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We have carried out high-resolution inelastic x-ray scattering measurements of the excitations of lithium dissolved in ammonia. The incident x-ray energy was 21.6 keV and the resolution was about 2 meV. Several different excitations are observed in the energy range of 0–60 meV (0–500 cm-1). In addition to acoustic phonons at low energies, we see excitations that are associated with vibrations of Li(NH3)4+ complexes. We examined these excitations as a function of momentum transfer, lithium concentration, temperature, and state of the system (solid versus liquid). Data are compared with Hartree-Fock and density-functional theory calculations of the excitations of this complex, which agree well with the measured excitation energies. [ABSTRACT FROM AUTHOR]

Ultrafast pump-probe spectroscopy within the X-ray regime is now possible owing to the development of X-ray Free Electrons Lasers (X-FELs) and is opening new opportunities for the direct probing of femtosecond evolution of the nuclei, the electronic and spin degrees of freedom. In this contribution we use wavepacket dynamics of the photoexcited decay of a new Fe(ii) complex, [Fe(bmip)2]2+ (bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)pyridine), to simulate the experimental observables associated with femtosecond Fe K-edge X-ray Absorption Near-Edge Structure (XANES) and X-ray emission (XES) spectroscopy. We show how the evolution of the nuclear wavepacket is translated into the spectroscopic signal and the sensitivity of these approaches for following excited state dynamics. [ABSTRACT FROM AUTHOR]

We have studied the photoinduced low spin (LS) to high spin (HS) conversion of aqueous Fe(bpy)3 with pulse-limited time resolution. In a combined setup permitting simultaneous X-ray diffuse scattering (XDS) and spectroscopic measurements at a MHz repetition rate we have unraveled the interplay between intramolecular dynamics and the intermolecular caging solvent response with 100 ps time resolution. On this time scale the ultrafast spin transition including intramolecular geometric structure changes as well as the concomitant bulk solvent heating process due to energy dissipation from the excited HS molecule are long completed. The heating is nevertheless observed to further increase due to the excess energy between HS and LS states released on a subnanosecond time scale. The analysis of the spectroscopic data allows precise determination of the excited population which efficiently reduces the number of free parameters in the XDS analysis, and both combined permit extraction of information about the structural dynamics of the first solvation shell. [ABSTRACT FROM AUTHOR]

We have studied the photoinduced low spin (LS) to highspin (HS)conversion of [Fe(bipy)3]2+in aqueous solution.In a laser pump/X-ray probe synchrotron setup permitting simultaneous,time-resolved X-ray diffuse scattering (XDS) and X-ray spectroscopicmeasurements at a 3.26 MHz repetition rate, we observed the interplaybetween intramolecular dynamics and the intermolecular caging solventresponse with better than 100 ps time resolution. On this time scale,the initial ultrafast spin transition and the associated intramoleculargeometric structure changes are long completed, as is the solventheating due to the initial energy dissipation from the excited HSmolecule. Combining information from X-ray emission spectroscopy andscattering, the excitation fraction as well as the temperature anddensity changes of the solvent can be closely followed on the subnanosecondtime scale of the HS lifetime, allowing the detection of an ultrafastchange in bulk solvent density. An analysis approach directly utilizingthe spectroscopic data in the XDS analysis effectively reduces thenumber of free parameters, and both combined permit extraction ofinformation about the ultrafast structural dynamics of the cagingsolvent, in particular, a decrease in the number of water moleculesin the first solvation shell is inferred, as predicted by recent theoreticalwork. [ABSTRACT FROM AUTHOR]

Abstract: The cobalt oxide system LaCoO3 and its Sr-doped child compounds have been intensively studied for decades due to their intriguing magnetic and electronic properties. Preparing thin La1− x Sr x CoO3 (LSCO) films on different substrates allows for studies with a new type of perturbation, as the films are subject to substrate-dependent epitaxial strain. By choosing a proper substrate for a thin film grow, not only compressing but also tensile strain can be applied. The consequences for the fundamental physical properties are dramatic: while compressed films are metallic, as the bulk material, films under tensile strain become insulating. The goal of this work is to determine the strain tensor in LSCO films prepared on LaAlO3 and SrTiO3 substrates by pulsed laser deposition using RBS/channelling methods. Apart from the composition and defect structure of the samples, the depth dependence of the strain tensor, the cell parameters, and the volume of the unit cell are also determined. Asymmetric behaviour of the strained cell parameters is found on both substrates. This asymmetry is rather weak in the case of LSCO film grown on LaAlO3, while stronger on SrTiO3 substrate. The strain is more effective at the interface, some relaxation can be observed near to the surface. [Copyright &y& Elsevier]

