Interstellar dust is part of the universal recycling process of matter. A major component of interstellar dust are silicon carbides, silicon oxides, and metal-containing silicates, as inferred from IR emission and the detection of grains in meteorites. On the other hand, small silicon-containing molecules (&lt;10 atoms) have firmly been detected in circumstellar shells by radioastronomy. Linking these two size limits from small molecules to micron-sized grains is a longstanding and still open issue. Although some hypotheses assume nucleation of seed particles, details of the growth mechanism(s), potential intermediates, and the impact of physical parameters such as radiation field, temperature, and chemical composition, remain largely unexplored.<br/> <br/>To shed further light on the nucleation process from the laboratory point of view, we investigate physical and chemical properties of small to medium-sized silicon carbide and silicon oxide clusters as a function of composition and charge state. To this end, the clusters are produced by laser vaporization techniques of various targets in molecular beams and probed by mass spectrometry, laser spectroscopy, and quantum chemistry. In a first step, geometric structures and chemical bonding of the clusters in the ground electronic state are obtained by IR spectroscopy using photodissociation and photoionization schemes, along with global optimization techniques in quantum chemical calculations. In a second step, optical and photochemical properties are obtained by UV-VIS photodissociation spectroscopy, providing important information about electronic structure and fragmentation properties (appearance energies, competing fragmentation channels and branching ratios, particularly stable fragments).

Photochemical properties of silicon clusters: Bridging the gap between diatomics and grains

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ACS Fall 2022

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