Thermal decomposition of HO2NO2 (peroxynitric acid, PNA):: Rate coefficient and determination of the enthalpy of formation

Rate coefficients for the gas-phase thermal decomposition of HO2NO2 (peroxynitric acid, PNA) are reported at temperatures between 331 and 350 K at total pressures of 25 and 50 Torr of N-2. Rate coefficients were determined by measuring the steady-state OH concentration in a mixture of known concentrations of HO2NO2 and NO. The measured thermal decomposition rate coefficients k(-1)(T,P) are used in combination with previously published rate coefficient data for the HO2NO2 formation reaction to yield a standard enthalpy for reaction 1 of DeltarHdegrees(298) K = -24.0 +/- 0.5 kcal mol(-1) (uncertainties are 2sigma values and include estimated systematic errors). A HO2NO2 standard heat of formation, Delta(f)Hdegrees(298) K(HO2NO2), of -12.6 +/- 1.0 kcal mol(-1) was calculated from this value. Some of the previously reported data on the thermal decomposition of HO2NO2, have been reanalyzed and shown to be in good agreement with our reported value.