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Mode-specific photoelectron scattering effects on CO2(+)(C2Sigmag+) vibrations
G J Rathbone1, E D Poliakoff, John D Bozek
1Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
The Journal of Chemical Physics
|July 23, 2004
Summary
High-resolution photoelectron spectroscopy reveals distinct energy-dependent behaviors for carbon dioxide (CO2) vibrational modes during photoionization. This study elucidates mechanisms populating symmetry-forbidden levels, offering new insights into molecular dynamics.
Area of Science:
- Molecular Physics
- Quantum Chemistry
- Spectroscopy
Background:
- Understanding photoionization dynamics in small molecules is crucial for interpreting molecular behavior.
- Vibrational branching ratios provide sensitive probes of electron scattering dynamics and molecular geometry changes.
Purpose of the Study:
- To determine energy-dependent vibrational branching ratios for CO2 photoionization across a wide spectral range (20-110 eV).
- To investigate the mechanisms responsible for populating symmetry-forbidden vibrational levels in CO2.
- To compare experimental results with theoretical calculations to understand shape resonance and interference effects.
Main Methods:
- High-resolution photoelectron spectroscopy was employed to measure vibrational branching ratios.
- Data were acquired over an extended energy range to observe mode-specific behaviors.
- Theoretical Schwinger variational calculations were performed to interpret the experimental findings.
Main Results:
- Distinct energy dependences were observed for different vibrational modes (symmetric stretch, bend, antisymmetric stretch) of CO2.
- The study successfully elucidated mechanisms for populating symmetry-forbidden vibrational levels.
- Theoretical calculations, primarily attributed to a 4sigmag-->ksigmau shape resonance, generally agreed with experimental trends.
- A notable discrepancy was found for the symmetric stretch vibrational branching ratio, suggesting unaccounted interference mechanisms.
Conclusions:
- Vibrationally resolved measurements are sensitive to molecular geometry changes and reveal mode-specific photoionization dynamics.
- The findings highlight the importance of considering interference effects beyond single-channel calculations for accurate theoretical descriptions.
- This work represents the first energy-dependent study of all vibrational modes in a polyatomic system with high resolution.