Absorption coefficients of solid NH_3 from 50 to 7000 cm^−1

Abstract

Thin-film spectra of solid NH3 at a resolution of 1 cm−1 were used to determine its absorption coefficient over the range 50–7000 cm−1. The thin films were formed inside a liquid N2 cooled dewar using a variety of substrates and dewar windows. The spectra were recorded with two Fourier spectrometers, one covering the range from 1 to 4 μm and the other from 2.6 to 200 μm. The thickness of the films was measured with a laser interference technique. The absorption coefficients were determined by application of Lambert's law and by a fitting procedure to the observed spectra using thin-film theory. Good agreement was found with the absorption coefficients recently determined by other investigators over a more restricted wavelength range. A metastable phase was observed near a temperature of 90°K and its absorption coefficient is reported. No other major spectral changes with temperature were noted for the range 88–120°K.