 Molecular orbital theory predicts the electronic ground state denoted by the molecular term symbol 3Σ, and two low-lying excited singlet states with term symbols 1Δg and 1Σ.These three electronic states differ only in the spin and the occupancy of oxygen's two antibonding πg-orbitals, which are degenerate (equal in energy).These two orbitals are classified as antibonding and are of higher energy.