Dynamics of solvation

Zimdars D, Dadap J I, Eisenthal K B and Heinz T F 1999 Femtosecond dynamics of solvation at the air/water interface Chem. Phys. Lett. 301 112-20... 

Stratt R M and Cho M 1994 The short-time dynamics of solvation J. Chem. Phys. 100 6700-8... 

Calculations on dynamics of solvation shells are still in their infancy. However, very recent papers on this subject, show that in most examples we cannot expect a realistic picture of solvent shells from a purely static approach. Most probably, molecular dynamics calculations and Monte Carlo methods will produce a variety of interesting data and will improve our knowledge on solvation of ions substantially. 

Ethylene glycol is a very viscous liquid and the molecule presents two close OH groups. It has to be noticed that, among all the different solvents studied by pulse radiolysis, the transition energy of the solvated electron absorption band is maximum in liquid ethylene glycol. For these reasons, the electron in EG seems to have a special behaviour and it is of great interest to study the dynamics of the formation of equilibrated solvated electron. Within this context, the present communication deals with the dynamics of solvation in EG of electrons produced by photoionisation of the solvent at 263 nm. The formation of solvated electrons is followed by pump-probe transient absorption spectroscopy in the visible spectral range from 425 to 725 nm and also in near IR. For the first time, the absorption spectrum of the precursor of the equilibrated electron is observed in EG. Our results are shortly compared by those obtained in water and methanol. 

Time-resolved fluorescence spectroscopy of polar fluorescent probes that have a dipole moment that depends upon electronic state has recently been used extensively to study microscopic solvation dynamics of a broad range of solvents. Section II of this paper deals with the subject in detail. The basic concept is outlined in Figure 1, which shows the dependence of the nonequilibrium free energies (Fg and Fe) of solvated ground state and electronically excited probes, respecitvely, as a function of a generalized solvent coordinate. Optical excitation (vertical) of an equilibrated ground state probe produces a nonequilibrium configuration of the solvent about the excited state of the probe. Subsequent relaxation is accompanied by a time-dependent fluorescence spectral shift toward lower frequencies, which can be monitored and analyzed to quantify the dynamics of solvation via the empirical solvation dynamics function C(t), which is defined by Eq. (1). 

Bagchi and co-workers [47-50] have explored the role of translational diffusion in the dynamics of solvation by employing a Smoluchowski-Vlasov equation (see also Calef and Wolyness [37] and Nichols and Calef [42]). A significant contribution to polarization relaxation is observed in certain cases. It is found that the Onsager inverted snowball model is correct only when the rotational diffusion mechanism of solvation dominates the polarization relaxation. The Onsager model significantly breaks down when there is an important translational contribution to the polarization relaxation [47-50]. In fact, translational effects can rapidly accelerate solvation near the probe. In certain cases, the predicted behavior can actually approach the uniform continuum result that rs = t,. 

The hydrated electron is characterized by its strong absorption at 720 nm (e = 1.9 x 104 dm3 mol-1 cm-1 (Hug 1981) the majority of the oscillator strength is derived from optical transitions from the equilibrated s state to the p-like excited state (cf. Kimura et al. 1994 Assel et al. 2000). The 720-nm absorption is used for the determination of its reaction rate constants by pulse radiolysis (for the dynamics of solvation see, e.g Silva et al. 1998 for its energetics see, e.g Zhan et al. 2003). IP only absorbs in the UV (Hug 1981), and rate constants have largely been determined by EPR (Neta et al. 1971 Neta and Schuler 1972 Mezyk and Bartels 1995) and competition techniques (for a compilation, see Buxton et al. 1988). In many aspects, H and eaq behave very similarly, which made their distinction and the identification of eaq" difficult (for early reviews, see Hart 1964 Eiben 1970 Hart and Anbar 1970), and final proof of the existence of the... 

Assel A, Laenen R, Laubereau A (2000) Femtosecond solvation dynamics of solvated electrons in neat water. Chem Phys Lett 317 13-22... 

B. Bagchi, Dynamics of solvation and charge-transfer reactions in dipolar liquids, Annu. Rev. Phys. Chem., 40 (1989) 115-141. 

Yang H, Snee PT, Kotz KT, Payne CK, Harris CB. Femtosecond infrared study of the dynamics of solvation and solvent caging. J Am Chem Soc 2001 123 4204-10. 

Hofer TS, Rode BM et al (2005d) Structure and dynamics of solvated Ba(II) in dilute aqueous solution - an ab initio QM/MM MD approach. Chem Phys 312 81... 

In this chapter we will mostly focus on the application of molecular dynamics simulation technique to understand solvation process in polymers. The organization of this chapter is as follow. In the first few sections the thermodynamics and statistical mechanics of solvation are introduced. In this regards, Flory s theory of polymer solutions has been compared with the classical solution methods for interpretation of experimental data. Very dilute solution of gases in polymers and the methods of calculation of chemical potentials, and hence calculation of Henry s law constants and sorption isotherms of gases in polymers are discussed in Section 11.6.1. The solution of polymers in solvents, solvent effect on equilibrium and dynamics of polymer-size change in solutions, and the solvation structures are described, with the main emphasis on molecular dynamics simulation method to obtain understanding of solvation of nonpolar polymers in nonpolar solvents and that of polar polymers in polar solvents, in Section 11.6.2. Finally, the dynamics of solvation with a short review of the experimental, theoretical, and simulation methods are explained in Section 11.7. 

Nowadays, however, molecular dynamics has been applied to study the dynamics of solvation of Cl53 as the solute in some polar solvents such as 1,4-dioxane and fluoroform. Cinacchi et al. [143] used an all-atom chemically detailed model of both... 

Other spectroscopic methods have also been used to study the statics and dynamics of solvation shells of ions and molecules [351-354], In this respect, solvation dynamics refers to the solvent reorganization e.g. rotation, reorientation, and residence time of solvent molecules in the first solvation shell) in response to an abrupt change in the solute properties, e.g. by photoexcitation of the solute with ultra-short laser-light pulses. Provided that this excitation is accompanied by an electron transfer or a change in the dipole moment, then the dynamics of this process correspond to how quickly the solvent molecules rearrange around the instantaneously created charge or the new dipole. 

Rentzepis PM, Jones RP, former J. (1973) Dynamics of solvation of an excess electron. J Chem Phys 59 766-773. 

Yang J, Kondoh T, Norizawa K, Nagaishi R, Tagushi M, Takahashi K, Rat oh R, Anishchik SV, Yoshida Y, Tagawa S. (2008) Picosecond pulse radiolysis Dynamics of solvated electrons in ionic liquid and geminate ion recombination in liquid alkanes. Radiat Phys Chem 77 1233-1238. 

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