QUANTUM-MECHANICAL ELUCIDATION OF REACTION-MECHANISMS OF HEAVY-LIGHT-HEAVY SYSTEMS - ROLE OF POTENTIAL RIDGE

A new idea to elucidate quantum reaction dynamics of heavy-light-heavy (HLH) systems is proposed on the basis of the hyperspherical elliptic coordinate approach. This coordinate system has a big advantage of ni cely expressing good vibrational adiabaticity in the HLH systems. Taki ng this advantage, the concept of potential ridge is introduced, for t he first time, in three-dimensional reactions. The potential ridge is proved to be very useful to extract some important avoided crossings w hich dominate the reaction dynamics, in fact, qualitative features of the reaction dynamics can be interpreted in terms of nonadiabatic tran sitions at those important avoided crossings near the potential ridge. Examples are: (i) onset of reaction for a specified initial rotationa l stale, and (ii) major reactive transition for a specified initial ro tational state. Avoided crossings to the left of the potential ridge a re also useful to interpret certain aspects of reactions accompanying vibrational transitions. The new idea mentioned above is applied to at ypical HLH reaction O(P-3)+HCl-->OH+Cl with the use of two types of po tential energy surfaces. (C) 1998 American institute of Physics. [S002 1-9606(98)51521-8]