Rate coefficients for the thermal decomposition of BrONO₂ and the heat of formation of BrONO₂

Rate coefficients (k_-7) for the thermal decomposition of bromine nitrate, BrONO₂ + M → BrO + NO₂ + 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 ΔH_f^o(298 K) data for BrONO₂ (10.1 ± 2.0 kcal/mol), BrO (30.4 ± 2.0 kcal/mol), HOBr (-14.1 ± 2.0 kcal/mol), and Br₂O (27.3 ± 2.0 kcal/mol). Additional measurements were made to determine the rate coefficient for Br atom reaction with BrONO₂ (k₁₁) relative to the rate coefficient for its reaction with CH₃CHO (k₁₂) at 298 K: k₁₁/k₁₂ = 12.5 ± 0.6. This relative rate measurement yields a rate coefficient of (4.9 ± 1.5) × 10^-11 cm³ molecule^-1 s^-1 for k₁₁, using the currently recommended value for k₁₂. Approximate rate constants for reaction of NO (reaction 17) and BrNO (reaction 19) with BrONO₂ were also obtained: k₁₇ = 3 × 10^-19 cm³ molecule^-1 s^-1, k₁₉ > 1 × 10^-16 cm³ molecule^-1 s^-1.