Time of an Ion Atmosphere

An idea of the time involved in the readjustment of the ionic cloud around the moving central ion can be obtained by a thought experiment suggested by Debye (Fig. 4.92). Consider a static central ion with an equilibrium, spherical ionic cloud around it. Let the central ion suddenly be discharged. This perturbation of the ion-ionic cloud system sets up a relaxation process. The ionic cloud is now at the mercy of the thermal 

The actual mechanism by which the ions constituting the ionic atmosphere are dispersed is none other than the random-walk process described in Section 4.2. Hence, the time taken by the ionic cloud to relax or disperse may be estimated by the use of the Einstein-Smoluchowski relation (Section 4.2.6) 

What distance jc is to be used hi other words, when can the ionic cloud be declared to have dispersed or relaxed These questions may be answered by recalling the description of the ionic atmosphere where it was stated that the charge density in a dr-thick spherical shell in the cloud declines rapidly at distances greater than the 

Debye-Huckel length k. Hence, if the ions diffuse to a distance k the central ion 

The Quantitative Measure of the Asymmetry of the Ionic Cloud around a Moving Ion 

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