Compound Model fit to D/cm -1 D 0 /cm -1 ∆/cm -1 γ/cm -1 J/cm -1 g z g z,0 g z,1 From a fit of the spin Hamiltonian parameters of Eq. 3 to the computed states the following parameters are obtained: ∆ = 478 cm -1 (energetic splitting of quartets without spin-orbit interaction), γ = 352 cm -1 (first-order spin-orbit coupling between the two quartet states) and D 0 = 15 cm -1