Technical Report 199, c4e-Preprint Series, Cambridge

Polar curved polycyclic aromatic hydrocarbons in soot formation

ref: Technical Report 199, c4e-Preprint Series, Cambridge

Associated Theme: Quantum Chemistry


Highlights
  • The earliest onset of curvature in pericondensed aromatic was determined to be six rings with at least one ring being pentagonal.
  • Interactions between curved PAH dimers were found to be similar to planar PAH for one or two pentagonal rings. Three pentagonal rings or greater bound with less energy.
  • Interactions between curved PAH and ions are considered to be substantial and should be explored further.
Abstract

abstractIn this paper, we consider the impact of polar curved polycyclic aromatic hydrocarbons (cPAH) on the process of soot formation by employing electronic structure calculations to determine the earliest onset of curvature integration and the binding energy of curved homodimers. The earliest (smallest size) onset of curvature integration was found to be a six ring PAH with at least one pentagonal ring. The σ bonding in the presence of pentagons led to curvature, however, the π bonding strongly favoured a planar geometry delaying the onset of curvature and therefore the induction of a flexoelectric dipole moment. The binding energies of cPAH dimers were found to be of similar magnitude to flat PAH containing one or two pentagons, with an alignment of the dipole moments vectors. For the more curved structures, steric effects reduced the dispersion interactions to significantly reduce the interaction energy compared with flat PAH. Homogeneous nucleation of cPAH at flame temperatures then appears unlikely, however, significant interactions are expected between chemi-ions and polar cPAH molecules suggesting heterogeneous nucleation should be explored.

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