Time-Resolved Optical Pump-Resonant X-ray Probe Spectroscopy of 4-Thiouracil: A Simulation Study

Area of Science:

• Ultrafast spectroscopy
• Photochemistry
• Quantum dynamics

Background:

• 4-thiouracil (4TU) is a key molecule for studying photoinduced processes.
• Understanding excited-state dynamics is crucial for photochemistry and photophysics.
• Element-specific techniques offer unique insights into molecular processes.

Purpose of the Study:

• To theoretically monitor the photoinduced ππ* → nπ* internal conversion in 4TU.
• To investigate the capabilities of element-sensitive resonant X-ray spectroscopy.
• To elucidate the excited-state dynamics of thiobases.

Main Methods:

• High-level electronic structure calculations for core-excited states.
• Quantum nuclear wavepacket dynamics on relevant nuclear modes.
• Time-resolved resonant X-ray spectroscopy tuned to S, O, and N K-edges.

Main Results:

• Sulfur and nitrogen K-edges show distinct spectral windows for ππ* and nπ* transitions.
• Resolved state-specific fingerprint of ππ* and timing of conical intersection at N K-edge.
• Identified spectral signature of nπ* transition, inaccessible by UV-vis spectroscopy.
• Oxygen K-edge showed no sensitivity to molecular deformations.

Conclusions:

• Element-specific resonant X-ray spectroscopy provides a detailed picture of electronic excited-state dynamics.
• This technique offers a sensitive window into the photophysics of thiobases.
• The study highlights the power of combining theoretical calculations with advanced spectroscopic methods.