Comparison of several frequency-dependent friction models for the description of liquid-phase reaction dynamics

Abstract

The rate of the photoinduced isomerization of the compounds 7-hydroxy,8-(N-morpholinomethyl)quinoline, HMMQ, and 7-hydroxy,8-(N,N′-dimethylaminomethyl)quinoline, HDMQ, is limited by the rotational diffusion of the mobile group attached to the aromatic ring system. The observed viscosity dependence of these photoisomerizations is compared with the predictions made using the theory of Grote and Hynes (J. Phys. Chem., 1980, 73, 2715) for liquid-phase chemical reactions. This theory has been combined with several models that describe the time dependence of the friction. Compared to the time-independent model of Kramers (Physica, 1940, 7, 284) for the friction, the hydrodynamic friction model as given by Zwanzig and Bixon (Phys. Rev. A, 1970, 2, 2005), leads to an insufficient improvement of the calculated rates. A simple Maxwell form for the friction yields a similar result as the Zwanzig–Bixon model. The calculated rates in the higher viscosity range studied, suggest a stronger frequency dependence of the friction than given by the simple Maxwell form.