Dimerization of polycyclic aromatic hydrocarbons in soot nucleation

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Materials Science

Background:

• Soot formation is a complex process impacting combustion efficiency and air quality.
• Polycyclic Aromatic Hydrocarbons (PAHs) are key precursors in soot nucleation.
• Understanding the molecular interactions of PAHs is crucial for controlling soot formation.

Purpose of the Study:

• To investigate a novel pathway for soot nucleation involving polycyclic aromatic hydrocarbons (PAHs).
• To elucidate the role of localized π electrons and multiradical characteristics in PAH binding.
• To determine the relationship between molecular structure, radical character, and binding energy in PAH dimerization.

Main Methods:

• Utilized density functional theory (DFT) and semiempirical computational methods.
• Analyzed the dimerization process of identical PAH molecules.
• Investigated the influence of radical character and aromaticity on covalent bond formation.

Main Results:

• The number of covalent bonds formed during PAH dimerization is directly correlated with the molecule's radical character.
• Bonding sites are determined by the aromaticity of the six-membered rings within the PAH structure.
• A linear relationship exists between binding energy and diradical character for PAHs in the soot nucleation range.

Conclusions:

• Localized π electrons facilitate the formation of stable polymer molecules from PAHs via covalent bonds.
• Radical character and aromaticity are critical parameters governing soot nucleation pathways.
• The findings provide a molecular-level understanding of soot formation, aiding in emission control strategies.