Carbon backbone stability of Polycyclic Aromatic Hydrocarbons

Abstract: In this thesis I present results from Collision-Induced Dissociation (CID) experiments of Polycyclic Aromatic Hydrocarbons (PAHs) colliding with a stationary target gas at center-of-mass collision energies in the 20–200 eV range. In this energy region nuclear stopping processes dominate, i.e. energy transfer due to nuclear scattering processes in the molecule are much more important than interactions with the electrons (electronic stopping). If the energy deposited in the molecule by the collision is redistributed among all degrees of freedom before the decay, dissociation often happens statistically through the lowest dissociation energy channels. However, in the collisions that we study, billiard-like, prompt knockout of a single carbon atom from the PAH can also be observed as a form of non-statistical fragmentation.Here I present measurements of the center-of-mass collision energy dependence for single carbon knockout. I further report results on two key properties. The first is the target dependent threshold energy—the minimum center-of-mass collision energy required for knocking out a single carbon atom. The second is the target independent displacement energy—the kinetic energy a single carbon atom must receive to be permanently removed from the PAH. I further present CID experiments on hydrogenated pyrene and compare them to molecular dynamics simulations for atomic knockout. I specifically show that statistical fragmentation is the dominant contribution to the single carbon loss channel for hydrogenated species of pyrene due to their lower dissociation energies.