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Project Progress

Molecular Beam Studies of Nitrogen Reactions on Iron-Sulfur Surfaces

(Minton & Schoonen)

The goal of this component of the ABRC is to understand the mechanisms by which molecular nitrogen reacts on iron-sulfur surfaces to produce ammonia or precursors to ammonia. The progress to date has included the setup of a molecular beam-surface scattering experiment and the collection of preliminary data. A deuterium atom plasma source was used to hydrogenate a pyrite surface with D atoms. The hydrogenated surface was bombarded with a molecular beam of energetic N₂ molecules. Reaction products that exited the surface were detected with a mass spectrometer. We have detected D₂S released from the surface, held at 100 °C, during bombardment by D atoms. The D₂S molecules have a velocity distribution corresponding to the surface temperature. An earlier observation in Dan Strongin’s group suggested that when pyrite is bombarded by H atoms the H₂S product does not emerge from the surface until the surface temperature is raised above 200 °C. Our observation of D₂S from a surface at 100 °C is new and suggests that H (or D) atoms can create defect sites on the surface more easily than previously thought. We have verified the increase in surface roughness from the D-atom-bombarded surface by monitoring the change in the inelastic scattering dynamics of N₂ molecules. Thus far, no ammonia (ND₃) product has been unambiguously detected when we directed an N₂ beam with 30 kcal/mol of translational energy at the D-bombarded pyrite surface. However, we have many experimental parameters to adjust before we can draw conclusions about the reactivity of incident N₂ molecules with a hydrogenated and defected pyrite surface. Additional work to this end is ongoing.