Midinfrared optical constants of calcite and their relationship to particle size effects in thermal emission spectra of granular calcite

Application of dispersion theory and the Fresnel reflection equations in this midinfrared (2000–400 cm −1 ) emission study of calcite enables 11 oscillators and their band parameters to be described. Of the 11, two have not been defined previously in the literature: one for the ordinary ray (at 891 cm −1 ) and one for the extraordinary ray (at 848 cm −1 ). Updated optical constants ( n and k ) of calcite are presented as well. Emissivity spectra of a suite of calcite particulate samples are also shown. The variations in the spectral shape of the fundamental and transparency bands that are influenced by particle size are related to the new optical constants. Type I, II, and III band behaviors are discussed as they relate to the optical and physical properties of the calcite particle size fractions. It is shown here that for Type II band behavior, the spectral bands that invert with decreased particle size shift to the position of maximum k for that band rather than to “lower frequencies,” as has been concluded in previous studies.