Surface protonation model calculations

By using this approach, it is possible to calculate vibrational state-selected cross-sections from minimal END trajectories obtained with a classical description of the nuclei. We have studied vibrationally excited H2(v) molecules produced in collisions with 30-eV protons [42,43]. The relevant experiments were performed by Toennies et al. [46] with comparisons to theoretical studies using the trajectory surface hopping model [11,47] fTSHM). This system has also stimulated a quantum mechanical study [48] using diatomics-in-molecule (DIM) surfaces [49] and invoicing the infinite-onler sudden approximation (lOSA). 

Felmy, A.R. Rustad, J.R. (1998) Molecular statics calculations of proton binding to goethite surfaces Thermodynamic modeling of the surface charging and protonation of goethite in aqueous solution. Geochim. Cosmochim. Acta 62 25—31... 

The Concentration of Edge Sites and Intrinsic Stability Constants of Protonation and Deprotonation of Silanol and Aluminol Sites of Montmorillonite Samples Calculated by the Surface Complexation Model... 

Figure 7. The effect of ligands and metal ions on surface protonation of a hydrous oxide is illustrated by two examples (1). Part a Binding of a ligand (pH 7) to hematite, which increases surface protonation. Part h Adsorption of Pb2+ to hematite (pH 4.4), which reduces surface protonation. Part c Surface protonation of hematite alone as a function of pH (for comparison). All data were calculated with the following surface complex formation equilibria (1 = 5 X 10"3 M >. Electrostatic correction was made by diffuse double layer model.

Table 5.21 illustrates dramatic difference (almost eight decades per one proton released) in the stability constant calculated for different number of protons released per one adsorbed Pb assumed in the model calculations. The effect of the assumed electrostatic position of Pb is less significant, namely, only one order of magnitude in the stabihty constant between the inner and outer sphere complex. It should be emphasized that all these results were calculated using the same model for primary surface charging (one set of TLM parametei-s). Table 5,21 illustrates how limited is... 

The stability constants of the silica-Pb surface complex (inner sphere, 1 proton released) calculated for different I-pK-Stern models are summarized in Table 5.29. 

Lutzenkirchen. J.. Influence of impurities on acid-base data for oxide minerals-analysis of observable surface charge and proton affinity distributions and model calculations for single crystal samples, Croat. Chem. Acta, 80, 333, 2007. 

The potential energy surface for the proton motion is not of a simple shape in our model calculation. Hence, the Eckart barrier formula is used for proton tunneling by adjusting the two variables in it [41]. Thus, the barrier for the proton transfer was fitted to the following Eckart formula ... 

Use of surface speciation models for prediction of adsorption and transport requires specification of the mode of bonding and speciation of oxyanions on oxide surfaces. FTIR spectroscopy (especially ATR and DRIFT) offers the potential to establish symmetry of surface species, protonation, and determination of monodentate or bidentate bonding. Determination of surface speciation is greatly enhanced when the spectroscopic information is combined with measurements of electrophoretic mobility (EM), calculation of point of zero charge and proton balance measurements before and after adsorption. We review adsorption of phosphate, carbonate, boron, selenate and selenite on Fe and A1 oxides. New preliminary spectra and EM and proton balance information for arsenate and arsenite adsorption on amorphous Fe and A1 oxide suggest that HASO4 and H2ASO3 are the dominant surface species. 

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