Photoionization affected by chemical anisotropy.

ABSTRACT

The kinetic constants of rhodamine 3B quenching by N,N-dimethyl aniline were extracted from the very beginning of the quenching kinetics, recently studied in a few solvents of different viscosities. They were well fitted with the conventional kinetic constant definition, provided the radial distribution function of simple liquids was ascribed to the reactant pair distribution and the contact electron transfer rate was different in all the cases. This difference was attributed to the chemical anisotropy averaging by the rotation of reactants, which is the faster in solvents of lower viscosity. With the proper choice of a space dependent encounter diffusion, the whole quenching kinetics was well fitted with an encounter theory, using the Marcus [J. Chem. Phys. 24, 966 (1956); 43, 679 (1965)] transfer rate instead of the contact Collins-Kimball [J. Colloid. Sci. 4, 425 (1949)] approximation. Not only the beginning and middle part of the quenching were equally well fitted, but the long time (Markovian) rate constant was also found to be the same as previously obtained. Moreover, the concentration dependencies of the fluorescence quantum yield and the Stern-Volmer constant were specified and await their experimental verification.