Density Functional Theory Analysis of Molybdenum Isotope Fractionation

Colin L. Weeks, Ariel Anbar, Laura E. Wasylenki, Thomas G. Spiro

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Analytical studies have found an enrichment of the lighter Mo isotopes in oxic marine sediments compared to seawater, with isotope fractionation factors of -1.7 to -2.0 ‰ for Δ97/95MO sediment-seawater. These data place constraints on the possible identities of dissolved and adsorbed species because the equilibrium isotope fractionation depends on the energy differences between the isotopomers of the adsorbed species, minor dissolved species, and the dominant solution species, MoO4 2-. Adsorption likely involves molybdic acid, whose structure is indicated by previous studies to be MoO3(H 2O)3. Here we used DFT calculations of vibrational frequencies to determine the isotope fractionation factors versus MoO 4 2-. The results indicate that isotope equilibration of MoO4 2- with MoO3(H2O)3, yielding Δ97/95Momolybdic acid-molybdate = -1.33 ‰, is most likely responsible for the isotope fractionation of Mo between oxic sediments and seawater. The difference between the calculated value of Δ97/95Momolybdic acid-molybdate for MoO 3(H2O)3 and the value observed in natural sediments and experiments is probably due to effects of solvation and adsorption onto the manganese oxyhydroxide surface.

Original languageEnglish (US)
Pages (from-to)12434-12438
Number of pages5
JournalJournal of Physical Chemistry A
Volume111
Issue number49
DOIs
StatePublished - Dec 13 2007

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molybdenum isotopes
Molybdenum
Fractionation
fractionation
Isotopes
Density functional theory
isotopes
density functional theory
sediments
Seawater
Sediments
molybdates
Oxic sediments
acids
Adsorption
adsorption
Acids
Solvation
Vibrational spectra
Manganese

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Density Functional Theory Analysis of Molybdenum Isotope Fractionation. / Weeks, Colin L.; Anbar, Ariel; Wasylenki, Laura E.; Spiro, Thomas G.

In: Journal of Physical Chemistry A, Vol. 111, No. 49, 13.12.2007, p. 12434-12438.

Research output: Contribution to journalArticle

Weeks, Colin L. ; Anbar, Ariel ; Wasylenki, Laura E. ; Spiro, Thomas G. / Density Functional Theory Analysis of Molybdenum Isotope Fractionation. In: Journal of Physical Chemistry A. 2007 ; Vol. 111, No. 49. pp. 12434-12438.
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