New upper limits for atmospheric constituents on Io

A spectrum of the satellite of Jupiter, Io, from 0.86 to 2.7 μm at a resolution of 3.36 cm^-1 and a signal to rms noise ratio of 120 is presented. No absorptions due to any atmospheric constituents on Io could be found on the spectrum. Upper limits of 0.12 cm-atm for NH₃, 0.12cm-atm for CH₄, 0.4cm-atm for N₂O, and 24cm-atm for H₂S were determined. Laboratory spectra of ammonia frosts as a function of temperature were compared with the spectrum of Io and showed as a frost not to be present at the surface of Io. A search for possible resonance lines of carbon, silicon, and sulfur as well as the 1.08μm line of helium proved negative and upper emission limits of 60, 18, 27, and 60 kilorayleighs, respectively, were established for these lines.