 Another transition, b2u-a2u, is a weak (orbitally forbidden singlet) but can still be observed in MCD.Because A- and B-terms arise from the properties of states, all singlet and triplet excited states are given in figure 2.Mixing of all these singlet and triplet states will occur and is attributed to the spin orbit coupling of platinum 5d orbitals (ζ ~ 3500 cm−1), as shown in figure 3.