2006ApJ...648.1181V

Thermochemical equilibrium and kinetic calculations are used to model sulfur and phosphorus chemistry in giant planets, brown dwarfs, and extrasolar giant planets (EGPs). The chemical behavior of individual S- and P-bearing gases and condensates is determined as a function of pressure, temperature, and metallicity. The results are independent of particular model atmospheres, and in principle, the equilibrium composition along the pressure-temperature profile of any object can be determined. Hydrogen sulfide (H₂S) is the dominant S-bearing gas throughout substellar atmospheres and approximately represents the atmospheric sulfur inventory. Silicon sulfide (SiS) is a potential tracer of weather in substellar atmospheres. Disequilibrium abundances of phosphine (PH₃) approximately representative of the total atmospheric phosphorus inventory are expected to be mixed upward into the observable atmospheres of giant planets and T dwarfs. In hotter objects, several P-bearing gases (e.g., P₂, PH₃, PH₂, PH, and HCP) become increasingly important at high temperatures.