enable the transition from the ground state to the defect state of the molecules.

Observations
------------

To get an idea about the possibilities to observe the effects of the (5,7)-member ring defects, Fig. \[mex1.fig\] and \[mex2.fig\] show a comparison of the defected molecule with the normal one in the region from 0 - 20 $\mu$m. In addition the transmission curve of the Earth’s atmosphere is plotted, calculated with the code LNFL/LBLRTM (Clough et al. [@clough]) for airmass = 1 and a years averaged atmospheric profile scaled to 3mm PWV (precipitable water vapor), a typical PWV value for Paranal. So one can get an impression of best detectable lines and bands best suited for a study. Fig. \[mex1.fig\] shows pyrene and its defected form, Fig. \[mex2.fig\] shows coronene and its defected form, all of them in their neutral states.

![A comparison between the IR spectra of pyrene (green) and pyrene exhibiting the (5,7)-member ring defect (blue), both neutral. The changes in intensity and shifts in positions of the lines in the spectrum are clearly visible. In grey we show the transmission curve of the atmosphere, to conditions as are customary for Paranal.[]{data-label="mex1.fig"}](postermexp3neu.eps){width="8.8cm"}

![A comparison between the IR spectra of coronene (green) 