Optical Constants in the Infrared for Aqueous Solutions of NaCl†

Relative specular reflectances of 1M, 3M, and 5M aqueous solutions of NaCl were measured in the 2–20-μm region of the infrared for the component of radiant flux with the electric vector linearly polarized perpendicular to the plane of incidence. Distilled water was the reflectance standard. The angle of incidence was 70.03°±0.23°. Absolute reflectances of the solutions for the same polarization and angle of incidence were computed by use of the measured relative reflectances, one of the Fresnel equations, and the optical constants of distilled water. Phase-shift and phase-difference spectra were obtained by applying a Kramers–Kronig dispersion analysis to the absolute- and relative-reflectance spectra, respectively. The optical constants of the solutions were determined by methods commonly associated with the Kramers–Kronig analysis. Spectral signatures that characterize the solute and the infrared bands of water were noted in the phase-difference spectra.