Optical constants of ammonium sulfate in the infrared

We have measured the spectral reflectance at near-normal incidence for 3.2M, 2.4M, and 1.6M solutions of ammonium sulfate, a compound found in the aerosols in the earth’s atmosphere. Values of the optical constants n(v) and k(v) have been determined from the measured spectral reflectance by Kramers-Kronig analysis. We have attempted to obtain a synthetic spectrum of crystalline ammonium sulfate by extrapolation of the k(v) values obtained for the solution to the absorber number densities of the NH4+ and SO4-- ions characteristic of the crystal. By subtractive Kramers-Kronig analysis we then obtain n(v) for the crystal. This method shows some promise of obtaining approximate values of the optical constants of soluble materials that cannot be obtained as large single crystals.