Position-Specific and Clumped Stable Isotope Studies: Comparison of the Urey and Path-Integral Approaches for Carbon Dioxide, Nitrous Oxide, Methane, and Propane

Webb, Michael; Miller, Thomas F.

doi:10.1021/jp411134v

Cited by 100 publications

(111 citation statements)

References 83 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The theoretical equilibrium line we calculated agrees well with published results from both path-integral Monte Carlo simulations (44) and harmonic oscillator assumption-based approaches (44)(45)(46). The results of results of calculations employing an anharmonic correction, however, differ slightly from results of models assuming harmonic-oscillator behavior [by ~0.3‰ near room temperature (44,45)].…”

Section: Heated Gas Calibrationssupporting

confidence: 85%

Nonequilibrium clumped isotope signals in microbial methane

Wang

Gruen

Lollar

et al. 2015

Science

213

362

View full text Add to dashboard Cite

What controls clumped isotopes? Stable isotopes of a molecule can clump together in several combinations, depending on their mass. Even for simple molecules such as O 2 , which can contain 16 O, 17 O, and 18 O in various combinations, clumped isotopes can potentially reveal the temperatures at which molecules form. Away from equilibrium, however, the pattern of clumped isotopes may reflect a complex array of processes. Using high-resolution gas-phase mass spectrometry, Yeung et al. found that biological factors influence the clumped isotope signature of oxygen produced during photosynthesis (see the Perspective by Passey). Similarly, Wang et al. showed that away from equilibrium, kinetic effects causing isotope clumping can lead to overestimation of the temperature at which microbially produced methane forms. Science , this issue p. 431; p. 428; see also p. 394

show abstract

Section: Heated Gas Calibrationssupporting

confidence: 85%

Nonequilibrium clumped isotope signals in microbial methane

Wang

Gruen

Lollar

et al. 2015

Science

213

362

View full text Add to dashboard Cite

show abstract

“…The theoretical equilibrium line we calculated agrees well with published results from both path-integral Monte Carlo simulations (Webb and Miller, 2014) and harmonic oscillator assumption-based approaches (Ma et al, 2008;Cao and Liu, 2012;Webb and Miller, 2014). The results of results of calculations employing an anharmonic correction, however, differ slightly from results of models assuming harmonic-oscillator behavior (by~0.3‰ near room temperature; Cao and Liu, 2012;Webb and Miller, 2014).…”

Section: Heated Gas Calibrationssupporting

confidence: 85%

“…The results of results of calculations employing an anharmonic correction, however, differ slightly from results of models assuming harmonic-oscillator behavior (by~0.3‰ near room temperature; Cao and Liu, 2012;Webb and Miller, 2014). Figure 2.5 shows results from recent studies comparing multiple computational approaches for estimating the temperaturedependence of the equilibrium ∆ 13 CH 3 D value.…”

Section: Heated Gas Calibrationsmentioning

confidence: 93%

“…The equilibrium curve (red line) was calculated following conventional equilibrium isotope fractionation theory under the harmonic oscillator assumption (Bigeleisen and Mayer, 1947); frequencies were calculated at the B3LYP level of theory using the 6-311G basis set as implemented in Gaussian 03 (Frisch et al). For comparison, results from published computational studies (Ma et al, 2008;Cao and Liu, 2012;Webb and Miller, 2014) are also plotted. …”

mentioning

confidence: 99%

See 1 more Smart Citation

The geochemistry of methane isotopologues

Wang¹

2017

View full text Add to dashboard Cite

This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12 CH 4 , 13 CH 4 , 12 CH 3 D, and 13 CH 3 D record the formation, transport, and breakdown of methane in selected settings.Chapter 2 reports precise determinations of 13 CH 3 D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13 CH 3 D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped-and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H 2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13 CH 3 D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow-and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300• C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O 2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13 C/ 12 C and D/H isotope fractionation factors alone.: Shuhei Ono, Ph.D. Acknowledgments I fear that this section will not do justice to the people I have not the space to thank individually. Alas, here goes. To those whose names are not specifically listed here, thank you too. I wish first to thank Shuhei Ono. The work this thesis represents could not have happened without his bold vision and the license to explore and question that working in his lab afforded. His unbridled optimism, breadth of scientific curiosity, personal integrity, and accessibility to his personnel are traits I one day hope to emulate. I thank him for his nonjudgmental yet appropriately measured support of many of my ideas-even those that led nowhere-, for believing in me even when I found it difficult to do so myself, and for teaching me to change pump oil, build vacuum lines, and drink Icelandic vodka.I also wish to thank my thesis committee members Jeff Seewald, Roger Summons, and John Pohlman, for their in...

show abstract

“…Carbon and hydrogen 31 isotope ratios have long been used to unravel the complex origins or source processes of samples in geo-32 chemistry and biogeochemistry (Craig, 1953;Schoell, 1984; Freeman, KH and Hayes, JM and Trendel, JM In previous work, we used path-integral methods to compute equilibrium clumped-isotope effects in 48 carbon dioxide and methane (Webb and Miller, 2014) for the flexible ethane molecule using path-integral Monte Carlo methods and a new full-dimensional, iso-53 topically independent intramolecular potential energy surface that is parameterized from more than 900 54 energies and gradients at the B3LYP/aug-cc-pVTZ level of theory. We compute fractionation factors for …”

mentioning

confidence: 99%

Equilibrium clumped-isotope effects in doubly substituted isotopologues of ethane

Webb

Wang

Braams

et al. 2017

Geochimica et Cosmochimica Acta

Self Cite

View full text Add to dashboard Cite

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 clumpedisotope 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.

show abstract

Position-Specific and Clumped Stable Isotope Studies: Comparison of the Urey and Path-Integral Approaches for Carbon Dioxide, Nitrous Oxide, Methane, and Propane

Cited by 100 publications

References 83 publications

Nonequilibrium clumped isotope signals in microbial methane

Nonequilibrium clumped isotope signals in microbial methane

The geochemistry of methane isotopologues

Equilibrium clumped-isotope effects in doubly substituted isotopologues of ethane

Contact Info

Product

Resources

About