Science Drivers

For the DREAM Endstation

Fundamental Dynamics of Energy & Charge

Charge migration, redistribution and localization, even in simple molecules, are not well understood at the quantum level. These fundamental phenomena are central to complex processes such as photosynthesis, catalysis, and bond formation/dissolution that govern all chemical reactions. Ultrafast soft X-rays at high-repetition-rate from LCLS-II will provide qualitatively new probes of excited-state energy and charge flow and how they work in simple and complex molecular systems. New LCLS-II instrumentation (NEH 1.1) will enable sophisticated coincidence measurement schemes for kinematically complete experiments at each time step of an evolving reaction. This experimental approach, known as a “molecular reaction microscope” will enable the complete spatial reconstruction of the excited-state charge transfer and subsequent dissociation at each time step for a fixed-in-space molecular orientation. This is a powerful new approach for visualizing a broad range of excited-state molecular dynamics.

First Experiments will Include

Fundamental studies of molecular dissociation trajectories and the role of electronic potential energy surface (PES) gradients in the Franck-Condon region; mapping excited-state isomerization trajectories of acetylene; mapping the ring-opening reaction of cyclohexadiene; capturing non-Born-Oppenheimer relaxation channels in the nucleobase thymine; and capturing the quantum symmetry breaking processes that mediate the emergence of chirality in model systems such as fluoroformaldehyde (HFCO).

See document on first experiments for NEH 1.1's DREAM endstation

For the NAMASTE Endstation

Quantum Systems in Strong Fields; Matter in Extreme Environments

The strong fields generated in a focused X-ray laser beam are of particular fundamental interest on the molecular scale. Ordinary sunlight or conventional X-ray sources interact with molecules fairly weakly, by the simple measure that the motion initiated by absorption of a single photon is completely concluded before the next absorption event. X-ray lasers break this routine. The collective effect of multiple X-ray photons concentrate the energy so that the extreme conditions in the target can mimic the interiors of large planets or stars. They also lead to nonlinear processes such as photon harmonic generation.

Photo–catalysis, Coupling of Electronic and Nuclear Dynamics

Energy from the sun powers most of the earth, and the intelligent use of sunlight for our energy needs will be a critical component in addressing urgent challenges in energy production, transformation, and storage—with reduced impact on the environment. Making viable carbon-neutral fuel from sunlight with sufficient energy efficiency and selectivity involves a myriad of complex processes spanning many orders of length and time scales—down to atoms and femtoseconds. These include light harvesting, electron hole separation, charge localization and migration, catalysis driven by electrons or by heat, energy conversion and storage.

The capabilities of LCLS-II for time-resolved, in-situ, element-specific and interface-sensitive studies will transform our ability to study many phenomena associated with these grand challenges in catalysis and photocatalysis. Understanding natural systems and man-made catalysts under their normal operating conditions, and across broad time- and length-scales will be critical to the design of robust, chemically selective, earth abundant and effective catalysts that will help us to meet pressing energy and environmental challenges.

See document on first experiments for NEH 1.1's NAMASTE endstation