Diffuse scattering from liquid solutions with white-beam undulator radiation for photoexcitation studies.

Scattering from molecules in solution is a natural way to study fast reactions in solution with X-ray probes. With the availability of reliable femtosecond laser systems and pulsed synchrotron sources with high brilliance, it has become possible to study picosecond time-resolved photoexcitation in condensed matter. Owing to the low scattering cross section and the high background from the non-excited solvent, high flux and long exposure times are required to obtain information about isolated molecules in the conventional monochromatic scattering scheme. It is proposed that the full spectrum of a single-line undulator be used to obtain the diffuse scattering distribution. The bandwidth of 2-5% of the first harmonic, which is easily achievable in current insertion devices, is sufficient to allow the derivation of molecular form factors even in diluted systems. The relaxed bandwidth augments the usable flux drastically.