Atmospheric Chemistry in Giant Planets , Brown Dwarfs , and Low - Mass Dwarf Stars II . Sulfur

We use thermochemical equilibrium and kinetic calculations to model sulfur and phosphorus chemistry in the atmospheres of giant planets, brown dwarfs, low-mass stars, and extrasolar giant planets (EGPs). The chemical behavior of individual Sand P-bearing gases and condensates is determined as a function of pressure, temperature, and metallicity. Our results are independent of any particular model atmosphere and the behavior of different gases can be used to constrain atmospheric structure and metallicity. Hydrogen sulfide is the dominant sulfur gas in substellar atmospheres and approximately represents the atmospheric sulfur inventory. Depending on the prevailing S and C chemistry, the abundance of minor sulfur gases may constrain atmospheric temperatures or metallicity. Disequilibrium abundances of PH 3 are expected in the observable atmospheres of substellar objects, and PH 3 is representative of the total P abundance in giant planets and T dwarfs. A number of other phosphorus gases become relatively abundant in substellar atmospheres with increasing effective temperatures.