Molecular Identification of the Deuterium-Rich Carrier in Insoluble Organic Matter in Carbonaceous Chondrites

Details Molecular Identification of the Deuterium-Rich Carrier in Insoluble Organic Matter in Carbonaceous Chondrites Molecular Identification of the Deuterium-Rich Carrier in Insoluble Organic Matter in Carbonaceous Chondrites

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p41a0218r&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P41A-0218

Physics

1041 Stable Isotope Geochemistry (0454, 4870), 1055 Organic And Biogenic Geochemistry, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5215 Origin Of Life, 6240 Meteorites And Tektites (1028, 3662)

Scientific paper

Insoluble organic matter (IOM) in primitive carbonaceous chondrites is known to be enriched in deuterium, with D/H ratios > 300×10 -6. It is also characterized by a high degree of isotopic heterogeneity, as demonstrated by the observation of D-rich "hot spots" in NanoSIMS ion microprobe images [1] and by GC-irMS studies [2]. Understanding the origin of this heterogeneity represents a fundamental challenge with implications for the origin and distribution of organics in the interstellar medium and in the protoplanetary disk from which our planetary system formed. We have determined the carrier of the isotopically anomalous hydrogen in IOM isolated from the carbonaceous chondrite Orgueil. Electron Paramagnetic Resonance spectroscopy has shown that hydrogen in the benzylic bond of organic radicals has a deuterium to hydrogen (D/H) ratio of 1.5±0.5×10-2 in Orgueil IOM, which is the highest solar system D/H ratio ever reported [3]. By combining these data with quantitative image analysis recorded at a high spatial resolution with the NanoSIMS, we are able to prove that the organic radicals can account for the deuterium excess in the IOM D-rich "hot spots". Furthermore, the radicals fall on a well-defined trend between D/H ratio and C-H bond energy [2], consistent with a new interpretation of the hydrogen isotopic variations in solar system organics according to which pre-existing organics exchange their D with highly deuterated gaseous molecules, such as H2D+ or HD2+. The distributions of these deuterated species has been theoritically mapped in protostellar disks [4]. This conclusion runs contrary to previous interpretations, according to which the IOM is an interstellar product reprocessed in the protosolar gas and deuterium-rich "hot spot" relics of pristine interstellar organic matter, which escaped solar nebula or parent body processes. [1] Busemann et al (2006) Science 312, 727-730; [2] Remusat L. et al. (2006) Earth Planet. Sci. Let. 243, 15-25 ; [3] Delpoux O. et al. (2007) 38th LPSC, #1138. [4] Ceccarelli C. and Dominik C. (2005) A&A 440, 583-593.

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