The behavior of spectral features in the infrared emission from particulate surfaces of various grain sizes

Several inorganic materials are used to illustrate that bands in infrared emission spectra of solids change shape as the particle size of the sample is altered, and that the way in which a particular band changes depends upon the value of its absorption coefficient. The relationship found to exist between corresponding band shape changes in emission and reflection spectra indicates that Kirchoff's law holds to a first-order approximation for particulate, or mat, surfaces. The implications of band shape changes are discussed in relation to remote compositional sensing, and it is pointed out as a consequence that the most obvious spectral features used for the identification of samples with polished surfaces are not necessarily the most useful for determining the composition of a target with a rough or mat surface.