Fig. 3.
From: Amorphous organic solids as a component of interstellar dust
ISO SWS01 spectra of the young planetary nebula IRAS 21282+5050 and the proto-planetary nebula IRAS 07134+1005, showing various aromatic C-H and C-C stretching and bending modes at 3.3, 6.2, 7.7, 8.6, and 11.3 μ m. The PPN spectra are characterized by the 12.1, 12.4, 13.3 μ m out-of-plane bending mode features from small aromatic units. The sharp rise to 20 μ m in the spectrum of IRAS 07134+1005 is due to the unidentified 21 μ m feature.