Transient x-ray scattering calculated from molecular dynamics

With the continued development of pulsed x-ray sources, it may in time be possible to use transient x-ray diffraction to follow the molecular dynamics of chemical reactions in the liquid and solid states. To explore this possibility from the theoretical side, we have calculated, using classical molecular dynamics, the picosecond time-resolved x-ray scattering of a simplified model for a liquid state chemical reaction of substantial interest: the photodissociation of I2 molecules in rare gas and hexane solvents. The time scale of the separation of the I atoms and the effect of the solvent on their motion are observed in the computed transient x-ray diffraction patterns, and such effects might also be observed in a suitably designed experiment. This illustrates that transient x-ray diffraction might be an experimental tool for discovering the molecular dynamics of chemical reactions, with the advantage over transient optical spectroscopies such as infrared, electronic, and Raman that the connections between dynamics and diffraction can be precisely computed without uncertainties due to imprecise knowledge of dipole moments, transition dipole moments, and polarizabilities.