Biradical character of D-rich carriers in the insoluble organic matter of carbonaceous chondrites: A relic of the protoplanetary disk chemistry

作者：Delpoux Olivier; Gourier Didier^*; Vezin Herve; Binet Laurent; Derenne Sylvie; Robert Francois

来源：Geochimica et Cosmochimica Acta, 2011, 75(1): 326-336.

DOI：10.1016/j.gca.2010.09.033

The insoluble organic matter (TOM) of the Orgueil meteorite contains deuterium-rich radicals detectable by Electron Paramagnetic Resonance (EPR) techniques (Gourier et al., 2008). However the structure of these deuterium carriers remains poorly constrained. In this work, their electronic structure is deduced from the measurement of the spin states S by transient nutation in pulsed-EPR. It is shown that these deuterium-rich radicals are dominated by biradicaloids (species with S = 0 ground state and thermally accessible S = 1 state) and biradicals (species with S = 1 ground state) representing similar to 61% and similar to 31% of the radicals in the IOM of Orgueil, respectively, while single radicals (S = 1/2) contribute only to similar to 8%. This is definitely different from mature terrestrial IOMs, which are known to contain almost exclusively S = 1/2 radicals. A structural model is proposed, whereby the occurrence of dominant biradicaloids and biradicals is the direct consequence of the structure of the IOM, made of a network of small aromatic moieties linked by branched and short aliphatic units. This implies that the formation of stable biradicaloids and biradicals by C-H breaking and their deuterium enrichment are produced after the formation of the IOM in the primitive solar system. These results reinforce the idea that the formation of the TOM and the deuterium-rich hotspots are the product of ion chemistry in the solar disk.

• 出版日期2011-1-1