all possible subtypes is required.

With the Infrared Space Observatory (ISO) and the Spitzer Space Telescope, a great variety of PAH bands was discovered (e.g., Spitzer Special Edition [@spitzer], Peeters et al. [@peeters04], Bauschlicher et al. [@bausch09]). The IR spectra are dominated by prominent emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 $\mu$m and many more. Those bands are known as the unidentified infrared (UIR) bands (Tielens [@tielens]), but the characteristics of emitting PAHs remain unclear so far. There is a clear variability in the PAH spectra from source to source and spatially within sources (Peeters [@peeters]). The high sensitivity of the space-based observations have shown that the IR emission features are omnipresent and can be found in most astronomical objects (Peeters [@peeters]).

A spectroscopic database of PAH molecules has been published by Bauschlicher et al. ([@bausch10]), which has recently been updated (Bauschlicher et al. [@bausch14]. The web site (http://www.astrochem.org/pahdb/) contains over 800 spectra of PAHs in their neutral and charged states, experimentally measured and theoretically computed. The database contains positive and negative charged molecules, PAHs with different elements substituted or metallic-cation PAH complexes, and all of the subgroups (e.g., Bakes et al. [@bakes], Knorke et al. [@knorke], Galue 