Polycyclic aromatic hydrocarbon (PAH) molecules are abundant and ubiquitous. For the past 20 years, they have been considered the carriers of unidentified infrared emission (UIE) features. This hypothesis assumes that the UIE features are the result of infrared fluorescence from large (> 50 carbon-atom) gas-phase PAH molecules being pumped by ultraviolet photons. However, it is unclear how such large molecules are formed in space.
It has been reported that C119+ and C118+ could be formed in collisions between keV alpha particles and van der Waals clusters of C60 fullerenes. In such experiments, a carbon atom or C2 is knocked out directly from a C60. The new formed C59+ or C58+ radicals react with a neighbour C60 to form a C119+ and C118+ in picoseconds. Similar process has been observed in pyrene clusters and small hydrocarbon chains clusters in which new molecules are formed following direct knockout of atoms via Rutherford-like ionatom scattering processes. However, none of these experiments explain the formation of astrophysically relevant PAHs (> 50 carbon-atom), unknown reactions must be hidden.
Our recent photodissociation experiments show multiple peaks around the dimer and trimer region on the mass spectra. The hydrogen losses behaviours in these regions are similar to the PAH monomers. We suspect that large PAH might be formed in these processes. For a detailed study such dynamic processes can only be studied using ab initio molecular dynamic (AIMD) simulations. Therefore we propose to perform AIMD simulations to investigate the formation of large PAHs in PAH cluster.