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Calculating Photoabsorption Cross-Sections for Atmospheric Volatile Organic Compounds
Antonio Prlj1, Emanuele Marsili1, Lewis Hutton1
1Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
ACS Earth & Space Chemistry
|January 28, 2022
Summary
Predicting sunlight absorption by atmospheric volatile organic compounds (VOCs) is crucial. The nuclear ensemble approach (NEA) shows promise for calculating photoabsorption cross-sections of reactive VOCs when experimental data is lacking.
Area of Science:
- Atmospheric Chemistry
- Computational Photochemistry
- Spectroscopy
Background:
- Understanding the photochemical reactivity of atmospheric volatile organic compounds (VOCs) requires knowledge of their sunlight absorption properties.
- Experimental determination of photoabsorption cross-sections for many transient VOCs is challenging due to their short lifetimes and high reactivity.
- Existing methods like structure-activity relationships (SARs) have limitations for complex molecules.
Purpose of the Study:
- To evaluate the nuclear ensemble approach (NEA) for predicting photoabsorption cross-sections of transient VOCs.
- To assess the impact of different nuclear sampling strategies on simulated absorption spectra.
- To investigate the limitations of current methods for flexible or microsolvated VOCs.
Main Methods:
- Employed the nuclear ensemble approach (NEA) to calculate photoabsorption cross-sections.
- Studied four exemplary VOCs: acrolein, methylhydroperoxide, 2-hydroperoxy-propanal, and microsolvated pyruvic acid.
- Compared Wigner sampling and ab initio molecular dynamics with a quantum thermostat for ground-state nuclear density sampling.
Main Results:
- The NEA successfully simulated absorption spectra for the chosen VOCs.
- Highlighted potential inaccuracies of using uncoupled harmonic modes in Wigner sampling for flexible/microsolvated VOCs.
- Identified limitations of SARs for multichromophoric VOCs.
Conclusions:
- The nuclear ensemble approach (NEA) is a powerful computational tool for predicting photoabsorption cross-sections of transient VOCs.
- NEA offers a viable alternative to experimental measurements where data is scarce.
- Further methodological development is needed to accurately model complex VOC systems.
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