期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：52
DOI：10.1073/pnas.2114221118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Both the physical effect and the chemical conditions at the origin of the oxygen isotope variations in the solar system have been puzzling questions for 50 y. The data reported here bring the MIF effect (the mass-independent fractionation originally identified on ozone) back to the center of the debate. Similar to Ti isotopes, we observe that the MIF effect for O and Mg is triggered by redox reactions in plasmas. These observations reinforce the idea of a universal mechanism observable in photochemical reactions when molecular collisions involving indistinguishable isotopes yield a symmetrical complex stabilized as a chemical product.
Enrichment or depletion ranging from −40 to +100% in the major isotopes
16O and
24Mg were observed experimentally in solids condensed from carbonaceous plasma composed of CO
2/MgCl
2/Pentanol or N
2O/Pentanol for O and MgCl
2/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 δ
25Mg versus δ
26Mg and between δ
17O versus δ
18O and the slopes calculated using the empirical MIF factor
η 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
