(Invited) Prediction of Excited State Dynamics for Element-Specific Transient X-Ray Spectroscopy

Abstract

Transient x-ray spectroscopy is evolving into a critical tool in photoelectrochemistry. X-rays can measure the coupled electronic and structural dynamics that underlie excited state polaron formation, molecular reaction dynamics, and hot carrier thermalization pathways. Element-specific responses can be used to measure electron or hole transport between each component of a photoelectrode (i.e. light absorber, oxide protection layer, catalyst). In this talk, we discuss progress towards the ab-initio prediction and interpretation of excited state x-ray spectra on a tens of femtoseconds to nanosecond timescale. The static and dynamic x-ray spectra are unique for each element or bonding scheme. It is typically unknown whether an element of choice will provide relevant dynamical information before performing the technically demanding transient x-ray experiment. We implement a Bethe-Salpeter equation approach with time-dependent electron and phonon populations from solving the Boltzmann transport equation. The calculation accurately includes core-hole excitonic effects in a range of test materials without needing to assume a model of the excited state processes (i.e. renormalization, lattice expansion, state-filling). The eventual goal is a distributable goal that can pre-screen transient x-ray experiments and interpret the measured excited state spectra.