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The spectra of eight crystals containing trivalent chromium have been measured, and the energy levels fitted to a four-parameter crystal-field theory. The values of the parameters derived from the spectra are discussed, and some mechanisms responsible for absorption intensities are evaluated.

Detailed absorption spectra of crystals containing cobalt (II) in octahedral or slightly distorted octahedral sites are reported. Prime consideration has been given to the observation of the doublet states and the assignments are discussed in relation to a four-parameter crystal field theory (Dq, ζ, B, and C).

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1.7 BM, which is still below the expected 2.2-2.5 BM for low-spin iron(III).These data strongly suggest dimerization with a bridging oxygen to permit superexchange between iron ions.25Acknowledgment. The authors wish to thank Professor W. E. Wallace for allowing the use of the instrumental facilities and the U. S. Atomic Energy Commission, Division of Biology and Medicine, for financial support through Contract AT(30-1)3859.(25) The X-ray crystal structure of this complex is presently being determined by J. L. Hoard at Cornell University.26 (26) Note Added in Proof. Fleischer has now reported the dimeric structure [E.