Abstract
SO 2 was photolyzed at 25 °C and 313.0 nm in the presence of allene and oxygen. The quantum yields of the gas phase products CO and C 2H 4 were determined over a wide range of allene and oxygen pressures as well as in the presence and absence of 600 Torr of CO 2. The quantum yield Φ {CO} of CO increased at constant [allene]/[SO 2] ratios with the addition of O 2 up to pressures of 1 – 30 Torr depending upon the [allene]/[SO 2] ratio. With further increases in O 2 pressure, Φ {CO} was quenched. The quantum yield Φ {C 2H 4} of C 2H 4 exhibited similar behavior. The addition of 600 Torr of CO 2 appeared to have little effect upon either the enhancement or quenching of Φ {CO}. The addition of increasing amounts of CO 2 to a constant [allene]/[SO 2]/[O 2] ratio decreased Φ {C 2H 4} to a limiting value of approximately 4 × 10 −3 at 600 Torr of CO 2. Both the singlet and triplet emitting states as well as two non-emitting states of SO 2 previously proposed to be important in the photochemistry of SO 2 are necessary to interpret the results of this study. A relatively complete mechanism is proposed, all the pertinent rate coefficients are tabulated, and from these values Φ {CO} and Φ {C 2H 4} values are computed and compared with the observed values. The proposed mechanism is found to underestimate total Φ {C 2H 4} at low allene and high O 2 pressures. There must be an additional source of C 2H 4 which is not included in the mechanism.
Published Version
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