Laboratory studies of irradiated nitrogen-methane mixtures: Applications to Triton

Laboratory transmission spectra in the region 0.8-2.5 μm of methane dissolved in liquid nitrogen are shown, and their applicability to the near-infrared spectrum of Triton is discussed. The collision-induced first overtone band of molecular nitrogen at 2.152 μm is overwhelmed by the strong methane band centered at 2.3 μm if the methane concentration in the liquid exceeds about 3% of the saturation value. γ-radiolysis of nitrogen-methane mixtures produces an unstable precipitate that appears to consist of ethane. hydrazine, ammonia, nitriles, and other miscellaneous hydrocarbons and nitrogen-bearing species. The yellowish color of the precipitate is qualitatively similar to the yellow color of Triton, but no specific absorption bands seen in the precipitate can be identified unambigously on Triton. If liquid nitrogen and methane coexist on Triton, the highly soluble methane can have no more than about 3% of the saturation value, and is therefore a minor constituent.