and coronene exhibiting the (5,7)-member ring defect (blue), both neutral. Same as for pyrene, the lines change in intensity and position within the spectrum. In grey again the transmission curve of our atmosphere, to get an idea about the observability and detectability.[]{data-label="mex2.fig"}](postermex7neu.eps){width="8.8cm"}

Conclusions
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PAHs observed in astrophysical environments are thought to be formed mainly in the surroundings of C-rich AGB stars. The growth of the aromatic hydrocarbon rings includes effects of 5-member and 7-member ring defects (Whitesides & Frenklach [@white]). The still unidentified IR features seen in the observations require further computational, laboratory and observational investigations. We have performed a theoretical study of the IR spectra of PAHs containing (5, 7)-member ring defects. Using density functional theory, we investigated the effect of such defects on the IR spectra of pyrene ($C_{16}H_{10}$) and coronene ($C_{24}H_{12}$) and their cations and anions. In addition, we explore parts of the potential energy surface of the neutral species.

The addition of (5, 7)-member ring defects into the skeleton of these small PAH molecules has an astonishing large effect on the IR spectra. Pyrene and coronene exhibiting a (5, 7)-member ring defect lose their typical spectroscopic signature. There is a clear difference in the spectrum 