Laboratory measurements and methane photochemistry modeling

Methane is photolyzed by the solar UV in the stratosphere of Saturn. Subsequent photochemistry leads to the production of acetylene (C2H2) and diacetylene (C4H2). These species are produced where it is relatively warm (T is greater than or equal to 140 K), but the tropopause temperature of Saturn (approximately 80 K) is low enough that these two species may freeze out to their respective ices. Numerical models which include both photochemistry and condensation loss make predictions about the mixing ratios of these species and haze production rates. These models are dependent upon knowing reaction pathways and their associated kinetic reaction rate constants and vapor pressures. How uncertainties in the chemistry and improvements in the vapor pressures affect model predictions for Saturn are discussed.