QXAFS study of CO and H adsorption on Pt in [PtAu(PPh)]-H[PMoO] solid.

The adsorption behaviors of H and CO molecules in crown-motif [PtAu(PPh)]-H[PMoO] (PtAu8-PMo12) solids were investigated by quick-scan X-ray absorption fine structure (QXAFS) measurements with a time resolution of 0.1 s. The electronic state of Pt in PtAu8-PMo12 was drastically changed by the adsorption of H and CO molecules because of the formation of Pt-H/Pt-CO interactions.

Simple renormalization schemes for multiple scattering series expansions.

A number of renormalization schemes for improving the convergence of multiple scattering series expansions are investigated. Numerical tests on a small Cu(111) cluster demonstrate their effectiveness, for example increasing the rate of convergence by up to a factor 2 or by transforming a divergent series into a convergent one. These techniques can greatly facilitate multiple scattering calculations, especially for spectroscopies such as photoelectron diffraction, Auger electron diffraction, low energy electron diffraction , where an electron propagates with a kinetic energy of hundreds of eV in a cluster of hundreds of atoms.

Imaging intramolecular hydrogen migration with time- and momentum-resolved photoelectron diffraction.

Imaging ultrafast hydrogen migration with few- or sub-femtosecond time resolution is a challenge for ultrafast spectroscopy due to the lightness and small scattering cross-section of the moving hydrogen atom. Here we propose time- and momentum-resolved photoelectron diffraction (TMR-PED) as a way to overcome limitations of existing methodologies and illustrate its performance in the ethanol molecule. By combining different theoretical methods, namely molecular dynamics and electron scattering methods, we show that TMR-PED, along with a judicious choice of the reference frame for multi-coincidence detection, allows for direct imaging of single and double hydrogen migration in doubly-charged ethanol with both few-fs and Å resolutions, all the way from its birth to the very end.

Photoinduced anisotropic distortion as the electron trapping site of tungsten trioxide by ultrafast W L-edge X-ray absorption spectroscopy with full potential multiple scattering calculations.

Understanding the excited state of photocatalysts is significant to improve their activity for water splitting reaction. X-ray absorption fine structure (XAFS) spectroscopy in X-ray free electron lasers (XFEL) is a powerful method to address dynamic changes in electronic states and structures of photocatalysts in the excited state in ultrafast short time scales. The ultrafast atomic-scale local structural change in photoexcited WO was observed by W L edge XAFS spectroscopy using an XFEL.

Capturing local structure modulations of photoexcited BiVO by ultrafast transient XAFS.

Ultrafast excitation of photocatalytically active BiVO was characterized by femto- and picosecond transient X-ray absorption fine structure spectroscopy. An initial photoexcited state (≪500 fs) changed to a metastable state accompanied by a structural change with a time constant of ∼14 ps. The structural change might stabilize holes on oxygen atoms since the interaction between Bi and O increases.

New Insight into the Local Structure of Hydrous Ferric Arsenate Using Full-Potential Multiple Scattering Analysis, Density Functional Theory Calculations, and Vibrational Spectroscopy.

Hydrous ferric arsenate (HFA) is an important arsenic-bearing precipitate in the mining-impacted environment and hydrometallurgical tailings. However, there is no agreement on its local atomic structure. The local structure of HFA was reprobed by employing a full-potential multiple scattering (FPMS) analysis, density functional theory (DFT) calculations, and vibrational spectroscopy.

Observation of scissors modes in solid state systems with a SQUID.

The occurrence of scissors modes in crystals that have deformed ions in their unit cells was predicted some time ago. The theoretical value of their energy is rather uncertain, however, ranging between ten and a few tens of eV, with the corresponding widths of 10(-7) to 10(-6) eV. Their observation by resonance fluorescence experiments therefore requires a photon spectrometer covering a wide energy range with a very high resolving power.

Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS.

