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Diffusion-Limited Acid-Base Nonexponential Dynamics Boiko Cohen and Dan Huppert*

Summary: Diffusion-Limited Acid-Base Nonexponential Dynamics
Boiko Cohen and Dan Huppert*
School of Chemistry, Raymond and BeVerly Sackler Faculty of Exact Sciences, Tel-AViV UniVersity,
Ramat-AViV, Tel-AViV 69978, Israel
Noam Agmon
The Fritz Haber Research Center, Department of Physical Chemistry, The Hebrew UniVersity,
Jerusalem 91904, Israel
ReceiVed: February 22, 2001; In Final Form: May 14, 2001
Using time-resolved fluorescence, we have measured the direct proton transfer reaction between a photoacid,
2-naphthol-6-sulfonate, and a base, acetate anion, in water-glycerol mixtures. The reaction shows clear evidence
for irreversible diffusion-controlled reactivity in agreement with the Smoluchowski model. As the solution
viscosity increases, from about 1 cP (neat water) to 40 cP at 0.4 mole fraction of glycerol, the initial ROH*
fluorescence decay becomes increasingly nonexponential, providing clear evidence for the transient regime
of the Smoluchowski model for a real chemical reaction.
The dynamics of fast bimolecular reactions in solution have,
for a long time, been a subject of interest to both experimental-
ists and theoreticians. The kinetics of many physical, chemical
and biological processes are influenced by diffusion.1 Electron
and hole trapping processes in semiconductors;2 fluorescence


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry