A study of the reactions of Fe⁺ with O₃, O₂ and N₂

Abstract

The reactions between Fe⁺(a⁶D) and O₃, O₂ and N₂ have been studied by the pulsed four-photon dissociation at 248 nm of ferrocene vapour in He bath gas, followed by time-resolved laser-induced fluorescence spectroscopy at 260.0 nm [Fe⁺(z⁶D_9/2^o–a⁶D_9/2)]. This yielded: k(Fe⁺+O₃→FeO⁺+O₂, 200–383 K)=(7.07±2.30)×10^-10 exp[-(1.08±0.12) kJ mol^-1/RT] cm³ molecule^-1 s^-1; k(Fe⁺+O₂+He→FeO₂⁺+He, 194–479 K)=(4.17±0.23)×10^-30 (T/300 K)^-1.86±0.15 cm⁶ molecule^-2 s^-1; and k(Fe⁺+N₂+He→FeN₂⁺+He, 196–482 K)=(1.96±0.05)×10^-30 (T/300 K)^-1.52±0.08 cm⁶ molecule^-2 s^-1, where the quoted uncertainties are a combination of the 1σ standard errors in the kinetic data and the systematic experimental errors. k(Fe⁺+O₃) is shown to be a factor of 2–3 slower than predicted by ion–polar molecule capture theory, with a small positive, rather than slightly negative, temperature dependence. The results for the recombination reactions are interpreted by combining abinitio quantum calculations on FeN₂⁺ and FeO₂⁺ with a semi-empirical formalism for ion–molecule association. Finally, the role of the reactions in the conversion of Fe⁺ to atomic Fe in the upper atmosphere is considered.

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