Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0356;
The Fritz Haber Research Center for Molecular Dynamics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel;
Proc Natl Acad Sci U S A. 2014 Oct 14;111(41):14704-9. doi: 10.1073/pnas.1410440111. Epub 2014 Sep 29.
Nitrogen isotopic distributions in the solar system extend across an enormous range, from -400‰, in the solar wind and Jovian atmosphere, to about 5,000‰ in organic matter in carbonaceous chondrites. Distributions such as these require complex processing of nitrogen reservoirs and extraordinary isotope effects. While theoretical models invoke ion-neutral exchange reactions outside the protoplanetary disk and photochemical self-shielding on the disk surface to explain the variations, there are no experiments to substantiate these models. Experimental results of N2 photolysis at vacuum UV wavelengths in the presence of hydrogen are presented here, which show a wide range of enriched δ(15)N values from 648‰ to 13,412‰ in product NH3, depending upon photodissociation wavelength. The measured enrichment range in photodissociation of N2, plausibly explains the range of δ(15)N in extraterrestrial materials. This study suggests the importance of photochemical processing of the nitrogen reservoirs within the solar nebula.
太阳系中的氮同位素分布范围非常广泛，从太阳风中的-400‰到碳质球粒陨石中有机物中的约 5000‰。这些分布需要对氮储库进行复杂的处理和非凡的同位素效应。虽然理论模型援引了原行星盘中的离子-中性交换反应和磁盘表面的光化学反应自屏蔽来解释这些变化，但没有实验来证实这些模型。本文介绍了在真空紫外波长下存在氢气的情况下 N2 光解的实验结果，结果表明，产物 NH3 中的 δ(15)N 值从 648‰到 13412‰不等，具体取决于光解波长。在 N2 光解中测量到的富集范围可以合理地解释外星物质中 δ(15)N 的范围。这项研究表明，在太阳星云内对氮储库进行光化学处理非常重要。
