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Title: Comparison of Experimental vs Theoretical Abundances of 13CH 3D and 12CH 2D 2 for Isotopically Equilibrated Systems from 1 to 500 °C

Abstract

Methane is produced and consumed via numerous microbial and chemical reactions in atmospheric, hydrothermal, and magmatic reactions. The stable isotopic composition of methane has been used extensively for decades to constrain the source of methane in the environment. A recently introduced isotopic parameter used to study the formation temperature and formational conditions of methane is the measurement of molecules of methane with multiple rare, heavy isotopes (“clumped”) such as 13CH 3D and 12CH 2D 2. In order to place methaneclumped isotope measurements into a thermodynamic reference frame that allows calculations of clumped isotope-based temperatures (geothermometry) and comparison between laboratories, all past studies have calibrated their measurements using a combination of experiment and theory based on the temperature dependence of clumped isotopologue distributions for isotopically equilibrated systems. These have previously been performed at relatively high temperatures (>150 °C). Given that many natural occurrences of methane form below these temperatures, previous calibrations require extrapolation when calculating clumped isotope-based temperatures outside of this calibration range. We provide a new experimental calibration of the relative equilibrium abundances of 13CH 3D and 12CH 2D 2 from 1 to 500 °C using a combination of γ-Al 2O 3- and Ni-based catalysts and compare them to newmore » theoretical computations using Path Integral Monte Carlo (PIMC) methods and find 1:1 agreement (within ±1 standard error) for the observed temperature dependence of clumping between experiment and theory over this range. This demonstrates that measurements, experiments, and theory agree from 1 to 500 °C, providing confidence in the overall approaches. Polynomial fits to PIMC computations, which are considered the most rigorous theoretical approach available, are given as follows (valid T ≥ 270 K): Δ13CH 3D ≅ 1000 × ln( K 13CH 3D) = (1.47348 × 10 19)/ T 7 – (2.08648 × 10 17)/ T 6 + (1.19810 × 10 15)/ T 5 – (3.54757 × 10 12)/ T 4 + (5.54476 × 10 9)/ T 3 – (3.49294 × 10 6)/ T 2 + (8.89370 × 10 2)/ T and Δ12CH 2D 2 ≅ 1000 × ln(8/3 K 12CH 2D 2) = –(9.67634 × 10 15)/ T 6 + (1.71917 × 10 14)/ T 5 – (1.24819 × 10 12)/ T 4 + (4.30283 × 10 9)/ T 3 – (4.48660 × 10 6)/ T 2 + (1.86258 × 10 3)/ T. We additionally compare PIMC computations to those performed utilizing traditional approaches that are the basis of most previous calibrations (Bigeleisen, Mayer, and Urey model, BMU) and discuss the potential sources of error in the BMU model relative to PIMC computations.« less

Authors:
ORCiD logo [1];  [2];  [3];  [3]; ORCiD logo [4]; ORCiD logo [2];  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  3. Univ. of California, Berkeley, CA (United States)
  4. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1575296
Alternate Identifier(s):
OSTI ID: 1580033
Grant/Contract Number:  
AC02-05CH11231; EAR-1911296; CHE-1611581
Resource Type:
Published Article
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 3; Journal Issue: 12; Journal ID: ISSN 2472-3452
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Methane Clumped Isotopes; Methane Isotope Equilibration; Methane Geochemistry; Path Integral Monte Carlo Calculations; 253 Ultra

Citation Formats

Eldridge, Daniel L., Korol, Roman, Lloyd, Max K., Turner, Andrew C., Webb, Michael A., Miller, Thomas F., and Stolper, Daniel A. Comparison of Experimental vs Theoretical Abundances of 13CH3D and 12CH2D2 for Isotopically Equilibrated Systems from 1 to 500 °C. United States: N. p., 2019. Web. doi:10.1021/acsearthspacechem.9b00244.
Eldridge, Daniel L., Korol, Roman, Lloyd, Max K., Turner, Andrew C., Webb, Michael A., Miller, Thomas F., & Stolper, Daniel A. Comparison of Experimental vs Theoretical Abundances of 13CH3D and 12CH2D2 for Isotopically Equilibrated Systems from 1 to 500 °C. United States. doi:10.1021/acsearthspacechem.9b00244.
Eldridge, Daniel L., Korol, Roman, Lloyd, Max K., Turner, Andrew C., Webb, Michael A., Miller, Thomas F., and Stolper, Daniel A. Mon . "Comparison of Experimental vs Theoretical Abundances of 13CH3D and 12CH2D2 for Isotopically Equilibrated Systems from 1 to 500 °C". United States. doi:10.1021/acsearthspacechem.9b00244.
@article{osti_1575296,
title = {Comparison of Experimental vs Theoretical Abundances of 13CH3D and 12CH2D2 for Isotopically Equilibrated Systems from 1 to 500 °C},
author = {Eldridge, Daniel L. and Korol, Roman and Lloyd, Max K. and Turner, Andrew C. and Webb, Michael A. and Miller, Thomas F. and Stolper, Daniel A.},
abstractNote = {Methane is produced and consumed via numerous microbial and chemical reactions in atmospheric, hydrothermal, and magmatic reactions. The stable isotopic composition of methane has been used extensively for decades to constrain the source of methane in the environment. A recently introduced isotopic parameter used to study the formation temperature and formational conditions of methane is the measurement of molecules of methane with multiple rare, heavy isotopes (“clumped”) such as 13CH3D and 12CH2D2. In order to place methaneclumped isotope measurements into a thermodynamic reference frame that allows calculations of clumped isotope-based temperatures (geothermometry) and comparison between laboratories, all past studies have calibrated their measurements using a combination of experiment and theory based on the temperature dependence of clumped isotopologue distributions for isotopically equilibrated systems. These have previously been performed at relatively high temperatures (>150 °C). Given that many natural occurrences of methane form below these temperatures, previous calibrations require extrapolation when calculating clumped isotope-based temperatures outside of this calibration range. We provide a new experimental calibration of the relative equilibrium abundances of 13CH3D and 12CH2D2 from 1 to 500 °C using a combination of γ-Al2O3- and Ni-based catalysts and compare them to new theoretical computations using Path Integral Monte Carlo (PIMC) methods and find 1:1 agreement (within ±1 standard error) for the observed temperature dependence of clumping between experiment and theory over this range. This demonstrates that measurements, experiments, and theory agree from 1 to 500 °C, providing confidence in the overall approaches. Polynomial fits to PIMC computations, which are considered the most rigorous theoretical approach available, are given as follows (valid T ≥ 270 K): Δ13CH3D ≅ 1000 × ln(K13CH3D) = (1.47348 × 1019)/T7 – (2.08648 × 1017)/T6 + (1.19810 × 1015)/T5 – (3.54757 × 1012)/T4 + (5.54476 × 109)/T3 – (3.49294 × 106)/T2 + (8.89370 × 102)/T and Δ12CH2D2 ≅ 1000 × ln(8/3K12CH2D2) = –(9.67634 × 1015)/T6 + (1.71917 × 1014)/T5 – (1.24819 × 1012)/T4 + (4.30283 × 109)/T3 – (4.48660 × 106)/T2 + (1.86258 × 103)/T. We additionally compare PIMC computations to those performed utilizing traditional approaches that are the basis of most previous calibrations (Bigeleisen, Mayer, and Urey model, BMU) and discuss the potential sources of error in the BMU model relative to PIMC computations.},
doi = {10.1021/acsearthspacechem.9b00244},
journal = {ACS Earth and Space Chemistry},
number = 12,
volume = 3,
place = {United States},
year = {2019},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acsearthspacechem.9b00244

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