have, however, only been performed for the neutral species.

All electronic structure calculations have been performed with the Gaussian 09 software (Frisch et al. [@frisch09]).

Results
=======

IR spectra
----------

The resulting spectra of both coronene and pyrene as well as for the defected state of the molecules and their cations and anions are given in Figures \[69.fig\], \[1015.fig\], \[1520.fig\] and \[20100.fig\]. All spectra of the unmodified coronene and pyrene were compared with the NASA Ames PAH IR Spectroscopic Database (Bauschlicher et al. [@bausch10]). We get exactly the same IR spectra for both molecules, which is at least an indication for the reliability of all our computed data.

![image](gesamt6_9neu.eps)

![image](gesamt10_15neu.eps)

![image](gesamt15_20neu.eps)

The first part of the spectra is the 6 - 10$\mu$m region, shown in Fig. \[69.fig\]. In this region, the vibrations are in accordance with C–C stretches and C–H in-plane bends. Especially in the 6 - 10$\mu$m area it is thought that the influence of ionization is very large, the IR emission can increases sharply. The emission originates from vibrationally excited cations, proceeding via electronic excitation and intersystem crossing to highly excited vibrational levels of the ground state (Allamandola et al. [@alla]). Our spectra follow this trend, the cation 