Solvation dynamics general observations

The continuum dielectric theory used above is a linear response theory, as expressed by the linear relation between the perturbation T> and the response , Eq. (15.1b). Thus, our treatment of solvation dynamics was done within a linear response framework. Linear response theory of solvation dynamics may be cast in a general form that does not depend on the model used for the dielectric environment and can therefore be applied also in molecular (as opposed to continuum) level theories. Here we derive this general formalism. For simplicity we disregard the fast electronic response of the solvent and focus on the observed nuclear dielectric relaxation. 

The previous sections have focused on a generie model of a very simple solvent, in which solvation dynamics is determined by molecular translations and reorientations only. These in turn are controlled by the solvent molecular mass, moment of inertia, dipole moment and short-range repulsive interactions. When the solvent is more eomplex we may expect specific structures and interaetions to play signifieant roles. Still, numerical simulations of solvation dynamics in more eomplex systems lead to some general observations ... 

An early application of this type of analysis was to decompose Pio/v( ) into its rotational, translational and their cross-correlation subspectra. It was shown through this decomposition that electrostatic solvation spectra for dipole and charge perturbations are dominated by rotational dynamics. More generally, it was shown how the range and symmetry of AP and molecular properties such as masses and moments of inertia are related to the relative contributions of rotational and translational degrees of freedom to SD. INM analysis has also proved useful in comparing the molecular mechaitisms contributing to short-time dynamics observed in different experiments,such as SD, optical Kerr ef-... 

The nonequilibrium solvation function iS (Z), which is directly observable (e.g. by monitoring dynamic line shifts as in Fig. 15.2), is seen to be equal in the linear response approximation to the time correlation function, C(Z), of equilibrium fluctuations in the solvent response potential at the position of the solute ion. This provides a route for generalizing the continuum dielectric response theory of Section 15.2 and also a convenient numerical tool that we discuss further in the next section. 

Continuum dielectric models of solvation can be generalized to include some aspects of the solvent molecularity. This has lead to the dynamic mean spherical approximation which improves the agreement between these kind of theories and experimental observations."... 

The couple S/S is selected with a specific and intense optical absorption of S or S , so that the electron-transfer reaction can be observed directly. In the early stages of atom coalescence, the redox potentials of the atom and of the smallest clusters are generally far below that of the donor and the transfer from S to the oligomer does not occur. The ion reduction is caused exclusively by solvated electrons and alcohol radicals (Eqs. 2, 8, and 9). The nucleation and coalescence dynamics are thus the same as in the absence of (Eqs. 10 and 11). Beyond a certain critical time, tc, that is large enough to enable the growth of clusters and the increase of their potential above the threshold imposed by the electron donor S , electron transfer from this monitor to the supercritical clusters is allowed (Eq. 32) and detected by the absorbance decay of S (Fig. 6). For n > ny. 

Salts, ions, and ionic liquids in water are widely studied in AIMD. Several anions [165-172], cations [153, 165, 173-182], and ion pairs [164, 183, 184], as weU as ionic hquids ion pairs [185] in water were studied using AIMD. In all cases structural as well as dynamical properties of the ion s hydration shell were examined. In some cases the influence of the solvated ions on the water molecules were studied within the Wannier approach. In general, little effect of the halogen ions on the dipole moments of the water molecules in the first hydration shell was observed, while further water molecules remain unaffected. In contrast to this, it was observed that cations increase the dipole moments of the first hydration shell water by approximately 0.2-0.5 D. The second hydration shell and the bulk phase water molecules were mostly unaffected with regard to the dipole moment by the cations as well [91]. 

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