Charged particles with condensed medium

B. Specific Features of the Interaction of Charged Particles with a Condensed Medium... 

Abel assumed that molecules of each.expl vibrate during deton and thus incite vibrations of the surrounding medium at a frequency characteristic for each. expl. The particles of the medium spread in all directions and, if another charge of the same expl is in the neighborhood, its particles start to vibrate in resonance and thus might initiate deton. This was an explanation of the phenomenon known now as "detonation by influence or "sympathetic detonation . The propagation of deton in condensed expls was assumed to be caused by. spread of vibrations in resonance with particles inside the expl. This theory was abandoned in 1883 in favor of the Berthelot Theory of Detonation, which is briefly described in Vol 2 of this Encycl, p B106-L. Berthelot s Theory was further developed by. P. Vieille... 

Following from formula (4.54), the transfer of energy on excitation of molecules has a noticeable probability even in the case where the impact parameter is much greater than their size d. Since the intermolecular spacings in a condensed medium are of order of d, a charged particle interacts with many of its molecules. The polarization of these molecules weakens the field of the particle, which, in its turn, weakens the interaction of the particle with the molecules located far from the track. This results in that the actual ionization losses are smaller than the value we would get by simply summing the losses in collisions with individual molecules given by formula (5.1). This polarization (density) effect was first pointed out by Swann,205 while the principles of calculation of ionization losses in a dense medium were developed by Fermi.206... 

Consider a spherical colloidal particle with a n ativety charged surface. This potyelectrotyte will tend to attract the positive ions from the dispersion medium around itself. As a result, the macromolecule will soon be surroimded by an ton atmosphere, a region in which there will be a statistical preference for ions of the opposite sign. Helmholtz likened this situation to the charge distribution in a parallel plate condenser. The condenser consists of two concentric spheres of opposite signs, and the two plates of the condenser constitute the so called rigid double layer (see Figure 3.7). 

An important subset of many-body potentials shown to be important for simulating interfacial systems are those referred to as polarizable force fields.Various aspects of polarizable force fields, especially for use in biomolecular modeling, is explained by Ren et al. in Chapter 3 of this volume. If one treats the fixed charges in Eq. [3] as parameters to be fitted to obtain the best agreement of the condensed phase simulations with experiments, in many cases one finds that the optimal values are considerably different from those obtained from a fit to a molecular (gas phase) dipole moment or from quantum calculations on isolated molecules. This is because in a condensed medium, the local electric field E, (at the location of a particle i) is determined by all the fixed charges and by all the induced dipoles in the system ... 

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