As has recently been emphasized by Jones, Fresnel reflectances resulting from the window-sample refractive index mismatch introduce significant errors in high precision infrared absorption measurements. Whereas these may be reduced by matching the window's index to the sample's, dispersion sets a limit to the effectiveness of the procedure.
Tomas Hirschfeld, "Control of the Dispersion Error in Quantitative IR Spectroscopy," Appl. Spectrosc. 29, 523-524 (1975)