Charge dynamic redistribution

When analyzing the optical properties of nanoparticles embedded in a medium, one should take into account effects arising at the particle-matrix interface, such as the static and dynamic redistributions of charges between electronic states in the particles and the environment in view of their chemical constitution [59]. 

In this chapter, we studied the formation of silver nanoparticles in PMMA by ion implantation and optical density spectra associated with the SPR effect in the particles. Ion implantation into polymers carbonizes the surface layer irradiated. Based on the Mie classical electrodynamic theory, optical extinction spectra for silver nanoparticles in the polymeric or carbon environment, as well as for sheathed particles (silver core -l- carbon sheath) placed in PMMA, as a function of the implantation dose are simulated. The analytical and experimental spectra are in qualitative agreement. At low doses, simple monatomic silver particles are produced at higher doses, sheathed particles appear. The quantitative discrepancy between the experimental spectra and analytical spectra obtained in terms of the Mie theory is explained by the fact that the Mie theory disregards the charge static and dynamic redistributions at the particle-matrix interface. The influence of the charge redistribution on the experimental optical spectra taken from the silver-polymer composite at high doses, which cause the carbonization of the irradiated polymer, is discussed. Table 8.1, which summarizes available data for ion synthesis of MNPs in a polymeric matrix, and the references cited therein may be helpful in practice. 

In the excited state, the redistribution of electrons can lead to localized states with distinct fluorescence spectra that are known as intramolecular charge transfer (ICT) states. This process is dynamic and coupled with dielectric relaxations in the environment [16]. This and other solvent-controlled adiabatic excited-state reactions are discussed in [17], As shown in Fig. 1, the locally excited (LE) state is populated initially upon excitation, and the ICT state appears with time in a process coupled with the reorientation of surrounding dipoles. 

For large laser intensities (i.e., a > 1) or for simulation times longer than (M/m)1/2 times the radiation period, the ion dynamics plays an important role in the strong laser-plasma interaction and specifically for the evolution of RES. Indeed, the ES field associated with the charge separation acts in order to redistribute the ion density. Two-dimensional [12,13] and three-... 

In view of the great importance of chemical reactions in solution, it is not surprising that basic aspects (structure, energetics, and dynamics) of elementary solvation processes continue to motivate both experimental and theoretical investigations. Thus, there is growing interest in the dynamical participation of the solvent in the events following a sudden redistribution of the charges of a solute molecule. These phenomena control photoionization in both pure liquids and solutions, the solvation of electrons in polar liquids, the time-dependent fluorescence Stokes shift, and the contribution of the solvent polarization fluctuations to the rates of electron transfer in oxidation-reduction reactions in solution. 

Because of the fundamental importance of solvent-solute interactions in chemical reactions, the dynamics of solvation have been widely studied. However, most studies have focused on systems where charge redistribution within the solute is the dominant effect of changing the electronic stale.[I,2] Recently, Fourkas, Benigno and Berg studied the solvation dynamics of a nonpolar solute in a nonpolar solvent, where charge redistribution plays a minor role.[3,4] These studies showed two distinct dynamic components a subpicosecond, viscosity independent relaxation driven by phonon-like processes, and a slower, viscosity dependent structural relaxation. These results have been explained quantitatively by a theory of solvation based on mechanical relaxation of the solvent in response to changes in the molecular size of the solute on excitation.[6] Here, we present results on the solvation of a nonpolar solute, s-tetrazine, by a polar solvent, propylene carbonate over the temperature range 300-160 K. In this system, comparisons to several theoretical approaches to solvation are possible. 

The solvation dynamics of Coumarin 133 in propylene carbonate has been studied by Barbara and cowoikers by femtosecond fluorescence spectroscopy.(151 This solute has a large charge redistribution in the excited state, and solvation is dominated by the dielectric response of the solvent to the new change distribution. We... 

The absence of temperature dependence of the EL decay dynamics indicates that the counter field is produced mainly by redistribution of charges, rather than by the motion of structural dipoles, since the latter is highly temperature dependent. 

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