Calculation of site-specific carbon-isotope fractionation in pedogenic oxide minerals.

ABSTRACT: Ab initio molecular dynamics and quantum chemistry techniques are used to calculate the structure, vibrational frequencies, and carbon-isotope fractionation factors of the carbon dioxide component [CO(2)(m)] of soil (oxy)hydroxide minerals goethite, diaspore, and gibbsite. We have identified two possible pathways of incorporation of CO(2)(m) into (oxy)hydroxide crystal structures: one in which the C(4+) substitutes for four H(+) [CO(2)(m)(A)] and another in which C(4+) substitutes for (Al(3+),Fe(3+)) + H(+) [CO(2)(m)(B)]. Calculations of isotope fractionation factors give large differences between the two structures, with the CO(2)(m)(A) being isotopically lighter than CO(2)(m)(B) by approximately 10 per mil in the case of gibbsite and nearly 20 per mil in the case of goethite. The reduced

SUBMITTER: Rustad JR 

PROVIDER: S-EPMC2475500 | biostudies-literature | 2008 Jul

REPOSITORIES: biostudies-literature