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Energetic processing of PAHs: isomerisation and dissociation

Polycyclic aromatic hydrocarbons are carbonaceous compounds of astrophysical and atmospherical interest, which have mostly been investigated in their most stable regular forms. Much less straightforward is the investigation of the evolution of these species receiving energy from collision with particles or photon absorption. Depending on the nature of the excitation and the amount of deposited energy different dissociation behaviors can occur leading to different fragment distributions. In addition to dissociation occurring through the simplest intuitive channels, a PAH may undergo isomerisation toward a variety of stable structures eventually followed by subsequent dissociation. These isomerisation reactions, occurring within a few eV above the PAH ground-state, include three particularly interesting classes, i.e. (i) migration of a hydrogen atom over the carbonaceous skeleton, possibly leading to evaporation of molecular hydrogen, (ii) formation of ethynyl derivatives, preliminary steps toward the loss of C2H2 fragments, and (iii) formation of pentagonal cycles possibly breaking the planar symmetry of the PAH. In this chapter, we review recent theoretical works that, in combination with experimental investigations, aim at giving a picture of the complex evolution of energetic PAHs.

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Print publication date
21 Feb 2018
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From the book series:
SPR - Chemical Modelling