Theoretical estimation of the equilibrium distribution of clumped isotopes in nature
Theoretical estimation of the equilibrium distribution of clumped isotopes in nature
复制标题
自然界中簇同位素平衡分布的理论估计
DOI：
10.1016/j.gca.2011.11.021
复制
发表时间：
2012-01
影响因子：
5
通讯作者：
Yun Liu
中科院分区：
文献类型：
--
作者：
Xiaobin Cao;Yun Liu
成团（或多取代）同位素地球化学作为一个新兴领域，已显示出一系列独特而有效的地质和大气应用。本文介绍了一种新的方法来计算平衡条件下多取代同位素体的浓度，特别是计算Δi（“i”指特定同位素体）和Δmass（“mass”指具有相同质量数的同位素体）。所提出的精确方法具有等效的精度，并且与Wang等人（2004）的方法相比，可以通过类似的努力水平来解决。然而，这里提出的近似方法可以处理具有同位素异构体的分子（例如，14N15N16O vs.15N14N16O），并能估算任何一种分子的Δ质量，无论单取代同位素体的Δ i值是小还是大。通过几个例子说明了所提出的方法的准确性和方便性（即，CO2、N2O和CH4）。对Δ i的高阶非谐修正进行了仔细的研究。我们的研究结果表明，这种修正是显着的，特别是对于同位素涉及氢原子。为了得到最精确的Δ or Δ质量值，建议在计算中加入高阶非谐修正。这种对Δ i的修正大约是百分之一，类似于对β因子的非调和修正。不同之处在于，高阶非谐波校正通常会降低β值，但会降低或增加Δ i值。例如，在300K时，校正可以将[公式：参见文本]减少5%，但将[公式：参见文本]增加2%。Δ计算中频率定标因子的选择与β因子的计算相似。缩放后的Δ i值将近似等于未缩放的Δ i乘以缩放因子，这表明频率缩放因子的不确定性（通常为百分比量级）可能会导致Δi计算中的较大误差。减少这种误差的最佳方法是使用高级理论方法来减少比例因子的不确定性，或者仔细选择频率比例因子。用该方法计算了大部分地质样品的CO2平衡Δ 47与δ 13 C和δ 18 O基本无关，表明体相同位素组成对Δ 47的影响可以忽略不计。我们发现所有单取代同位素体的Δ i之和将近似等于零，使得我们能够从实验中确定同位素体的随机浓度。
Clumped (or multiply substituted) isotope geochemistry, as an emerging field, has displayed an array of unique and effective geological and atmospheric applications. In this study, we introduce a new method to facilitate the calculation of concentrations of multiply substituted isotopologues at equilibrium conditions, especially for the calculation of Δi(“i” refers to a specific isotopologue) and Δmass(“mass” refers to isotopologues with the same mass number). The proposed exact method has equivalent accuracy and can be solved by similar level of effort compared to that of Wang et al. (2004). However, the approximate method proposed here can handle molecules with isotopomers (e.g.,14N15N16O vs.15N14N16O) and can estimate Δmassof any kind of molecule, whether the Δivalues of singly-substituted isotopologues are small or large. The accuracy and convenience of the proposed method are illustrated through several examples (i.e., CO2, N2O and CH4). Higher-order anharmonic corrections to Δihave been studied carefully. Our results suggest that such corrections are significant, especially for isotopologues involving hydrogen atoms. To obtain the most precise Δior Δmassvalue, including those higher-order anharmonic corrections into the calculation is recommended. Such corrections to Δiare on the order of percent and are similar to anharmonic corrections for the β factor. The difference is that higher-order anharmonic corrections usually reduce β values, but would either reduce or increase Δivalues. For example, the corrections can reduce [Formula: see text] by five percent but increase [Formula: see text] by two percent at 300K. The choice of the frequency scaling factor in the Δicalculation is also found similar to the calculation of β factors. The scaled Δivalue will approximately equal the un-scaled Δitimes the scaling factor, suggesting that the uncertainty in the frequency scaling factor (usually on the order of percent) could possibly cause large errors in the calculation of Δi. The best way to reduce such errors is to use high-level theoretical methods to reduce the uncertainty of the scaling factor, or to choose frequency scaling factors carefully. Using the method proposed, the equilibrium Δ47of CO2is found to be roughly independent of δ13C and δ18O for most geologic samples, suggesting the effects of bulk isotope compositions on Δ47are negligible. We find that the sum of Δifor all of the singly substituted isotopologues will be equal to zero approximately, enabling us to determine the stochastic concentrations of isotopologues from experiments.
登录
查看更多内容
影响因子：
1.7
作者：
D. L. Gray;A. G. Robiette
通讯作者：
D. L. Gray;A. G. Robiette
影响因子：
5
作者：
H. Affek;M. Bar-Matthews;A. Ayalon;A. Matthews;J. Eiler
通讯作者：
H. Affek;M. Bar-Matthews;A. Ayalon;A. Matthews;J. Eiler
影响因子：
2.3
作者：
Huntington, K. W.;Eiler, J. M.;Came, R.
通讯作者：
Came, R.
影响因子：
5
作者：
Zhengrong Wang;E. Schauble;J. Eiler
通讯作者：
Zhengrong Wang;E. Schauble;J. Eiler
影响因子：
3.9
作者：
M. Méheut;M. Lazzeri;E. Balan;F. Mauri
通讯作者：
M. Méheut;M. Lazzeri;E. Balan;F. Mauri