The reactions of FeO with O3, H2, H2O, O2 and CO2

Abstract

The FeO(X 5Δ) radical plays a central role in the atmospheric chemistry of meteor-ablated iron and in the iron-catalysed inhibition of flames. This paper reports a kinetic study of a series of FeO reactions, using the pulsed two-photon dissociation at 248 or 193 nm of ferrocene vapour in the presence of NO2 or O3, respectively, followed by time-resolved laser-induced fluorescence spectroscopy of FeO at 582.0 nm [FeO(D′ 5Δ4–X 5Δ4)]. For the recombination reactions of FeO with O2, CO2 and H2O, ab initio quantum calculations on FeO3, FeCO3 and Fe(OH)2 were coupled with RRKM theory to show that the first two reactions were close to their low pressure limits under the experimental conditions, yielding k(FeO+O2+N2, 196–519 K)=(3.86±0.07)×10−30 (T/300 K)+0.50±0.06 and k(FeO+CO2+N2, 233–475 K)=(3.09±0.22)×10−31 (T/300 K)−1.19±0.24 cm6 molecule−2 s−1, at the 95% confidence level. By contrast, the much faster FeO+H2O (+N2) reaction was found to be in the fall-off region over the experimental pressure range; an RRKM fit to the results yields: log10(krec,0)=−31.05+4.438log10T−1.218log102T, krec,∞=5.35×10−10 exp(−611/T), Fc=0.28, with an uncertainty of 15% over the experimental range of 298–527 K and 3.1–8.3 Torr. The corresponding reactions with He as the third body were slower by factors of 2–4. The reaction between FeO and O3 is fast with a small T-dependence: k(FeO+O3→FeO2+O2 , 194–341 K)=(2.94±0.43)×10−10 exp[(−1.45±0.29) kJ mol−1/RT] cm3 molecule−1 s−1. No reaction was observed between FeO and H2, indicating an upper limit of k(FeO+H2→Fe+H2O, 320 K)⩽7×10−14 cm3 molecule−1 s−1. Finally, the atmospheric implications of these results are discussed.