In this Wikipedia link about the excited states of oxygen, this diagram is shown. The left most molecular orbital diagram is the first excited state of oxygen, and the MO diagram in the middle is the second excited state of oxygen. It seems to imply that the energy of pairing is less than the exchange energy, and thus the first excited state exhibits the two electrons with opposite spins in the same MO, while the second excited state exhibits the two electrons with opposite spins in separate MOs.
These two diagrams seem to have different orders for the first and second excited states. Which energy energy state, having both electrons with opposite spin and in the same orbital, or having both electrons with opposite spin and in separate orbitals, has higher energy?