A kinetic study of the reactions of Fe(a 5D) and Fe+(a 6D) with N2O over the temperature range 294–850 K

Abstract

The reaction between Fe and N₂O has been studied by the pulsed two-photon dissociation at 193 nm of ferrocene vapour to produce Fe atoms in an excess of N₂O and N₂ bath gas, followed by time-resolved laser induced fluorescence (LIF) spectroscopy of atomic Fe at 248.3 nm [Fe(x⁵F⁰₅–a ⁵D₄)]. This yielded k(487 < T/K < 850)=(2.3^+1.8_–1.0)× 10^–10 exp[–(49.4 ± 3.0) kJ mol^–1/RT] cm³ molecule^–1 s^–1, where the quoted uncertainty is 2σ. The large activation energy can be explained by the high ionization potential of atomic Fe and the substantial energy required to promote the valence 4s electron to the virtual 4p orbital, in accord with the theory of Futerko and Fontijn. The reaction between Fe⁺ and N₂O was studied by the pulsed four-photon dissociation at 248 nm of ferrocene vapour, producing Fe⁺ in an excess of N₂O and He bath gas. The Fe⁺ ions were then monitored by time-resolved LIF at 260.0 nm [Fe⁺(z⁶D⁰_9/2–a ⁶D_9/2)], yielding k(294 < T/K < 773)=(5.3^+2.3_–1.6)× 10^–10 exp[–(6.2 ± 1.3) kJ mol^–1/RT] cm³ molecule^–1 s^–1. The form of this Arrhenius expression can be reconciled with the excitation function measured in an ion-beam gas experiment if it is assumed that the reaction is activated by vibrational excitation of N₂O.