Portraits of Soot Molecules Reveal Pathways to Large Aromatics, Five-/Seven-Membered Rings, and Inception through...

Area of Science:

• Physical Chemistry
• Materials Science
• Combustion Science

Background:

• Soot formation is a complex process in combustion, influencing air quality and energy efficiency.
• Understanding the initial molecular structures of soot is crucial for controlling its formation.
• Previous studies lacked atomic-level resolution of incipient soot species.

Purpose of the Study:

• To investigate the atomic structure and orbital densities of single incipient soot molecules.
• To elucidate the mechanisms of aromatic cross-linking and ring formation in early soot.
• To characterize the different types of open-shell π-radical species present in nascent soot.

Main Methods:

• High-resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM).
• Preparation of single soot molecules on a model surface (bilayer NaCl on Cu(111)).
• Atomic-scale imaging and electronic structure analysis.

Main Results:

• Resolved extended catacondensed and pentagonal-ring linked (pentalinked) aromatic species.
• Identified embedded pentagonal and heptagonal rings, suggesting dual growth mechanisms.
• Characterized three classes of open-shell π-radicals, including localized radicals and triplet diradicals.
• Observed rapid clustering of π-diradicals via van der Waals interactions.

Conclusions:

• The study reveals detailed atomic structures and growth pathways of incipient soot molecules.
• Nonhexagonal rings and diverse radical species provide new insights into soot formation mechanisms.
• Findings could inform strategies for cleaner combustion and sustainable hydrogen production.