Reaction of OH with HO₂NO₂ (Peroxynitric Acid):  Rate Coefficients between 218 and 335 K and Product Yields at 298 K

Rate coefficients ( k 3 ( T )) for the reaction of OH with HO 2 NO 2 (peroxynitric acid, PNA) in the gas phase were measured in the temperature range of 218−335 K by producing OH via pulsed laser photolysis and detecting it via laser-induced fluorescence. The PNA concentration was measured in situ by UV and IR absorption. The H 2 O 2, HNO 3, and NO 2 impurities present in the PNA sample were quantified by mass spectrometry and/or UV/IR absorption. The measured value of k 3 (298 K) is (3.4 ± 1.0) × 10 -12 cm 3 molecule -1 s -1 . The temperature dependence of k 3 is best described by the relation k 3 ( T ) = (8.8 ± 2.6) × 10 -19 T 2 exp[(1130 ± 20)/ T ] cm 3 molecule -1 s -1 . The quoted errors for k 3 are at the 2σ level and include estimated systematic errors, which contribute the most to this uncertainty. The measured values of k 3 ( T ) were independent of pressure between 10 and 100 Torr of helium. The branching ratios of the reaction OH + HO 2 NO 2 → products, for the production of HO 2 and HNO 3 and of NO 3 and H 2 O 2, respectively, were determined to be <10% and <5%, respectively, at 298 K. Thus, it was deduced that the main pathway for reaction 3 produces H 2 O, O 2, and NO 2 at 298 K. Our measurements reduce the uncertainties but do not significantly alter the currently calculated impacts of HO 2 NO 2 in the upper troposphere and lower stratosphere. In the course of this study, the rate coefficient for the reaction of OH with H 2 O 2 was measured to be k 4 ( T ) = (2.9 ± 1.8) × 10 -12 exp[−(110 ± 150)/ T ] cm 3 molecule -1 s -1 in the temperature range of 273−356 K.