Properties of Sc3, Y3, and Sc13 molecules at low temperatures, as determined by ESR

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Abstract
Sc 3 and Y3 molecules have been isolated in rare gas matrices at temperatures near 4 K. ESR spectra establish that the structure of Sc3 is an equilateral triangle at 4–30 K with a 2A′1 ground state. The possibility remains that Sc3 is a fluxional bent molecule with a very low barrier to pseudorotation. The 45Sc hyperfine splitting indicates that the unpaired electron has little s character and is delocalized in 3d orbitals on the three equivalent atoms. Y3, however, is not equilateral and is most probably a bent molecule at these temperatures with the spin again distributed over the 3d atomic orbitals, but in a 2B2 ground state. La3 was not observed and is therefore judged to be a linear orbitally degenerate molecule. Under special conditions, a cluster of exceptional stability Scx, where x≥9 is formed in neon matrices. From its uniqueness and from the hyperfine structure in its ESR spectrum, it is suggested that it may be Sc13 with an icosahedral structure. This places 12 equivalent atoms at the vertices and one at the center of the icosahedron and leads to a 2Ag ground state. However, Scx as observed at 4 K could also be a dynamic Jahn–Teller molecule with only a small barrier between its distorted conformations.

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