et al. [@galue], Hudgins et al. [@hudgins], Bauschlicher et al. [@bausch08], Simon & Joblin [@simon]).

The influence of size and symmetry on the IR spectra of the PAHs as well as PAHs with different elements added has been studied in the past (e.g., Pauzat & Ellinger [@pauzat], Hudgins et al. [@hudgins], Galue et al. [@galue], Bauschlicher et al. [@bausch08], [@bausch09], Ricca & Bauschlicher [@ricca3], Knorke et al. [@knorke]). These studies could provide many insights and a lot of knowledge about the observed PAHs was gained. The astrophysical environments were studied in detail, but still there are many unresolved questions.

PAHs are thought to be formed in the late stages of the asymptotic giant branch (AGB) phase (Allamandola et al. [@alla]). Especially the carbon-rich AGB stars are an ideal environment for PAH formation. During the growth of large, aromatic molecules, the (5, 7)-member ring defects play an important role.

The molecules chosen in this work are pyrene ($C_{16}H_{10}$) and coronene ($C_{24}H_{12}$), shown in Fig.\[molecules.fig\]. Both of them are very unique for different reasons and they can be seen as limiting or prototypical cases. Coronene and pyrene are among the smallest hydrocarbons that can exhibit a (5,7)-member ring defect, pyrene is the 