FORMATION OF GAS-PHASE BROMINE COMPOUNDS BY REACTION OF SOLID NABR WITH GASEOUS CLONO2, CL2, AND BRCL AT 298-K

The reactions at 298 K of solid NaBr with ClONO2(g), Cl2(g), and BrCl(g) at concentrations of (0.9-19.4) x 10(13) molecules cm-3 as mixtures in He flowing over the salt were investigated. The gaseous products, analyzed by mass spectrometry, were as follows: for the ClONO2 reaction, Br2 initially and subsequently BrCl and Cl2; for the Cl2 reaction, Br2 followed by BrCl; and for the BrCl reaction, Br2. Ion chromatographic analysis did not show significant replacement of bromide by chloride or nitrate in the bulk solid NaBr. Nitrate formation, however, was verified by FTIR in the ClONO2-NaBr reaction. Surface analyses of the reacted NaBr salts were carried out using X-ray photoelectron spectroscopy. Detectable amounts of surface products (> 50% monolayer coverage for chloride) could be seen only when NaBr was exposed to high concentrations of Cl2 for days in a static system. Mechanisms of formation of the gaseous products in these reactions are hypothesized. The potential role of the ClONO2-NaBr reaction in converting both the bromide ion in NaBr and the chlorine atom in ClONO2 into highly photochemically labile gaseous compounds in the troposphere and stratosphere is discussed.