Abstract
The outcome of molecule–surface collisions can be modified by pre-aligning the molecule; however, experiments accomplishing this are rare because of the difficulty of preparing molecules in aligned quantum states. Here we present a general solution to this problem based on magnetic manipulation of the rotational magnetic moment of the incident molecule. We apply the technique to the scattering of H2 from flat and stepped copper surfaces. We demonstrate control of the molecule’s initial quantum state, allowing a direct comparison of differences in the stereodynamic scattering from the two surfaces. Our results show that a stepped surface exhibits a much larger dependence of the corrugation of the interaction on the alignment of the molecule than the low-index surface. We also demonstrate an extension of the technique that transforms the set-up into an interferometer, which is sensitive to molecular quantum states both before and after the scattering event.
Highlights
The outcome of molecule–surface collisions can be modified by pre-aligning the molecule; experiments accomplishing this are rare because of the difficulty of preparing molecules in aligned quantum states
As we demonstrated in the past for the case of ortho-H2O molecules[19], a hexapole magnetic lens can be used to focus some molecular quantum states and extract others from the beam line
In summary, we have presented a general experimental approach for controlling, and studying the role of, the rotation projection states of a molecule scattering from a surface
Summary
The outcome of molecule–surface collisions can be modified by pre-aligning the molecule; experiments accomplishing this are rare because of the difficulty of preparing molecules in aligned quantum states. Whereas the incentive to do so is high, the ability to experimentally resolve the role of rotation projection states in molecule–surface scattering has so far been restricted to a rather small subset of systems for which specific innovative experimental approaches could be applied These approaches include deflection of paramagnetic and polar molecules, photo-excitation of desorbed molecules and exploiting correlations between velocity and rotational alignment in supersonic beams[1,5,12]. We present a general approach to tackle this problem, and demonstrate its effectiveness by both probing and controlling the initial rotation projection quantum state of a hydrogen molecule, and correspondingly the outcome of its collision with the surface. Each of these states responds differently to magnetic fields, and it is this response that allows us to probe and control the different states involved in the scattering event
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