Effect of the disproportionation reaction of ferrous iron in impact-evaporation processes

Evidence for the disproportionation of iron was found in model experiments imitating impact melting, evaporation, and condensation. The experiments were carried out using a laser system at a characteristic temperature of ～3000–4000 K and a pulse duration of ～10^?3 s in a He atmosphere (P = 1 atm). Augite and mixtures of peridotite with MnO₂ and WO₃ were used as starting target materials. Experimental products (condensed vapor phase) were analyzed by X-ray photoelectron spectroscopy. The results of condensate analysis provided compelling evidence for the presence of iron in three oxidation states (Fe⁰, Fe²⁺, and Fe³⁺). In an experiment with augite, the proportions of iron species of different valences were similar to the stoichiometry of the disproportionation reaction. Similar evidence for this reaction was first found in a condensate from the samples of the fine fraction of the Luna 16 regolith. In the layers of the lunar condensate, the proportions of the valence states of iron were on average Fe⁰:Fe²⁺:Fe³⁺ = 1.2: 1.9: 0.7.