Calculation of site-specific carbon-isotope fractionation in pedogenic oxide minerals.
Proc Natl Acad Sci U S A
; 105(30): 10297-301, 2008 Jul 29.
Article
em En
| MEDLINE
| ID: mdl-18641124
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 partition function ratio of CO(2)(m)(B) structure in goethite differs from CO(2)(g) by <1 per mil. The predicted fractionation for gibbsite is >10 per mil higher, close to those measured for calcite and aragonite. The surprisingly large difference in the carbon-isotope fractionation factor between the CO(2)(m)(A) and CO(2)(m)(B) structures within a given mineral suggests that the isotopic signatures of soil (oxy)hydroxide could be heterogeneous.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Óxidos
/
Isótopos de Carbono
/
Geologia
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Proc Natl Acad Sci U S A
Ano de publicação:
2008
Tipo de documento:
Article
País de afiliação:
Estados Unidos