Identification of BrONO as the Major Product in the Gas-Phase Reaction of Br with NO₂

Products of the gas-phase reaction of Br atoms with NO₂ have been quantitatively determined at temperatures between 215 and 300 K in an environmental chamber interfaced to an FT-IR spectrometer. The major product of the reaction (yield > 75%) was found to be the cis isomer of BrONO, which was identified and quantified by means of its N=O stretching fundamental at 1660 cm^-1; this represents the first gas-phase detection of this species. Although rapid thermal decomposition back to Br and NO₂ precludes its detection at room temperature (lifetime < 1 s), BrONO was detected at temperatures at and below 263 K. Isomerization of the BrONO to BrNO₂ was found to be an important fate of BrONO at low temperatures. The rate coefficient for this process was found to increase with decreasing pressure, indicative of a heterogeneous process. At 700 Torr, this isomerization rate was (0.013 ± 0.003) s^-1, independent of temperature over the range 218-243 K. Evidence was also obtained for rapid reactions between Br atoms and both BrONO and BrNO₂ (10^-10 > k > 10^-11 cm³ molecule^-1 s^-1).