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Conformational analysis of ethyl-substituted Criegee intermediate by FTMW spectroscopy
Carlos Cabezas1, Jean-Claude Guillemin2, Yasuki Endo1
1Department of Applied Chemistry, National Chiao Tung University, Science Building II, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan.
The Journal of Chemical Physics
|December 18, 2016
Summary
Researchers identified three structures of the ethyl-substituted Criegee intermediate (C2H5CHOO) using microwave spectroscopy. They determined the energy barriers for internal rotation within the molecule.
Area of Science:
- Atmospheric Chemistry
- Molecular Spectroscopy
- Quantum Chemistry
Background:
- Criegee intermediates are key transient species in atmospheric oxidation processes.
- Understanding their structure and dynamics is crucial for accurate atmospheric modeling.
- Ethyl-substituted Criegee intermediates are relevant to combustion and atmospheric chemistry.
Purpose of the Study:
- To spectroscopically characterize the ethyl-substituted Criegee intermediate (C2H5CHOO).
- To determine the molecular structures of its different conformers.
- To investigate the internal rotation of the methyl group and its associated energy barriers.
Main Methods:
- Generation of C2H5CHOO in a discharged plasma of a 1,1-diiodopropane/O2 gas mixture.
- High-resolution characterization using Fourier transform microwave spectroscopy in a pulsed supersonic jet.
- Ab initio calculations to support experimental data and structural assignments.
Main Results:
- Unambiguous identification of three stable conformers of C2H5CHOO based on experimental rotational constants and ab initio calculations.
- Observation of splittings in rotational transitions attributed to methyl internal rotation.
- Determination of the barrier heights for the hindered methyl rotation.
Conclusions:
- The study provides definitive structural information for three C2H5CHOO conformers.
- Methyl internal rotation barriers were successfully determined, offering insights into molecular dynamics.
- Conformational abundances and the absence of a fourth conformer were explained by interconversion processes and specific molecular interactions.
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