Excited Electronic States in Total Isotropic Scattering From Molecules

TL;DR

This paper introduces an analytical method to compute total isotropic x-ray scattering from ab initio electronic densities, enabling differentiation of electronic states and analysis of scattering components in ultrafast experiments.

Contribution

It presents a novel analytical approach for calculating isotropic scattering directly from electronic wavefunctions, including elastic, inelastic, and mixed scattering, enhancing interpretation of ultrafast x-ray data.

Findings

The method can distinguish between electronic states based on scattering signatures.

Electron density redistribution impacts the total scattering signal significantly.

The approach allows analysis of elastic and inelastic scattering contributions separately.

Abstract

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.