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Interpreting the subtle spectral variations of the 11.2 and 12.7 μm polycyclic aromatic hydrocarbon bands

We report new properties of the 11 and 12.7 μm emission complexes of polycyclic aromatic hydrocarbons (PAHs) by applying a Gaussian-based decomposition technique. Using high-resolution \textit{Spitzer} Space Telescope data, we study in detail the spectral and spatial characteristics of the 11 and 12.7 μm emission bands in maps of reflection nebulae NGC 7023 and NGC 2023 (North and South) and the star-forming region M17. Profile variations are observed in both the 11 and 12.7 μm emission bands. We identify a neutral contribution to the traditional 11.0 μm PAH band and a cationic contribution to the traditional 11.2 μm band, the latter of which affects the PAH class of the 11.2 μm emission in our sample. The peak variations of the 12.7 μm complex are explained by the competition between two underlying blended components. The spatial distributions of these components link them to cations and neutrals. We conclude that the 12.7 μm emission originates in both neutral and cationic PAHs, lending support to the use of the 12.7/11.2 intensity ratio as a charge proxy.