Structural analysis of ultrafast extended x-ray absorption fine structure with subpicometer spatial resolution:...

Area of Science:

• Physical Chemistry
• Materials Science
• Spectroscopy

Background:

• Understanding light-induced molecular transformations is crucial in chemistry and materials science.
• Time-resolved X-ray absorption fine structure (EXAFS) spectroscopy offers insights into ultrafast dynamics.
• Characterizing excited-state structures and dynamics requires advanced analytical methods.

Purpose of the Study:

• To present a novel analysis method for time-resolved EXAFS spectra.
• To apply this method to study the light-induced spin-state conversion in aqueous [Fe(II)(bpy)(3)](2+).
• To precisely determine the structural changes, specifically bond elongation, in the excited high-spin state.

Main Methods:

• Development of a fitting procedure for experimental transients from optical pump/X-ray probe experiments.
• Simulation of EXAFS spectra for potential high-spin structures.
• Subtraction of ground-state spectra to generate transient absorption (TA) spectra.
• Least-squares statistical analysis comparing simulated and experimental TA spectra.

Main Results:

• The novel analysis method successfully determined the excited-state structure.
• A precise value for the Fe-N bond elongation in the high-spin state was obtained (0.203 ± 0.008 Å).
• The method provided a unique solution for fractional population and excited-state structure.

Conclusions:

• The developed analysis technique is effective for time-resolved EXAFS data.
• This method enables precise characterization of ultrafast structural dynamics following photoexcitation.
• The study provides accurate structural parameters for the high-spin state of [Fe(II)(bpy)(3)](2+).