Model Calculations of the Thermochemical Properties of Gaseous Metal Halides.
SRI INTERNATIONAL MENLO PARK CA
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Two semi-empirical models that have proved useful in estimating the thermochemical properties of gaseous halides are the Rittner electrostatic model and the ionicity-corrected Birge-Sponer extrapolation. These two models, their limitations and their areas of applicability are reviewed so that their potential utility in estimating missing thermochemical data can be assessed realistically. A comparison of results of the gaseous II A metal mono- and dihalides, where thermochemical and molecular constant data are relatively complete, shows that the electrostatic model yields dissociation energies with an accuracy of 10 kcalmol or better. Application of the electrostatic model to the scandium-group and lanthanide halides is also discussed. There is considerable uncertainty about the nature of the overlap repulsion contribution for the polyatomic halides, but an empirically selected repulsion parameter seems to give satisfactory results. For diatomic molecules, the application of an ionicity correction to the linear Birge-Sponer value generally yields dissociation energies which are accurate to within ten percent or better, but the results are sensitive to the quality of the spectroscopic constants used in the evaluation. When used properly, the two models can be very helpful in providing reliable estimates of thermochemical properties. Author
- Physical Chemistry