  After some introductory comments relating to antiferromagnetism of
crystalline O_2, and brief remarks on the geometry of ozone, Hartree-Fock (HF)
theory plus second-order Moller-Plesset (MP2) corrections are used to predict
the nuclear structure of low-lying isomers of free-space O_n clusters, for n=6,
8, and 12. The equilibrium nuclear-nuclear potential energy is also discussed
in relation to the number n of oxygen atoms in the cluster.