The dynamics of the local electronic and geometric structures of WO3 following photoexcitation were studied by femtosecond time-resolved X-ray absorption fine structure (XAFS) spectroscopy using an X-ray free electron laser (XFEL). We found that the electronic state was the first to change followed by the local structure, which was affected within 200 ps of photoexcitation.

EIS: the scattering beamline at FERMI.

The Elastic and Inelastic Scattering (EIS) beamline at the free-electron laser FERMI is presented. It consists of two separate end-stations: EIS-TIMEX, dedicated to ultrafast time-resolved studies of matter under extreme and metastable conditions, and EIS-TIMER, dedicated to time-resolved spectroscopy of mesoscopic dynamics in condensed matter. The scientific objectives are discussed and the instrument layout illustrated, together with the results from first exemplifying experiments.

Nanoclusters synthesized by synchrotron radiolysis in concert with wet chemistry.

Wet chemical reduction of metal ions, a common strategy for synthesizing metal nanoparticles, strongly depends on the electric potential of the metal, and its applications to late transition metal clusters have been limited to special cases. Here, we describe copper nanoclusters grown by synchrotron radiolysis in concert with wet chemistry. The local structure of copper aggregates grown by reducing Cu(II) pentanedionate using synchrotron x-ray beam was studied in situ by x-ray absorption spectroscopy.

A two rotor model with spin for magnetic nanoparticles.

We argue that a kind of magnetic nanoparticle might exist characterized by the locking of the constituent spins with the density profile of the macrospin. We represent such a nanoparticle by two interacting rigid rotors, one of which has a large spin attached to the body, namely a two rotor model with spin. By this model we can describe in a unified way the cases of nanoparticles free and stuck in an elastic or a rigid matrix.

Full-potential multiple scattering theory with space-filling cells for bound and continuum states.

We present a rigorous derivation of a real-space full-potential multiple scattering theory (FP-MST) that is free from the drawbacks that up to now have impaired its development (in particular the need to expand cell shape functions in spherical harmonics and rectangular matrices), valid both for continuum and bound states, under conditions for space partitioning that are not excessively restrictive and easily implemented. In this connection we give a new scheme to generate local basis functions for the truncated potential cells that is simple, fast, efficient, valid for any shape of the cell and reduces to the minimum the number of spherical harmonics in the expansion of the scattering wavefunction. The method also avoids the need for saturating 'internal sums' due to the re-expansion of the spherical Hankel functions around another point in space (usually another cell center).

Full-potential multiple scattering for core electron spectroscopies.

We present a rigorous derivation of a real space full-potential multiple-scattering theory (FP-MST), valid both for continuum and bound states, that is free from the drawbacks that up to now have impaired its development, in particular the need to use cell shape functions and rectangular matrices. In this connection we give a new scheme to generate local basis functions for the truncated potential cells that is simple, fast, efficient, valid for any shape of the cell and reduces to the minimum the number of spherical harmonics in the expansion of the scattering wavefunction. This approach provides a straightforward extension of MST in the muffin-tin (MT) approximation, with only one truncation parameter given by the classical relation l(max) = kR(b), where k is the photo-electron wavevector and R(b) the radius of the bounding sphere of the scattering cell.

A full multiple scattering model for the analysis of time-resolved X-ray difference absorption spectra.

A full multiple theoretical model (MXAN) is applied to fit picosecond difference X-ray absorption spectra at the ruthenium L(3) edge upon photoexcitation of aqueous [RuII(bpy)3]2+. We show that fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the (3)MLCT state are in good agreement with recently published values.

Full quantitative multiple-scattering analysis of X-ray absorption spectra: application to potassium hexacyanoferrat(II) and -(III) complexes.

A recently developed method to the full quantitative analysis of the XAS spectra extending from the absorption edge to the high-energy region is presented. This method is based on the use of two independent approaches to the analysis of the EXAFS and XANES data, the well-known GNXAS and the newly developed MXAN procedures. Herein, we report the application of this technique to two iron complexes of known structure where multiple-scattering effects are prominent, the potassium hexacyanoferrat(II) and -(III) crystals and aqueous solutions.