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Dynamics of Diffusion-Controlled Recombination of Ions in Ionic Solutions. Limits of Validity of the Debye - Smoluchowski Equation

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The diffusion and recombination process in an ensemble of isolated single pairs of opposite charges is usually described by the Debye Smoluchowski equation. The present work is an overview of a series of computer simulations of diffusion and recombination of ions in solution performed with the aim to determine the limits of validity of the Debye - Smoluchowski equation In the first part of the project, the calculations were performed for the media with the short mean free path MFP of the free movement of ions between scattering events, i.e., for the conditions of the diffusion model of the ion transport. Results were obtained on the probability of ion survival as a function of time and the probability of ion escape from recombination at infinite time. The recombination processes in the clusters of non-separable ion pairs and the bulk recombination of ions in solution were simulated. The deviations of the multi-pair kinetics and escape probability from the corresponding results of the calculations performed on a basis of the Debye-Smoluchowski theory are significant but we found that the Debye - Smoluchowski recombination rate constant can be applied for all concentrations of ions. We also consider the effects of restricted geometry and anisotropy of the medium on the kinetics of the recombination of oppositely charged species in each others field and the escape probability. This model roughly corresponds to the electron - cation recombination in organic crystals. The results for short MFPs were then compared with the results of the calculations of the electron - cation recombination in the systems characterized by long MFP of electron between the scattering events.

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  • Physical Chemistry
  • Crystallography
  • Atomic and Molecular Physics and Spectroscopy

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