Intermolecular potential calculations for polynuclear aromatic hydrocarbon clusters

Area of Science:

• Physical Chemistry
• Astrochemistry
• Combustion Science

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are crucial in combustion and interstellar chemistry.
• Understanding PAH aggregation is key to modeling soot formation and interstellar dust.

Purpose of the Study:

• To calculate intermolecular potentials for PAH clusters.
• To investigate how binding energies scale with molecular size and composition.
• To relate these findings to PAH growth in flames and astrophysical settings.

Main Methods:

• Computational chemistry methods were used to model homo- and hetero-molecular clusters of 24 peri-condensed PAHs.
• Binding energies were calculated for dimers and larger stacks.
• Results were analyzed in relation to monomer mass and reduced mass.

Main Results:

• PAH dimer binding energies increase with molecular size, approaching graphite's exfoliation energy (5.0 kJ mol⁻¹ C⁻¹).
• Hetero-molecular dimer binding energies correlate with the reduced mass of the pair.
• Stack binding energies increase with size, approaching a limit proportional to monomer mass.

Conclusions:

• PAH aggregation follows predictable trends based on size and composition.
• These trends are relevant for understanding PAH growth in combustion and astrophysical environments.
• The study provides a foundation for more accurate models of soot formation and interstellar chemistry.