Quantum controlled collisions; an empirical approach for studying the interaction potential of molecule-surface systems.

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The interaction of molecules with surfaces plays a pivotal role in many processes, from star formation in the interstellar medium to manufacturing chemicals on an industrial scale. Despite their importance, calculating how a molecule interacts with a surface is extremely challenging and cannot be performed exactly. Instead, approximate methods have to be used. Whilst these are constantly being developed and further improved, and unquestionably provide important insight into many surface phenomena, they often lack the accuracy and reliability to interpret and predict experimental observations. Existing and new experimental techniques, of the type we will employ, are needed to further develop and improve theoretical methods.In this project, we will develop and apply a new joint experimental-theoretical approach for studying the interaction between a molecule and a surface, with the aim of being able to extract information about this interaction directly from our experimental measurements rather than it having to be calculated. One unique aspect of this proposal is that we will use a magnetic molecular interferometer (MMI) for measuring molecule-surface collisions. This newly established state-to-state scattering technique has been shown to be capable of quantifying changes in the magnitude and phase of the rotational wavefunction of a ground state hydrogen molecule colliding with a surface. The sensitivity of the interference signal to changes in the quantum state of the molecule will be used in this program to reconstruct the interaction potential between the molecule and the surface. The program will include a wide range of MMI measurements of hydrogen molecules scattering from various surfaces, including ionic surfaces, flat metallic surfaces and stepped surfaces, representing different types of interactions and different levels of reactivity. Through a collaboration with the theoretical chemistry group in Leiden, we will develop a procedure for calculating MMI signals from analytical potential energy surfaces. This will allow us to compare calculated and measured signals and identify the functional forms and potential parameters which best reproduce the experiment. We will also further develop our unique experimental methodology to maximise its sensitivity to subtle differences in the interaction potential, to be able to distinguish between different theoretical models which accurately reproduce other state-of-the-art experimental data. The results of this project should provide unprecedented insight into the interaction of hydrogen with various solid surfaces as well as stringent experimental benchmarks which will help to develop new accurate theoretical models of gas-surface interactions.