Mechanism of phosphine photolysis. Application to Jovian atmospheric photochemistry

PH3 is photolyzed to H2 and P2H4 and the P2H4 in turn is converted to red phosphorus. The initial quantum yield of H2 formation was redetermined and found to be 0.93 +/- 0.07. Red phosphorus was identified by its chemical properties and the absence of P-H stretching bands in its infrared spectrum. The reaction pathway was not changed by lowering the PH3 partial pressure from 90 to 11 torr or by performing the photolysis in a 70-fold excess of H2. The initial quantum yields at 11 torr of PH3 are phi P2H4 = 0.04 +/- 0.02 and phi H2 = 0.74 +/- 0.08. The initial rate of P2H4 formation was not affected by lowering the PH3 temperature to 227 or 157 K. The yield was greater at 157 K because the P2H4 condensed and was protected from further destruction. The initial quantum yields for the formation of P2H4 and H2 in PH3-NH3 mixtures were comparable to those observed for PH3 alone. Photolysis of mixtures in which NH3 was absorbing 90% of the light resulted in the rapid formation of P2H4. No N2 was formed when PH3-NH3 mixtures were photolyzed, suggesting that the destruction of NH3 is quenched by PH3. The application of these findings to Jovian atmospheric chemistry is discussed.