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Evidence of magnetic isotope effects during thermochemical sulfate reduction

  1. James Farquhara,1
  1. aDepartment of Geology and Earth System Science Interdisciplinary Center (ESSIC), University of Maryland, College Park, MD 20742;
  2. cDepartment of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742;
  3. dGeophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015; and
  4. bDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307
  1. Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved August 23, 2011 (received for review May 24, 2011)

  1. Scheme 1.

    Pyrolytic decomposition products of glycine. Solid-state NMR and high resolution ESI-MS (in positive mode) confirm the presence of polymers in the reaction mixture.

  2. Scheme 2.

    Proposed ion-radical pair mechanism showing spin evolution between triplet and singlet states during thermochemical sulfate reduction.

  3. Fig. 1.

    S-isotope plots of Δ36S versus Δ33S (A) and δ33S versus δ34S (B) for Carius tube and flow reactor experiments, abbreviated as GSW (Graphic), GSSW (Graphic), and GSDW (Graphic). Typical mass-dependent arrays are plotted in both panels. Most data follow a tightly constrained, mass-dependent relationship of δ33S?=?0.515(?±?0.008)?×?δ34S (B). Deviations from this array and the Δ36S versus Δ33S array are interpreted as magnetic isotope effects. The MIE trends are distinct from sulfur photoexcitation experiments and are not a likely explanation for the Archean sulfur isotope record. Error bars represent 1σ analytical uncertainties of 0.02 and 0.2 for Δ33S and Δ36S, respectively.

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