IR- und XUV-Spektroskopie an Nanopartikeln, Erzeugung und Untersuchung von atmosphärenchemisch relevanten Sytemen, Reaktionsdynamik von Säure-Base-Reaktionen in der Aerosolphase

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Cold molecular aggregates with sizes ranging from subnanometers to microns (here referred to as ice nanoparticles) play an important role as aerosols in atmospheric processes and as reactive sites in interstellar dust3. As atmospheric aerosols they have significant impact on the climate of the Earth and of other planets and moons in our solar system. These tiny aggregates critically influence the energy balance and the composition of these atmospheres, through phase transitions, mass transfer processes, and chemical and photochemical reactions. They often consist of small molecules such as H2O, NH3, CH4, CO2, and simple organic molecules. On Earth, water and its ices are the obvious focus of interest, but recent high-profile space missions have found other simple molecules (NH3, CH4) to play a similar role in the atmospheres of planets and moons of our solar system 4. New data on aerosols in atmospheres of planets and their moons have put cold molecular aggregates very much into the focus of the scientific community. For example, the recent Cassini-Huygens mission to Saturn s moon Titan has borne out the importance of cold methane aerosols for Titan s weather and the analogy to the role of water ice clouds in the Earth s atmosphere.The aim of the present proposal is to elucidate the properties of several pure and especially multi-component ice systems with relevance in planetary atmospheres and interstellar dust chemistry. Nowadays we are still far from a detailed characterization and understanding of such complex nanosystems. The reason lies in the difficulties to generate and characterize such tiny sensitive systems in the laboratory. This is in particular true for aerosol particles with sizes below 100 nm. The Signorell laboratory currently houses highly specialized instrumentation for the generation and characterization of aerosol ice nanoparticles, which is the focus of the present proposal. Different collisional cooling methods and various supersonic expansions including rapid expansion from supercritical media are available in the laboratory. In collisional cells the cold aggregates are formed in thermal equilibrium with the surrounding gas phase, which for example makes it a unique method to study phase transitions. Spectroscopic methods play a crucial role in the characterization of such weakly bound aggregates since they are sensitive, non-invasive, and are often the only methods for remote sensing. The Signorell laboratory has the required expertise in sensitive infrared spectroscopic methods with which the ice particles can be investigated in situ with high sensitivity and a time resolution in the ms region. To study the interaction of high-frequency light with cold molecular aggregates a photoion/photoelectron spectrometer with mass-sensitive imaging detection is available. The main objective of this proposal is the detailed spectroscopic characterization of such tiny ice particles to unravel the microscopic origins of the characteristic patterns found in the spectra and to provide essential reference data for remote sensing. To this end the determination of spectroscopic properties will be combined with modeling on a molecular level. During the last years, Signorell and coworkers have developed modeling methods specially adapted to the treatment of these ice particles.