Contribution of Coulomb explosion to form factors and mosaicity spread in single particle X-ray scattering.

The Coulomb explosion of the octamer water cluster has been studied employing time-dependent density functional theory explicitly accounting for the laser field and thus not imposing any constraint on the interaction between the laser pulse and the cluster. We focus on the effects of electron density changes in the system under high-intensity (10(16) and 10(15) W cm(-2)) soft X-ray laser pulses and their fingerprint in the reciprocal space, namely the ultrafast changes in X-ray diffuse scattering signals in k-space (in the investigated k-space range from 10(-3) up to 10 angstrom(-1)). The present simulations indicate that diffusional components in X-ray intensity changes propagate from low reciprocal resolution (resembling the small-angle X-ray scattering regime) to very high resolution (the wide-angle X-ray scattering regime) during the Coulomb explosion process

Ab initio treatment of time-resolved x-ray scattering: Application to the photoisomerization of stilbene

In this work we present a general theoretical outline for calculating time-dependent x-ray scattering signal changes from first principles. We derive a formalism for the description of atom-atom correlation functions as Fourier transforms of quantum-chemically calculated electron densities and show their proportionality to the molecular form factor. The formalism derived in this work is applied to the photoisomerization of stilbene. We can demonstrate that wide-angle x-ray scattering offers a possibility to study the changes in electron densities in nonperiodic complex systems, which renders it a suitable technique for the investigation of (bio)organic systems

Limitations of high-intensity soft X-ray laser fields for the characterisation of water chemistry: coulomb explosion of the octamer water cluster

In this work, the Coulomb explosion of the octamer water cluster has been studied employing a theoretical approach. Instead of the usual methodology that makes use of classical molecular dynamics, time-dependent density functional theory has been applied to tackle the problem. This method explicitly accounts for the laser field and thus does not impose any constraint on the interaction between the laser pulse and the cluster. We focus on the effects of energetic changes in the system under high-intensity soft X-ray laser pulses. The motions of the ions and their velocities during this process show significant differences for the three applied laser intensities (10(14), 10(15) and 10(16) W cm(-2)). Very strong soft X-ray free electron laser (FEL) pulses must be short to allow for investigations of ultra-fast wet chemistry, according to the principle of collect and destroy

Development of Ultrafast X-ray Free Electron Laser Tools in (Bio)Chemical Research

The chapter will focus on fundamental aspects and methodological challenges of X-ray free electron laser research and recent developments in the related field of ultrafast X-ray science. Selected examples proving “molecular movie capabilities” of Free-electron laser radiation investigating gas phase chemistry, chemistry in liquids and transformations in the solid state will be introduced. They will be discussed in the context of ultrafast X-ray studies of complex biochemical research, and time-resolved X-ray characterisation of energy storage materials and energy bionics

Ultrafast Dynamical Study of Pyrene- N,N

Femtosecond optical pump probe spectroscopy has been employed for studying the directly linked electron donor acceptor system pyrene-N,N-dimethylaniline (PyDMA) in solid state. This DMA-pyrene derivative discussed is being applied as a molecular diode system switching on an ultrafast time scale. Our ultrafast solid-state studies reveal a complex photochemistry of this molecular crystal system. Strong couplings of the optically induced charge-transfer state with the radical ion pair state allow a femtosecond transition of the latter. One could see on the highest occupied molecular orbital lowest unoccupied molecular orbital (HOMO-LUMO) description that a pure optical transition switches the system from a conducting to a blocked system because the molecular orbitals (MOs) of DMA moiety lie in a node plane of the LUMO. Within 800 fs the system relaxes back to the ground state and/or forms a radical ion pair, which is the surprising result of our study; when the system was probed further, the system underwent vibrational cooling and enhanced population inversion of the radical ion pair