Electronic Coherence in Ultrafast X-Ray Scattering from Molecular Wave Packets

Abstract

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Excited Electronic States in Total Isotropic Scattering from Molecules

“…The I J scattering terms play a critical role in coherent mixed scattering, which appears when there is a coherence between two electronic states. 35,40,41 This concludes the presentation of the fundamental theory.…”

“…We show that it is applicable not only to elastic and total scattering but also to inelastic and coherent mixed terms between different electronic states. 22,35 We make use of our methodology to investigate the different components comprising the total scattering by a model multielectron two-state system, namely the ground and first excited states of ammonia along the umbrella normal mode. We demonstrate that in this particular case, the change in the scattering signal upon optical excitation cannot be simply attributed to changes in the molecular conformation only, and is in fact strongly influenced by the electron density redistribution in the excited state due to excitation.…”

Simulation of ultrafast excited-state dynamics and elastic x-ray scattering by quantum wavepacket dynamics

“…18 They found moderate discrepancies from the widely adapted independent atom model (IAM) utilizing the Debye scattering equation, but only for wide angle X-ray scattering (WAXS). Theoretical frameworks for the simulation of TR X-ray scattering of molecules 19,20 are under continuous development; most recent contributions were achieved by Kirrander et al [21][22][23] Their ab initio method is based on the evaluation of matrix elements of the scattering operator, utilizing high-level multiconfigurational electronic wave functions and nuclear wavepackets (WPs) obtained from quantum dynamics (QD) simulations. Their approach did not only yield high-accuracy results, but also accessed the inelastic and coherent mixed components 20,[24][25][26] of the scattering signal, in addition to elastic X-ray scattering.…”

Theory of ultrafast x-ray scattering by molecules in the gas phase

“…The elastic and the inelastic signals are usually integrated on the detector and the inelastic contribution cannot generally be assumed to be constant. 28,29 The reorganization of the electron density due to bonding or electronic excitation is furthermore not accounted for in the framework of the IAM. 30,31 A particularly dramatic failure of the assumption that the time-dependent scattering signal is elastic was demonstrated in a seminal paper by Dixit, Vendrell, and Santra, who showed that the scattering signal of an electronic wave packet deviates substantially from the Fourier transform of the time-dependent electron density.…”