期刊
出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2114221118
关键词
isotopes; MIF; plasma; cosmochemistry
资金
- National Center for Scientific Research MITI (ISOTOP 2020, COSMIFs) from ANR [ANR-20-CE49-0011-01]
- European Research Advanced Grant PaleoNanoLife [161764]
- Agence Nationale de la Recherche (ANR) [ANR-20-CE49-0011] Funding Source: Agence Nationale de la Recherche (ANR)
Experimental observations show enrichment or depletion of major isotopes O-16 and Mg-24 in solids condensed from carbonaceous plasma, with MIF effects potentially induced by chemical reactions in the plasma. Micrometer-sized hotspots of isotopic effects in NanoSims imaging are found embedded in a carbonaceous matrix, with Mg hotspots localized in carbonaceous grains exhibiting both positive and negative isotopic effects, while no specific structure is observed at O hotspots. The similarity between linear correlations of delta Mg-25 versus delta Mg-26 and delta O-17 versus delta O-18 observed and those calculated using the empirical MIF factor eta from ozone suggests a ubiquitous process.
Enrichment or depletion ranging from 240 to +100% in the major isotopes O-16 and Mg-24 were observed experimentally in solids condensed from carbonaceous plasma composed of CO2/MgCl2/ Pentanol or N2O/Pentanol for O and MgCl2/Pentanol for Mg. In NanoSims imaging, isotope effects appear as micrometer-size hotspots embedded in a carbonaceous matrix showing no isotope fractionation. For Mg, these hotspots are localized in carbonaceous grains, which show positive and negative isotopic effects so that the whole grain has a standard isotope composition. For O, no specific structure was observed at hotspot locations. These results suggest that MIF (mass-independent fractionation) effects can be induced by chemical reactions taking place in plasma. The close agreement between the slopes of the linear correlations observed between delta Mg-25 versus delta Mg-26 and between delta O-17 versus delta O-18 and the slopes calculated using the empirical MIF factor eta discovered in ozone [M. H. Thiemens, J. E. Heidenreich, III. Science 219, 1073-1075; C. Janssen, J. Guenther, K. Mauersberger, D. Krankowsky. Phys. Chem. Chem. Phys. 3, 4718-4721] attests to the ubiquity of this process. Although the chemical reactants used in the present experiments cannot be directly transposed to the protosolar nebula, a similar MIF mechanism is proposed for oxygen isotopes: at high temperature, at the surface of grains, a mass-independent isotope exchange could have taken place between condensing oxides and oxygen atoms originated form the dissociation of CO or H2O gas.
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