X-ray absorption spectroscopy with time-tagged photon counting: application to study the structure of a Co(i) intermediate of H2 evolving photo-catalyst.

In order to probe the structure of reaction intermediates of photochemical reactions a new setup for laser-initiated time-resolved X-ray absorption (XAS) measurements has been developed. With this approach the arrival time of each photon in respect to the laser pulse is measured and therefore full kinetic information is obtained. All X-rays that reach the detector are used to measure this kinetic information and therefore the detection efficiency of this method is high.

Probing the dynamics of plasmon-excited hexanethiol-capped gold nanoparticles by picosecond X-ray absorption spectroscopy.

Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au-Au bond length and a large increase in disorder associated with melting of the NPs.

Field-driven dynamics of correlated electrons in LiH and NaBH4 revealed by femtosecond x-ray diffraction.

We study the quasi-instantaneous change of electron density in the unit cells of LiH and NaBH4 in response to a nonresonant strong optical field. We determine for the first time the related transient electron density maps, applying femtosecond x-ray powder diffraction as a structure probe. The light-induced charge relocation in NaBH4 exhibits an electron transfer from the anion (BH(4)(-)) to the Na(+) cation.

Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction.

The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy)3](2 +)) complexes and their [Formula: see text] counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy)3](2 +) complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the [Formula: see text] counterions to the bipyridine units.

Ultrafast large-amplitude relocation of electronic charge in ionic crystals.

The interplay of vibrational motion and electronic charge relocation in an ionic hydrogen-bonded crystal is mapped by X-ray powder diffraction with a 100 fs time resolution. Photoexcitation of the prototype material KH(2)PO(4) induces coherent low-frequency motions of the PO(4) tetrahedra in the electronically excited state of the crystal while the average atomic positions remain unchanged. Time-dependent maps of electron density derived from the diffraction data demonstrate an oscillatory relocation of electronic charge with a spatial amplitude two orders of magnitude larger than the underlying vibrational lattice motions.

Concerted electron and proton transfer in ionic crystals mapped by femtosecond x-ray powder diffraction.

X-ray powder diffraction, a fundamental technique of structure research in physics, chemistry, and biology, is extended into the femtosecond time domain of atomic motions. This allows for mapping (macro)molecular structure generated by basic chemical and biological processes and for deriving transient electronic charge density maps. In the experiments, the transient intensity and angular positions of up to 20 Debye Scherrer reflections from a polycrystalline powder are measured and atomic positions and charge density maps are determined with a combined spatial and temporal resolutions of 30 pm and 100 fs.

Microfocus Cu K(alpha) source for femtosecond x-ray science.

We demonstrate a subpicosecond 1 kHz femtosecond x-ray source with a well-accessible quasi-point size (10 microm diameter) providing Cu K(alpha) emission with a maximum flux of 6.8 x 10(10) photons/s for continuous operation of 10 h. A new geometry that essentially facilitates the adjustment and diminishes the temporal jitter between the x-ray probe and the laser pump pulse is implemented for time-resolved diffraction experiments.