Institut Origine et Evolution, Muséum National d'Histoire Naturelle, Sorbonne Université, IMPMC-UMR 7590 CNRS, 75005 Paris, France;
Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France.
Proc Natl Acad Sci U S A. 2021 Dec 28;118(52). doi: 10.1073/pnas.2114221118.
Enrichment or depletion ranging from -40 to +100% in the major isotopes O and Mg were observed experimentally in solids condensed from carbonaceous plasma composed of CO/MgCl/Pentanol or NO/Pentanol for O and MgCl/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 δMg versus δMg and between δO versus δO and the slopes calculated using the empirical MIF factor discovered in ozone [M. H. Thiemens, J. E. Heidenreich, III. 219, 1073-1075; C. Janssen, J. Guenther, K. Mauersberger, D. Krankowsky. 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 HO gas.
在由 CO/MgCl/戊醇或 NO/戊醇组成的碳质等离子体中冷凝而成的固体中，实验观察到主要同位素 O 和 Mg 的富集或耗尽范围为-40%至+100%。在 NanoSims 成像中，同位素效应表现为嵌入在无同位素分馏的碳质基质中的微米大小的热点。对于 Mg，这些热点定位于显示正和负同位素效应的碳质颗粒中，使得整个颗粒具有标准的同位素组成。对于 O，在热点位置没有观察到特定的结构。这些结果表明，MIF（质量独立分馏）效应可以通过等离子体中发生的化学反应诱导。观察到的δMg 与 δMg 之间和 δO 与 δO 之间的线性相关的斜率与在臭氧中发现的经验 MIF 因子[M. H. Thiemens，J. E. Heidenreich，III. 219，1073-1075；C. Janssen，J. Guenther，K. Mauersberger，D. Krankowsky. 3，4718-4721]计算的斜率之间的紧密一致性证明了该过程的普遍性。尽管本实验中使用的化学反应物不能直接转化为原太阳星云，但提出了一种类似的氧同位素 MIF 机制：在高温下，在颗粒表面，凝结氧化物与源自 CO 或 HO 气体解离的氧原子之间可能发生了质量独立的同位素交换。
