Ultrafast solvent dynamics

Giraud, G., Gordon, C. M., Dunkin, 1. R., and Wynne, K., The effects of anion and cation substitution on the ultrafast solvent dynamics of ionic liquids A time-resolved optical Kerr-effect spectroscopic study, /. Chem. Phys., 119,464-477,2003. 

Stokes Law and Walden s Rule - Role of Ultrafast Solvent Dynamics... 

M. Cho, S. J. Rosenthal, N. F. Scherer, L. D. Ziegler, and G. R. Fleming, J. Chem. Phys., 96, 5033 (1992). Ultrafast Solvent Dynamics Connection between Time Resolved Fluorescence and Optical Kerr Measurements. 

Rasaiah, J. and Zhu, J. (1994) Solvent dynamics and electron transfer reactions,in Gauduel, Y. and Rossky, P. J.(eds.), Ultrafast reaction dynamics and solvent effects, AIP Press, New York,pp.421-434. 

In the case of electron transfer reactions, besides data on the dynamic Stokes shift and ultrafast laser spectroscopy, data on the dielectric dispersion (w) of the solvent can provide invaluable supplementary information. In the case of other reactions, such as isomerizations, it appears that the analogous data, for example, on a solvent viscosity frequency dependence 17 ( ), or on a dynamic Stokes fluorescence shift may presently be absent. Its absence probably provides one main source of the differences in opinion [5, 40-43] on solvent dynamics treatments of isomerization. 

H.-H. Limbach, G. Scherer, L. Meschede, F. Aguilar-Parrilla, B. Wehrle, J. Braun, Ch. Hoelger, H. Benedict, G. Buntkowsky, W. P. Fehlhammer, J. Elguero, J. A. S. Smith and B. Chaudret in Ultrafast Reaction Dynamics and Solvent Effects, Experimental and Theoretical Aspects, (Eds. Y. Gauduel and P. J. Rossky), American Institute of Physics, 1993. 

Han P, Bartels DM (1994) Encounters of H and D atoms with 02 in water relative diffusion and reaction rates. In Gauduel Y, Rossky P (eds) AIP conference proceedings 298. "Ultrafast reaction dynamics and solvent effects." AIP Press, New York, 72 pp Hasegawa K, Patterson LK (1978) Pulse radiolysis studies in model lipid systems formation and behavior of peroxy radicals in fatty acids. Photochem Photobiol 28 817-823 Herdener M, Heigold S, Saran M, Bauer G (2000) Target cell-derived superoxide anions cause efficiency and selectivity of intercellular induction of apoptosis. Free Rad Biol Med 29 1260-1271 Hildenbrand K, Schulte-Frohlinde D (1997) Time-resolved EPR studies on the reaction rates of peroxyl radicals of polyfacrylic acid) and of calf thymus DNA with glutathione. Re-examination of a rate constant for DNA. Int J Radiat Biol 71 377-385 Howard JA (1978) Self-reactions of alkylperoxy radicals in solution (1). In Pryor WA(ed) Organic free radicals. ACS Symp Ser 69 413-432... 

We have already mentioned in the Introduction (Section 3.7.1) the importance of conical intersections (CIs) in connection with excited electronic state dynamics of a photoexcited chromophore. Briefly, CIs act as photochemical funnels in the passage from the first excited S, state to the ground electronic state S0, allowing often ultrafast transition dynamics for this process. (They can also be involved in transitions between excited electronic states, not discussed here.) While most theoretical studies have focused on CIs for a chromophore in the gas phase (for a representative selection, see refs [16, 83-89], here our focus is on the influence of a condensed phase environment [4-9], In particular, as discussed below, there are important nonequilibrium solvation effects due to the lack of solvent polarization equilibration to the evolving charge distribution of the chromophore. 

K. Kakitani, N. Matsuda, T. Denda, N. Mataga, and Y. Enomoto, Ultrafast Reaction Dynamics and Solvent Effects, AIP Conf. Proc., New York, Y. GauduelandP. J. Rossky, eds., 1993, p. 298. 

