¹Nathan Asset, ¹Marc Chaussidon, ²Guillaume Lombardi, ³Johan Villeneuve, ⁴Romain Tartèse, ⁵Smail Mostefaoui, ⁵François Robert
Proceedings of the National Academy of Sciences of the United States of America (PNAS) 122, e2426711122 Link to Article [https://doi.org/10.1073/pnas.2426711122]
¹Universite Paris-Cite, Institut de Physique du Globe de Paris, CNRS, Paris F-75005, France
²Laboratoire des Sciences des Procédés et des Matériaux (LSPM—CNRS), Université Sorbonne Paris Nord, Villetaneuse F-93430, France
³Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR 7358, Vandœuvre-lès-Nancy 54501, France
⁴Department of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom
⁵Institut Origine et Evolution, Muséum National d’Histoire Naturelle, Sorbonne Université, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie – UMR 7590 CNRS, Paris 75005, France

Contrary to all terrestrial rocks, planets and meteorites exhibit oxygen isotope variations decorrelated with the mass difference of their atomic nuclei. It has been proposed that, in the protosolar nebula (PSN), these variations could result from mass independent isotopic fractionation (MIF) either during specific chemical reactions similar to those responsible for the formation of ozone in the Earth’s atmosphere or during ultraviolet (UV)-photolysis of carbon monoxide (CO) gas in the PSN. However, these potential chemical MIF reactions (Chem-MIFs) are not identified in conditions close to the PSN, and there is no experimental demonstration that large MIF signature can be transferred to solids forming in the PSN. Here, we show that MIFs, up to 60‰ depletion in 16O, are produced by high-temperature reactions in a plasma during the condensation of carbonaceous solids from a gas containing two of the most abundant PSN molecular species (H2O and CH4). This effect is attributed to the formation in the plasma of the activated complex H2O2* followed by its stabilization by reactions with CHx• radicals. Although it is premature to assert that this reaction represents the main process resulting in MIF of oxygen isotopes in the solar system, our result demonstrates the potential importance of a Chem-MIF effect in a PSN where plasma zones develop.