Theoretical estimation of the equilibrium distribution of clumped isotopes in nature

	Theoretical estimation of the equilibrium distribution of clumped isotopes in nature
	Xiaobin Cao; Yun Liu
通讯作者	Yun Liu
	2012
发表期刊	Geochimica et Cosmochimica Acta
卷号	77 期号:15 页码:292-303
摘要	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 Di (“i” refers to a specific isotopologue) and Dmass (“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 Dmass of any kind of molecule, whether the Di values 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 Di have been studied carefully. Our results suggest that such corrections are significant, especially for isotopologues involving hydrogen atoms. To obtain the most precise Di or Dmass value, including those higher-order anharmonic corrections into the calculation is recommended. Such corrections to Di are on the order of percent and are similar to anharmonic corrections for the b factor. The difference is that higher-order anharmonic corrections usually reduce b values, but would either reduce or increase Di values. For example, the corrections can reduce D13CDH3 by five percent but increase D18O13C16O by two percent at 300 K. The choice of the frequency scaling factor in the Di calculation is also found similar to the calculation of b factors. The scaled Di value will approximately equal the un-scaled Di times 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 Di. 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 D47 of CO2 is found to be roughly independent of d13C and d18O for most geologic samples, suggesting the effects of bulk isotope compositions on D47 are negligible. We find that the sum of Di for all of the singly substituted isotopologues will be equal to zero approximately, enabling us to determine the stochastic concentrations of isotopologues from experiments.
学科领域	计算地球化学
收录类别	SCI
语种	英语
文献类型	期刊论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/4115
专题	矿床地球化学国家重点实验室_矿床地球化学国家重点实验室_期刊论文
通讯作者	Yun Liu
推荐引用方式 GB/T 7714	Xiaobin Cao,Yun Liu. Theoretical estimation of the equilibrium distribution of clumped isotopes in nature[J]. Geochimica et Cosmochimica Acta,2012,77(15):292-303.
APA	Xiaobin Cao,&Yun Liu.(2012).Theoretical estimation of the equilibrium distribution of clumped isotopes in nature.Geochimica et Cosmochimica Acta,77(15),292-303.
MLA	Xiaobin Cao,et al."Theoretical estimation of the equilibrium distribution of clumped isotopes in nature".Geochimica et Cosmochimica Acta 77.15(2012):292-303.

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