Kinetic isotopic fractionation of argon and neon during air–water gas transfer
Kinetic isotopic fractionation of argon and neon during air–water gas transfer
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空气-水气体转移过程中氩和氖的动力学同位素分馏
DOI：
10.1016/j.marchem.2013.04.002
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发表时间：
2013
期刊：
影响因子：
3
通讯作者：
S. Emerson
中科院分区：
文献类型：
--
作者：
K. Tempest;S. Emerson
使用惰性气体同位素比值22 Ne/20 Ne和40 Ar/36 Ar作为环境条件（即来自地下水的大陆古温度）和过程（即空气-海洋气体交换）的地球化学示踪剂需要动力学和平衡同位素分馏（α k和α eq）的精确值。到目前为止，这些值已经使用不同的理论模型进行了近似计算。在这里，我们通过在20 ° C的实验室实验中测量氩和氖的主要和次要同位素在空气-水界面交换过程中的相对传质速率来评估动力学和平衡分馏因子，气体饱和度从0变化到100%。氩（40/36）和氖（22/20）的动力学同位素分馏因子α k分别为0.9961 ± 0.0001（ε k = − 3.9 ± 0.1 ‰）和0.9931 ± 0.0004（ε k = − 6.9 ± 0.4 ‰）。动力学同位素分馏因子更接近于由分子动力学模拟确定的理论值，而不是使用分子约化质量的平方根计算的值。在20 ° C时，氖（22/20）的平衡分馏因子为1.00104 ± 0.00005（ε eq = 1.04 ± 0.05 ‰）。在20 ° C下测定的氩平衡分馏因子为1.00107 ± 0.00002（ε eq = 1.07 ± 0.02 ‰），与先前在2 ° C和25 ° C下测量值的线性插值一致（Nicholson等人，2010年）。
The use of the noble gas isotope ratios22Ne/20Ne and40Ar/36Ar as geochemical tracers of environmental conditions (i.e. continental paleotemperatures from groundwater) and processes (i.e. air–sea gas exchange) requires accurate values for kinetic and equilibrium isotopic fractionations (αkand αeq). Until now, these values have been approximated using different theoretical models. Here we evaluated both the kinetic and equilibrium fractionation factors experimentally by measuring the relative mass transfer rates of the major and secondary isotopes of argon and neon in laboratory experiments at 20°C during exchange across the air–water interface as gas saturations evolved from 0 to 100%. The kinetic isotopic fractionation factors, αk, for argon (40/36) and neon (22/20) are determined to be 0.9961±0.0001 (εk=−3.9±0.1‰) and 0.9931±0.0004 (εk=−6.9±0.4‰), respectively. The kinetic isotopic fractionation factors are much closer in agreement to theoretical values determined by molecular dynamics simulations than to values calculated using the square root of molecular reduced masses. The equilibrium fractionation factor for neon (22/20) at 20°C is determined to be 1.00104±0.00005 (εeq=1.04±0.05‰). An argon equilibrium fractionation factor of 1.00107±0.00002 (εeq=1.07±0.02‰) determined at 20°C agrees with a linear interpolation of previous measured values at 2°C and 25°C (Nicholson et al., 2010).