Warm dust in the neutral interstellar medium.

A comparative study of H I and IRAS maps of a 20 x 18 deg field at high galactic latitude is presented. The galactic infrared emission is shown to be well correlated with the H I distribution. A quantitative relation between H I column density and far-infrared surface brightness is derived. From this correlation the possible use of IRAS observations to map high galactic latitude extinction is discussed. The infrared spectrum of one diffuse H I cloud, from 12 to 100 microns is presented. Its emission in the mid-infrared (12 and 25 microns) is several orders of magnitude larger than predicted by standard dust models. The power radiated at 12 microns represents 25 percent of the 100 microns emission. The spectrum presents a minimum at 25 microns. The implications of these results on interstellar dust properties are discussed.