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Photoinduced hydrogen dissociation in thymine predicted by coupled cluster theory
Eirik F Kjønstad1,2,3, O Jonathan Fajen4,5, Alexander C Paul6
1Department of Chemistry, Stanford University, Stanford, CA, USA. eirik.kjonstad@ntnu.no.
Ultraviolet radiation causes thymine to rapidly decay via a ππ* to nπ* transition. New simulations also reveal a potential hydrogen dissociation pathway, prompting further experimental investigation.
Area of Science:
- Photochemistry
- Quantum Chemistry
- Molecular Dynamics
Background:
- The excited-state decay of thymine after UV radiation is debated.
- Current theories suggest a radiationless transition from ππ* to nπ* states.
Purpose of the Study:
- To simulate the early gas-phase ultrafast dynamics of thymine.
- To clarify the excited-state decay pathways of thymine.
Main Methods:
- Wavepacket dynamics simulations.
- Coupled cluster method for high-level theory.
- Comparison with experimental X-ray absorption spectra.
Main Results:
- Confirmed ultrafast ππ* to nπ* transition (41 ± 14 fs).
- Predicted oxygen-edge X-ray absorption spectra match experimental data.
- Identified a novel πσ* channel leading to N-H bond dissociation.
Conclusions:
- The ππ* to nπ* transition is confirmed as a primary decay pathway.
- A previously uncharacterized hydrogen dissociation pathway is predicted.
- Further experiments are needed to validate the predicted πσ* channel.
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