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Rotational Characterization of the Elusive gauche-Isoprene.
Jessica P Porterfield1, J H Westerfield2, Lincoln Satterthwaite3
1Harvard-Smithsonian Center for Astrophysics , Cambridge , Massachusetts 02138 , United States.
The Journal of Physical Chemistry Letters
|March 23, 2019
Summary
Researchers characterized gauche-isoprene, a challenging atmospheric molecule, using advanced spectroscopy. They successfully determined its structural parameters and inversion splitting, providing new insights into its atmospheric behavior.
Area of Science:
- Atmospheric Chemistry
- Molecular Spectroscopy
- Physical Chemistry
Background:
- Isoprene is a major atmospheric hydrocarbon, second only to methane.
- Structural characterization of gauche-isoprene is difficult due to its low abundance, weak polarity, and complex motions.
Purpose of the Study:
- To structurally characterize gauche-isoprene, a high-energy rotamer.
- To determine rotational parameters and inversion splitting for gauche-isoprene.
Main Methods:
- Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy with cryogenic buffer gas cooling.
- Cavity-enhanced FTMW spectroscopy with a pulsed discharge source.
- Theoretical calculations at increasing levels of sophistication.
Main Results:
- Observed gauche-isoprene using two complementary spectroscopic techniques.
- Demonstrated thermal enhancement of gauche-isoprene population from 1.7% to 10.3% by preheating.
- Determined rotational parameters for the inversion states (0+/0-) for the first time.
- Derived inversion splitting (ΔE) and Fbc Coriolis coupling constant.
Conclusions:
- Successfully characterized the structure of gauche-isoprene.
- Provided key molecular parameters for understanding isoprene's atmospheric chemistry.
- Demonstrated efficient isolation of high-energy rotamers under experimental conditions.
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