Short-range Effects Exchange

In second order one has the (., -ind energies which were found 

The terms defined in (l)-(5) provide a complete description (to second order) of AE in any complex. Now there are many complexes in which the ground state of AB acquires some ionic character A B . Formally, this transfer of a 

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The dipole moment of a Van der Waals dimer consists in principle of three contributions the dipole moments of the two monomers and the interaction dipole moment. In the usual Van der Waals molecules the interaction dipole is in the order of 0.1 D which for a large part arises from induction. That is, permanent moments on the one monomer induce a dipole moment on the other. Obviously, this effect is absent in the case of a dimer consisting of two noble gases. Here the interaction dipole moment is an order of magnitude smaller and is largely due to the short range effects exchange and penetration . 

This consideration gives an explanation of the existence of surface-inactive ions for which the attractive contribution due to the short-range (electron exchange) metal surface-ion interaction is absent or insufficiently strong to compensate the aforementioned repulsive effect. It may also be responsible for the strong influence of the iodide adsorption on the hydrogen evolution, despite the absence of marked specific adsorption of H3O+ ions [260]. 

Eaker and Porath studied the elution of amino acids on Sephadex 6-10 with particular focus on the eluant ionic strength and composition (e.g. acetic acid or pyridine content) (11). They described the gel as a "weak exchanger," thus accounting for effective separations of mixtures of up to seven amino acids. They noted that K ec increases with ionic strength, and attributed this effect to variations in the "effective size" of the ion, which includes the "electrical double layer and the hydration layer." In addition to discussing the effects of ionic sites on gel and solute, Eaker and Porath also discussed the "aromatic adsorption" of solutes with coplanar II electron systems, and the hydrophobic adsorption of partly apolar solutes (accompanied by a positive enthalpy change). They pointed out that such "short range" effects require "intimate contact" between solute and gel and are unlikely to occur in the presence of electrical repulsion. 

The first two terms describe each subsystem dressed with the interaction of each other. It is now apparent that exchange forces between the two subsystems have to be included in order to get the total force acting on the nuclei. This latter force is usually mimicked with a repulsive short range potential. A pseudo potential method can also be used in a microscopic approach to the surrounding medium effects [104,105],... 

Figure 11.14 (A) Internal Rb-Sr isochron for a system composed of three crystalline phases of initial compositions Aq, Bq, and Q formed at time t = 0 and thereafter closed to isotopic exchanges up to time of measurement t, when they acquired compositions A, and C. (B) Effects of geochronological resetting resulting from metamorphism or interaction with fluids. X, X2, and X3 bulk isotopic compositions of the three rock assemblages. In cases of short-range isotopic reequilibration, the three assemblages define crystallization age and original ( Sr/ Sr)o of the system the three internal isochrons (concordant in this example) define resetting age.

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