Diffusion mechanism collinear

The first of the theoretical chapters (Chapter 9) treats approaches to the calculation of thermal rate constants. The material is familiar—activated complex theory, RRKM theory of unimolecular reaction, Debye theory of diffusion-limited reaction—and emphasizes how much information can be correlated on the basis of quite limited models. In the final chapt, the dynamics of single-collision chemistry is analyzed within a highly simplified framework the model, based on classical mechanics, collinear collision geometries, and naive potential-energy surfaces, illuminates many of the features that account for chemical reactivity. 

Frenkel defects and impurity ions can diffuse through the silver halide lattice by a number of mechanisms. Silver ions can diffuse by a vacancy mechanism or by replacement processes such as collinear or noncollinear interstitialcy jump mechanisms [18]. The collinear interstitial mechanism is one in which an interstitial silver ion moves in a [111] direction, forcing an adjacent lattice silver ion into an interstitial position and replacing it The enthalpies and entropies derived from temperature-dependent ionic conductivity measurements for these processes are included in Table 4. The collinear interstitial mechanism is the most facile process at room temperature, but the other mechanisms are thought to contribute at higher temperatures. 

Clausius-Clapeyron equation., 101 Collinear collision, 197 Coltrin, M.E, 33 Complete segregation, 455 Complex mechanisms, 226 Concentration gradient, 360 Confidence interval, 519, 523, 537 Configurational diffusion, 360 Connor, E.F., 17... 

In this mechanism, an interstitial ion or atom moves onto a regular lattice site by shoving the particle which was originally there onto an interstitial site. If the particles are charged, and if a linear impulse is assumed, then in one elementary step of interstitialcy diffusion the electrical charge is transported twice the distance of each of the two individual ions involved. However, the advancement of the two particles will not necessarily occur in a straight line (i. e. collinear). 

For interstitialcy diffusion of Ag in AgBr the value of f equals 2/3 for a collinear jump and 0.97 for a non-collinear jump. Following Eq.6.64 one would thus expect that Dt/Dr would range from 0.33 for a collinear jumps to 0.728 for non-collinear jumps. On this basis Friauf (1957, 1962) concluded that the interstitialcy diffusion is the important mechanism in AgBr and that collinear jumps are most important at low temperatures while non-collinear jumps become increasingly important the higher the temperature. 

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