Infrared reflectance spectra of Na 2S with contaminant Na 2CO 3: Effects of adsorbed H 2O and CO 2 and relation to studies of Io

Abstract

A previously published IR reflectance spectrum of Na 2S, a candidate surface component on Jupiter's satellite Io, showed a weak but distinct band at approximately 4.04 μm that was interpreted as due to chemisorbed H 2S or SO 2. New spectra have been obtained on Na 2S powder showing that this 4-μm band is not due to H 2S or SO 2, but rather Na 2CO 3, a contaminant present in the original material. The carbonate is spectrally masked by the presence of contaminant adsorbed H 2O. Thermal drying of the sample diminishes the strength of the water bands, revealing the carbonate bands which become very strong due to reaction of the Na 2S with adsorbed atmospheric H 2O and CO 2 in the spectrometer sample chamber while heated by the hot IR source. Because of the extreme hygroscopic nature of Na 2S, a reflectance spectrum of pure Na 2S is not yet available. But the apparent high IR brightness of Na 2S and the spectral neutrality in the range 1–5 μm suggest that it could be a component on Io's surface.