Beyond Born-Oppenheimer: Impact of a Conical Intersection
(by Lorenz Cederbaum)


Non-adiabatic effects play an important role in many areas of physics and chemistry. The coupling between electrons and nuclei may, for example, lead to the formation of a conical intersection between potential energy surfaces, which provides an efficient pathway for radiationless decay between electronic states. At such intersections the Born-Oppenheimer approximation breaks down, and unexpected dynamical processes result, which can be observed spectroscopically. We review the basic theory required to unterstand and describe conical, and related, intersections. An example is also given using wavepacket dynamics simulations to demonstrate the prototypical features of how a molecular system passes through a conical intersection. Several additional questions are addressed. What happens to the conical intersection if the interacting electronic states are non-stationary? Does a conical intersection support vibronic resonances? Can a conical intersection give rise to bound states in the continuum?