Atomistic characterization of the active-site solvation dynamics of a model photocatalyst

The interactions between the reactive excited state of molecular photocatalysts and surrounding solvent dictate reaction mechanisms and pathways, but are not readily accessible to conventional optical spectroscopic techniques. Here we report an investigation of the structural and solvation dynamics following excitation of a model photocatalytic molecular system [Ir 2 (dimen) 4 ] 2+, where dimen is para-diisocyanomenthane. The time-dependent structural changes in this model photocatalyst, as well as the changes in the solvation shell structure, have been measured with ultrafast diffuse X-ray scattering and simulated with Born-Oppenheimer Molecular Dynamics. Both methods provide direct access to the solute-solvent pair distribution function, enabling the solvation dynamics around the catalytically active iridium sites to be robustly characterized. Our results provide evidence for the coordination of the iridium atoms by the acetonitrile solvent and demonstrate the viability of using diffuse X-ray scattering at free-electron laser sources for studying the dynamics of photocatalysis. © The Author(s) 201617111sciescopu

Anti Stokes resonant x ray Raman scattering for atom specific and excited state selective dynamics

Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x rays have been poor at picking up excited state moieties from the unexcited ones. With time resolved anti Stokes resonant x ray Raman scattering AS RXRS performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe CO 5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS RXRS with transform limited x ray pulses is given which will be covered experimentally by upcoming transform limited x ray source

Anti Stokes resonant x ray Raman scattering for atom specific and excited state selective dynamics

Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x rays have been poor at picking up excited state moieties from the unexcited ones. With time resolved anti Stokes resonant x ray Raman scattering AS RXRS performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe CO 5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS RXRS with transform limited x ray pulses is given which will be covered experimentally by upcoming transform limited x ray source

Ultrafast laser-induced melting and ablation studied by time-resolved diffuse X-ray scattering

Time-resolved diffuse X-ray scattering with 50 fs, 9.5 keV X-ray pulses from the Linear Coherent Light Source was used to study the structural dynamics in materials undergoing rapid melting and ablation after fs laser excitation

Carrier density dependant lattice stability in InSb

The ultrafast decay of the x-ray diffraction intensity following laser excitation of an InSb crystal has been utilized to observe carrier dependent changes in the potential energy surface. For the first time, an abrupt carrier dependent onset for potential energy surface softening and the appearance of accelerated atomic disordering for a very high average carrier density have been observed. Inertial dynamics dominate the early stages of crystal disordering for a wide range of carrier densities between the onset of crystal softening and the appearance of accelerated atomic disordering

Experimental strategies for optical pump - Soft x-ray probe experiments at the LCLS

Free electron laser (FEL) based x-ray sources show great promise for use in ultrafast molecular studies due to the short pulse durations and site/element sensitivity in this spectral range. However, the self amplified spontaneous emission (SASE) process mostly used in FELs is intrinsically noisy resulting in highly fluctuating beam parameters. Additionally timing synchronization of optical and FEL sources adds delay jitter in pump-probe experiments. We show how we mitigate the effects of source noise for the case of ultrafast molecular spectroscopy of the nucleobase thymine. Using binning and resorting techniques allows us to increase time and spectral resolution. In addition, choosing observables independent of noisy beam parameters enhances the signal fidelity