Licentiate Thesis: Carbon backbone stability of Polycyclic Aromatic Hydrocarbons
by
Michael Wolf(Stockholm University, Department of Physics)
→
Europe/Stockholm
FD41
FD41
Description
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-ofmass
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 nonstatistical
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.
