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We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon–iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.

The non monochromatic beamline BL1 at the FLASH free electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end station, CAMP, was installed. This multi purpose instrument is optimized for electron and ion spectroscopy, imaging and pump probe experiments at free electron lasers. It can be equipped with various electronand ion spectrometers, along with large area single photon counting pnCCD X ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end station are presented, as well as results from its commissioning

The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of CH2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.

We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X-ray scattering (RIXS) spectra from aqueous Ni2+ ions and find that the relative RIXS intensities of ligand-to-metal charge-transfer final states with respect to the ligand-field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L-3-edge allows to determine that the Ni 3d orbitals have on average 5.5% of water character. We propose that 2p3d RIXS at the Ni L-3-edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations.

Small polaron optical properties are studied comprehensively in thin film samples of the narrow bandwidth manganite Pr1−xCaxMnO3 by optical absorption spectroscopy as a function of doping and temperature. A broad near infrared double-peak absorption band in the optical conductivity spectras is observed and interpreted in the framework of photon-assisted small polaron intersite hopping and on-site Jahn-Teller excitation. Application of quasiclassical small polaron theory to both transitions allows an approximate determination of polaron specific parameters like the polaron binding energy, the characteristic phonon energy, as well as the Jahn-Teller splitting energy as a function of temperature and doping. Based on electronic structure calculations, we consider the impact of the hybridization of O2p and Mn 3d electronic states on the Jahn-Teller splitting and the polaron properties. The interplay between hopping and Jahn-Teller excitations is discussed in the alternative pictures of mixed valence Mn3+/Mn4+ sites (Jahn-Teller polaron) and equivalent Mn(3+x)+ sites (Zener polaron). We give a careful evaluation of the estimated polaron parameters and discuss the limitations of small polaron quasiclassical theory for application to narrow bandwidth manganites.

Small polaron optical properties are studied comprehensively in thin film samples of the narrow bandwidth manganite Pr$_{1−x}$Ca$_{x}$MnO$_{3}$ by optical absorption spectroscopy as a function of doping and temperature. A broad near infrared double-peak absorption band in the optical conductivity spectras is observed and interpreted in the framework of photon-assisted small polaron intersite hopping and on-site Jahn-Teller excitation. Application of quasiclassical small polaron theory to both transitions allows an approximate determination of polaron specific parameters like the polaron binding energy, the characteristic phonon energy, as well as the Jahn-Teller splitting energy as a function of temperature and doping. Based on electronic structure calculations, we consider the impact of the hybridization of O2p and Mn 3d electronic states on the Jahn-Teller splitting and the polaron properties. The interplay between hopping and Jahn-Teller excitations is discussed in the alternative pictures of mixed valence Mn$^{3+}$/Mn$^{4+}$ sites (Jahn-Teller polaron) and equivalent Mn$^{(3+x)+}$ sites (Zener polaron). We give a careful evaluation of the estimated polaron parameters and discuss the limitations of small polaron quasiclassical theory for application to narrow bandwidth manganites.

We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1–5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure(NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFSmeasurements were carried out in the “water-window” region (2.28 nm–4.36 nm) on the manganite Pr$_{0.7}$Ca$_{0.3}$MnO$_3$, investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources

In time-resolved X-ray diffraction (TR-XRD), two different entities can be investigated as a function of time: the structural response function of a system upon photoexcitation and/or the population changes of short-living intermediates during the time course of a reaction. The time scales of these response functions might vary between hours and picoseconds, depending on the effects measured. By correlating the time evolution of structural changes with varying optical properties, it is possible to derive structure–function relationships in a time-dependent manner. The time-dependence of these relationships and the development of relevant methodologies is a major current interest in our group. Systems under investigation are organic materials with optical functionalities (molecular crystals, electron donor–acceptor systems) and solid state reactions (such as topochemical reactions).

This report contains a comprehensive technical description of a new international research infrastructure, the European X-Ray Free-Electron Laser (XFEL) Facility. It was written between October 2005 and June 2006 and provides a realistic cost estimate and a compelling assessment of the scientific pay-off. The report has been prepared with the contribution of hundreds of people from many laboratories in Europe and even beyond. Their contributions have been harmonised and merged by many editors, and the whole effort has been coordinated by the European Project Team, generously supported and hosted by the Deutsches Elektronen-Synchrotron (DESY) laboratory.