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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Isotopic evidence from an Antarctic carbonaceous chondrite for two reaction pathways of extraterrestrial PAH formation
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Isotopic evidence from an Antarctic carbonaceous chondrite for two reaction pathways of extraterrestrial PAH formation

机译：来自南极碳质球粒陨石的同位素证据表明地球外PAH形成的两个反应途径

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Polycyclic aromatic hydrocarbons (PAHs) are one of the most ubiquitous organic compounds in the universe. PAHs are sometimes used as a molecular marker for biological activity, however, they are also formed by abiogenic processes. Carbon isotopic compositions of individual PAHs have important clues to clarify their origins and formation mechanisms for the better understanding in organic cosmogeochemistry of PAHs. In the Asuka-881458 carbonaceous chondrite which was recovered from Antarctica in 1989, more than 70 PAHs were identified from naphthalene to benzo(ghi)perylene, where fluoranthene and pyrene are the most abundant. Carbon isotopic compositions of individual PAHs range from -26 to 8‰ (relative to PDB). More condensed PAHs are more depleted in ~(13)C as the H/C ratio decreases. The carbon isotope distribution of PAHs containing more than three rings is similar to that from the Murchison meteorite, but clearly different from that of the terrestrial PAHs. The isotope distribution suggests that the PAHs in carbonaceous chondrites are formed under kinetic control rather than by thermodynamic equilibrium. In particular, two reaction pathways ('pyrene series' and 'fluoranthene series') can be distinguished assuming kinetic control. The relatively large isotopic fractionation could occur during cyclization and/or carbon addition in the interstellar or meteorite parent body environment.
机译：多环芳烃（PAHs）是宇宙中最普遍的有机化合物之一。 PAHs有时被用作生物活性的分子标记，但是，它们也是由非生物过程形成的。单个PAHs的碳同位素组成具有重要的线索，以阐明它们的起源和形成机理，以便更好地理解PAHs的有机宇宙地球化学。在1989年从南极洲回收的Asuka-881458碳质球粒陨石中，从萘到苯并（ghi）ylene中发现了70多种PAH，其中荧蒽和pyr最丰富。各个PAH的碳同位素组成范围为-26至8‰（相对于PDB）。随着（H）/ C比率的降低，更多的稠合PAH在〜（13）C中的消耗更多。含三个以上环的PAHs的碳同位素分布与Murchison陨石的碳同位素分布相似，但与陆地PAH的碳同位素分布明显不同。同位素分布表明，碳质球粒陨石中的多环芳烃是在动力学控制下而不是通过热力学平衡形成的。特别地，假定动力学控制，可以区分两个反应途径（“ py系列”和“荧蒽系列”）。在星际或陨石母体环境中，在环化和/或碳添加过程中可能发生相对较大的同位素分馏。

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