Rate Coefficients for the Thermal Decomposition of BrONO₂and the Heat of Formation of BrONO₂

Rate coefficients ( k - 7 ) for the thermal decomposition of bromine nitrate, BrONO 2 + M → BrO + NO 2 + M, have been obtained at temperatures between 320 and 340 K and pressures between 100 and 1000 Torr. These data are combined with recommended values for the reverse reaction to obtain an equilibrium constant for the reaction pair, K P,7 = 5.44 × 10 -9 exp(14192/T) atm -1, and a heat of reaction for the thermal dissociation of 28.2 ± 1.5 kcal/mol at 298 K. This reaction enthalpy is used in conjunction with literature data to arrive at a consistent set of Δ H f °(298 K) data for BrONO 2 (10.1 ± 2.0 kcal/mol), BrO (30.4 ± 2.0 kcal/mol), HOBr (−14.1 ± 2.0 kcal/mol), and Br 2 O (27.3 ± 2.0 kcal/mol). Additional measurements were made to determine the rate coefficient for Br atom reaction with BrONO 2 ( k 11 ) relative to the rate coefficient for its reaction with CH 3 CHO ( k 12 ) at 298 K: k 11 / k 12 = 12.5 ± 0.6. This relative rate measurement yields a rate coefficient of (4.9 ± 1.5) × 10 -11 cm 3 molecule -1 s -1 for k 11, using the currently recommended value for k 12 . Approximate rate constants for reaction of NO (reaction 17) and BrNO (reaction 19) with BrONO 2 were also obtained: k 17 = 3 × 10 -19 cm 3 molecule -1 s -1, k 19 > 1 × 10 -16 cm 3 molecule -1 s -1 .