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We present 16 - 50 $\mu$m spectrophotometry of the Cas A supernova remnant obtained using the Goddard Cooled Grating Spectrometer on the Kuiper Airborne Observatory. The emission from young supernova remnants in this wavelength range appears to be dominated by thermal emission from collisionally heated dust and by fine structure emission from the dominant ionization states of abundant elements. Fine structure line observations provide determinations of the abundance of the ion, the ionization balance if lines of several ionization states are observed, and temperature if fine structure lines arising from excited electronic states are detectable. We have measured the spectrum of the infrared bright North rim of Cas A. The continuum dust emission is very unusual, rising steeply from 17 $\mu$m to a peak at 22 $\mu$m, declining to longer wavelengths. A strong emission line is seen at 26 $\mu$m and a line is weakly detected near 35 $\mu$m. The 26 $\mu$m line arises from either Fe II or O IV; Fe II also has a line at 35.3 $\mu$m. We will discuss the dust composition and energy balance, and the implications of the 26 $\mu$m line emission.
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