Deuterium exchange rate between and organic CH bonds: Implication for D enrichment in meteoritic IOM

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• 作者：Franç ; ois  ; Robert  ; ;   ; ^{robert@mnhn.fr} ; Sylvie  ; Derenne ; Auré ; lien  ; Thomen ; Christelle  ; Anquetil ; Khaled  ; Hassouni
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2011
• 出版时间：1 December 2011
• 年：2011
• 卷：75
• 期：23
• 页码：7522-7532
• 全文大小：399 K

文摘

The rate of the transfer of deuterium from to the three types (benzylic, aliphatic and aromatic) of bonds of 2-Ethylnaphthalene (and Methylnaphthalene) has been measured in the laboratory. The D/H ratio of each bond was calculated from the mass spectrum of the different isotopomers produced in the source of the GC mass spectrometer. The relations between the D/H ratio of the different isotopomers allow to calculate the internal isotopic fractionation factors (¦Á_i?i>j = (D/H)_i/(D/H)_j) between the 3 bonds: ¦Á_{Benzylic¨CAromatic} = 1.99 ¡À 0.38 and ¦Á_{Aliphatic¨CAromatic} = 1.22 ¡À 0.39. Isotopic exchange rate constants are ?.2 ¡Á 10^?¡À0.4 s^?, determined at room temperature for 10^? g of 2-Ethylnaphthalene in contact with 5 ¡Á 10¹² cm^? of . These results are compatible with those measured in the insoluble organic matter (IOM) isolated from the Orgueil meteorite (), i.e., ¦Á_{Benzylic¨CAromatic} = 1.96 ¡À 0.05 and ¦Á_{Aliphatic¨CAromatic} = 1.35 ¡À 0.05. Using the calculated dust and H₂D⁺ densities from the models of deuterium chemistry in protostellar disks, the duration needed to enrich the IOM up to its measured D/H ratio is ?0^4¡À1 s. These laboratory results are in agreement with a late deuteration of the insoluble organic matter taking place in the solar T-Tauri disk by interaction of the organic dust with H₂D⁺.