Kinetic and equilibrium mass-dependent isotope fractionation laws in nature and their geochemical and cosmochemical significance
Kinetic and equilibrium mass-dependent isotope fractionation laws in nature and their geochemical and cosmochemical significance
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DOI：
10.1016/s0016-7037(01)00832-8
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发表时间：
2002-03-01
影响因子：
5
通讯作者：
Nagahara, H
中科院分区：
文献类型：
--
作者：
Young, ED;Galy, A;Nagahara, H
描述同位素分配的质量相关分馏定律对于动力学反应和平衡反应是不同的。这些定律的特征在于两个同位素比率的分馏因子的指数，使得α（2/1）= α（3/1）（β）。平衡交换指数P为（1/m（1）- 1/m（2））/（1/m（1）- 1/m（3）），其中m（1）为原子质量，m（1）< m（2）< m（3）。对于动力学分馏，用于评估β的质量取决于运动中的同位素种类。减少的质量适用于断裂键，而分子或原子质量适用于传输过程。在每种情况下，动力学β的函数形式为ln（M-1/M-2）/ln（M-1/M-3），其中M1是还原的分子质量或原子质量。新的高精度镁同位素比数据证实，独特的平衡和动力学分馏法可以解决同位素比的变化只有3%每AMU。质量相关分馏定律的变化足以解释对流层O-2相对于岩石的负Δ（17）O，以及火星陨石中碳酸盐、羟基和无水硅酸盐之间Δ（17）O的差异。(For简单地说，在本文中，当计算β时，我们使用整数amu值作为质量。）版权所有（C）2002 Elsevier Science Ltd.
The mass-dependent fractionation laws that describe the partitioning of isotopes are different for kinetic and equilibrium reactions. These laws are characterized by the exponent relating the fractionation factors for two isotope ratios such that alpha(2/1) = alpha(3/1)(beta). The exponent P for equilibrium exchange is (1/m(1) - 1/m(2))/(1/m(1) - 1/m(3)), where m(i) are the atomic masses and m(1) < m(2) < m(3). For kinetic fractionation, the masses used to evaluate beta depend upon the isotopic species in motion. Reduced masses apply for breaking bonds whereas molecular or atomic masses apply for transport processes. In each case the functional form of the kinetic beta is ln(M-1/M-2)/ln(M-1/M-3), where M-i are the reduced, molecular, or atomic masses. New high-precision Mg isotope ratio data confirm that the distinct equilibrium and kinetic fractionation laws can be resolved for changes in isotope ratios of only 3% per amu. The variability in mass-dependent fractionation laws is sufficient to explain the negative Delta(17)O of tropospheric O-2 relative to rocks and differences in Delta(17)O between carbonate, hydroxyl, and anhydrous silicate in Martian meteorites. (For simplicity, we use integer amu values for masses when evaluating beta throughout this paper.) Copyright (C) 2002 Elsevier Science Ltd.