Using stereodynamical portraits to visualize polarized rotational angular momentum distributions in H2–surface collisions

The magnetic molecular interferometer (MMI) is a molecular beam scattering apparatus, which allows the polarization of the rotational angular momentum (J) of ortho-H2 molecules to be controlled using tunable magnetic fields before they collide with a surface, and their J' polarization to be determined after the collision. In the current work, quantum population distribution functions, or "stereodynamical portraits," are used to visualize the rotational angular momentum polarization of ortho-H2 molecules that the MMI creates before the collision with the surface, revealing that the sensitivity of the MMI to stereodynamic effects which depend on the orientation of J with respect to the surface normal can be increased by manipulating the H2 molecules with two perpendicular magnetic fields rather than just a single field. They can also be used to depict the polarization dependence of a H2-surface collision, as shown by the example considered here, where it is found that when H2 molecules undergo diffractive scattering from a Cu(511) surface, different J polarizations are selected to scatter into different diffraction channels, just as different polarizations of J' are created after scattering. Signals measured with the MMI are necessarily dependent on both the rotational polarization the MMI creates and the dependence of the molecule-surface collision on this, and it is demonstrated that for flux detection measurements it would be possible to analyze the data directly in terms of the polarization moments which characterize these two properties to gain a more immediate insight into the stereodynamics of the collision than is possible using alternative analysis methods.