discussed the role of 5-member rings.

The defect may not only be formed in the growing process of the PAHs. Also transitions between the ground state and the defected form might play a role (see Fig. \[Entstehung.fig\]). As we have discussed in section 3.2, the minimum activation barriers for transforming pyrene and coronene into their (5,7)-member ring defected forms is 8.21 eV for pyrene and 8.41 eV for coronene, respectively. The energy required to build (5,7)-member ring defects seems to be insensitive to the size of the PAH molecule. We will now discuss how these barriers can be overcome. A very recent study of Champeaux et al. ([@champ]) discussed the physical interactions of PAHs with stellar particle radiation, especially the interaction of coronene with protons. An interaction will not necessarily destroy or fragment the molecules. If the particle has enough energy and hits exactly on a knot of the molecule, a change of the ring structure from 6-membered rings into pentagons and heptagons may occur (Huber et al. [@huber]). The particle has to have at least enough energy to overcome the activation barrier. Clearly not every hit with sufficient energy will cause a deformation, but also maybe ionization, dissociation or 