Search

Cell size fundamentally affects all biosynthetic processes by determining the scale of organelles and influencing surface transport (1,2). Although extensive studies have identified many mutations affecting cell size, the molecular [...]

In our experimental setup (Fig. 1a), the valence electronic structure of Fe[(CO).sub.5] is probed with femtosecond-resolution resonant inelastic X-ray scattering (RIXS) at the Fe [L.sub.3]-edge (Fe [L.sub.3]-RIXS, illustrated in Fig. [...], Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion (1,2). Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site (3-11) that need to be controlled to optimize complexes for photocatalytic hydrogen production (8) and selective carbon-hydrogen bond activation (9-11). An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe[(CO).sub.5] in solution, that the photo-induced removal of CO generates the 16-electron Fe[(CO).sub.4] species, a homogeneous catalyst (12,13) with an electron deficiency at the Fe centre (14,15), in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe[(CO).sub.5] (refs 4, 16-20), was made possible by the ability of femto-second X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.

Highly charged iron ([Fe.sub.16+], here referred to as Fe XVII) produces some of the brightest X-ray emission lines from hot astrophysical objects (1), including galaxy clusters and stellar coronae, and [...]

The experiment was performed at the LCLS soft X-ray materials science instrument (SXR), where a 1.0-µm-thick aluminium (Al) foil was irradiated with 80-fs X-ray pulses at photon energies in the [...], Matter with a high energy density (> [10.sup.5] joules per [cm.sup.3]) is prevalent throughout the Universe, being present in all types of stars (1) and towards the centre of the giant planets (2,3); it is also relevant for inertial confinement fusion (4). Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities (5,6). With the advent of the Linac Coherent Light Source (LCLS) X-ray laser (7), high-intensity radiation (>[10.sup.17] watts per [cm.sup.2], previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated (8). An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of [10.sup.6] kelvin on inertial-confinement time-scales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray-matter interactions, and illustrate the importance of electron-ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions.

Time-resolved x-ray diffraction measures the dynamics of antiferromagnetic correlations by reconstructing the reciprocal-space scattering volume for the magnetic Bragg peak. Modifications in the scattering line shape along the three principal reciprocal lattice directions are measured.