Site and bond-specific dynamics of reactions at the gas-liquid interfaceElectronic supplementary information (ESI) available. See DOI: 10.1039/c3cp54107j

The dynamics of the interfacial reactions of O( 3 P) with the hydrocarbon liquids squalane (C 30 H 62 , 2,6,10,15,19,23-hexamethyltetracosane) and squalene (C 30 H 50 , trans -2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene) have been studied experimentally. Laser-induced fluorescence (LIF) was used to detect the nascent gas-phase OH products. The O( 3 P) atoms are acutely sensitive to the chemical differences of the squalane and squalene surfaces. The larger exothermicity of abstraction from allylic C-H sites in squalene is reflected in markedly hotter OH rotational and vibrational distributions. There is a more modest increase in translational energy release. A larger fraction of the available energy is deposited in the liquid for squalene than for squalane, consistent with a more extensive geometry change on formation of the allylic radical co-product. Although the dominant reaction mechanism is direct, impulsive scattering, there is some evidence for OH being accommodated at both liquid surfaces, resulting in thermalised translation and rotational distributions. Despite the H-abstraction reaction being strongly favoured energetically for squalene, the yield of OH is substantially lower than for squalane. This is very likely due to competitive addition of O( 3 P) to the unsaturated sites in squalene, implying that double bonds are extensively exposed at the liquid surface. Unsaturated sites at the surface of a liquid hydrocarbon dramatically affect the dynamics of the interfacial H-abstraction reaction with O( 3 P).