, Volume 226, Issue 1, pp 149-163

Silicon carbide in circumstellar environment

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The presence of small clusters of silicon carbide (SiC) in circumstellar dust shells surrounding late-type stars is inferred from a broad emission feature peaking at around 11µm in infrared spectra [1]. These clusters are expected to condense from molecular arrangements composed of a few carbon and silicium atoms which are present in stellar winds surrounding carbon-rich late-type stars. We have searched for the possible geometric structures of SiC n + radicals (n ≤ 5) on the basis ofab initio calculations. It is predicted that the linear structures are energetically favored compared to the other planar and 3D ones, except for SiC 2 + where a doubt subsists and for SiC 3 + where the rhombic structure is clearly more stable than the linear one. In the same way, a conspicuous even-odd alternation of the stability with the number of carbon atoms along the subset of linear species is shown. Vibrational frequencies of all the structures under consideration have then been determined. The possible destabilizing influence of a finite temperature effect on these structures has also been analyzed by using general considerations of thermal statistics.