Time-Resolved Measurement of Interatomic Coulombic Decay in Ne_2

The lifetime of interatomic Coulombic decay (ICD) [L. S. Cederbaum et al., Phys. Rev. Lett. 79, 4778 (1997)] in Ne_2 is determined via an extreme ultraviolet pump-probe experiment at the Free-Electron Laser in Hamburg. The pump pulse creates a 2s inner-shell vacancy in one of the two Ne atoms, whereupon the ionized dimer undergoes ICD resulting in a repulsive Ne^{+}(2p^{-1}) - Ne^{+}(2p^{-1}) state, which is probed with a second pulse, removing a further electron. The yield of coincident Ne^{+} - Ne^{2+} pairs is recorded as a function of the pump-probe delay, allowing us to deduce the ICD lifetime of the Ne_{2}^{+}(2s^{-1}) state to be (150 +/- 50) fs in agreement with quantum calculations.Comment: 5 pages, 3 figures, accepted by PRL on July 11th, 201

Preparation of intergrown P/O-type biphasic layered oxides as high-performance cathodes for sodium ion batteries

This study reports on the solid-state synthesis and characterization of novel quaternary P/O intergrown biphasic Na$_{0.8}$MnyNi$_{0.8-y}$Fe$_{0.1}$Ti$_{0.1}$O$_{2}$ (y = 0.6, 0.55, 0.5, 0.45) cathode materials. Electrochemical tests reveal superior performance of the P/O biphasic materials in a sodium ion battery compared to the single P2 or O3 phases, proving the beneficial effect of the intergrowth of P2 and O3 materials. The nature of the P/O interface was studied by transmission electron microscopy. The analysis shows a semi-coherent interface grown along the a/b and c axes with local differences in the transition metal concentration along the interface between the two phases. EDX and EELS characterization revealed a charge compensation mechanism across the phase boundary based on variation of the transition element distribution, balancing the different sodium contents in the P and O phases. The results reported in this study provide a better understanding of P/O biphasic materials

Multiple ionization and fragmentation dynamics of molecular iodine studied in IR-XUV pump-probe experiments

The ionization and fragmentation dynamics of iodine molecules (I-2) are traced using very intense (similar to 10(14) W cm(-2)) ultra-short (similar to 60 fs) light pulses with 87 eV photons of the Free-electron LASer at Hamburg (FLASH) in combination with a synchronized femtosecond optical laser. Within a pump-probe scheme the IR pulse initiates a molecular fragmentation and then, after an adjustable time delay, the system is exposed to an intense FEL pulse. This way we follow the creation of highly-charged molecular fragments as a function of time, and probe the dynamics of multi-photon absorption during the transition from a molecule to individual atoms

Electron Rearrangement Dynamics in Dissociating I 2 n Molecules Accessed by Extreme Ultraviolet Pump Probe Experiments

The charge rearrangement in dissociating In 2 molecules is measured as a function of the internuclear distance R using extreme ultraviolet pulses delivered by the free electron laser in Hamburg. Within an extreme ultraviolet pump probe scheme, the first pulse initiates dissociation by multiply ionizing I2, and the delayed probe pulse further ionizes one of the two fragments at a given time, thus triggering charge rearrangement at a well defined R. The electron transfer between the fragments is monitored by analyzing the delay dependent ion kinetic energies and charge states. The experimental results are in very good agreement with predictions of the classical over the barrier model demonstrating its validity in a thus far unexplored quasimolecular regime relevant for free electron laser, plasma, and chemistry application

Watching the acetylene vinylidene intramolecular reaction in real time

It is a long-standing dream of scientists to capture the ultra-fast dynamics of molecular or chemical reactions in real time and to make a molecular movie. With free-electron lasers delivering extreme ultraviolet (XUV) light at unprecedented intensities, in combination with pump-probe schemes, it is now possible to visualize structural changes on the femtosecond time scale in photo-excited molecules. In hydrocarbons the absorption of a single photon may trigger the migration of a hydrogen atom within the molecule. Here, such a reaction was filmed in acetylene molecules (C2H2) showing a partial migration of one of the protons along the carbon backbone which is consistent with dynamics calculations on ab initio potential energy surfaces. Our approach opens attractive perspectives and potential applications for a large variety of XUV-induced ultra-fast phenomena in molecules relevant to physics, chemistry, and biology.Comment: 21 pages, 3 figures, submitte

Le bruxisme (état des connaissances en 2007)

Le bruxisme est une activité parafonctionnelle diurne ou nocturne qui inclut le serrement, le grincement ou le frottement des dents antagonistes, et les contractures des muscles masticateurs. Si, actuellement, la connaissance de la pathologie et de sa prise en charge est mieux connue, il n'en demeure pas moins que les étiologies restent très vagues. L'approche diagnostique et thérapeutique doit être pluridisciplinaire. De part sa prévalence dans la population et par les conséquences sur l'organe dentaire et les réhabilitations prothétiques, l'objectif n'est plus seulement d'atténuer les signes mais d'approcher l'arrêt complet de la maladie. Ce travail a pour but de présenter un point de vue global sur le bruxisme, que ce soit sur ses causes, ses conséquences ou encore les moyens mis en œuvre pour sa prise en charge.TOULOUSE3-BU Santé-Centrale (315552105) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Nanoporous Au: An unsupported pure gold catalyst?

The unique properties of gold especially in low temperature CO oxidation have been ascribed to a combination of various effects. In particular, particle sizes below a few nanometers and specific particle-support interactions have been shown to play important roles. In contrast, recent reports revealed that monolithic nanoporous gold (npAu) prepared by leaching a less noble metal, such as Ag, out of the corresponding alloy can also exhibit a remarkably high catalytic activity for CO oxidation, even though no support is present. Therefore, it was claimed to be a pure and unsupported gold catalyst. We investigated npAu with respect to its morphology, surface composition, and catalytic properties. In particular, we studied the reaction kinetics for low temperature CO oxidation in detail, taking the mass transport limitation due to the porous structure of the material into account. Our results reveal that Ag, even if removed almost completely from the bulk, segregates to the surface, resulting in surface concentrations of up to 10 atom %. Our data suggest that this Ag plays a significant role in activating of molecular oxygen. Therefore, npAu should be considered a bimetallic catalyst rather than a pure Au catalyst