Antiferromagnetic Solid Oxygen

The lowest-temperature phase of solid oxygen is antiferromagnetic and blue in color. A review of the electronic properties of the diatomic molecule indicates that the ground state 3Σg− of the lowest configuration is paramagnetic with the spin degeneracy lifted by spin orbit and dipolar forces. This splitting approximately 4 cm−1 leaves the Ms = 0 state lowest. Excited states of this configuration, the 1Σg+ and 1Δg, lie at 13 120 cm−1 and 7882 cm−1. All higher configurations lie above 30 000 cm−1. Both of the above mentioned properties of alpha oxygen can be understood on the basis of a ``single molecule'' but slightly perturbed due to neighboring molecules. The exchange and the orbital overlaps between molecules are responsible for both the antiferromagnetism and the blue color. The latter arises from single photon absorption inducing transitions within the lowest configuration on two neighboring molecules. The magnon spectra and magnon-exciton side band spectra justify this model.

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