The ground state structure of Si3is found to be cyclic (1A1, C2vsymmetry) with an apex bond angle of bartil;80deg;. The linear form, analogous to the known structure of C3, is found to be a saddle point which transforms without activation to the cyclic structure. There is a lowhyphen;lying triplet state (3Arsquo;2,D3hsymmetry) which lies only a few kcal/mol higher in energy. The nature of the bending potential surface of the ground state structure is also discussed.
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