In the Figure Smith and coworkers are proposing a detailed interpretation for the origin of the bands. For instance, SL is the band corresponding to the breathing modes for small aromatic regions, whereas S is the breathing mode of the rings containing 7+ carbons, including benzene ring breathing modes. DS represents the breathing modes for most PAHs, and D the combined breathing/Kekulé vibrations for PAHs. Then we have modes A1 (breathing of 5-membered rings with Kekulé vibrations) and A2 (breathing and asymmetric stretch vibrations of carbons near defects). GG is the Gaussian distributed asymmetric vibrations for distribution of small PAHs, whereas GL is the Lorentzian E2g mode for large PAHs.