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Chemistry · Glossary

What is Racah parameters?

Definition 18.7 University Chemistry — Year 3 · Chapter 18 — Electronic Spectra and Magnetism of Complexes

The Racah parameters AA, BB and CC are combinations of the Slater integrals of the dd shell that express all the electron-repulsion energies of a dnd^n configuration; the energy differences between terms of the same configuration depend only on BB and CC, and those between terms of the same highest multiplicity on BB alone (for d2d^2, d3d^3, d7d^7, d8d^8: E(P)−E(F)=15BE(\mathrm P) - E(\mathrm F) = 15B).

Examples

Example 18.8 (Free-ion Racah parameters)

The levels of the free CrX3+\ce{Cr^{3+}} ion put the centre of gravity (weights 2J+12J + 1) of 4^4F at 547 cm−1547\,\mathrm{cm}^{-1} and that of 4^4P at 14 305 cm−114\,305\,\mathrm{cm}^{-1} above the ground level: 15B=13 758 cm−115B = 13\,758\,\mathrm{cm}^{-1}, B=917 cm−1B = 917\,\mathrm{cm}^{-1}. The same calculation gives B=755B = 755 for VX2+\ce{V^{2+}} and 1056 cm−11056\,\mathrm{cm}^{-1} for NiX2+\ce{Ni^{2+}}.

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