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Reactive scattering dynamics in atom+polyatomic systems: F+C2H6-->HF(v,J)+C2H5
Erin S Whitney1, Alexander M Zolot, Anne B McCoy
1JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.
The Journal of Chemical Physics
|April 20, 2005
Summary
This study reveals a linear correlation between HF product recoil and available energy in fluorine atom reactions with ethane. This suggests simple dynamics in exothermic atom-polyatomic scattering, with minor ethyl vibrations excited.
Area of Science:
- Chemical Physics
- Molecular Dynamics
- Reaction Kinetics
Background:
- Understanding the dynamics of exothermic atom-polyatomic reactions is crucial for chemical kinetics.
- Previous studies on similar systems have suggested complex intramolecular vibrational energy flow.
- The reaction of fluorine atoms with ethane (F+C2H6) provides a model system for investigating these dynamics.
Purpose of the Study:
- To investigate the state-to-state scattering dynamics of the F+C2H6 reaction.
- To determine the rovibrational and translational energy distributions of the HF product.
- To elucidate the underlying dynamical mechanisms and compare them with theoretical models.
Main Methods:
- High-resolution infrared laser absorption spectroscopy was used to detect nascent HF(v,J) product states.
- Doppler absorption profiles were recorded for state-resolved HF transitions.
- Density-to-flux analysis was employed to convert product densities into probabilities.
Main Results:
- A linear correlation was observed between the translational recoil of HF(v,J) and the available energy (Eavail).
- An impulsive model based on linear and angular momentum conservation accurately predicted experimental observations.
- Deviations from the model indicated minimal excitation of ethyl vibrations, contrary to expectations of extensive energy flow.
Conclusions:
- The dynamics of F+C2H6 scattering are relatively simple, resembling early barrier dynamics in atom-diatom systems.
- Impulsive recoil coupling at the transition state significantly influences translational-rotational degrees of freedom.
- Franck-Condon excitation of the methylene CH2 bending mode is consistent with the observed dynamics.