PAH anions as carriers of the mid-IR emission bands in planetary nebulae

We present results of the mid-IR spectra decomposition for planetary nebulae and compact H II regions in our Galaxy and Magellanic Clouds. The striking correlation between the required PAH component with "7.7" μm band shifted to about 7.8 μm and electron densities of the modeled sources allows us to argue that this PAH component may be in fact PAH anions (PAH₋).