Attosecond Science with X-ray Free Electron Lasers 

The ultrafast motion of electrons is a key to our understanding of chemical reactivity. Electronic rearrangement is the means by which light energy is harnessed in photochemistry. The timescale for coherent electron dynamics spans from few-femtosecond to attosecond timescales. While the initial charge dynamics following impulsive excitation begins as a purely electronic motion, the wavepacket will quickly couple to other degrees of freedom in the system (i.e. nuclear motion or chemical dynamics) and lead to localization of the charge.  The transfer of electronic charge across molecular bonds is fundamental to an understanding of charge transfer phenomena. The study of these fundamental phenomena requires state-of-the-art light sources, such as the Linac Coherent Light Source (LCLS), an X-ray free electron laser (XFEL) facility which produces high-brightness, ultrashort pulses, with wavelength continuously tunable across the x-ray regime and pulse durations capable of resolving electronic motion. In my talk I will highlight our recent developments in probing electronic motion in small molecular systems, resolving electronic transients in both core-excited, and valence-excited systems. Our recent progress in developing nonlinear x-ray techniques (such as impulsive stimulate X-ray Raman scattering) to initiatate and probe ultrafast electron dynamics point toward stratigies for realizing control of chemical reactivity thru coherent electron motion (charge-directed reactivity).