Deuterium exchange rate between D-3(+) and organic CH bonds: Implication for D enrichment in meteoritic IOM

作者：Robert Francois^*; Derenne Sylvie; Thomen Aurelien; Anquetil Christelle; Hassouni Khaled

来源：Geochimica et Cosmochimica Acta, 2011, 75(23): 7522-7532.

DOI：10.1016/j.gca.2011.09.016

The rate of the transfer of deuterium from D-3(+) 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 (alpha(i-j) = (D/H)(i)/(D/H)(j)) between the 3 bonds: alpha(Benzylic) (Aromatic) = 1.99 +/- 0.38 and aAliphatic-Aromatic = 1.22 +/- 0.39. Isotopic exchange rate constants are >= 2.2 x 10(-7 +/- 0.4) s(-1), determined at room temperature for 10(-3) g of 2-Ethylnaphthalene in contact with 5 x 10(12) cm(-3) of D-3(+). These results are compatible with those measured in the insoluble organic matter (IOM) isolated from the Orgueil meteorite (Remusat et al., 2006), i.e., alpha(Benzylic-Aromatic) - 1.96 +/- 0.05 and alpha(Aliphatic-Aromatic) - 1.35 +/- 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 <= 10(4+1) 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+.

• 出版日期2011-12-1