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?