Imaging collisions of OH radicals with liquid surfaces

The interactions of gas-phase molecules with the surfaces of liquids are important in a number of real-world environments. Their study presents a number of serious experimental challenges, because of the difficulties of developing surface-sensitive methods that can be coupled with liquid-phase samples. One important class of these reactions is the uptake of OH radicals at the surfaces of atmospheric aerosol particles; these processes have important climatic implications. We have been studying the fundamental primary events in the collisions of OH radicals with liquid surfaces chosen as proxies for the chemical functionality present at the surfaces of aerosols. We have extended our previous work by introducing a molecular-beam source of the OH radicals and combining it with a novel, laser-based imaging method. This has opened the way to making new classes of dynamical measurements, where we can obtain the correlations between the speed and angular distributions of the scattered OH molecules and their internal quantum states. We are able to determine the extent to which OH molecules that survive a collision with the surface have lost their ‘memory’ of their initial direction of travel, and how much of their initial kinetic energy has been converted to rotational motion or lost to the liquid surface. These characteristics are highly indicative of the balance between competing direct and more-complex collisional mechanisms at the surface. This insight is valuable, both in this particular context and also in helping to inform the general field of gas-liquid interfacial chemistry more widely.

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The Institute of Chemical Sciences (ICS) is an excellent environment for PhD research, with a thriving community of academics, post-doctoral and PhD researchers spread across three sections: Molecular Chemistry, Materials Chemistry, and Dynamics and Structure. ICS also has many links to the other research institutes within the overall umbrella of the School of Engineering and Physical Sciences, providing a strong interdisciplinary theme to our research. Heriot-Watt University occupies an attractive campus site on the outskirts of Edinburgh, with excellent public transport links to the centre of one of the Europe’s most exciting cities.