Reciprocity is when the scattering amplitude of wave propagation satisfies a symmetry property, connecting a scattering process with an appropriate reversed one. We report on an experiment using nuclear resonance scattering of synchrotron radiation, which demonstrates that magneto-optical materials do not necessarily violate reciprocity. The setting enables us to switch easily between reciprocity and its violation. In the latter case, the exhibited reciprocity violation is orders of magnitude larger than achieved by previous wave scattering experiments. [ABSTRACT FROM AUTHOR]

Abstract: We report on resonant inelastic X-ray scattering measurements on Na0.7CoO2 and on the corresponding hydrated compound Na0.35CoO2 · yH2O at the Co K-edge. The spectra exhibit a single excitation at 10eV energy transfer which resonates at the energy of the Co K white line. The experimental results are analyzed within the linear muffin-tin orbital approach and compared to the calculated electronic density of states and optical conductivity spectra. The poor agreement between calculations and experiment is attributed to effective screening effects from electrons in the Fermi sea. The 10eV feature can be tentatively attributed to a charge transfer excited state, or more likely to a damped plasmon mode. [Copyright &y& Elsevier]

Abstract: X-ray Raman spectra of bulk amorphous SiO have been measured at energy losses around the Si LII,III-edges for different momentum transfers at beamline ID16 of ESRF. The spectra are compared with measurements of the LII,III-edges of Si powder and with results of first-principles calculations for Si and α-quartz SiO2. Indications of sub-oxidic contributions to the LII,III-edges are found in the experiment and discussed with respect to the model of interface clusters mixture in bulk amorphous SiO. [Copyright &y& Elsevier]

We used X-ray absorption in the partial fluorescence yield mode (PFY-XAS), and resonant X-ray emission (RXES) to study the pressure dependence of Yb valence in the intermediate valence compound YbAl2. We find that the Yb valence changes from 2.25 at ambient pressure to 2.95 at 385 kbar, and that the valence transition is completed around 200 kbar. The combined use of complementary spectroscopic techniques considerably reduces the uncertainties in the extracted valence values. [Copyright &y& Elsevier]

The properties of transition-metal complexes and their chemical dynamics can be effectively modified with ligand substitutions, and theory can be a great aid to such molecular engineering. In this paper, we first theoretically explored how substitution with a Cl atom at different positions of the terpyridine ligand affects the electronic structure of the [Fe(terpy) 2 ] 2+ complex. We found that besides the substitution at position 4', the next most promising candidate to cause substantial electronic effects is that where the side pyridine ring is substituted at position 5 (β). Therefore, next, we examined in detail the Fe(II) complexes of the 5-chloro and 5,5″-dichloro derivatives of terpy, theoretically and experimentally, to reveal how these substitutions modify the ground state properties and the lifetime of the excited quintet state in such complexes. In addition, we extend the investigation to the complexes of the analogously substituted derivatives of 4'-SMe-terpy. The substitution at position(s) 5 (and 5″) with Cl lowers the energy of the quintet state and increases its lifetime; the results on the 4'-SMe-substituted complexes show similar changes with these two substitutions, verifying that these effects are more or less additive. This study contributes to the enhancement of our molecular engineering toolset for modifying the potential energy landscape of similar complexes.

Photochemical reactions in solution are governed by a complex interplay between transient intramolecular electronic and nuclear structural changes and accompanying solvent rearrangements. State-of-the-art time-resolved X-ray solution scattering has emerged in the last decade as a powerful technique to observe solute and solvent motions in real time. However, disentangling solute and solvent dynamics and how they mutually influence each other remains challenging. Here, we simultaneously measure femtosecond X-ray emission and scattering to track both the intramolecular and solvation structural dynamics following photoexcitation of a solvated copper photosensitizer. Quantitative analysis assisted by molecular dynamics simulations reveals a two-step ligand flattening strongly coupled to the solvent reorganization, which conventional optical methods could not discern. First, a ballistic flattening triggers coherent motions of surrounding acetonitrile molecules. In turn, the approach of acetonitrile molecules to the copper atom mediates the decay of intramolecular coherent vibrations and induces a further ligand flattening. These direct structural insights reveal that photoinduced solute and solvent motions can be intimately intertwined, explaining how the key initial steps of light harvesting are affected by the solvent on the atomic time and length scale. Ultimately, this work takes a step forward in understanding the microscopic mechanisms of the bidirectional influence between transient solvent reorganization and photoinduced solute structural dynamics., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)