Reactions involving more than one potential surface

4 Reactions involving more than one potential surface 

In reactions involving electronically excited states, the interaction of two potential energy surfaces is likely to be involved. This interaction is reasonably well understood and easy to visualize in the case of potential curves for diatomic systems, but for systems containing more than two atoms, the situation is considerably less tractable. One tries to develop a description, starting from the observed kinetics of a reaction and using whatever spectroscopic data may be available. 

In discussing molecular systems which must be described in terms of more than one potential surface, it is desirable to have a clear definition of the variously used term crossing. It is also important to distinguish between (a) interaction of potential surfaces, and (b) transitions from one adiabatic surface to another induced by coupling between nuclear and electronic motions (failure of the Bom-Oppenheimer approximation). 

The distinction between interaction of different zero order electronic states for clamped nuclei, and interaction of different Bom-Oppenheimer states due to the 

---