Phosphine photochemistry in Saturn’s atmosphere

Abstract

The phosphine photochemistry on Saturn is studied with a 1D photochemical model. The PH3 concentration is rapidly depleted with height (scale height 3.5 km) in the upper troposphere. Formation of P, a probable precursor of P4, (a potential red chromophore in the atmosphere), is highly improbable unless the rate constant for the recombination reaction PH + H2 + M → PH3 + M is less than 10−41 cm6 molec−2 sec−1. Coupling of PH3 and hydrocarbon photochemistry, specifically the C2H2 catalyzed photodissociation of CH4, is important. Column production rates of the organophosphorus compounds CH3PH2 and HCP of ∼3 × 108 cm−2 sec−1 are predicted, with potentially observable column densities of >1 × 1017 cm−2.