PHOTODISSOCIATION OF CLONO2 .2. TIME-RESOLVED ABSORPTION STUDIES OF PRODUCT QUANTUM YIELDS

The quantum yield for NO3 production in the UV photolysis of ClONO2 wa s measured via transient 661.9 nm absorption of NO3 following pulsed l aser photolysis and was found to be 0.93 +/- 0.24 at 352.5 nm, 0.67 +/ - 0.09 at 308.15 nm, 0.60 +/- 0.09 at 248.25 nm, and 0.18 +/- 0.04 at 193 nm. The Cl atom quantum yield was measured by reacting Cl with ClO NO2 to produce NO3 through the reaction Cl + ClONO2 --> Cl-2 + NO3 and was found to be 0.73 +/- 0.14 at 308.15 nm, 0.60 +/- 0.12 at 248.25 n m, and 0.45 +/- 0.08 at 193 nm. The estimated O atom yields were <0.4 at 248.25 nm and <0.9 at 193 nm. Quoted error limits are at the 95% co nfidence level and include estimated systematic errors. The results fr om this study are compared with those from previous studies. On the ba sis of this work and that of Goldfarb et al. (Goldfarb, L.; Schmoltner , A.-M.; Gilles, M. K.; Burkholder, J. B.; Ravishankara, A. R. J. Phys . Chem. 1997, 101, 6658.), it is concluded that Cl and NO3 are the maj or products in the photolysis of ClONO2 at wavelengths important in th e stratosphere and that the total quantum yield for dissociation is cl ose to 1. The implications of these findings to stratospheric chemistr y are discussed.