The image to the right shows a schematic representation of a reactive conical intersection in the space of a dissociative (stretching) and a bound (angular) coordinate. Conical intersections are nowadays recognized as key topologies triggering primary photochemical processes and nonadiabatic excited state dynamics.

For a monograph on the field, see:
W. Domcke, D. R. Yarkony and H. Köppel (Eds.), Conical Intersections: Electronic Structure, Dynamics and Spectroscopy (World Scientific, 2004).

For a set of tutorial reviews on a related field, see:
H. Köppel, H. Barentzen and D. R. Yarkony (Eds.), The Jahn-Teller Effect: Fundamentals and Implications for Physics and Chemistry (Springer Verlag, 2009).