Isomerization dynamics in solution

Recent advances in the dynamics of photochem. isomerization reactions in soln. are reviewed with 92 refs. The isomerization reactions in soln. show diverse behavior depending on the nature of the solvent, the viscosity of the soln. and the sharpness of the activation barrier. The results of recent time-resolved spectroscopic measurements on several isomerizing mols. different solvents are discussed. The rate consts. of these isomerization reactions lie in the picosecond regime. The stochastic, Markovian theories of chem. kinetics in soln., including the well known Kramers' theory are discussed. Contrary to the traditional belief, recent expts. reveal an apparent breakdown of kramers' theory at large viscosities. This breakdown is most dramatic for isomerizing mols. with sharp barriers. The failure of kramers' theory for these cases can be traced to the assumption that the solvent forces on reactive motion are delta-correlated in time. The recent generalization of Kramers' theory by Grote and Hynes, who removed the white-noise assumption of Kramers' theory by including the frequency dependence of friction is discussed. This generalized theory can qual. explain the new exptl. data. Both exptl. and theor. studies on isomerization reactions in the absence of an activation barrier are reviewed. The reason why the early theory of Forster and Hoffman is inconsistent, and the recent theory of Bagchi, Fleming and Oxtoby on isomerization in soln. in the absence of a barrier are also discussed. The importance of nonequil. solvation dynamics on fast isomerization reactions in soln. is noted. Recent computer simulation studies are reviewed