Ultrafast x-ray scattering and electronic coherence at avoided crossings: complete isotropic signals

Nonadiabatic transitions at conical intersections and avoided crossings play a pivotal role in shaping the outcomes of photochemical reactions. Using the photodissociation of LiF as a model, this theoretical study explores the application of gas phase nonresonant ultrafast x-ray scattering to map nonadiabatic transitions at an avoided crossing, utilizing the part of the scattering signal that probes electronic coherence directly. The presented scattering signals are rotationally averaged and calculated from two- rather than one-electron (transition) densities, which inherently accounts for all possible electronic transitions driven by the x-ray photon. This approach provides quantitative predictions of the experimental signals, thereby facilitating future experimental endeavors to observe nonadiabatic effects and coherent electron dynamics with ultrafast x-ray scattering

Time-resolved X-ray scattering by electronic wave packets: analytic solutions to the hydrogen atom

This paper demonstrates how the time-dependent scattering signal of electronic wave packets in the hydrogen atom can be expressed analytically.</p

Excited Electronic States in Total Isotropic Scattering from Molecules

Ultrafast x-ray scattering experiments are routinely analyzed in terms of the isotropic scattering component. Here we present an analytical method for calculating total isotropic scattering directly from ab initio two-electron densities of ground and excited electronic states. The method is generalized to compute isotropic elastic, inelastic, and coherent mixed scattering. The computational results focus on the potential for differentiating between electronic states and on the composition of the total scattering in terms of elastic and inelastic scattering. By studying the umbrella motion in the first excited state of ammonia, we show that the associated electron density redistribution leaves a comparably constant fingerprint in the total signal that is similar in magnitude to the contribution from the changes in molecular geometry