Observing Molecular Dynamics using Frequency Resolved X-Ray Scattering

Time resolved x-ray scattering (TRXS) has the potential to provide femtosecond timescale glimpses into atomic motion in molecules. In this scheme, an optical laser pulse photo excites a molecular system and is followed with a variable delay by an x-ray pulse that forward scatters onto an area detector. The scattering process takes place in momentum, or reciprocal space, and thus the recorded scattering patterns need to be spatially Fourier transformed into real space to extract atomic motion. This is often complex or impossible to perform de novo [1,2], and we use an alternate method where instead a temporal Fourier transform is performed on the pump-probe delay dimension of the data to observe the relevant frequencies of atomic motion within a molecule [3], which are often the goal of ultrafast spectroscopies. We have applied this method to TRXS data from photo-excited molecular iodine to successfully observe both bound and dissociative motion.