Reversible reactions attended by energy diffusion and slow solvent relaxation

The dynamics of an elementary reaction step under conditions of ballistic m otion along the chemical coordinate and slow adjustment is considered. The process is analyzed within a one-dimensional model describing concurrently the motion along the: slow solvent made and energy diffusion (ED) responsib le for over-barrier transitions. When relaxation of the environment is slow , the presence of the second potential well is shown to dramatically affect the activation process pattern. Within a certain range of governing parame ters ED provides equilibration of the fast mode, the reaction in this case boils down to diffusion along the coordinate of the environment and to over coming the barrier in the mean-force potential. Equilibration rules out the effect of passing around the saddle point and non-exponential nature of th e kinetics which are inherent in slow relaxing media. Analytical expression s for calculating the rate constant within the entire range of friction of the chemical mode are derived and changes in the rate constant-versus-visco sity dependence (Kramers turnover) caused by solvent effects and by reactio n of the potential well of the products are determined.