Counterion effects in intramolecular charge transfer in radical anions
- Argonne National Lab., IL (United States) Univ. of New Orleans, LA (United States)
- Argonne National Lab., IL (United States)
The influence of the presence of an electrolyte in a low-polarity solvent (tetrahydrofuran) on the rate of a weakly exoergic ([approx]50 meV) nonadiabatic intramolecular charge shift reaction and on the position of the charge transfer absorption band in a degenerate system has been studied by pulse radiolysis. The investigation focused in particular on the dependence of the effect on the size of the cation of the chemically inert electrolyte. Electrolytes caused dramatic rate reductions of 2-3 orders of magnitude. Unexpectedly, the rate reduction was found to increase with an increasing size of the cation. The recorded spectral blue shifts were as large as 0.5 eV and exhibited the expected tendency; the smaller counterions produced larger spectral shifts, due to a stronger Coulombic interaction. In both cases the effects exceeded the limits predicted by the continuum approach and pointed to the ion-pairing mechanism. The discrepancy between the dependence of the thermal electron transfer and the optically assisted electron transfer on the radius of the counterion could not be easily explained on purely energetic grounds, and the dynamics of the counterion had to be considered. Unfortunately, no agreement between the experimental results and the Eigen model of dissociative diffusion of ion pairs in the zero ionic strength limit could be found. However, a qualitative correlation between the measured rates and the dissociation constants of the used salts, as well as the counterion mobilities was observed. 34 refs., 8 figs., 3 tabs.
- DOE Contract Number:
- W-31109-ENG-38; FG05-92ER14310
- OSTI ID:
- 5041371
- Journal Information:
- Journal of Physical Chemistry; (United States), Vol. 97:50; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AROMATICS
ELECTRON TRANSFER
MOLECULAR STRUCTURE
ANIONS
CHEMICAL REACTION KINETICS
COULOMB IONIZATION
ELECTROLYTES
ION PAIRS
PHOTOMETRY
PULSED IRRADIATION
RADICALS
RADIOLYSIS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
DECOMPOSITION
IONIZATION
IONS
IRRADIATION
KINETICS
ORGANIC COMPOUNDS
RADIATION EFFECTS
REACTION KINETICS
400201* - Chemical & Physicochemical Properties
661300 - Other Aspects of Physical Science- (1992-)