NO2 quantum yield from the 248 nm photodissociation of peroxynitric acid (HO2NO2)

Peroxynitric acid (PNA) was photolyzed at 248 nm, and the NO2 photoproduct was detected by laser-induced fluorescence (LIF). The quantum yield for the production of NO2 was determined by comparison with HNO3 photolysis data t aken under identical experimental conditions. Measurements made over a rang e of pressures, flows, and precursor concentrations resulted in an NO2 quan tum yield of 0.56 +/- 0.17, where the statistical uncertainty is 2 standard deviations. Calculations of potential energy curves for several low-lying singlet and triplet states of PNA are presented. The calculations show that while the singlet excitations occur via an n-pi* transition on the NO2 moi ety, the dissociative channels forming OH + NO3 and HO2 + NO2 likely occur via predissocation on different surfaces, Excitation energies at the MRCI a nd CCSD(T) level of theory show that excited states of PNA are not accessib le at wavelengths longer than 407 nm (similar to3.0 eV).