Fig. 4.
Molecular orbital scheme. (A) Schematic orbital energy level diagram showing the evolution of bonding and antibonding orbitals of the (O2)4 cluster from the interactions of eight degenerate π* orbitals of four O2 molecules. (B) Topology of π* orbital interactions in the (O2)4 cluster, illustrating the two different interactions in which each π* orbital participates as the cluster is formed from four O2 molecules. The energy levels of an idealized (O2)2 dimer in A illustrate the effect of the two interactions. A paired spin model is not proposed for the dimer, however.