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Examination of the Electronic Structure of Oxygen-Containing PAH Dimers and Trimers

Jennifer A. Giaccai and J. Houston Miller

Abstract: Interactions of oxygen with polynuclear aromatic hydrocarbons (PAH) can occur both in the flame and during oxidation of soot atmospherically. Past experimental measurements of PAH in soot samples collected either immediately after combustion, from the atmosphere, or in a flame show a variety of oxygen moieties within the PAH structures. This study investigated the electronic structure of oxygen-containing PAH to gain insight into their interaction with light both to better interpret spectroscopic measurements and to recognize the role of oxygen-containing PAH in atmospheric radiative forcing. Our research has shown that oxygen in ethers and hydroxyl moieties on PAH showed little change to the HOMO-LUMO gap (HLG), whereas ketones and aldehydes show a HLG decrease of 0.5 eV. The effect is enhanced when more than one ketone is present on a PAH molecule and further enhanced in subsequent dehydrogenation to a quinone-like structure. The presence of an oxygen-containing PAH with a ketone functional group in a dimer and trimer will substantially lower the HLG of the PAH stack. This may have a significant effect in the interaction of atmospheric soot with solar radiation.

 

Molecular orbitals for ketone-ketone and ketone-parent dimers showing electron density remains on the ketone containing monomer in the HOMO and LUMO orbitals. In the ketone/parent dimer the ketone molecule is the upper molecule. Parent molecule is naphtha[8,1,2-abc]coronene.

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Proceedings of the Combustion Institute,Volume 37, Issue 1, 2019
Pages 903-910

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