REVERSIBLE CHEMICAL-REACTIONS IN SLOWLY RELAXING ENVIRONMENTS - KRAMERS TURNOVER OF THE RATE-CONSTANT

The turnover behavior of the rate constant as a function of the fricti on coefficient of the chemical mode is studied in a slowly relaxing en vironment/solvent, In rapidly adjusting environments, the turnover pro blem has been solved by Mel'nikov and Meshkov. The reaction dynamics i s studied with a special focus on the influence of long-distance recro ssings, Such recrossings take place when the potential of mean force a long the chemical coordinate has a double-well structure, Two kinds of the turnover behavior have been discovered. When the relaxation is no t too slow, the turnover is not accompanied by variation of the activa tion energy of the rate constant like in a fast environment. However, when the relaxation is slow enough, a significant decrease of the acti vation energy accompanies the turnover. (C) 1998 Elsevier Science B.V. All rights reserved.