Anticorrelated stereodynamics of scattering and sticking of H2 molecules colliding with a reactive surface

When hydrogen molecules collide with a surface, they can either scatter away from the surface or stick to the surface through a dissociation reaction which leaves two H atoms adsorbed on the surface. The relative probabilities of these two potential outcomes can depend on the rotational orientation of the impinging molecules, however, direct measurements of this dependence were not available due to the difficulty of controlling the rotational orientation of ground state H2 molecules. Here, we use magnetic manipulation to achieve rotational orientation control of the molecules just before they collide with the surface, and show that molecules approaching the surface in a helicopter orientation have a higher probability to react and dissociate, whereas those which approach in a cartwheel orientation are more likely to scatter.