Babikov Dmitri
Department of Chemistry, Marquette University, Milwaukee, WI 53021
Proc Natl Acad Sci U S A. 2017 Mar 21;114(12):3062-3067. doi: 10.1073/pnas.1620977114. Epub 2017 Mar 3.
A hierarchy of isotopically substituted recombination reactions is formulated for production of sulfur allotropes in the anoxic atmosphere of Archean Earth. The corresponding system of kinetics equations is solved analytically to obtain concise expressions for isotopic enrichments, with focus on mass-independent isotope effects due to symmetry, ignoring smaller mass-dependent effects. Proper inclusion of atom-exchange processes is shown to be important. This model predicts significant and equal depletions driven by reaction stoichiometry for all rare isotopes: S, S, and S. Interestingly, the ratio of capital [Formula: see text] values obtained within this model for S and S is -1.16, very close to the mass-independent fractionation line of the Archean rock record. This model may finally offer a mechanistic explanation for the striking mass-independent fractionation of sulfur isotopes that took place in the Archean atmosphere of Earth.
为了在太古宙地球的缺氧大气中生成硫的同素异形体，构建了一个同位素取代复合反应的层级体系。对相应的动力学方程组进行了解析求解，以获得同位素富集的简洁表达式，重点关注由于对称性导致的质量无关同位素效应，忽略较小的质量相关效应。结果表明，正确纳入原子交换过程很重要。该模型预测，所有稀有同位素（³³S、³⁴S和³⁵S）都会因反应化学计量比而出现显著且相等的亏损。有趣的是，该模型中³⁴S和³³S的大写[公式：见原文]值之比为-1.16，非常接近太古宙岩石记录的质量无关分馏线。该模型最终可能为地球太古宙大气中发生的显著的硫同位素质量无关分馏提供一个机理解释。
