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Dissociative multiphoton ionization of NO2 studied by time-resolved imaging
André T J B Eppink1, Benjamin J Whitaker, Eric Gloaguen
1School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom.
The Journal of Chemical Physics
|October 16, 2004
Summary
This study investigates the multiphoton ionization of nitrogen dioxide (NO2) using advanced laser techniques. Researchers observed NO+ ions resulting from two competitive dissociation pathways, revealing insights into molecular dynamics.
Area of Science:
- Physical Chemistry
- Molecular Spectroscopy
- Quantum Dynamics
Background:
- Understanding molecular dissociation dynamics is crucial for chemical reaction mechanisms.
- Multiphoton ionization provides a powerful tool to probe excited electronic states of molecules.
Purpose of the Study:
- To investigate the dissociative multiphoton ionization of nitrogen dioxide (NO2).
- To elucidate the competitive mechanisms governing NO+ ion formation and decay dynamics.
- To analyze wave packet motion during dissociation using time-resolved imaging.
Main Methods:
- Time-resolved velocity map imaging technique.
- Two-color pump-probe experiment utilizing 400 nm and 266 nm laser harmonics.
- Analysis of NO+ ion kinetic energy and temporal decay profiles.
Main Results:
- Predominant formation of NO+ ions with a peak kinetic energy of approximately 0.28 eV.
- Observation of ~600 fs period oscillations in NO+ decay, indicating wave packet motion.
- Biexponential decay of the NO+ ion signal, attributed to two distinct dissociation pathways.
Conclusions:
- Two competitive mechanisms contribute to NO2 dissociative ionization: three-photon absorption followed by ionization, and one-photon absorption to the 2B2 state followed by two-photon ionization.
- The fast decay component suggests direct dissociation via the bending mode of the pumped state.
- The study provides detailed insights into the ultrafast dynamics of nitrogen dioxide dissociation.