DETECTION OF THE OVERTONE OF THE 3.3-MICRON EMISSION FEATURE IN IRAS-21282+5050

The 1.6-1.8 mu m spectrum of the planetary nebula, IRAS 21282+5050, a strong emitter of the unidentified interstellar bands, contains a 0.02 mu m wide emission feature centered at 1.680 mu m, which is well matc hed by laboratory spectra of the 0-2 CH stretching mode in polycyclic aromatic hydrocarbons. We identify the new feature as the overtone of the well-known 3.3 mu m band. In view of the high excitation required for emission in this band, the identification indicates that the emiss ion is by free molecules rather than molecular moieties in solid dust grains. Modeling of the intensity ratio of the 2-0 to 1-0 band implies that the PAHs emitting in these bands contain about 60 carbon atoms. It is inferred that the upsilon = 2-1 hot band of the CH stretching mo de occurs at about 3.43 mu m and contributes to the long-wavelength sh oulder of the 3.40 mu m feature. The main 3.40 mu m feature probably i s due to aliphatic sidegroups on PAH molecules.