A kinetic study of the reactions FeO+ + O, Fe +·N2 + O, Fe+·O2 + O and FeO+ + CO: Implications for sporadic E layers in the upper atmosphere

These gas-phase reactions were studied by pulsed laser ablation of an iron target to produce Fe+ in a fast flow tube, with detection of the ions by quadrupole mass spectrometry. Fe+·N2 and Fe+·O2 were produced by injecting N2 and O2, respectively, into the flow tube. FeO+ was produced from Fe+ by addition of N2O, or by ligand-switching from Fe+·N2 following the addition of atomic O. The following rate coefficients were measured: k(FeO+ + O → Fe+ + O2, 186–294 K) = (3.2 ± 1.5) × 10−11; k(Fe+·N2 + O → FeO++ N2, 294 K) = (4.6 ± 2.5) × 10−10; k(Fe+·O2 + O → FeO+ + O2, 294 K) = (6.3 ± 2.7) × 10−11; and k(FeO+ + CO → Fe+ + CO2, 294 K) = (1.59 ± 0.34) × 10−10 cm3 molecule−1 s−1, where the quoted uncertainties are a combination of the 1σ standard errors in the kinetic data and the systematic experimental errors. The surprisingly slow reaction between FeO+ and O is examined using ab initio quantum calculations of the relevant potential energy surfaces. The importance of this reaction for controlling the lifetime of sporadic E layers is then demonstrated using a model of the upper mesosphere and lower thermosphere