NO2 Quantum Yield from the 248 nm Photodissociation of Peroxynitric Acid (H02N02)

Peroxynitric acid (PNA) was photolyzed at 248 nm, and the NO_2 photoproduct was detected by laser-induced fluorescence (LIF). The quantum yield for the production of NO_2 was determined by comparison with HNO_3 photolysis data taken under identical experimental conditions. Measurements made over a range of pressures, flows, and precursor concentrations resulted in an NO_2 quantum 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−π* transition on the NO_2 moiety, the dissociative channels forming OH + NO_3 and HO_2 + NO_2 likely occur via predissocation on different surfaces. Excitation energies at the MRCI and CCSD(T) level of theory show that excited states of PNA are not accessible at wavelengths longer than 407 nm (∼3.0 eV).