The reactions of FeO with O-3, H-2, H2O, O-2 and CO2

The FeO(X (5)Delta) radical plays a central role in the atmospheric chemist ry of meteor-ablated iron and in the iron-catalysed inhibition of flames. T his paper reports a kinetic study of a series of FeO reactions, using the p ulsed two-photon dissociation at 248 or 193 nm of ferrocene vapour in the p resence of NO2 or O-3, respectively, followed by time-resolved laser-induce d fluorescence spectroscopy of FeO at 582.0 nm [FeO(D' (5)Delta(4)-X (5)Del ta(4))]. For the recombination reactions of FeO with O-2, CO2 and H2O, ab i nitio quantum calculations on FeO3, FeCO3 and Fe(OH)(2) were coupled with R RKM theory to show that the first two reactions were close to their low pre ssure limits under the experimental conditions, yielding k(FeO + O-2 + N-2, 196-519 K) = (3.86 +/- 0.07) x 10(-30) (T/300 K)(+0.50 +/- 0.06) and k(FeO + CO2 + N-2, 233-475 K) = (3.09 +/- 0.22) x 10(-31) (T/300 K)(-1.19 +/- 0. 24) cm(6) molecule(-2) s(-1), at the 95% confidence level. By contrast, the much faster FeO + H2O (+ N-2) reaction was found to be in the fall-off reg ion over the experimental pressure range; an RRKM fit to the results yields : log(10)(k(rec,0)) = -31.05 + 4.438log(10)T-1.218log(10)(2)T, k(rec, infin ity) = 5.35 x 10(-10) exp(-611/T), F-c = 0.28, with an uncertainty of 15% o ver 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 rea ction between FeO and O-3 is fast with a small T-dependence: k(FeO + O-3 -- > FeO2 + O-2, 194-341 K) = (2.94 +/- 0.43) x 10(-10) exp[(-1.45 +/- 0.29) k J mol(-1)/RT] cm(3) molecule(-1) s(-1). No reaction was observed between Fe O and H-2, indicating an upper limit of k(FeO + H-2 --> Fe + H2O, 320 K) le ss than or equal to 7 x 10(-14) cm(3) molecule(-1) s(-1). Finally, the atmo spheric implications of these results are discussed.