Tracking the Electron Density Changes in Excited States -- A Computational Study on Pyrazine

TL;DR

This paper combines X-ray scattering theory and trajectory surface hopping to track electron density changes in excited states, providing insights into molecular dynamics and structural changes during electronic transitions.

Contribution

It introduces a computational approach to analyze ultrafast electron density changes in excited molecules, specifically applying it to pyrazine.

Findings

Key features of reaction pathways identified

Structural changes associated with electronic transitions captured

Method enables analysis of ultrafast electronic and structural dynamics

Abstract

The development of X-ray free-electron lasers (XFELs) has enabled ultrafast X-ray diffraction (XRD) experiments, which are capable of resolving electronic/vibrational transitions and structural changes in molecules, or capturing molecular movies. While time-resolved XRD has received increasing attention, the extraction of information content from signals is challenging and requires theoretical support. In this work, we combined X-ray scattering theory and trajectory surface hopping approach to resolve dynamical changes in the electronic structure of photo-excited molecules by studying time evolution of electron density changes between electronic excited states and ground state. Using pyrazine molecule as an example, we show that key features of reaction pathways can be identified, enabling the capture of structural changes associated with electronic transitions for a photo-excited molecule.