Initial excitation energy

Figure 3-18 Fluorescence excitation/emission geometries lo is the initial excitation energy ExM is the excitation monochromator C is the sample cuvet If is the fluorescence intensity EmM is the emission monochromator and D is the detector.

The result (8.107) shows that in the course of the relaxation process the width of the energy level distribution increases (due to the last term in (8.107)) before decreasing again. This effect is more pronounced for larger [( )o — (n)eq]. that is, when the initial excitation energy is much larger than hgT. 

The search for a phenomenological alternative to RRKM inversion distribution mapping does not represent a novel idea. The first step in the RRKM modeling procedure for a chemically activated species involves the a priori characterization of its initial excitation energy distribution (70,89,90). For species produced from exoergic reactions this information is normally obtained from thermochemical data. A correspondingly simple direct method has not yet emerged for hot atom activation processes, because the associated dynamics are incompletely imderstood. 

The following input data are required (i) a quantitative description of the initial excitation energy distribution function [f(Ei)] (ii) a set... 

In case of Stokes radiation the initial state of the molecules may be the vibrational ground state, while for the emission of anti-Stokes lines the molecules must have initial excitation energy. Because of the lower population density in these excited levels, the intensity of the anti-Stokes lines is lower by a factor exp(-hcov/kT). 

The efficiency of FRET is often represented by the Forster distance (Rq), which is that separation at which the rate of FRET is equal to all other decay rates of the donor, i.e. when 50 % of the initial excitation energy will be transferred to the acceptor. The rate constant for FRET at any separation R is then given by ... 

Sparse information indicates that is independent on the initial excitation energy of ip (in the range 850-880 nm), presumably precluding vibronic dependence of... 

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