Collision dynamics and uptake of water on alcohol-covered ice
1Department of Chemistry and Molecular Biology, Atmospheric Science, University of Gothenburg, 412 96, Gothenburg, Sweden
2Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology, 412 96, Gothenburg, Sweden
3Laboratory of Photochemistry and Kinetics, Department of Chemistry, University of Crete, 71003 Heraklion, Crete, Greece
Abstract. Molecular scattering experiments are used to investigate water interactions with methanol and n-butanol covered ice between 155 K and 200 K. The inelastically scattered and desorbed products of an incident molecular beam are measured and analyzed to illuminate molecular scale processes. The residence time and uptake coefficients of water impinging on alcohol-covered ice are calculated. The surfactant molecules are observed to affect water transport to and from the ice surface in a manner that is related to the number of carbon atoms they contain. Butanol films are observed to reduce water uptake by ice by 20%, whereas methanol monolayers pose no significant barrier to water transport. Water colliding with methanol covered ice rapidly permeates the alcohol layer, but on butanol has mean surface lifetimes of ≲0.6 ms, enabling some molecules to thermally desorb before reaching the water ice underlying the butanol. These observations are put into the context of cloud and atmospheric scale processes, where such surfactant layers may affect a range of aerosol processes, and thus have implications for cloud evolution, the global water cycle, and long term climate.