Reaction of size-selected iron-oxide cluster cations with methane: a model study of rapid methane loss in Mars’ atmosphere

Abstract

We report gas-phase reactions of free iron-oxide clusters, Fe_nO_m⁺, and their Ar adducts with methane in the context of chemical processes in Mars’ atmosphere. Methane activation was observed to produce Fe_nO_mCH₂⁺/Fe_nO_mCD₂⁺ and Fe_nO_mC⁺, where the reactivity exhibited size and composition dependence. For example, the rate coefficients of methane activation for Fe₃O⁺ and Fe₄O⁺ were estimated to be 1 × 10⁻¹³ and 3 × 10⁻¹³ cm³ s⁻¹, respectively. Based on these reaction rate coefficients, the presence of iron-oxide clusters/particles with a density as low as 10⁷ cm⁻³ in Mars’ atmosphere would explain the rapid loss of methane observed recently by the Curiosity rover.