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Equilibrium Clumped-Isotope Effects in Doubly Substituted Isotopologues of Ethane

Webb, Michael A. and Wang, Yimin and Braams, Bastiaan J. and Bowman, Joel M. and Miller, Thomas F., III (2017) Equilibrium Clumped-Isotope Effects in Doubly Substituted Isotopologues of Ethane. Geochimica et Cosmochimica Acta, 197 . pp. 14-26. ISSN 0016-7037. doi:10.1016/j.gca.2016.10.001.

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We combine path-integral Monte Carlo methods with a new intramolecular potential energy surface to quantify the equilibrium enrichment of doubly substituted ethane isotopologues due to clumped-isotope effects. Ethane represents the simplest molecule to simultaneously exhibit ^(13)C–^(13)C, ^(13)C–D, and D–D clumped-isotope effects, and the analysis of corresponding signatures may provide useful geochemical and biogeochemical proxies of formation temperatures or reaction pathways. Utilizing path-integral statistical mechanics, we predict equilibrium fractionation factors that fully incorporate nuclear quantum effects, such as anharmonicity and rotational-vibrational coupling which are typically neglected by the widely used Urey model. The magnitude of the calculated fractionation factors for the doubly substituted ethane isotopologues indicates that isotopic clumping can be observed if rare-isotope substitutions are separated by up to three chemical bonds, but the diminishing strength of these effects suggests that enrichment at further separations will be negligible. The Urey model systematically underestimates enrichment due to ^(13)C–D and D–D clumped-isotope effects in ethane, leading to small relative errors in the apparent equilibrium temperature, ranging from 5 K at 273.15 K to 30 K at 873.15 K. We additionally note that the rotameric dependence of isotopologue enrichment must be carefully considered when using the Urey model, whereas the path-integral calculations automatically account for such effects due to configurational sampling. These findings are of direct relevance to future clumped-isotope studies of ethane, as well as studies of ^(13)C–^(13)C, ^(13)C–D, and D–D clumped-isotope effects in other hydrocarbons.

Item Type:Article
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URLURL TypeDescription
Webb, Michael A.0000-0002-7420-4474
Miller, Thomas F., III0000-0002-1882-5380
Additional Information:© 2016 Elsevier B.V. Received 13 July 2016; accepted 1 October 2016; available online 11 October 2016. This research was supported by the Resnick Sustainability Institute and the Department of Energy (DE-SC0006593). The work of B. J. B. was performed while he was at Emory University and supported by the Office of Basic Energy Sciences and the National Science Foundation. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. The authors also thank John Eiler, Alex Sessions, and Brian Peterson for helpful discussions as well as three anonymous reviewers for their helpful and constructive comments.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Resnick Sustainability InstituteUNSPECIFIED
Department of Energy (DOE)DE-SC0006593
Department of Energy (DOE)DE-AC05-00OR22725
Subject Keywords:Clumped isotope geochemistry; Ethane; Equilibrium isotope effects; Path-integral methods; Vibrational anharmonicity
Record Number:CaltechAUTHORS:20161024-085559620
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Official Citation:Michael A. Webb, Yimin Wang, Bastiaan J. Braams, Joel M. Bowman, Thomas F. Miller III, Equilibrium clumped-isotope effects in doubly substituted isotopologues of ethane, Geochimica et Cosmochimica Acta, Volume 197, 15 January 2017, Pages 14-26, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71374
Deposited By: Melissa Ray
Deposited On:24 Oct 2016 17:26
Last Modified:11 Nov 2021 04:44

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