of 2-propanol monomer with a purity of 90% and a beam density of cm were obtained. These samples were utilized to study the femtosecond-laser-induced strong-field multi-photon ionization and fragmentation of 2-propanol using non-resonant 800 nm light with peak intensities of W/cm
An effective approach to electroweak baryogenesis
No full textThe asymmetry between matter and antimatter is one of the big outstanding questions of particle physics and cosmology. In this talk, I will argue that electroweak baryogenesis is an interesting mechanism to generate the baryon asymmetry. The new physics needed for electroweak baryogenesis come into play at a relatively low scale and can thus be tested in experiment.I will address three issues related to Electroweak baryogenesis. First I will explain whether electroweak baryogenesis can be studied in the model-independent framework of the Standard Model Effective Field Theory. Second, I will compare the contributions to the value of the asymmetry resulting from CP-violating interactions of different Standard Model particles. Third, I will discuss the validity of the so-called vev-insertion approximation, that is used to compute the value of the baryon asymmetry
Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard split-and-delay
No full textThe ability to deliver two coherent X-ray pulses with precise time-delays ranging from a few femtoseconds to nanoseconds enables critical capabilities of probing ultra-fast phenomena in condensed matter systems at X-ray free electron laser (FEL) sources. Recent progress made in the hard X-ray split-and-delay optics developments now brings a very promising prospect for resolving atomic-scale motions that were not accessible by previous time-resolved techniques. Here, we report on characterizing the spatial and temporal coherence properties of the hard X-ray FEL beam after propagating through split-and-delay optics. Speckle contrast analysis of small-angle scattering measurements from nanoparticles reveals well-preserved transverse coherence of the beam. Measuring intensity fluctuations from successive X-ray pulses also reveals that only single or double temporal modes remain in the transmitted beam, corresponding to nearly Fourier transform limited pulses
Budgeting the Emittance of Photoemitted Electron Beams in a Space-Charge affected Emission Regime for Free-Electron Laser Applications
No full textFree-electron laser based x-ray facilities require high-brightness photoinjectors to provide low emittance electron beams at a fixed bunch charge. The emittance optimization in the injector determines the lowest achievable emittance. Based on experimental emittance optimization at the photoinjector test facility at DESY in Zeuthen, a space-charge affected emission regime is identified, in which the optimum transverse beam emittance is achieved and thus, the injector is routinely operated in this regime. An advanced modeling approach is proposed to consider a dynamic emission process in the simulation of injector beam dynamics, meanwhile allowing detailed studies of the impact of strong space-charge fields during emission on the slice formation of the emitted electron bunch at the cathode. As an application, the proposed approach is used to analyze the budget of the optimized transverse beam emittance. An interplay, taking place in the identified emission regime, between intrinsic cathode emittance and space-charge induced emittance is demonstrated. The resolved behavior by simulation is consistent with the corresponding measurement under practical operation conditions of interest. The obtained results are reported
Possible quantum fluctuations in the vicinity of the quantum critical point of revealed by high-energy x-ray diffraction
No full textProbing the Surface of in Water Vapor by In Situ Photon-In / Photon-Out Spectroscopy
No full textResonant inelastic X-ray scattering (RIXS) is a promising method for elucidating detailed electronic structure of materials in a broad range of chemical and physical applications. Here, we use the fine fluorescence energy resolution of a RIXS spectrometer to obtain various proxies of the Mn-L edge X-ray absorption spectra (XAS) of the perovskite La0.6Sr0.4MnO3 (LSMO) as a model catalyst for the oxygen evolution reaction (OER) and evaluate the suitability for in situ surface studies of this electrocatalyst. We conclude that the inverse partial fluorescence yield (IPFY) of the O2p−1s transition and the partial fluorescence yield of the 3s−2p transition (3s-PFY) are most suitable for determining changes at the surface of the perovskite because distortions at grazing incidence measurements are low. In particular, the negligible angular dependence of the 3s-PFY spectra can be perfectly simulated by using a fluorescence model in the thin sample limit which is justified by low reabsorption of 3s photons. Remarkably, the 3s-PFY reveals an influence of water vapor on the electronic reconstruction of the LSMO surface. Thus, our work paves the road for quantitative distortion-free X-ray spectroscopy of transition metal oxide surfaces under in situ conditions, which is needed to understand fundamental chemical processes such as corrosion and catalysis
Structure of bismuth tellurite and bismuth niobium tellurite glasses and anti-glass by high energy X-ray diffraction
No full textGlass and anti-glass samples of bismuth tellurite (BiO–(100 − x)TeO) and bismuth niobium tellurite (BiO–xNbO–(100 − 2)TeO) systems were prepared by melt-quenching. The bismuth tellurite system forms glasses at low BiO concentration of 3 to 7 mol%. At 20 mol% BiO, the glass forming ability of the BiO–TeO system decreases drastically and the anti-glass phase of monoclinic BiTeO is produced. Structures of glass and the anti-glass BiTeO samples were studied by high-energy X-ray diffraction, reverse Monte Carlo simulations and Rietveld Fullprof refinement. All glasses have short short-range disorder due to the existence of at least three types of Te–O bonds of lengths: 1.90, 2.25 and 2.59 Å, besides a variety of Bi–O and Nb–O bond-lengths. The medium-range order in glasses is also disturbed due to the distribution of Te–Te pair distances. The average Te–O co-ordination (N) in the glass network decreases with an increase in BiO and NbO mol% and is in the range: 4.17 to 3.56. The anti-glass BiTeO has a long-range order of cations but it has vibrational disorder and it exhibits sharp X-ray reflections but broad vibrational bands similar to that in glasses. Anti-glass BiTeO has an N of 2.96 and is significantly lower than in glass samples