Technical Report 130, c4e-Preprint Series, Cambridge

Authors: Dongping Chen, Tim Totton, Jethro Akroyd, Sebastian Mosbach, and Markus Kraft*

Reference: Technical Report 130, c4e-Preprint Series, Cambridge, 2013

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The size-dependent melting behaviour of clusters of polycyclic aromatic hydrocarbon (PAH) molecules is studied computationally using the isotropic PAHAP potential (Totton et al., 2012, Physical Chemistry Chemical Physics 14 4081–4094). The investigation aims to shed light on the understanding of the liquid-like behaviour of PAH clusters. Detailed molecular dynamic (MD) simulations are performed to investigate the size-dependent melting of two representative homogeneous PAH clusters composed of either pyrene (C16H10) or coronene (C24H12) molecules. The evolution of the intermolecular energy and the Lindemann Index are used to estimate the melting points of individual nano-clusters. The results from the MD simulations show that individual PAH molecules within nano-clusters are highly mobile below typical flame temperatures. A detailed morphological investigation of coronene500 further reveals that the coronene clusters evolve from a columnar particle in the solid phase to an irregular spherical particle in the liquid phase. In contrast, no such evolution is observed for pyrene300 which remains in a spherical configuration. A linear decrease in the reduced melting temperature is found with increasing inverse particle size. The melting process of these clusters starts from the surface and the liquid layer grows inwards with increasing temperature.

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