Core-Level Binding Energy Reveals Hydrogen Bonding Configurations of Water Adsorbed on TiO_{2}(110) Surface.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D_{2}O) and dissociated (OD) water in the hydrated stoichiometric TiO_{2}(110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D_{2}O∶OD ratio and the core-level binding energy of D_{2}O (ΔBE) decrease with temperature. The observed variations in ΔBE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

Femtosecond bond breaking and charge dynamics in ultracharged amino acids.

Historically, structure determination of nanocrystals, proteins, and macromolecules required the growth of high-quality crystals sufficiently large to diffract X-rays efficiently while withstanding radiation damage. The development of the X-ray free-electron laser has opened the path toward high resolution single particle imaging, and the extreme intensity of the X-rays ensures that enough diffraction statistics are collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. In this study, we use first-principles based methods to study the impact of radiation induced ionization of six amino acids on the reconstruction process. In particular, we study the fragmentation and charge rearrangement to elucidate the time scales involved and the characteristic fragments occurring.

Ultrafast nonthermal heating of water initiated by an X-ray Free-Electron Laser.

The bright ultrafast pulses of X-ray Free-Electron Lasers allow investigation into the structure of matter under extreme conditions. We have used single pulses to ionize and probe water as it undergoes a phase transition from liquid to plasma. We report changes in the structure of liquid water on a femtosecond time scale when irradiated by single 6.86 keV X-ray pulses of more than 106 J/cm2 These observations are supported by simulations based on molecular dynamics and plasma dynamics of a water system that is rapidly ionized and driven out of equilibrium. This exotic ionic and disordered state with the density of a liquid is suggested to be structurally different from a neutral thermally disordered state.