Multiple traversals of a conical intersection: electronic quenching in Na∗ + H2

The conical intersection in the collision of a Na(3p 2P) atom with H2 occurs at large HH distances. Time dependent quantal computations exhibit many sequential non-adiabatic couplings, each of which is localized in time, where the quenching probability per traversal is small. During the collision, the population of the ground state increases almost in a random walk fashion until the partners recede after many H2 vibrational periods. Changing the masses suggests that other systems can also exhibit such a snarled quenching process which cannot be described as a single non-adiabatic event per collision.