The emission structure between 11 and 13 mu-m across the Orion ionization front.

Spectrophotometric observations at 11-13 microns along a north-south line across the ionization front to the south-east of the Trapezium in Orion are presented. Spectral structure, in the form of a step on the short wavelength edge of the well known emission band at 11.3 microns, is revealed together with a resolved emission feature at 12.7 microns and an underlying continuum. These three components of 11-13-micron emission peak just outside the ionized region and decrease in intensity with distance away from ionization front. The underlying continuum or plateau of emission falls off more slowly with distance than the bands at 11.3 and 12.7 microns. These observations lend some support to the idea that the emission bands may be produced by stimulation of molecules such as polycyclic aromatic hydrocarbons, but the existence of two well defined bands in the 11-13-micron region argues for a relatively small number of dominant species.