Levich polaron mechanism

For example, Levich and co-workers put forward a polaronic energy transfer mechanism (which is applicable firstly in solid crystals) for the activation of ions in solution, the object being to explain the continuity in the current-potential relation. This is because in their view, the vibrational-rotational levels of ions in solution remain separated by the same amounts as in the gas phase. However, this objection is not cogent. Thus, the results of Moore et show that there are enough translator frequencies in water to justify a model in which liquid water contains a sufficient number of free... 

Hence, a polaronic type of energy transfer mechanism may not be necessary. The polaron is a clear concept in a crystal, but in a liquid the lack of order and periodicity over distances which would be involved in the model suggested by Levich makes efficient energy transfer by this means, over distances above some 10 A, difficult to accept. 

A decrease of the theoretical value of kq in this exothermic region is due to a decrease of the k23-value which is ascribed to small values of Franck-Condon factors in this process. A similar theoretical consideration was given by Levich and Dogonadze, using the polaron model (5). A quantum mechanical treatment of electron transfer was developed by Kestner et al. (6). These results indicated a similar bell-shaped curve for the relation between log kq and AG23. None of the treatments can interpret the experimental results. 

Marcus[195] gave a quantitative interpretation of this idea and above all, the role of solvent rearrangement within the framework of the absolute rate theory. Later, he also extended these concepts to electrochemical processes[196]. Similar concepts were also developed by Hush[197,198]. An important result of this work was the establishment of the relation between the transfer coefficient for adiabatic reactions and the charge distribution in the transient state. Gerischer[93,199] proposed a very useful and lucid treatment of the process of electron transfer in reactions with metallic as well as semiconductor electrodes. While the works mentioned above were mainly based on transition state theory, a systematic quantum-mechanical analysis of the problem was started by Levich, Dogonadze, and Chizmadzhev[200-202] and continued in a series of investigations by the same group. They extensively used the results and methods of solid state physics, and above all the Landau-Pekar polaron theory[203]. 

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See also in sourсe #XX -- [ , ]

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