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Updated: Aug 26, 2025
09:33
Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
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E-Z Isomerization in Guanidine: Second-order Saddle Dynamics, Non-statisticality, and Time-frequency Analysis.
Richa Rashmi1, Pankaj Kumar Yadav1, Aniruddha Seal1
1National Insitute of Science Education and Research (NISER) Bhubaneswar, An OCC of Homi Bhabha National Institute P. O. Jatni, Khurdha, Odisha, 752050, India.
Summary
This study reveals that 15% of guanidine E-Z isomerization reactions follow a second-order saddle path, demonstrating highly non-statistical dynamics deviating from standard models.
Area of Science:
- Chemical Dynamics
- Theoretical Chemistry
- Reaction Mechanisms
Background:
- Previous simulations highlighted the role of second-order saddles (SOS) in guanidine isomerization.
- The non-statistical nature of the reaction dynamics remained unconfirmed.
Purpose of the Study:
- To investigate the influence of SOS on guanidine E-Z isomerization.
- To explore the role of intramolecular vibrational energy redistribution (IVR) in reaction dynamics.
- To confirm the non-statistical behavior of the isomerization.
Main Methods:
- Thousands of on-the-fly trajectories were computed using MNDO level forces.
- Analysis included survival probabilities, time-dependent frequencies, and frequency ratio spaces.
Main Results:
- 15% of trajectories utilized the SOS pathway, distinct from traditional transition state routes.
- Reaction dynamics exhibited significant non-statistical behavior, deviating from Rice–Ramsperger–Kassel–Marcus (RRKM) theory.
- Resonance junctions and quasi-periodic trajectories indicated regular dynamics contributing to non-RRKM behavior.
Conclusions:
- Second-order saddles play a significant role in a subset of guanidine E-Z isomerization reactions.
- Intramolecular vibrational energy redistribution influences non-statistical dynamics.
- The findings challenge traditional statistical theories for this reaction system.
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