Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser.

Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray-matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the -edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm.

As-Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe-Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering.

A novel mixed-valent hybrid chiral and polar compound, FeAsSe(en)(HO), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [FeSe] chains connected via [AsSe]-Se pentagonal linkers and charge-balancing interstitial [Fe(en)] complexes ( = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing.

Revisiting Bond Breaking and Making in EuCo P : Where are the Electrons?

X-ray absorption spectroscopy (XAS) was used to elucidate changes in the electronic structure caused by the pressure-induced structural collapse in EuCo P . The spectral changes observed at the L -edge of Eu and K-edges of Co and P suggest electron density redistribution, which contradicts the formal charges calculated from the commonly used Zintl-Klemm concept. Quantum-chemical calculations show that, despite the increase in the oxidation state of Eu and the formation of a weak P-P bond in the high-pressure phase, the electron transfer from the Eu 4f orbitals to the hybridized 5d and 6s states causes strengthening of the Eu-P and P-P bonds.