folding the frequencies and intensities with a normalized Gaussian lineshape function. Usually a FWHM of 30 cm$^{-1}$ is taken as the natural line width of emission lines of molecules in the ISM (Bauschlicher et al. [@bausch09]). For the bands shorter than 10 $\mu$m, we have used this value (see Fig. \[69.fig\]). To get better resolved spectra, we adopted a value of 10 cm$^{-1}$ for the line with in the region between 10 and 15 $\mu$m (see Fig. \[1015.fig\]). It is thought that this value is more consistent with current observations as well as theoretical calculations (Bauschlicher et al. [@bausch09]). To continue to match the observations (Van Kerckhoven et al. [@kerck]) in the 15 - 20 $\mu$m bands, a FWHM of 5 cm$^{-1}$ is used there (see Fig. \[1520.fig\]). For longer wavelengths, the FWHM will decrease even more. We adopt a value of 1 cm$^{-1}$ for all wavelengths above 20 $\mu$m (see Fig. \[20100.fig\]). This is sufficient for our purposes in this region, as we want to show only the impact of the defects in the spectra.

The harmonic frequency calculations provide as unit for the synthetic spectra cm$^{-1}$ on the x-axis. Since the astrophysical observations are usually presented in $\mu$m, 