Abstract

Considerable interest centers around the relationship between isomerization rates and solvent viscosity. These isomerizations are viewed as activated processes which proceed across a barrier. This barrier differs from the classical barrier of transition-state theory by possessing both an activation (potential) energy and friction. The viscosity determines the friction at the barrier. Both excessively low and excessively high viscosities tend to hinder the isomerization; high viscosities decelerate the rate of crossing at the top of the barrier, while low viscosities provide insufficient thermal coupling with the solution for activation to proceed efficiently. The frictional force is not determined by the static viscosity alone, and much work has gone into studying dynamic frictional forces (6).

© 1986 Optical Society of America