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.

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Resonant inelastic x-ray scattering spectra excited at the fluorine K resonances of SF6 have been recorded. While a small but significant propensity for electronically parity-allowed transitions is found, the observation of parity-forbidden electronic transitions is attributed to vibronic coupling that breaks the global inversion symmetry of the electronic wavefunction and localizes the core hole. The dependence of the scattering cross section on the polarization of the incident radiation and the scattering angle is interpreted in terms of local π/σ symmetry around the S–F bond. This symmetry selectivity prevails during the dissociation that occurs during the scattering process.

Liquid water plays a significant role, especially as a solvent in the fields of biology and biochemistry. Its strong impact on protein function and activity in the direct surrounding of proteins led to the coining of the term biological water. [1] Investigations of the hydration of polar and nonpolar protein sites, or of systems which can mimic this interaction, such as mixtures of water with solvents of different polarity, are of great interest. However, even for pure liquid water the complex nature of the hydrogen-bond (HB) network is still in the course of clarification. One open question in this context is whether in the dynamic bond-building and -breaking equilibrium of liquid water a continuum of almost tetrahedral bond configurations [2] or rather a number of distinct preferential species of broken and unbroken HB configurations exists.[3] X-ray absorption (XA) and X-ray emission (XE) spectroscopy, which reveal information about the local electronic structure, have been used to pursue this question. [3b, 4] In XA spectroscopy a core electron is excited to the unoccupied states of a molecule, and thus probes the corresponding local electronic structure. The oxygen K-edge XA spectrum of liquid water shows three main features: a pre-edge at 535 eV, a main edge around 537 eV and a postedge around 540 eV. Isotope-, temperature-, and phasedependent measurements on water in combination with theoretical simulations led to the proposal that these features are correlated to distinct HB conformations: the post-edge to tetrahedrally bonded water molecules and the pre-and main edges to conformations with broken HBs. [3,5] This interpretation indicated that a significant number of water molecules with only one strong donating and one strong accepting HB is present in the liquid phase, challenging the traditional tetrahedral model. This new interpretation has been questioned, and based on theoretical modeling it has been argued that XA spectra are rather insensitive to the HB network.[6] X-ray emission spectroscopy probes the occupied electronic states on detecting the energy distribution of the radiative decay of the core-hole state. The recent development of high-resolution XE spectrometers for liquid samples drew particular attention to the observation of the splitting of the sharpest peak in the spectrum associated with the lonepair orbital of the free water molecule.[4a,f,g] Tokushima et al. interpreted the double feature as further proof for the existence of two different structures, the tetrahedral and strongly distorted H-bonded species.[4g] Fuchs et al. assign the two distinct peaks to emission from species before and after core-hole-induced ultrafast dissociation.[4a] Experimental approaches to clarify the origin of the peak splitting included temperature-, isotope-, and state-of-aggregation-dependent measurements, as well as the study of the proposed dissociated species.To shed further light on this issue we present XA and XE spectra of the water molecule in a chemical environment in which the HB configura...