The Photochemistry of Hydrocarbons in the Jovian Atmosphere

Abstract

A detailed quantitative study of the photochemistry of CH4, C2H2, C2H4 and C2H6 which includes eddy and molecular diffusion is presented for the Jovian upper atmosphere composed of 90% H2, 10% He with a CH4 mixing ratio of 7?10?4. The densities of the following constituents are calculated: CH4, CH, 1CH2, CH3, C2H2, C2H3, C2H4, C2H5, C2H6, H. The C2H6 mixing ratio is ?10?5 and the C2H2 concentration ?109 cm?3 throughout the upper stratosphere and lower mesosphere. The concentration of C2H2 near the mesopause is sufficiently large to make it the most important radiator of infrared energy. C2H2 is also an efficient catalyst in the recombination of H atoms. In the region of photolysis approximately 20% of the dissociated CH4 molecules are irreversibly converted to heavier hydrocarbons. Density profiles of atomic hydrogen which are needed to interpret Lyman-α albedo measurements of Jupiter are calculated with H2 dissociation and ionization and CH4 dissociation as sources of H.