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Dissociation of polycyclic aromatic hydrocarbons at high energy : MD/DFTB simulations versus collision experiments

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Authors : A. Simon, J. P. Champeaux, M. Rapacioli, P. Moretto Capelle, F. X. Gadéa, M. Sence
Abstract : The whole process following collisions of polycyclic aromatic hydrocarbons (PAHs) with high energetic protons is modeled and compared to the experimental mass spectrum, allowing to propose a coherent scenario. Fragmentation of cationic pyrene C16H10+ is extensively studied by molecular dynamics simulations obtained by computing the electronic structure at the selfconsistent- charge density functional-based tight binding (MD/SCC-DFTB) on-the-fly. An atomic model is used to quantify the energy transferred to the target after proton impact, and assuming fast internal conversion for the produced cations. From this model, after ionization, the molecules show a broad distribution of internal energy with a rough exponential decrease. This distribution is used as an input for further extensive MD/SCC-DFTB simulations. The good agreement between experimental and theoretical spectra globally validates the SCC-DFTB potential, the wide distribution of fragments corresponding to statistical dissociation. The scenario for both the internal energy deposited distribution and the fast internal conversion assumption is validated. Using these assumptions, dissociation is shown to occur within a few hundreds of picoseconds. Moreover, adjusting the experimental mass spectrum with the theoretical spectra obtained for the various internal energies nicely returns the distribution modeled from the atomic contributions, reinforcing the coherence of the global approach. This study lays the foundations for further synergistic theoretical and experimental studies that will be devoted to other PAHs and prebiotic molecules of astrophysical interest.
Journal : Theoretical Chemistry Accounts (2018) 137:106 DOI