The Many Faces of Tunneling

We consider classically forbidden events which control chemically and spectroscopically important processes. We focus on dynamical tunneling, which is tunneling in the absence of potential barriers, and tunneling between two Born−Oppenheimer potential energy surfaces. The former drives intramolecular vibrational relaxation (IVR) in molecules; the latter controls much of photochemistry, spectroscopy, and energy transfer.