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X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics.
Jérémy R Rouxel1, Markus Kowalewski1, Kochise Bennett1
1Department of Chemistry and Department of Physics and Astronomy, University of California, Irvine, California 92697, USA.
Physical Review Letters
|June 30, 2018
Summary
We developed a new nonlinear X-ray technique to image valence electron excitations, capturing transition charge densities. This method overcomes limitations of traditional diffraction for monitoring electronic dynamics after optical excitation.
Area of Science:
- Chemical Physics
- Materials Science
- Quantum Mechanics
Background:
- X-ray diffraction images molecular charge density, tracking nuclear motion.
- Standard diffraction struggles to monitor valence electron density changes due to core electron interference.
Purpose of the Study:
- To present a novel nonlinear X-ray technique for imaging valence electron excitations.
- To overcome limitations in observing electronic dynamics upon optical excitation.
Main Methods:
- Utilizing novel free electron laser sources.
- Employing sum frequency generation with a visible pump and broadband X-ray diffraction pulse.
- Performing ab initio simulations for transition charge density imaging.
Main Results:
- The technique provides spatial electron density images of valence electron excitations.
- Snapshots of transition charge densities, representing electron density variations, are obtained.
- Simulations illustrate imaging of optically induced electronic dynamics in substituted stilbenes.
Conclusions:
- The presented nonlinear X-ray technique enables direct imaging of electronic excitations.
- This method offers a new pathway to study ultrafast electron dynamics in molecules.
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