Photodissociation of ClONO₂: 2. Time-resolved absorption studies of product quantum yields

The quantum yield for NO₃ production in the UV photolysis of ClONO₂ was measured via transient 661.9 nm absorption of NO₃ following pulsed laser 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 ClONO₂ to produce NO₃ through the reaction Cl + ClONO₂ → Cl₂ + NO₃ and was found to be 0.73 ± 0.14 at 308.15 nm, 0.60 ± 0.12 at 248.25 nm, 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% confidence level and include estimated systematic errors. The results from this study are compared with those from previous studies. On the basis 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 major products in the photolysis of ClONO₂ at wavelengths important in the stratosphere and that the total quantum yield for dissociation is close to 1. The implications of these findings to stratospheric chemistry are discussed.