Spectral timescale

PA at l. 48 eV appeal s instantaneously, shows spectral relaxation to the red, and decays on the same timescale of SE, as shown in Figure 8-9. We assign the observed PA to singlet Bu exciton transitions towards higher lying even parity (A ) states. We can speculate on the nature of this state within the proposed model. A possible candidate for the final slate is the inirachain biexciton. However, its energy level is located below the two-exciton stale by an amount equal to the bind-... 

F ure 4.4. TRIR difference spectra averaged over the timescales indicated following 266 nm laser photolysis of diphenyl diazomethane (6.3mM) in C02-saturated cyclohexane and cyclohexane-4i2. Since the detection of transient species is more problematic in regions with strong solvent bands due to the low transmission of IR light, cyclohexane-4i2 was required for the spectral region below 1600 cm. Reprinted with permission from B. M. Showalter and J. P. Toscano, J. Phys. Org. Chem. 2004,14, 743. Copyright 2004, John Wiley Sons Limited. 

Normally, time-resolved FT-IR spectroscopy (TRS FT-IR) possesses the same data characteristics. In a typical TRS FT-IR experiment, interferograms are assembled for a specific delay time after the photolysis pulse, and the data produced are normally finer-grained in frequency than in time. This type of experiment is complementary to experiments with fine-grained time information. It is particularly useful where a wide spectral range is necessary and works reasonably well for highly reproducible events which occur on relatively long timescales (fractions of seconds) (83). It is also an appealing system for use on shorter timescales, and it has... 

In order to study the resonant behavior of spectral density, let us plot the SNR as function of driving frequency go. From Fig. 22 one can see, that SNR as function of co has strongly pronounced maximum. The location of this maximum at co = mlnax approximately corresponds to the timescale matching condition mlnax 7i/Tmm, where Tmm is the minimal transition time from one state to another one. 

From the point of view of the study of dynamics, the laser has three enormously important characteristics. Firstly, because of its potentially great time resolution, it can act as both the effector and the detector for dynamical processes on timescales as short as 10 - s. Secondly, due to its spectral resolution and brightness, the laser can be used to prepare large amounts of a selected quantum state of a molecule so that the chemical reactivity or other dynamical properties of that state may be studied. Finally, because of its coherence as a light source the laser may be used to create in an ensemble of molecules a coherent superposition of states wherein the phase relationships of the molecular and electronic motions are specified. The dynamics of the dephasing of the molecular ensemble may subsequently be determined. 

Finally, and perhaps most importantly, is that many rheological processes operate over a very broad range of timescales, much broader than IR or UV spectral widths. The relaxation processes are often wider than those readily achievable by experimental measurement on any rheometer. We can extend our knowledge of the material to an extent beyond the operating ranges qualitatively by comparing data gathered in different tests with their transforms. 

Slow reorganization dynamics in the adsorbate/adsorbent complex after excitation of the Franck-Condon state. This could explain the spectral redshift of fluorescence with time (Figure 8.8, upper right, and Figure 8.9). In liquid solution, the excited state equilibrates on the picosecond timescale, but is has been shown(23) that this process can slow down on surfaces to 10-50 nsec. 

Finally, it is worthy of remark that, though the comparison between the timescales leads to an almost perfect agreement between the predictions of the Allegra and Ganazzoli model and the collective and self-motion results, it is evident that clear differences appear when comparing the spectral shapes of the respective functions. The model delivers close to exponential decays for both correlators while experimentally one observes significantly stretched relaxation function (j0=O.5). 

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