Free iron clusters react readily with O₂ and H₂S but are inert toward methane

New experiments at the interface of a dense flow reactor and molecular beam show that free Fe clusters are extraordinarily reactive toward O₂ and H₂S but unreactive toward methane. These results are believed to represent the true low-temperature reactivities of free Fe clusters, with molecular addition of O₂ (e.g., Fe_xO₂ for 2 ≤ x ≤ 15) and formation of dehydrogenated sulfides (Fe_xS) observed as primary chemical processes. Significantly, no reaction of any of these small molecules with the Fe atom has been detected, and after large increases for smallest clusters the apparent reactivity toward H₂S or O₂ levels off for clusters x > 6.