Explanation-based variable generalization

General models of the electron-capture process are based on the kinetic model of Wentworth and co-workers [254,293,295,298,313-315]. The ionization chamber is treated as a homogeneous reactor into which electrons are continuously introduced at a constant rate and electron-capturing solutes are added at a variable rate in a constant flow of carrier gas. The major consumption of electrons is via electron capture and recombination with positive ions. The model can be expanded to allow for the presence of electron-capturing contaminants and the formation of excited state negative ions. The kinetic model provides a reasonable explanation of the influence of pulse sampling conditions and temperature on the detector response, but exactly calculated solutions are rare. Again, this is because the necessary rate constants are usually unavailable, and the identity and relative concentration of all species present in the detector are uncertain. The principal reactions can be summarized as follows ... 

Characterization of Acidity/Basicity. The acid-base properties of a metal oxide play a crucial part in catalysis and are generally a function of pretreat-ment/preparation variables and catalyst morphology. It is important to be able to fully characterize the surface in terms of the strength and number of acid and base sites. Frequently, TPD methods involving probe molecules have been applied. However, caution must be exercised to simple TDP measurements, as it is often not clear whether the probe molecule is behaving in the acid-base manner assumed. An illustrative example of this is provided in a study of desorption of NH3 from CaO, in which the high temperature of desorption may lead one to believe that CaO is a strong acid (280). The explanation for this... 

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