Detection of Aliphatically Bridged Multi-Core Polycyclic Aromatic Hydrocarbons in Sooting Flames with...

Area of Science:

• Combustion Chemistry
• Chemical Physics
• Mass Spectrometry

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are crucial in combustion and soot formation.
• The structures of aliphatically substituted and bridged PAHs have been hypothesized but experimentally unconfirmed.
• Understanding these species is key to controlling PAH growth and nucleation.

Purpose of the Study:

• To provide experimental evidence for the chemical structures of aliphatically substituted and bridged PAHs.
• To elucidate the role of these species in PAH growth mechanisms.
• To identify foundational aromatic building blocks in combustion environments.

Main Methods:

• Sampling gaseous constituents from an atmospheric pressure inverse coflow diffusion flame of ethylene.
• Utilizing high-resolution tandem mass spectrometry (MS-MS) with vacuum ultraviolet (VUV) ionization.
• Employing collision-induced dissociation (CID) and reflectron time-of-flight mass spectrometry for structural analysis.

Main Results:

• Identified aliphatically substituted and bridged single- and multicore aromatic species.
• Observed fragmentation patterns corresponding to the loss of up to six carbon atoms from saturated and unsaturated units.
• Revealed smaller single-ring and pericondensed aromatics as foundational building blocks for larger PAHs.
• Provided detailed CID data for molecular ions at masses 202 and 434.

Conclusions:

• Experimental evidence confirms the presence and structures of key aliphatically substituted and bridged PAHs.
• These species play a significant role in PAH growth and soot nucleation pathways.
• PAH growth involves oxidation of alkylated aromatics and recombination to form larger, bridged structures.