Carbonates Electronic structures and properties

Molecular orbitals Carbon atomic Oxygen atomic Interatomic Extramolecular 

X-ray emission peaks they generate are significantly different in shape. Similarly, the calculated ionization potentials are based upon either a Koopmans theorem or on a transition-state approach and do not correct for many-body effects, which are important for quantitative matching with spectra (Cederbaum et al., 1977). This is particularly important for the O 2s region, which does not show the clear two-peak structure expected on the basis of the SCF calculations in the x-ray photoelectron 

The XANES of carbonates have been studied by Madix et al. (1988), who observed a transition at 290 eV to an orbital they identified as 7T c o corresponding to the Za/ orbital in Fig. 5.25, about 1 eV above the C li ionization potential (Fig. 5.27 Tegeler et al., 1980). The carbon x-ray emission spectrum and XANES calculated for C(OH)j by Tossell (1986) are compared with experimental values in Table 5.12 and show reasonable agreement. Note that the previously calculated C Is ionization potential of Tossell (1986) was too high by almost 20 eV (306.4 versus 288.8 eV), leading to the erroneous conclusion that the C Is— XANES peak lay below the C Is ionization threshold. As observed in numerous other cases, the core ct resonance (C ls- 4e in this case) is sensitive to nearest-neighbor distance and is thus a measure of R(C-0). 

Based on the carbon and oxygen x-ray emission and XANES energies in Figs. 5.26 and 5.27, we would estimate a le — Za/ uv excitation energy of about 7 eV (—533 for the O ls- 2a XANES, less —526 for the O s- e x-ray emission). Studies of carbonate in solution give an absorption that goes off scale at about 6 eV, with a distinguishable shoulder at 5,7 eV (Muller et al., 1967), consistent with expectations from the x-ray spectra. 

Transition Calculated value [for C(0H 3+ cluster] Experimental value 

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