Spectroscopy laser, ultrafast

Netzel, T.L. In "Biological Events Probed by Ultrafast Laser Spectroscopy" R.R. Alfano, Ed. Academic Press, New York, 1983 p. 79. 

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. 

This narrative echoes the themes addressed in our recent review on the properties of uncommon solvent anions. We do not pretend to be comprehensive or inclusive, as the literature on electron solvation is vast and rapidly expanding. This increase is cnrrently driven by ultrafast laser spectroscopy studies of electron injection and relaxation dynamics (see Chap. 2), and by gas phase studies of anion clusters by photoelectron and IR spectroscopy. Despite the great importance of the solvated/ hydrated electron for radiation chemistry (as this species is a common reducing agent in radiolysis of liquids and solids), pulse radiolysis studies of solvated electrons are becoming less frequent perhaps due to the insufficient time resolution of the method (picoseconds) as compared to state-of-the-art laser studies (time resolution to 5 fs ). The welcome exceptions are the recent spectroscopic and kinetic studies of hydrated electrons in supercriticaF and supercooled water. As the theoretical models for high-temperature hydrated electrons and the reaction mechanisms for these species are still rmder debate, we will exclude such extreme conditions from this review. 

L. J. Noe, in Biological Events probed by Ultrafast laser Spectroscopy (Ed., R. R. Alfano), Academic Press, New York, 339, 1982. 

The ultrafast PT, which occurs typically on time scales of 10 13-10 14 s will not be considered. Such transfers are observed in molecular systems in which the potential energy surface (PES) governing the proton motion is essentially barrierless but has different minima positions in different electronic states, so that the proton finds itself in an off-equilibrium position after electronic excitation and relaxes to the new equilibrium position. The contribution of tunneling may be disregarded and the rate of these processes does not depend very strongly on temperature. These reactions, which are of great current interest, are intensely studied by ultrafast laser spectroscopy and are reviewed elsewhere [16,17],... 

We conclude that putting the emphasis on the time resolution without offering adequate spectroscopic base would ensure a new stalemate. Therefore, the development of fast, highly selective and sensitive techniques for detection of short-lived intermediates in spurs is the most urgent experimental problem in radiolysis of liquids. Ultrafast laser spectroscopy must be utilized to prepare the ground for the ultrafast pulse radiolysis with the development of better detection techniques. 

The measurement of ultrafast energy relaxation times (represented by T ) in various materials is also important in ultrafast laser spectroscopy. Examination of using non-transform-limited incoherent or coherent light for this purpose is an attractive subject as well as for the purpose of determining T2. For this purpose, however, other types of optical processes than those dealt with in the previous sections are required to be considered. 

The conclusions derivable here are of course limited to a certain extent because they are still based on a restricted model of calculation, and more refined theoretical and corresponding experimental studies must be promoted to establish this type of spectroscopic method. The present results are, however, hoped to provide a useful guide to the future trend of ultrafast laser spectroscopy. 

Light harvesting in photosynthetic purple bacteria is reviewed in detail based on recent advances in structure determination and ultrafast laser spectroscopy. Knowledge obtained from photosynthesis research forms a solid ground for studies of various artificial light harvesting systems. 

R.R. Alfano (ed.) Biological Events Probed by Ultrafast Laser Spectroscopy (Academic, New York 1982)... 

Center for Ultrafast Laser Spectroscopy Adam Mickiewicz University Poznan, Poland... 

Because the high quantum yield originates from the high-rate isomerization, which competes with other relaxation processes in the excited state of rhodopsin, ultrafast laser spectroscopies were applied to investigate the isomerization process of the retinal chromophore. Picosecond time-resolved spectroscopy was appHed to the photochemistry of rhodopsin, and the formation of the primary intermediates was reported, such as photorhodopsin and bathorhodopsin at room temperature. - - However, the time resolution needed to be improved in order to detect the cis-tram isomerization process in the excited state of rhodopsin. The direct observation of the rhodopsin excited state was reported in 1991, in which the primary intermediate photorhodopsin formed from the excited state of rhodopsin within 200 fs. Later, the effects of oscillatory features with a period of 550 fs (60 cm ) on the formation kinetics of photorhodopsin, were observed, suggesting that the primary step in vision is a vibrationally coherent process. 

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