Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers

The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 cm/sup -1/ (approx.29--125 ..mu..m) with a Michelson interferometer aboard the NASA G. P. Kuiper Airborne Observatory. The frequency spectrum peaks at approx.185 cm/sup -1/. A simple model of the emission implies that the temperature is in the range 70--95 K, and that the optical depth is > or =0.2 at the peak frequency. A possible absorption is seen at approx.176 cm/sup -1/. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.