Infrared absorption in spheroidal crystallites

Infrared absorption spectra of spheroidal particles of polar crystals are calculated by using the point matching method. Retardation effects are taken into account, so that the dependnece of the spectrum on the size of the particle can be investigated. It is found that the surface mode absorption peaks broaden and shift to lower frequencies with increasing particle size. Comparison with the absorption spectra of equivolumic spheres is performed and some consequences regarding the interpretation of experimental spectra are discussed.