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"If the oxidation on the surface of Mars does not have a biological cause, as the Viking experiments suggest, what DOES cause the oxidation?"
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Molecular Beam Studies of Nitrogen Reactions on Iron-Sulfur Surfaces
Project Investigators: Timothy Minton, Martin Schoonen
Other Project Members
Daniel Strongin (No Role Selected)Summary
It is generally accepted that surface-mediated reactions occur on defect sites. The role of defects in the formation of ammonia is being evaluated using molecular beam-surface scattering experiments in which a deuterium atom plasma source is used to hydrogenate a pyrite surface with D atoms. The hydrogenated surface is subsequently bombarded with a molecular beam of energetic N2 molecules and the conversion of N2 to products such as ammonia is probed through mass spectrometry.
Astrobiology Roadmap Objectives:
- Objective 3.1: Sources of prebiotic materials and catalysts
- Objective 3.2: Origins and evolution of functional biomolecules
- Objective 3.3: Origins of energy transduction
- Objective 7.1: Biosignatures to be sought in Solar System materials
- Objective 7.2: Biosignatures to be sought in nearby planetary systems
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.
- Biomimetic Cluster Synthesis: Bridging the Structure and Reactivity of Biotic and Abiotic Iron-Sulfur Motifs
- Computational Chemical Modeling the Link Between Structure and Reactivity of Iron-Sulfur Motifs
- Molecular Beam Studies of Nitrogen Reactions on Iron-Sulfur Surfaces
- Origin of Life and Catalysis - Philosophical Considerations
- Probing the Structure and Nitrogen Reduction Activity of Iron-Sulfur Minerals
- Structure, Function, and Biosynthesis of the Complex Iron-Sulfur Clusters at the Active Sites of Nitrogenases and Hydrogenases
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