Spatial Mapping of Valence Excited-State Landscapes Using Time-Resolved Shake-Down Spectroscopy

Area of Science:

• Chemical Physics
• Molecular Spectroscopy
• Photochemistry

Background:

• Understanding photodissociation dynamics is crucial for chemical reaction mechanisms.
• X-ray photoelectron spectroscopy (XPS) provides insights into electronic structure and bonding.
• Time-resolved techniques enable the study of transient species and reaction pathways.

Purpose of the Study:

• To investigate the photodissociation dynamics of 2-iodothiophene using time-resolved XPS.
• To explore the utility of shake-down transitions as probes of ultrafast structural changes.
• To establish a direct structural mapping of C-I bond cleavage.

Main Methods:

• Excitation of 2-iodothiophene using 262 nm laser.
• Time-resolved X-ray photoelectron spectroscopy (XPS) measurements.
• Analysis of transient XPS features, including direct ionization and shake-down peaks.
• Correlation of spectral shifts with simulated C-I bond lengths.

Main Results:

• Observed direct ionization signals with minimal energy shifts during C-I bond cleavage.
• Detected pronounced shake-down satellite peaks exhibiting a substantial 5 eV shift.
• Established a direct structural mapping by correlating shake-down shifts with C-I bond lengths.
• Demonstrated the exceptional sensitivity of shake-down channels to molecular geometry.

Conclusions:

• Shake-down transitions in XPS are highly sensitive to molecular geometry.
• These transitions serve as a powerful new probe for ultrafast structural dynamics.
• Time-resolved XPS provides detailed insights into photodissociation reaction coordinates.