Towards new experiments in ultrafast x-ray scattering

Ultrafast time-resolved x-ray scattering on free molecules in the gas phase provides a window onto the ultrafast dynamics induced by photoexcitation of molecules. Significant advances in resolving transient nuclear structural dynamics in excited molecules have already been made. However, scattering provides rich information beyond structure and the rapid advances at x-ray free electron lasers (XFELs) are yielding highly resolved and information rich signals. We will discuss the types of experiments that one can anticipate over the coming years, and the computational tools that will allow us to interpret these experiments. Detailed simulations of potential experiments allow us to assess the physical insights gained from different types of scattering. Strikingly, the distinction between scattering techniques for structural dynamics on one hand and spectroscopy on the other becomes increasingly blurred. This points towards future directions that may include the characterization of valence electronic states and direct measurements of the effects of electron correlation and coherence using x-ray scattering.