Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

Physical, biological, and chemical transformations are initiated by changes in theelectronic configuration of the species involved. These electronic changes occur onthe timescales of attoseconds (10-18s) to femtoseconds (10-15s) and drive allsubsequent electronic reorganization as the system moves to a new equilibrium orquasi-equilibrium state. The ability to detect the dynamics of these electronicchanges is crucial for understanding the potential energy surfaces upon whichchemical and biological reactions take place. Here, we report on the determinationof the electronic structure of matter using a single self-seeded femtosecond x-raypulse from the Linac Coherent Light Source hard x-ray free electron laser. Bymeasuring the high energy resolution off-resonant spectrum (HEROS), we wereable to obtain information about the electronic density of states with a singlefemtosecond x-ray pulse. We show that the unoccupied electronic states of thescattering atom may be determined on a shot-to-shot basis and that the measuredspectral shape is independent of the large intensity fluctuations of the incomingx-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shotcapability and limitations of HEROS, which enables the technique to track theelectronic structural dynamics in matter on femtosecond time scales, making it anideal probe technique for time-resolved X-ray experiments.ISSN:2329-777