Direct spectroscopic evidence for ionized polycyclic aromatic hydrocarbonsin the interstellar medium

Long-slit 8-13 mu m spectroscopy of the nebula around NGC 1333 SVS 3 reveal s spatial variations in the strength and shape of emission features that ar e probably produced by polycyclic aromatic hydrocarbons (PAHs). Close to SV S 3, the 11.2 mu m feature develops an excess at similar to 10.8-11.0 mu m, and a feature appears at similar to 10 mu m. These features disappear with increasing distance from the central source, and they show striking simila rities to recent laboratory data of PAH cations, providing the first identi fication of emission features arising specifically from ionized PAHs in the interstellar medium.