Subject: Breakdown of Born-Oppenheimer approx.

From: Ahmed Bouferguene <[email-masked]>
Date: Mon, 25 Aug 1997 19:43:08 -0400 (EDT)

Hi all,

	Does anybody know a good reference dealing with the limitations of
Born-Oppenheimer approximation and the way(s) used to solve such a 
problem ?

	Thanks all.  

 Ahmed Bouferguene

---

From: Charles & <[email-masked]>
Date: Mon, 25 Aug 1997 22:49:14 -0400

> Born-Oppenheimer approximation and the way(s) used to solve such a 
	Perhaps you could be more specific.  

	It is well known that the  Born-Oppenheimer approximation
breaks down, for example, for excited states.  This is precisely
what happens during the radionationless decay of certain molecules.
There are a variery of different examples of such excited state
decay processes.  A common case arises when a molecule isomerizes
while in its excited state.  This is generally treated using
Landau-Zener hopping, or some more sophisticated variant thereof.
Another standard case arises when an excited state decays because it
couples to the dense manifold of vibrational levels of another, nearby
state (i.e  a low-lying triplet, or the ground state, etc.) , even
though the excited state geometry is relatively fixed. This is
a very good case of how the  Born-Oppenheimer approximation breaks
down, and the analytic theory has been worked in out in detail by
Freed (i.e. the energy-gap law for excited state decay).

	Is this of any help?

	Chuck Martin
	QTP, University of Florida
	[email-masked]