Quantum yields of OH, HO2 and NO3 in the UV photolysis of HO2NO2.

Quantum yields, phi, of OH and HO2 in the ultraviolet photolysis of HO2NO2 (peroxynitric acid, PNA) at 193 and 248 nm and that of NO3 at 193, 248 and 308 nm are reported. Quantum yields were measured using pulsed excimer laser photolysis combined with pulsed laser induced fluorescence (PLIF) detection of OH radicals and cavity ring-down (CRD) detection of NO3 radicals. HO2 radicals were quantified by converting them to OH via the HO2 + NO --> OH + NO2 reaction and detecting OH. The quantum yields obtained at 296 K are: phi193 nm(OH) = 0.21 +/- 0.12, phi248 nm(OH) = 0.085 +/- 0.08, phi193 nm(HO2) = 0.56 +/- 0.09, phi248 nm(HO2) = 0.89 +/- 0.26, phi193 nm(NO3) = 0.35 +/- 0.09, phi248 nm(NO3) = 0.08 +/- 0.04 and phi308 nm(NO3) = 0.05 +/- 0.02. The quoted uncertainties are 2sigma (95% confidence level) and include estimated systematic errors. Our results are compared with the previous quantum yield measurements of OH (MacLeod et al., J. Geophys. Res., 1988, 93, 3813) and NO2 (Roehl et al., 2001, J. Phys. Chem., 105, 1592) at 248 nm and the discrepancies are discussed. The rate coefficients at 298 K for reactions of OH with HO2NO2, H2O2, HNO3 and NO are also reported.