10 mu m silicate bands and the structure of grains

Absorption and emission bands at similar to 10 mu m attributed to silicate dust grains do not closely match those obtained for laboratory silicates. The Si-O stretch mode wavelength is dependent on the number of non-bridging oxygen atoms (NBO) per tetrahedral silicate unit (NBO/T). In amorphous silicates there is a distribution of NBO/T values and so 10 mu m band profiles contain contributions from different tetrahedral units. The bulk composition determines the NBO/T distribution, which in turn determines the structure of the silicate grain material. 10 mu m silicate band profiles thus carry the structural signature of grains.