Rate constants of the reaction Fe + O₂ + M ↔ FeO₂ + M in the low- and high-pressure limits

Abstract

The thermochemical and kinetic characteristics of the reaction Fe + O₂ + M ↔ FeO₂ + M are obtained based on an analysis within the framework of an RRKM model with account of the excited electronic states of the three isomeric forms of the FeO₂ molecule. A new method for determining the dissociation energy and the entry energy barrier for the recombination reaction is proposed. The enthalpy of formation and Gibbs energy function of the FeO₂ molecule are determined: Δ _f H°(FeO₂, 0) = 77 ± 10 kJ mol⁻¹; Φ°(FeO₂, T), J mol⁻¹ K⁻¹ = 421.4552 + 59.9779lnx − 0.0073327x ⁻² + 0.9598x ⁻¹ (x = 10⁻⁴ T; 250 < T < 3000 K). The best description of the available experimental data on the rate constants of reactions (I) and (−I) in the low-pressure limit in the framework of the proposed model is achieved with k _1,0(250 < T < 3000 K) = 2.8 · 10¹⁸(T/1000)^−2.6exp (−3002/T) cm⁶ mol⁻² s⁻¹ and k _−1,0(1000 < T < 3000 K) = 3.5 · 10¹⁹(T/1000)^−4.0 × exp(−44371/T) cm³ mol⁻¹ s⁻¹. The corresponding high-pressure rate constants are k _1,∞(250 < T < 3000 K) = 1.2 · 10¹⁴exp(−2646/T) cm³ mol⁻¹ s⁻¹ and k _-1,∞ (1000 < T < 3000 K) = 1.0 · 10¹⁵(T/1000)^−1.2exp (−43657/T) s⁻¹. It is shown that the available experimental data on the rate constants of reactions (I) and (−I) can be satisfactorily described only with consideration given to the electronically excited states of the FeO₂ molecule.