Quantum state control of a ground state H2 dissociation reaction.

When hydrogen molecules collide with a surface, they can either scatter away from the surface or undergo a dissociation reaction leaving two hydrogen atoms adsorbed on the surface. The relative probabilities of these two potential outcomes could depend on the rotational orientation of the impinging molecules, however, due to the lack of steric control techniques for ground state hydrogen, direct measurements of this dependency were previously inaccessible to experiments. Here, we demonstrate that magnetic field manipulation can be used to control the rotational orientation of the impinging H ₂ and change the balance between reactive and scattering collision events. Analysing the controlled collision experiments reveals 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.