Averaged anharmonic IR spectra of cata- and peri-condensed PAHs. For cata-condensed PAHs, averages are taken over one to six ring systems for cationic (C) and anionic (A) states and one to five ring systems for the neutral (N) state, while peri-condensed PAHs include one to six ring systems for all three charge states (C, N, A). Three spectral regions are shown: (a) C–H stretching (3.0–3.4 μm), (b) C–C stretching and C–H in-plane bending (6.0–9.0 μm), and (c) C–H out-of-plane bending (11.0–13.0 μm). Observational data are obtained from ISO-SWS (taken from https://irsa.ipac.caltech.edu/data/ISO/SWS/). The dotted vertical lines represent the observed positions of AIBs. The spectra have been baseline corrected, emission line suppressed, and normalized to enhance the dynamic range and enable comparison.