Photodissociation of ClONO2: 1. Atomic Resonance Fluorescence Measurements of Product Quantum Yields

Abstract

The quantum yields for the production of Cl, O, and ClO in the photolysis of ClONO2, measured by detecting Cl and O atoms by atomic resonance fluorescence, are reported. The resonance fluorescence signals were calibrated by generating known concentrations of Cl and O atoms from the photolysis of Cl2, HCl, O3, or N2O. The quantum yields for Cl in the 193.2, 222.0, 248.25, and 308.15 nm photolysis of ClONO2 were 0.53 ± 0.10, 0.46 ± 0.10, 0.41 ± 0.13, and 0.64 ± 0.20, respectively. The yields for O atoms at these wavelengths were, respectively, 0.37 ± 0.08, 0.17 ± 0.05, <0.10, and <0.05. The quoted uncertainties are 2σ precision of the measurements. ClO radical was converted to Cl via addition of NO and its signal compared to the Cl atom signal produced by photolysis of ClONO2. The obtained quantum yields for ClO were 0.29 ± 0.20, 0.64 ± 0.20, 0.39 ± 0.19, and 0.37 ± 0.19, at 193.2, 222.0, 248.25, and 308.15 nm, respectively. It appears that Cl + NO3 and ClO + NO2 are the major products in the photodissociation of ClONO2, except at 193 nm. The measured quantum yields were found to be independent of pressure (40−100 Torr) and bath gas (He and N2). Our results are compared with those from previous measurements.