Revealing the Dual Role of Hydrogen for Growth Inhibition
and Defect Healing in Polycyclic Aromatic Hydrocarbon Formation: QM/MD
Simulations
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Abstract
Quantum mechanical molecular dynamics
simulations are employed
to reveal the influence of hydrogen on polycyclic aromatic hydrocarbon
(PAH) formation in oxygen-lean combustion. While higher hydrogen concentration
leads to the inhibition of PAH growth, it simultaneously facilitates
pentagon and heptagon defect healing, leading to thermodynamically
more stable PAH fragments with more hexagons. We therefore propose
the existence of an optimal H/C ratio that facilitates the growth
of all-hexagon-containing PAH species. Analysis of the PAH edge reconstruction
in our simulations shows a near-equal ratio of armchair and zigzag
edge structures. As armchair edge structures are thermodynamically
considerably more stable than zigzag edge structures, the present
simulations show that both kinetic and thermodynamic factors are needed
to understand PAH/graphene edge reconstruction