Radical collisions with liquid surfaces: from pure sources to scattering mechanisms Maksymilian Roman 1 , Lok Yu Wu 1,2 , Brianna R. Heazlewood 1 , Adam G. Knight 3 , Daniel R. Moon 3 , Paul D. Lane 3 , Matthew L. Costen 3 , Kenneth G. McKendrick 3 1 Department of Physics, University of Liverpool, UK, 2 Physical and Theoretical Chemistry Laboratory, University of Oxford, UK, 3 Institute of Chemical Sciences, Heriot-Watt University, UK In the past three decades, scattering experiments have been used to uncover the mechanisms governing the interactions occurring on the gas-liquid interfaces[1]. Such information is crucial for understanding many natural and anthropogenic processes, of which a particularly topical example is the “ageing” of atmospheric aerosol surfaces, where OH radicals formed during daylight hours attack and change the composition of the outer surfaces of the aerosols[2]. Recently, a new real-space imaging technique developed at the Heriot-Watt University has been used to study the inelastic scattering of OH from liquid surfaces[3]. It combined a molecular beam source of radicals with a planar laser-induced fluorescence detection system to record the scattering process. This has been used to study the scattering on the surfaces of the long-chain hydrocarbons squalane and squalene, common proxies of functionalities found on aerosol surfaces. The measured survival probabilities and angular distributions (among other characteristics) of the scattered OH indicated significant differences in the scattering mechanisms on the two surfaces. Currently, these differences have been attributed to the presence of an additional reaction channel on squalene, but greater control of the experimental parameters is required to fully understand the underlying dynamics. One way to achieve this would be to use a “magnetic radical filter”, which has recently been developed at the University of Liverpool[4]. This device has been shown to produce a beam of state- and velocity-selected hydrogen atoms that was also free from any unwanted species, including by-products of radical formation and carrier gases[5]. Here, I present results on the characterisation of a second-generation device designed specifically to work for atomic oxygen and OH radicals in addition to the latest OH-liquid scattering experimental results. The combination of these two methods in the future would provide greater understanding of the processes occurring on gas-liquid interfaces. References 1. Rudich et al., Annu. Rev. Phys. Chem. 67, 515 (2016); doi: 10.1146/annurev-physchem-040215-112355 2. Tesa-Serrate et al. Annu. Rev. Phys. Chem. 58, 321 (2007); doi: 10.1146/annurev.physchem.58.032806.104432
3. Bianchini et al. J. Chem. Phys. 151, 054201 (2019); doi: 10.1063/1.5110517 4. Toscano et al. J. Chem. Phys. 149, 174201 (2018); doi: 10.1063/1.5053656 5. Miossec et al. J. Chem. Phys. 153, 104202 (2020); doi: 10.1063/5.0020628
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