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Abstract:
The reactions of FeO+ with H-2 and of Fe+ with N2O were studied with respect to the production and reactivity of electronically excited Fe-4(+) cations. The reaction of electronic ground state (FeO+)-Fe-6 with H-2 was found to predominantly produce electronically excited Fe-4(+) as opposed to electronic ground state Fe-6(+) corresponding to a spin-allowed reaction. Fe-4(+) was observed to react with N2O with a rate constant of 2.3 (+0.3/-0.8) x 10(-11) cm(3) molecule(-1) s(-1), smaller than the ground state Fe-6(+) rate constant of 3.2 (+/- 0.5) x 10(-11) cm(3) molecule(-1) s(-1) (at room temperature). While the overall reaction of (FeO+)-Fe-6 with H-2 within the Two-State-Reactivity concept is governed by efficient sextet-quartet spin-inversion in the initial reaction complex, the observation of predominant Fe-4(+) production in the reaction is attributed to a much less efficient quartet-sextet back-inversion in the final reaction complex. Average spin-inversion probabilities are estimated by statistical modeling of spin-inversion processes and related to the properties of spin-orbit coupling along the reaction coordinate. The reaction of FeO+ with H-2 served as a source for Fe-4(+), subsequently reacting with N2O. The measured rate constant has allowed for a more detailed understanding of the ground state Fe-6(+) reaction with N2O, leading to a significantly improved statistical modeling of the previously measured temperature dependence of the reaction. In particular, evidence for the participation of electronically excited states of the reaction complex was found. Deexcitation of Fe-4(+) by He was found to be slow, with a rate constant <3 x 10(-14) cm(3) molecule(-1) s(-1).
