Bromine Nitrate Photochemistry: Quantum Yields for O, Br, and BrO Over the Wavelength Range 248−355 nm

Abstract

A laser flash photolysis−resonance fluorescence technique has been employed to investigate the production of Br, O, and BrO from photodissociation of bromine nitrate (BrONO2) at wavelengths in the range 248−355 nm. The values obtained for the Br atom quantum yields are 0.35 ± 0.08, 0.65 ± 0.14, >0.62 ± 0.11, and 0.77 ± 0.19 at 248, 266, 308 and 355 nm, respectively. The values obtained for the O atom quantum yields are 0.66 ± 0.15, 0.18 ± 0.04, <0.13 ± 0.03, and <0.02 at 248, 266, 308, and 355 nm, respectively. Quantum yields for BrO production were investigated at some of the above wavelengths by converting photolytically generated BrO to Br via the reaction BrO + NO → Br + NO2. Measured BrO quantum yields are 0.37 ± 0.12 at 266 nm and 0.23 ± 0.08 at 355 nm. Uncertainties in the above quantum yields are estimates of absolute accuracy at the 95% confidence limit. No evidence for pressure-dependent quantum yields was observed over the range 20−200 Torr in N2 bath gas. No evidence for temperature-dependent quantum yields was observed either, although only a few experiments were done at temperatures other than room temperature. The above results are considered in conjunction with recently reported NO3 quantum yields [Harwood; et al. J. Phys. Chem. A 1998, 102, 1309] in order to examine the role of BrONO2 photochemistry in the catalytic destruction of stratospheric ozone.