Collision dynamics as a tool to investigate the interactions of radicals with liquid surfaces

Abstract

This thesis presents new results which are aimed at furthering the understanding of collision dynamics at gas-liquid interfaces. These experiments included the use of open shell radicals such as OH and both ground sate O(3P) and excited state O(1D) oxygen. The liquids used included an un-reactive standard per fluoropolyether, Krytox 1506 but were mostly focussed on the potentially reactive saturated and unsaturated counterparts squalane and squalene. The products of scattering from these liquid surfaces were detected by laser induced fluorescence (LIF). The radicals were all used as a “chemical probe” of the liquid surface. Using information on the translational and internal energy distributions of the scattered species the structure and reactivity of each liquid surface could be investigated. Important findings included the first measurements of the reaction of O(1D) with a liquid hydrocarbon surface. The data collected were analysed to provide the first comparisons of O(1D) scattering from a liquid with previous gas phase measurements. Relevant mechanisms identified for these comparable gas-phase reactions were assigned as far as possible to the new results. For the first time, the interactions of rotationally excited OH radicals with liquid surfaces were investigated. Liquid surfaces of atmospheric relevance were studied. This work was compared to that completed previously using a rotationally near-thermal source of OH radicals. Important scattering mechanisms were identified and assigned to the results collected. A possible loss mechanism for OH radicals interacting with unsaturated species was identified. The first comparison of the interfacial reaction of O(3P), with squalane and its unsaturated counterpart, squalene was conducted. Scattering mechanisms were identified and characterised where possible. Differences in scattering dynamics were observed with the unsaturated liquid surface, which were attributed to differences in the chemical nature of the bonds present in the liquid. Where possible, all results were related to reactions which occur in the atmosphere.