Helen Chadwick

Dr Chadwick obtained her PhD in gas phase scattering from the University of Oxford, UK, before moving to the EPFL in Switzerland where she performed experiments which studied the effect that vibrational excitation of methane molecules has on the probability that they dissociate in collisions with platinum surfaces. She obtained a Swiss National Science Foundation Advanced Mobility post-doctoral research Fellowship which funded a two year stay in the theoretical chemistry group at the University of Leiden in the Netherlands, performing calculations on the systems she had studied experimentally in Lausanne. Dr Chadwick then returned to the UK where she joined the Surface Dynamics team at Swansea University, where her main focus has been studying the scattering of hydrogen molecules from surfaces using a unique molecular beam interferometer. In 2024, she was awarded a Future Leaders Fellowship with the aim of developing the apparatus and methodology to be able to study molecule-surface reactions for the first time.

Abstract

Rotational orientation effects in hydrogen surface scattering

Hydrogen is the most abundant molecule in the universe, and its interaction with surfaces underpins a huge range of processes, from the industrial manufacture of chemicals to developing a hydrogen economy. Understanding collisions of hydrogen with surfaces at a fundamental, molecular level therefore has great value. One property of ground-state H2 that it was particularly difficult to control was its rotational orientation with respect to the surface, which classically corresponds to whether it is rotating like a helicopter (rotational plane parallel to the surface) of like a cartwheel (rotational plane perpendicular to the surface).Using a unique magnetic molecular interferometry technique [1], which combines homogeneous and inhomogeneous magnetic fields, we can control and manipulate the rotational orientation of the H2 molecule before it collides with a surface, and explore what effect it has on the outcome of the molecule-surface collision. In this presentation I will introduce the MMI technique and present results from recent elastic scattering measurements [2,3], before discussing how the technique can be extended to also study the dissociation of H2 when it collides with a surface.

Figure 1: Photo of the experimental apparatus used to perform magnetic molecular interferometry measurements.

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