Hematite reflectance spectra

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

A theoretical analysis of the system consisting of either the ZnSe or Ge IRE, an Fe or hematite substrate layer, an adsorbate layer, and a solution of methylene chloride has been performed by Loring and Land [88], The system consisting of the ZnSe IRE, AI2O3 intermediate layer, the sputtered Si substrate layer, and water has been analyzed within the framework of the Fresnel formalism by Sper-line et al. [89], Calculations also reveal that within a narrow wavelength range and at a certain ratio of the optical refractive indices, enhancement of intensities is observed in the spectrum of a given layer in an arbitrary two-layer structure located on an IRE. The ATR spectra of such structures were considered in detail in Ref. [66], This enhancement is attributed to interference of the radiation, as is the enhancement of the reflectivity in BML-IRRAS (Section 2.3.3). 

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