Self-energy and adsorption

As an illustration consider the adsorption of molecules into zeolites, discussed in Chapter 2. If an adsorbate molecule or atom is immersed in a medium of dielectric constant z( ) instead of a vacuum, the dispersion selfenergy is modified, and now takes a form corresponding to eq. (3.1) 

The expression immediately gives an estimate of the enthalpy of adsorption in taking an atom from the gaseous (vacuum) state to a liquid, or to a composite medium like a zeolite, characterised by its measured dielectric frequency dependent response (o ). It is, exactly as for the electrostatic Bom self-energy in taking an ion from vacuum to water  

The measured enthalpies of adsorption of alkanes into zeolites are very large, and can be calculated from this formula [13]. The dielectric constants for the open networks formed by the aluminium silicate frameworks of zeolites can be related to the known and measured dielectric and optical properties of bulk quartz. The calculation assiunes that the zeolite framework tessellates a hyperbolic surface as described in Chapter 2. The polarisabilities of different adsorbate alkanes are also known. When the calculations are carried out for a whole range of alkanes as adsorbate molecules and for different zeolites (with differing pore structure and size) the agreement between measured and predicted heats of adsorption is excellent (cf. Fig. 3.2). The results depend 

This paradox, of physics, is more apparent than real, and the chemists have persisted with the fiction that objects exist. The concept of a chemical bond, ionic, van der Waals, covalent, is taken for granted and is essential to chemistry. The first two make no sense except in the context of an infinite crystal. (An ion pair in solution, or a hydrophobic bond in water between two methane molecules is due to complex statistical mechanical solvent mediated association behaviom , to be discussed below.) 

even for the simplest conceivable cases of ionic and van der Waals crystals, global properties, many-body forces that depend on the arrangement of atoms, and local force properties are linked. 

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