Can Energetic Terahertz Pulses Initiate Surface Catalytic Reactions on the Picosecond Time Scale?

In preparation for picosecond pump-probe experiments at the SwissFELX-ray laser facility, the feasibility of collectively initiating surface chemical reactions using energetic pulses of terahertz radiation is being tested

Establishing nonlinearity thresholds with ultraintense X-ray pulses

X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state

Teratoma Sacrococcígeo

Paciente de 17 anos, primigesta, sem alterações em exames laboratoriais, realizou ecografia na 30ª semana de gestação que evidenciou volumosa massa tumoral sacrococcígea no feto. Realizado parto cesáreo a termo, sem intercorrências; recém nascido feminino, com  Apgar 9/9 levado à excisão cirúrgica do tumor logo após o parto. O anatomopatológico diagnosticou Teratoma Imaturo. Houve boa evolução pós-operatória e bom prognóstico sem recidiva tumoral, criança atualmente com 5 anos.O Teratoma é um tumor de células germinativas, cuja localização extragonadal mais comum é a região sacrococcígea. É a neoplasia fetal mais freqüente, apresentando incidência de 1 a cada 30000-40000 nascidos vivos e sendo mais comum no sexo feminino. A maioria é benigna no momento do diagnóstico, e o risco de malignidade aumenta com a idade, sendo sua identificação e tratamento precoces de fundamental importância para o prognóstico. O tratamento é cirúrgico, e alcança taxas de cura de até 95%

Probing the electronic and geometric structure of ferric and ferrous myoglobins in physiological solutions by Fe K-edge absorption spectroscopy

We present an iron K-edge X-ray absorption study of carboxymyoglobin (MbCO), nitrosylmyoglobin (MbNO), oxymyoglobin (MbO(2)), cyanomyoglobin (MbCN), aquomet myoglobin (metMb) and unligated myoglobin (deoxyMb) in physiological media. The analysis of the XANES region is performed using the full-multiple scattering formalism, implemented within the MXAN package. This reveals trends within the heme structure, absent from previous crystallographic and X-ray absorption analysis. In particular, the iron-nitrogen bond lengths in the porphyrin ring converge to a common value of about 2 A, except for deoxyMb whose bigger value is due to the doming of the heme. The trends of the Fe-Ne (His93) bond length is found to be consistent with the effect of ligand binding to the iron, with the exception of MbNO, which is explained in terms of the repulsive trans effect. We derive a high resolution description of the relative geometry of the ligands with respect to the heme and quantify the magnitude of the heme doming in the deoxyMb form. Finally, time-dependent density functional theory is used to simulate the pre-edge spectra and is found to be in good agreement with the experiment. The XAS spectra typically exhibit one pre-edge feature which arises from transitions into the unoccupied d(sigma) and d(Pi) - Pi l(igand)* orbitals. 1s -> d(Pi) transitions contribute weakly for MbO(2), metMb and deoxyMb. However, despite this strong Fe d contribution these transitions are found to be dominated by the dipole (1s -> 4p) moment due to the low symmetry of the heme environment

Retrieving photochemically active structures by time-resolved EXAFS spectroscopy

Describing the nature and structure of molecular excited states is important in order to understand their chemical reactivity and role as intermediates in photochemical reactions. The recent implementation of x-ray absorption spectroscopy in the ultrafast time domain allows studying the electronic and structural dynamics of photochemically active molecules in solutions. In this work we present the structural determination of a photoexcited diplatinum molecule, [Pt-2(P2O5H2)(4)](4-), which plays a photocatalytic role in important chemical conversions. A novel analysis of time-resolved EXAFS spectra based on the fitting of the experimental transients obtained from optical pump/x-ray probe experiments has been performed to derive a contraction of 0.31(5) angstrom of the two Pt atoms and a ligand expansion of 0.010(6) angstrom. The former is assigned to the formation of a transient Pt-Pt bond in the excited state, while the latter indicates a concomitant weakening of the Pt-ligand coordination bonds

Disentangling the Evolution of Electrons and Holes in photoexcited ZnO nanoparticles

The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy and ab-initio molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The X-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the X-ray absorption signal is found to rise in ~1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly-charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of ~100 cm-1, which corresponds to a phonon mode of the system involving the Zn sub-lattice

Observing Solvation Dynamics with Simultaneous Femtosecond X-ray Emission Spectroscopy and X-ray Scattering

In liquid phase chemistry dynamic solute–solvent interactions often govern the path, ultimate outcome, and efficiency of chemical reactions. These steps involve many-body movements on subpicosecond time scales and thus ultrafast structural tools capable of capturing both intramolecular electronic and structural changes, and local solvent structural changes are desired. We have studied the intra- and intermolecular dynamics of a model chromophore, aqueous [Fe(bpy)3]2+, with complementary X-ray tools in a single experiment exploiting intense XFEL radiation as a probe. We monitored the ultrafast structural rearrangement of the solute with X-ray emission spectroscopy, thus establishing time zero for the ensuing X-ray diffuse scattering analysis. The simultaneously recorded X-ray diffuse scattering patterns reveal slower subpicosecond dynamics triggered by the intramolecular structural dynamics of the photoexcited solute. By simultaneous combination of both methods only, we can extract new information about the solvation dynamic processes unfolding during the first picosecond (ps). The measured bulk solvent density increase of 0.2% indicates a dramatic change of the solvation shell around each photoexcited solute, confirming previous ab initio molecular dynamics simulations. Structural changes in the aqueous solvent associated with density and temperature changes occur with ∼1 ps time constants, characteristic for structural dynamics in water. This slower time scale of the solvent response allows us to directly observe the structure of the excited solute molecules well before the solvent contributions become dominant

Materials Science at the Swiss Light Source

This article describes a state-of-the-art hard X-ray beamline for materials science at a third-generation synchrotron light source presently being commissioned in Switzerland, together with two typical pieces of experimental work for which the beamline is being optimized. After a discussion of the motivation, photon source, optics and experimental stations of the beam line, we present the results of some X-ray scattering studies of order–disorder phenomena that were recently performed at other synchrotron radiation sources (HASYLAB, Hamburg, and ESRF, Grenoble). The phenomena to be discussed are spontaneous ordering in epitaxial AlxGa1-xAs films and confinement-induced ordering of colloidal solutions

Phase contrast tomography: an alternative approach

Conventional microtomography is widely used for reconstructing the three-dimensional (3D) distribution of the absorption coefficient of a sample from a set of radiographic projections. The question here is whether the 3D distribution of the phase (refractive index) of a weakly absorbing object can be, alternatively to the combined phase retrieval-backprojection methods presented up to now, directly reconstructed from a single tomographic data set. In this letter a solution to this problem based on a direct filtered backprojection approach, derived from the transport of intensity equation, is investigated numerically and experimentally for monochromatic and polychromatic x rays. The results show that the contrast is increased, while keeping dose minimal and spatial resolution equivalent to the conventional absorption based technique. This method is therefore very promising for imaging of biological specimens