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Electron transfer from solute to solvent has a crucial role in chemistry, but this process has not yet been visualized in real time. Messina et al.provide the first real-time observation of the dynamic rearrangement of water cages around aqueous halides before full electron ejection.

Linearly polarized orbital angular momentum-carrying hard X-ray beams are induced using spiral Fresnel zone plates. By sending the hard X-ray beams to disordered enantiopure molecular complexes, the helicity-dependent and chiral-sensitive signal is obtained.

Fe(II) complexes display transitions between spin states that can be triggered externally. Now the light-induced ΔS = 2 transition upon excitation of the metal-to-ligand charge-transfer states of Fe(II)-polypyridine complexes has been investigated at high time-resolution in the visible and the ultraviolet range. It has been shown to occur in less than 50 fs — that is, on a sub-vibrational timescale.

A detailed understanding of solute–solvent interactions is crucial to appreciating the important role aqueous ions play in various biological and catalytic processes. Now soft X-ray spectroscopy reveals new features in aqueous ion spectra that are due to solute–solvent interaction and electron transfer.

Water vibrational motion, which occurs on the few-femtosecond timescale and underpins energy transfer within the hydrogen bonding network, has remained challenging to observe in real time due to constraints in time resolution. Here, the authors investigate the ground state vibrational dynamics of liquid water using a sub-5 fs near-infrared pump pulse and few-fs ultraviolet probe pulses, observing rapid dephasing of the OH stretch mode that precedes its relaxation via coupling to the bend modes.

The Mahan exciton, exotic quasiparticle predicted in 1967, had never been found in room temperature semiconductors. With ultrafast optics and many-body theory, Palmieri et al. show that methylammonium lead bromide perovskites are ideal platforms to unveil Mahan exciton physics at room temperature.

The change from low-spin hexacoordinated to high-spin pentacoordinated domed form in heam upon ligand detachment and the reverse process underlie the respiratory function. The authors, using femtosecond time-resolved X-ray emission spectroscopy, capture the transient states connecting the two forms in myoglobin-NO upon NO photoinduced detachment.

Solvated electrons can be formed through photo-induced charge-transfer-to-solvent electronic states of halide ions in water. Here, the authors use machine learning accelerated molecular dynamics simulations to follow the evolution of these states for aqueous iodide in detail.

Complex molecules show element- and enantio-specific properties and reactivity. Here the authors demonstrate identification of the element- and enantiomer-selective motion of Ibuprofen molecule using X-ray photons at the carbon K-edge.

Despite much research, the high-spin-state relaxation mechanism of Fe(II) spin-crossover complexes is unresolved. Using ultrafast circular dichroism spectroscopy it has now been revealed that the spin relaxation is driven by a torsional twisting mode, which breaks the chiral symmetry of a prototypical Fe(II) compound. Stereocontrolling the configuration of the complex can thus be used to slow down the spin relaxation.

Metal-oxide nanostructures are used in a range of light-driven applications, yet the fundamentals behind their properties are poorly understood. Here the authors probe photoexcited zinc oxide nanoparticles using time-resolved X-ray spectroscopy, identifying photocatalytically-active hole traps as oxygen vacancies in the lattice.

The first lasing results at SwissFEL, an X-ray free-electron laser, are presented, highlighting the facility’s unique capabilities. A general comparison to other major facilities is also provided.

Here the authors combine steady-state angle-resolved photoemission spectroscopy, ellipsometry and ultrafast two-dimensional ultraviolet spectroscopy to examine the role of many-body correlations in anatase TiO₂, revealing the existence of strongly bound excitons in single crystals and nanoparticles.

New sources of extreme-ultraviolet to hard X-ray photons have enabled a wide range of short-wavelength nonlinear optical and spectroscopic methods over the past decade, and, for the future, offer unique opportunities to probe elementary dynamics in various systems.

Recent spectroscopic studies have elucidated light-matter interactions in exciton-polaritons at room temperature, yet their precise excited-state dynamics remain unclear. Here, broadband 2D Fourier transform spectroscopy reveals the relaxation between polaritonic states and the role of dark states.

A four-wave mixing technique is developed in the hard X-ray range. A diamond phase grating in an X-ray beam path creates a periodic excitation pattern on a sample via the Talbot effect. The response of the periodic excitation is probed by an optical pulse.

Using hard X-rays for transient grating (TG) spectroscopy, fundamental excitations can be followed with femtosecond temporal and nanometer spatial resolution, selecting momenta, chemical elements and their chemical environment. The authors demonstrate the first experiment of all X-ray TG on an amorphous film of FeGd and on a silicon single crystal.