Intermediate scanning function

The information on the normalized intermediate scattering function is given by the ratio of the oscillation amplitude and the limiting intensities (lup- fdown). The amplitude a=R S(Q, t) contains information on the instrumental resolution R = t] lo, t) jexp(-2 2o) and S(Q, t) and can be extracted from the results of the symmetry scan... 

In order to study absorbance change as a function of wavelength, we are currently modifying the flow apparatus to include a Perkin-Elmer Model 108 Rapid-Scan Monochromator. This will allow us to study absorbance as a function of both wavelength and time and should help in the assigning of decay rates of the various bands. It should also allow us to detect absorbing intermediates with lifetimes of a few milliseconds or longer. 

Electrochemical simulations of the concentration and scan-rate dependence of the voltammetry potentially provide the composition of the intermediates formed during the reaction cycle together with estimates of the rate and equilibrium constants. As shown in the preceding section spectroscopic information can greatly assist the elucidation of the molecular details of these reactions, however, reliable deduction of the structure is greatly enhanced by the incorporation of structural and computational information (Section 1.6). The rapid advance in computer power and implementation of density-functional theory allows a more quantitative approach for evaluation of proposed structures based on spectroscopic information and estimation of the relative energies of the proposed spe-cies. The recent computational study of the electrocatalytic reaction cycle proposed for illustrates the opportunities presented by the approach. 

Fig. 8. The rapid-scanning spectroscopic time courses for the reaction of 0.17 mM Co(II)-T6 with 100 mM phenol at pH 8.0 in the absence (A, C) and presence (B, D) of 100 mM chloride ion are shown. (A) Reaction in the absence of chloride ion. The time interval between scans is 8.54 ms for the first five spectra, followed by spectra at successively longer intervals afterward (see insets in C and D). The total acquisition time was 1.71 s for the 25 spectra collected only spectra numbers 1-5,7,10,12,15,18,21, and 25 are shown. (B) Reaction in the presence of 100 mM chloride ion. The timing sequence of the spectra is the same as that used in (A). For clarity, spectra 6, 8,10,12,14-16, 18-20, and 22-24 have been omitted. (C) The scaled, subtracted spectra, calculated from the second to the sixth spectrum of part A, correspond to the time-course for intermediate formation. The time course plotted in the inset shows the absorbance change at 560 nm for the complete set of scaled, subtracted spectra as a function of time. (D) Scaled, subtraction spectra numbers 2 to 6, as in part C, for the data part B, with chloride ion present. The inset plot also shows the time course at 560 nm obtained from the complete set. (Taken from Gross and Dunn (55) with permission.]...

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