Core Competency: Chemistry
The most powerful tool a chemist has is the ability to describe matter in terms of bond lengths and angles. Chemical reactions and physical transformations involve the breaking and rearranging of intra- or intermolecular bonds for which the time scale of fundamental steps is on the order of femtoseconds or picoseconds and distance is measured in angstroms. Since every chemical or physical transformation involves structural changes on an atomic scale, the direct observation of these processes would necessarily require an instrument with the power to resolve molecular bond lengths spatially and molecular vibrations temporally. Only an extraordinary apparatus, such as the Linac Coherent Light Source (LCLS), has sufficient spatial and temporal resolution to follow molecular motion in real time. LCLS chemical dynamics studies will begin with the most fundamental of chemical reactions: photodissociation of isolated gas phase molecules. It will also be possible to study photochemically induced bond breakage in solution and the subsequent recombination within the solvent cage. The LCLS will make it possible to trace atomic motions during these reactions in real time. Photosynthetic processes present a higher level of complexity. Traditionally, the studies in the field of photosynthesis have been divided into structure determination and time-resolved dynamics. The LCLS can be used to observe the structural transformations of photosynthesis in real time. When a crystalline sample is excited with an intense short laser pulse, extreme states of matter can be produced. Melting on picosecond and femtosecond time scales have been reported. The LCLS can be used to probe the dynamics of these ultra-fast transformations by characterizing the time-evolving structures.