Seaming is believing

http://www.nature.com/nature/journal/v467/n7314/full/467412a.html

Most of the modern understanding of chemistry, including the very notion of a well-defined molecular structure, rests on the concept of a potential energy surface (PES) — a 3N-dimensional 'landscape' that plots the total energy of a collection of N atoms as a function of the atomic positions. The PES can be used to determine several useful features, such as the most stable configuration of atoms, or the pathway along which atoms 'travel' during a reaction. Intersections of these surfaces (known as conical intersections) are thought to have an important role in transitions from excited states to ground states of molecules, but direct evidence of this has been hard to find. Reporting on page 440 of this issue, Polli et al.¹ use ultrafast optical spectroscopy to follow the motion of the molecule retinal — whose light-induced isomerization forms the basis of vision — through a conical intersection. This provides much-needed experimental evidence of the involvement of conical intersections in de-excitations.