Multiple traversals of a conical intersection: Electronic quenching in Na* + H₂

The conical intersection in the collision of a Na(3p²P) 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.