Table I. Spin Ladder of Co₂Rad^a.

ΔE/cm–1	S	assignment	Jeff/cm–1
0.0	5/2	0 J
198.1	3/2	1/2 J	396.3
394.5	1/2	J	394.5
783.9	5/2
783.7	5/2
919.2	1/2	2 J	459.6
973.8	3/2
974.1	3/2
1119.1	3/2	5/2 J	447.6
1165.6	1/2
1167.1	1/2
1319.9	5/2	3 J	440.0
1383.6	7/2	7/2 J	395.3

^aΔE are the relative MS-CASPT2 energies of the states in the absence of spin-orbit coupling. The levels are assigned to the spin-ladder states of the Heisenberg Hamiltonian, eq 8, resulting in effective values for the J parameter, J_eff.