Hydrogen isotope fractionation in methane plasma

Area of Science:

• Astrochemistry
• Isotope Geochemistry
• Planetary Science

Background:

• The hydrogen isotope ratio (D/H) is crucial for understanding the origins of water and organic matter in the early solar system.
• Insoluble organic matter (IOM) in meteorites exhibits significant deuterium enrichments, suggesting interstellar or protosolar nebula origins.
• The molecular structure of IOM implies a role for organic radicals in gas-phase synthesis.

Purpose of the Study:

• To investigate the formation pathways of organic compounds in the early solar system.
• To experimentally reproduce the chemistry of organic radicals relevant to IOM formation.
• To analyze hydrogen isotopic anomalies in synthetic organic residues.

Main Methods:

• Microwave plasma experiments using methane (CH4) to generate organic residues.
• Ion microprobe analysis to determine hydrogen isotope ratios (D/H) at submicrometric resolution.
• Comparison of experimental isotopic heterogeneities with those found in meteorite IOM.

Main Results:

• A black organic residue was synthesized using methane plasma.
• Submicrometric hydrogen isotopic anomalies ('hot' and 'cold' spots) were detected in the synthetic residue.
• These anomalies are comparable to those observed in meteorite IOM.

Conclusions:

• The experimental results support the hypothesis that polymerization of CHx radicals with varying D/H ratios formed meteorite IOM.
• Isotopic heterogeneities in organic matter likely originated from variations in radical D/H ratios.
• The presence of organic radicals in ionized regions of the early solar disk may have initiated the formation of complex organic compounds.