The contribution of Compton ionization to ultrafast x-ray scattering

Ziems, Karl Michael, Simmermacher, Mats, Gräfe, Stefanie and Kirrander, Adam (2023) The contribution of Compton ionization to ultrafast x-ray scattering. Journal of Chemical Physics, 159 (4), [044108]. (doi:10.1063/5.0156363).

Abstract

We investigate the role of Compton ionization in ultrafast non-resonant x-ray scattering using a molecular model system, which includes the ionization continuum via an orthonormalized plane wave ansatz. Elastic and inelastic components of the scattering signal, as well as coherent-mixed scattering that arises from electron dynamics, are calculated. By virtue of a near-quantitative distinction between scattering related to electronic transitions into bound and continuum states, we demonstrate how Compton ionization contributes to the coherent-mixed component. Analogous to inelastic scattering, the contribution to the coherent-mixed signal is significant and particularly manifests at intermediate and high-momentum transfers. Strikingly, for molecules with inversion symmetry, the exclusion of bound or continuum transitions may lead to the prediction of spurious coherent-mixed signals. We conclude that qualitative and quantitative accuracies of predicted scattering signals on detectors without energy resolution require that elements of the two-electron density operator are used. This approach inherently accounts for all accessible electronic transitions, including ionization.

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Contributors

Author: Karl Michael Ziems

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