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EXCITED STATE EQUILIBRATION AND THE FLUORESCENCE-ABSORPTION RATIO.

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Robert S. Knox,

**University of Rochester, Rochester, NY 14627-0171 USA**

**(e-mail: rsk@pas.rochester.edu;
Fax: (716) 242 0851)**
Ideally, in any system the fluorescence and absorption spectra are connected
by a simple relation. Essentially, F, the logarithm of their ratio
at a given frequency is a decreasing function of photon frequency, with
slope proportional to the inverse ambient temperature [1-4]. Ideal
circumstances include excited state thermal equilibration. Although
impossible in principle because of finite lifetimes, this is often approximated
in that F is often nearly linear (example: [5]). An effective temperature
[6], defined locally on F, seems a very sensitive detector of deviations
from linearity and, we believe, from equilibrium in the excited state.
Plots of this temperature display various features. Peaks can be
shown to be characteristic of slow equilibration between two internally
well-equilibrated excited manifolds [6,7]. A chlorophyll-a anomaly
[8] can be analyzed on this model, indicating a previously unnoticed weakly
fluorescent state. The case of chlorophyll and many others will be
included in a general review of the application of the universal relation
to studies of fluorescent systems.

(Supported by USDA grant NRICGO-95-37306 and by NSF grants 94-00059,
94-15583)

1. E. H. Kennard (1926), Phys. Rev. **28**, 672-683

2. B. I. Stepanov (1957), Dokl. Akad. Nauk SSSR **112**, 839-842

3. B. S. Neporent (1958), Dokl. Akad. Nauk SSSR **119**, 682-685

4. D. E. McCumber (1964), Phys. Rev. **136**, A954-A957

5. See, e. g., J. Hevesi, L. Kozma, and L. Szalay (1966), Acta Phys.
Polonica **29**, 57-64

6. D. A. Sawicki and R. S. Knox (1996), Phys. Rev. **A 54**, 4837-4841

7. R. S. Knox (1997), Pure and Appl. Chem. **69**, 1163-1170

8. R. S. Knox, P. D. Laible, D. A. Sawicki, and M. F. J. Talbot (1997),
J. Luminescence **72-74**, 580-581