1996A&A...315L.309C

We report spectrophotometric observations of the HII region/neutral medium interface in M 17 obtained with the ISOCAM Circular Variable Filter (CVF) in the spectral range 5.15 to 16.5µm. The lines of singly-ionized species come mainly from the clumpy "neutral" interface, while the HII region dominates the line emission by higher-ionization species. The emission in the Unidentified Infrared Bands (UIBs) comes from the molecular cloud and the interface and extends into the HII region. In the regions where the radiation field is larger than about 10⁴ times the standard interstellar one, the continuum is dominated by the emission of very small grains which are bigger than those responsible for the UIBs.