Untangling the Cosmic Dust Catalyzed Synthesis of Complex Organic Molecules in the Interstellar Medium

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Owing to the constant improvement of earth- and space-based radio telescopes, more than 200 molecules have been detected in the interstellar medium by now. Due to the harsh conditions with low densities and temperatures, the amount and complexity of these molecules cannot be accounted for by gas-phase reactions alone. According to the current state of research, dust particles in molecular clouds play a crucial role in the formation of the detected molecules. The low temperatures inside molecular clouds – down to 5 K – lead to an accretion of frozen gases on the dust particles. These ices consist mainly of water, carbon monoxide, carbon dioxide, methanol, methane, formaldehyde, and ammonia. The higher density in the ices increases the probability of reactions between different molecules and also helps dissipate the energy released by exothermal reactions. In the last decades numerous laboratory based studies have shown that subjecting such ices to ionizing radiation leads to the formation of complex molecules, parts of which are biologically relevant. However, most of these studies neglected a possible role of the dust particle in the center of the ice. Instead, most experiments are conducted in ices grown on either metal substrates or IR transmissive crystals to facilitate spectroscopic characterization. Recently some studies revealed that the surface on which the ice is grown can play a crucial role in the reactions by either favoring the formation of some molecules or by partly or completely preventing it. The primary goal of this project is therefore a systematic study of the influence of cosmic dust on the formation of several key classes of molecules in the ices. To achieve this, different gas mixtures mimicking ices found in different regions of the interstellar medium are condensed onto the surface of a silver mirror held at temperatures of 5 K in a UHV chamber. Microparticles with a structure and composition similar to that of cosmic dust are entrailed in the gas to be incorporated into the ice. Afterwards the ices are subjected to VUV radiation with a spectral composition that simulates that of the internal radiation field in the molecular clouds. Exploiting different complementary spectroscopy schemes, molecules synthesized in the ice are detected isomer-selectively. Lastly a quantitative comparison of the molecules detected with those synthesized in ices of the same compositions but without microparticles will then allow to assess the influence of the cosmic dust analogues on the synthesis of different molecules.