Pressure and Temperature Dependence of the Reaction NO2 + NO3 + M -> N2O5 + M

Article abstract of DOI:10.1021/j150663a037

The kinetics of the reaction NO2 + NO3 + M -> N2O5 + M (1) were studied with flash photolysis/visible absorption by monitoring the disappearance of NO3 under pseudo-first-order conditions over the temperature range 236-358 K and pressure range 20-700 torr of helium and nitrogen.Reaction 1 was found to be in the falloff region between second- and third-order kinetics in this range.Falloff parameters were obtained by fitting the experimental data to the falloff equation of Troe and co-workers.When one uses a published temperature-dependent broadening factor (F_c), the data are described by k₀(N2) = 4.5 x 1E-30 cm⁶ molecule^-2 s^-1 and k_infinite = 1.65 x 1E-12 cm³ molecule^-1 s^-1 at 298 K with T dependencies of T^-3.4 and T^-0.4 for k₀ and k_infinite, respectively.This expression was used in conjunction with recent measurements of the rate constant for N2O5 thermal decomposition to obtain an improved measurement ΔH_f⁰(298) for NO3, which was determined to be 17.3 +/- 0.7 kcal mol^-1.From these data the recommended equilibrium constant expression is K_eq = k₁/k_-1 = 2.31 x 1E-8 exp(11350/T) (atm^-1).