Formation of interstellar complex polycyclic aromatic hydrocarbons:
  Insights from molecular dynamics simulations of dehydrogenated benzene
  Small organic molecules are thought to provide building blocks for the
formation of complex interstellar polycyclic aromatic hydrocarbons (PAHs).
However, the underlying chemical mechanisms remain unclear, particularly
concerning the role of interstellar dust. Using molecular dynamics, we simulate
the chemical reaction between dehydrogenated benzene molecules in the gas phase
or on the surface of an onion-like carbon nanoparticle (NP). The reaction leads
to the formation of PAHs of complex structures. The size of the formed
molecules is found to roughly increase with increasing temperature up to 800 K,
and to be correlated with the level of dehydrogenation. Morphology analysis
features the formation of large rings that contain up to 32 carbon atom at high
temperature. Density functional theory (DFT) calculations are performed to
search the fundamental energetic reaction pathways. The DFT results
quantitatively confirm the correlation between the reactivity and the
dehydrogenation level, and the formation of stable C-8 rings. Moreover, the
nanostructures formed on the NP surface point to a possible layer-by-layer
formation mechanism for interstellar fullerene and carbon onions.
