Site-specific Interrogation of an Ionic Chiral Fragment During Photolysis Using an X-ray Free-Electron Laser

TL;DR

This study demonstrates how two-color, polarization-controlled X-ray pump-probe experiments at XFELs can track and analyze the stereochemical dynamics of chiral molecules during photolysis, enabling site-specific chiral recognition.

Contribution

It introduces a novel method using polarized X-ray pump-probe schemes at XFELs to investigate chiral molecular fragments with site-specific and stereochemical sensitivity.

Findings

Successful site-specific interrogation of fluorine-containing fragments during photolysis.

Experimental and theoretical validation of stereochemical sensitivity in X-ray probing.

Potential for XFELs to be used as tools for chiral recognition in molecular dynamics.

Abstract

Short-wavelength free-electron lasers with their ultrashort pulses at high intensities have originated new approaches for tracking molecular dynamics from the vista of specific sites. X-ray pump X-ray probe schemes even allow to address individual atomic constituents with a 'trigger'-event that preludes the subsequent molecular dynamics while being able to selectively probe the evolving structure with a time-delayed second X-ray pulse. Here, we use a linearly polarized X-ray photon to trigger the photolysis of a prototypical chiral molecule, namely trifluoromethyloxirane (C$_3$H$_3$F$_3$O), at the fluorine K-edge at around 700 eV. The evolving fluorine-containing fragments are then probed by a second, circularly polarized X-ray pulse of higher photon energy in order to investigate the chemically shifted inner-shell electrons of the ionic motherfragment for their stereochemical sensitivity. We experimentally demonstrate and theoretically support how two-color X-ray pump X-ray probe experiments with polarization control enable XFELs as tools for chiral recognition.