Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. Although numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, remains elusive. We used tunable femtosecond soft x-ray pulses from an x-ray free electron laser to reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The isolated resonance associated with the valence hole (H2O+/OH) enabled straightforward detection. Molecular dynamics simulations revealed that the x-ray spectra are sensitive to structural dynamics at the ionization site. We found signatures of hydrated-electron dynamics in the x-ray spectrum.

Extreme ultraviolet and X-ray free-electron lasers (FELs) produce short-wavelength pulses with high intensity, ultrashort duration, well-defined polarization and transverse coherence, and have been utilized for many experiments previously possible only at long wavelengths: multiphoton ionization, pumping an atomic laser and four-wave mixing spectroscopy. However one important optical technique, coherent control, has not yet been demonstrated, because self-amplified spontaneous emission FELs have limited longitudinal coherence. Single-colour pulses from the FERMI seeded FEL are longitudinally coherent, and two-colour emission is predicted to be coherent. Here, we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5nm ionized neon, and we controlled the asymmetry of the photoelectron angular distribution by adjusting the phase, with a temporal resolution of 3as. This opens the door to new short-wavelength coherent control experiments with ultrahigh time resolution and chemical sensitivity

FIG. 3. Calculated equilibrium density profiles of a deformable 4 He cylinder rotating around its symmetry axis at fixed L SF =N He ¼ 7.83ℏ for different numbers of vortices. Streamlines are shown in black. The positions of the vortex cores are marked by red dots for visualization. The color bar shows the density in units of Å −3 .

Ultrafast x-ray heating of clusters leads to bond contraction in the solid-to-plasma transition.

The development of next-generation perovskitebased optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr 3 perovskites that the Pb−Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron−phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of timeresolved and temperature-dependent studies at Br K and Pb L 3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperaturedependent XAS results rules out thermal effects as the primary source of distortion of the Pb−Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr 3 perovskites' photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.