Most recently we have investigated ultrafast ET (as fast as ca. 10 3 j-l) between excited dye and weakly polar electron-donating solvent molecules [10-14]. These systems have several interesting features. (1) The electron donor and acceptor are in contact and there is no translational difhision to induce ET. (2) Non-equilibrium reaction caused by solvent dynamics can be observed. (3) Some systems have a rate of ET much faster than that of solvent relaxation. In this case the reaction is mainly due to the nuclear dynamics and is independent of solvent dynamics. (4) A clear substituent effect of electron acceptor molecules on the rates of ET is observed. 

P. F. Baibara and W. Jaizeba, Adv. Photochem. IS, 1 (1990) Dynamics andMechanizms of Photoinduced Electron Transfer and Related Phenomena, ed. N.Mataga, T. Okada, and H. Masuhaia, (Elsevier, Amsterdam, 1992) " Ultrafast Reaction Dynamics aid Solvent Effects", Y. Gauduel and P. J. Rossky Eds., AH Conference Proceedings 298 (1994). 

J. A. S. Smith, B. Chaudret, in Ultrafast Reaction Dynamics and Solvent Effects, Experimental and Theoretical Aspects, Y,.Gauduel, P.J. Rossky (Eds.),... 

Belloni, J. Khatouri, J. Mostafavi, M. Amblard, J. In Ultrafast Reaction Dynamics and Solvent Effects Rossky, P. J. Gauduel, Y., Eds. American Institute of Physics College Park, MD, 1994 p 527. 

Figure 11. Schematic representation of sequential events of an SNj ionization reaction in a polar liquid. Elementary events involve contact ion pairs (CIP) and solvent-separated ion pairs (SSIP). In ionic aqueous solutions, the influence of different ion-pair configurations on early electron-transfer trajectories can be considered through the investigation of ultrafast electronic dynamics and radical ion-...

J. Belloni, J. Khatouri, M. Mostafavi, J. Amblard, in Ultrafast reaction dynamics and solvent effects, P.J. Rossky and Y. Gauduel (eds). Am. Inst. Phys., (1993) 541. 

Since the solvation time correlation function is known both from experiments and from computer simulations, we can easily carry out the above exercise. When this is done, the theory predicts a lack of, or weak, dependence of the electron transfer rate on solvent dynamics, for weakly adiabatic reactions the reason being the dominance of the ultrafast component in SD of water, so the solvent moves too fast to offer any retardation ... 

In fluid solvents at room temperature, spectral relaxation is usually comjdete prior to emission and occurs within abont 10 ps. This process is too rapid to be resolved with the usual instrumentation for TD or FD fluorescence. However, advances in laser technology and methods for ultrafast spectroscopy have resulted in an increasing interest in picosecond and femtosecond solvent dynaaiics. Becmise of the rapid timescale, the data on solvent dynamics are usually obtained using flurvescence upconversion. Hiis method is described in Section 4.7.C. lypical data are... 

The information presented in Sections 5.1.1.1-5.1.1.4 and Table 5.1, although construed to pertain to the effects of ions on the structure of the solvent, in the sense of whether it is enhanced or loosened by the presence of ions, actually reflects the effects on the dynamics of the solvent in the immediate neighborhood of the ions. The mean residence times of water molecules in the vicinity of ions are indirectly measures of the effect of the ions on the structure of the water as described in Section 5.2.1. There are aspects of solvent dynamics that are not covered by these effects, such as the orientational relaxation rate and hydrogen-bond lifetimes. Two experimental methods have mainly been employed for obtaining such information ultrafast mid-infrared and dielectric relaxation spectroscopy on the fs to ps time scales. Some slower processes were studied by NMR relaxation studies. Computer simulations added additional information, since it could be applied to individual ions rather than salts. As for the ion effects dealt with in the previous sections, the vast majority of the studies dealt with ions in aqueous solutions and only few ones considered ions in nonaqueous solvents... 

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