¹C.M.O’D.Alexander,²M.J.Nilges,¹G.D.Cody,³C.D.K.Herd
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.10.007]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015, USA
²EPR Laboratory, School of Chemical Sciences, Univ. Illinois at Urbana-Champaign, 505 S. Mathews Avenue, Urbana, IL 61801, USA
³Dept. Earth and Atmospheric Sciences, Univ. Alberta, Edmonton, Alberta T6G 2E3, Canada
Copyright Elsevier

The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to δD≈3500 ‰ in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (δD≥95000 ‰). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (δD≈600-3500 ‰) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk δD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and δD, and increasing aromaticity.

¹Tajana Schneiderman,²Luca Matrà,^3,4Alan P. Jackson,^5,6Grant M. Kennedy,⁷Quentin Kral,^8,9Sebastián Marino,¹⁰Karin I. Öberg,¹¹Kate Y. L. Su,¹⁰David J. Wilner,⁸Mark C. Wyatt
Nature 598, 425-428 Link to Article [https://doi.org/10.1038/s41586-021-03872-x]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
²Centre for Astronomy, School of Physics, National University of Ireland Galway, Galway, Ireland
³Centre for Planetary Sciences, University of Toronto at Scarborough, Toronto, Ontario, Canada
⁴School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
⁵Department of Physics, University of Warwick, Coventry, UK
⁶Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK
⁷LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, Meudon, France
⁸Institute of Astronomy, University of Cambridge, Cambridge, UK
⁹Jesus College, University of Cambridge, Cambridge, UK
¹⁰Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA
¹¹Steward Observatory, University of Arizona, Tucson, AZ, USA

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