Secondary minima phenomena

The small secondary minimum (well depth 2.3 kcal/mol) at the edge-to-edge half-way point does not affect the trajectories very much even for the lowest total energy. However, there are some rare exceptions where the representative point of the molecule spends rather a long time in this region of the potential energy surface (for certain trajectories, the integration was stopped after 1.5 10 second and the molecule was still trapped into the well). Then, the final outcome of the reaction is quite a random phenomenon. 

FIGURE 10.16. In many colloidal systems, the interaction energy curve will have a small minimum, the secondary minimum, M , that allows the particles to undergo a lose, reversible flocculation. In some systems of relatively large, monodisperse particles, the secondary minimmn may lead to an optical phenomenon called opalescence in which a very regular structure is developed (similar to a crystal structure) that produces beautiful and interesting patterns with incident light. 

Concerning the slow dynamics below the crossover temperature Tc, the predictive power of the theory seems to be rather limited. In particular, the emergence of intrinsic slow secondary processes, which seems to be associated with the dynamic crossover in the experimental spectra, is not contained even in the extended versions of the theory consequently, the slow dynamics spectrum is not reproduced correctly. In this respect, the extended theory introducing the hopping mechanism for describing the susceptibility minimum below Tc is misleading. On the other hand, the most prominent prediction of MCT below Tc is the anomaly of the nonergodicity parameter, which, as discussed, is found by different model-independent approaches. However, within the framework of MCT, this anomaly is closely connected with the appearance of a so-called knee feature in the spectral shape of the fast dynamics spectrum below Tc. This feature, however, has not been identified experimentally in molecular liquids, and only indications for its existence are observed in colloidal systems [19]. In molecular systems, merely a more or less smooth crossover to a white noise spectrum has been reported in some cases [183,231,401]. Thus, it may be possible that the knee phenomenon is also smeared out. 

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