Torsion-vibration interactions determined from (far) infrared spectra
Jason R Gascooke1, Dominique Appadoo2, Warren D Lawrance1
1College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.
The Journal of Chemical Physics
|October 2, 2021
Summary
Methyl torsion and wagging vibrations interact in molecules like toluene. Infrared spectroscopy reveals these interactions, providing insights into molecular dynamics and aiding in extracting torsional constants.
Area of Science:
- Molecular Spectroscopy
- Quantum Chemistry
- Chemical Physics
Background:
- Torsional and vibrational motions in molecules are crucial for understanding their structure and dynamics.
- Previous studies using 2D-LIF identified methyl torsion-wagging interactions in fluorotoluenes.
- These interactions can affect constants derived from rotational spectra, assuming independent motions.
Purpose of the Study:
- To investigate the widespread nature of torsion-vibration interactions in molecules with methyl groups.
- To develop alternative experimental methods beyond 2D-LIF for studying these interactions.
- To analyze the far infrared absorption spectrum of toluene to probe torsion-vibration coupling.
Main Methods:
- Utilized two-dimensional laser-induced fluorescence (2D-LIF) for initial observations.
- Employed infrared absorption spectroscopy, specifically far infrared, as an alternative method.
- Analyzed torsional sequence bands accompanying the methyl wagging transition in toluene's spectrum.
Main Results:
- Confirmed interactions between methyl torsion and out-of-plane wagging vibrations.
- Demonstrated that infrared spectroscopy, particularly torsional sequence bands, is sensitive to these interactions.
- Analyzed toluene's far infrared spectrum (M20 band) to probe higher torsional states (up to m=7).
Conclusions:
- Torsion-vibration interactions are potentially widespread in methylated aromatic compounds.
- Infrared spectroscopy offers a viable method to study these interactions in molecules not amenable to 2D-LIF.
- The analysis of torsional sequence bands allows for the extraction of torsion-vibration coupling and torsional constants.
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