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The uptake of peroxynitric acid (PNA), HO2NO2 or HNO4, on solid H2O ice at 193 K (-80 C) was studied using a fast flow-mass spectrometric technique. An uptake coefficient of 0.15 +/- 0.10 was measured, where the quoted uncertainty denotes 2 standard deviations. The uptake process did not result in the production of gas phase products. The composition of the condensed phase was investigated using programmed heating (3 K/min) of the substrate coupled with mass spectrometric detection of desorbed species. Significant quantities of HNO, and HNO3 desorbed from the substrates at temperatures above 225 K and 246 K, respectively. The desorbed HNO3, which was less than 9% of the desorbed HNO, and remained unchanged upon incubation of the substrate, was likely due to impurities in the HNO4 samples rather than reaction of HNO, on the substrate. The onset temperatures for HNO4 desorption increased with increasing H2O to HNO4 ratios, indicating that HNO4, like HNO3, tends to be hydrated in the presence of water. These observations suggest possible mechanisms for removal of HNO4 or repartitioning of total odd nitrogen species in the Earth's upper troposphere and stratosphere.

The photolysis of chlorine nitrate was studied using broadband flash photolysis coupled with long-path ultraviolet-visible absorption spectroscopy. Branching ratios for the Cl + NO3 and ClO + NO2 product channels were determined from time-dependent measurements of ClO and NO3 concentrations. Yields of the ClO and NO3 products displayed a dependence on the bath gas density and the spectral distribution of the photolysis pulse. Product yields decreased with increasing bath gas density regardless of the spectral distribution of the photolysis pulse; however, the decrease in product yield was much more pronounced when photolysis was limited to longer wavelengths. For photolysis in a quartz cell (lambda > 200 nm) the yield decreased by a factor of 2 over the pressure 10-100 Torr. In a Pyrex cell (lambda > 300 nm), the yield decreased by a factor of 50 over the same pressure range. When photolysis was limited to lambda > 350 nm, the yield decreased by a factor of 250. Branching ratios for the photolysis channels [ClONO2 + h.nu yields ClO + NO2 (1a) and ClONO2 + h.nu yields Cl + NO3 (lb)] were determined from the relative ClO and NO3 product yields at various pressures. Although the absolute product yield displayed a pressure dependence, the branching between the two channels was independent of pressure. The relative branching ratios (assuming negligible contributions from other channels) are 0.61 +/- 0.20 for channel 1a and 0.39 +/- 0.20 for channel lb for photolysis with lambda > 200 nm and 0.44 +/- 0.08 for channel 1a and 0.56 +/- 0.08 for channel 1b for photolysis with lambda > 300 nm. The implications of these results for the chemistry of the lower stratosphere are discussed.

The products of the reaction of OClO with NO3 were investigated between 220 and 298 K using a flow reactor and infrared, visible, and ultraviolet analysis. At temperatures below 250 K new infrared and ultraviolet absorption features were observed and assigned to the novel compound chloryl nitrate (O2ClONO2). Additionally, ClO and NO2 were observed as reaction products, indicating the existence of a second reaction channel. O2ClONO2 formation predominates at temperatures below 230 K. The reaction rate constant at 220 K is estimated to be on the order of 10 exp -14 cu cm/molecule s in 1-5 Torr of helium. These observations suggest that O2ClONO2 may exist in the terrestrial stratosphere.

The reaction between BrO and ClO was studied over the pressure range 50-700 torr and temperature range 220-400 K, using the flash photolysis-ultraviolet absorption method described by Watson et al. (1979). In order to investigate the mechanism of the BrO + ClO reaction, the product branch reactions Br + Cl2O yielding ClO + BrCl and Cl2O + h(nu) yielding products were examined. The rate constant for the overall reaction and the Arrhenius expression for the Br + Cl2O reaction are given, as well as the quantum yield for the production of atomic oxygen from the Cl2O photolysis.

The kinetics and product branching ratios of the reaction between ClO and BrO were studied at 1 torr pressure over the temperature range 220-400 K, using the method of discharge-flow mass spectrometry. Three product channels were identified and quantified: Br + ClOO, Br + OClO, and BrCl + O2, indicating that the reaction mechanism of ClO + BrO involves metastable intermediates. The overall reaction rate coefficient and the rate coefficients for the three channel reactions are given.

High-resolution (0.005/cm) FTIR spectra of the X2Pi(i)-X2Pi(i) (1-0) rovibrational bands of (C-35)(O-16) and (Cl-37)(O-16) were obtained in 1 torr of helium carrier gas. After measuring the strengths of approximately 830 individual IR lines from several spectra, a total band strength of 13.1 + or - 1.1/sq cm atm and a first Herman-Wallis coefficient of (4.12 + or - 0.62) x 10 to the -3rd were determined.

The absorption spectrum of the gas-phase NO3 radical has been studied between 220 and 700 nm by using both flash photolysis and discharge flow reactors for the production of NO3. In the flash photolysis method, cross sections at the peak of the (0,0) band at 661.9 nm were measured relative to the cross section of ClONO2 at several different wavelengths. From the best current measurements of the ClONO2 spectrum, the NO3 cross section at 661.9 nm was determined to be (2.28 + or 0.34) x 10 to the -17th sq cm/molecule at 298 K. Measurements at 230 K indicated that the cross section increases by a factor of 1.18 at the peak of the (0,0) band. The discharge flow method was used both to obtain absolute cross sections at 661.9 nm and to obtain relative absorption spectra between 300 and 700 nm at 298 and 230 K. A value of (1.83 + or - 0.27) x 10 to the -17th sq cm/molecule was obtained for sigma NO3 at 661.9 nm at 298 K. Upper limits to the NO3 cross sections were also measured between 220 and 260 nm with the discharge flow method.

Peroxyacetyl nitrate (PAN) vapor was photolyzed at 248 nm, and the NO2 photoproduct was detected by laser-induced fluorescence. The quantum yield for the production of NO2 from PAN photolysis was determined by comparison to HNO3 photolysis data taken under identical experimental conditions. The average of data collected over a range of total pressures, precursor concentrations, and buffer gases was 0.83 +/- 0.09 for the NO2 quantum yield, where the statistical uncertainty is 2 standard deviations.