MIDINFRARED AND FAR-INFRARED ABSORPTION-SPECTRA OF FINE FUSED QUARTZ GRAINS

Far-infrared absorption spectra of fine fused quartz grains buried in polyethylene sheets have been measured over the wavelength range 28-400 mum. The sample grains are nearly spherical and the mean diameters range from 60 angstrom to 1.8 mum. The mid-infrared extinction coefficients are in general agreement, but on close investigation. they are seen to differ slightly from each other. This slight disagreement might be due to particle clustering, the difference in bulk properties, or structural defects. The far-infrared extinction coefficients obtained have a strong dependence on the mean particle size: lambda-2 for 400 angstrom-1.8 mum particles and lambda-1 for 60-160 angstrom. Two interpretations are proposed as an explanation for this dependence: it is either due to something intrinsic, such as a surface effect, or to the aggregation of very small particles: