Knowledge Bank

In view of the importance of $NH3$ in the atmospheres of the major planets, there is a need for knowledge of the optical constants of $NH3$ in condensed states. We have attempted to obtain these constants for liquid $NH3$ by quantitative measurements of spectral reflectance and spectral absorptance. Spectral reflectance at near-normal incidence was measured from 5100 to $350cm-1$ by comparing the reflection at a free liquid surface with reflection from a plane reference mirror, the mirror’s reflectance having been measured in an auxiliary reflectometer. The Lambert absorption coefficients for liquid $NH3$ from 7000 to $980cm-1$ were determined by the methods used in our earlier study of $water.1$ The imaginary part of $ni$ of the refractive index was determined directly from the Lambert coefficients. From the spectral reflectance data and $ni$, the real part $nr$ of the refractive index can be determined from the Fresnel equation. Values of $ni$ and $nr$ can also be determined from an analysis of the spectral reflectance data using the Kramers-Kroning relations. There was close agreement between the $nr$ values determined by the two methods.