Surface complex structures modelled with quantum chemical calculations: carbonate, phosphate, sulphate, arsenate and arsenite

European Journal of Soil Science - Tập 58 Số 4 - Trang 932-944 - 2007
James D. Kubicki1, Kideok D. Kwon1, Kristian W. Paul1, Donald L. Sparks1
1aThe Pennsylvania State University, Department of Geosciences and the Earth and Environmental Systems Institute, University Park, PA 16802, and bUniversity of Delaware, Department of Plant and Soil Sciences, Newark, DE 1971,7 USA

Tóm tắt

SummaryHybrid molecular orbital/density functional theory (MO/DFT) calculations on molecular clusters were used to model infrared (IR) vibrational frequencies and interatomic distances obtained via extended X‐ray absorption fine structure (EXAFS) spectroscopy. Molecular clusters were found to provide good agreement with experimental observations for the oxyanions carbonate, phosphate, sulphate, arsenate and arsenite. The results show a consistent tendency to form bidentate bridging surface complexes at low pH, but the protonation and hydration states play a significant role in the results obtained from calculation as various protonation states of monodentate surface complexes are also predicted to be stable as pH increases (i.e. the number of H+ ions in the model are decreased). A method for estimating the Gibbs free energy of adsorption (ΔGads) is discussed to complement the comparisons of experimental and theoretical spectroscopic parameters. Calculated ΔGads values were consistent with the interpretations based on modelling observed spectra.

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Thông tin xuất bản

European Journal of Soil Science

Tập 58 Số 4

932-944

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