Iron cation catalyzed reduction of N2O by CO: gas-phase temperature dependent kinetics

Abstract

The ion–molecule reactions Fe⁺ + N₂O → FeO⁺ + N₂ and FeO⁺ + CO → Fe⁺ + CO₂, which catalyze the reaction CO + N₂O → CO₂ + N₂, have been studied over the temperature range 120–700 K using a variable temperature selected ion flow tube apparatus. Values of the rate constants for the former two reactions were experimentally derived as k₂ (10⁻¹¹ cm³ s⁻¹) = 2.0(±0.3) (T/300)^{−1.5(±0.2)} + 6.3(±0.9) exp(−515(±77)/T) and k₃ (10⁻¹⁰ cm³ s⁻¹) = 3.1(±0.1) (T/300)^{−0.9(±0.1)}. Characterizing the energy parameters of the reactions by density functional theory at the B3LYP/TZVP level, the rate constants are modeled, accounting for the intermediate formation of complexes. The reactions are characterized by nonstatistical intrinsic dynamics and rotation-dependent competition between forward and backward fluxes. For Fe⁺ + N₂O, sextet–quartet switching of the potential energy surfaces is quantified. The rate constant for the clustering reaction FeO⁺ + N₂O + He → FeO(N₂O)⁺ + He was also measured, being k₄ (10⁻²⁷ cm⁶ s⁻¹) = 1.1(±0.1) (T/300)^{−2.5(±0.1)} in the low pressure limit, and analyzed in terms of unimolecular rate theory.