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Cr(lll) have a intense colour why is it Laporte forbidden
Accepted Answer
Cr(III) complexes often exhibit intense colors due to d-d transitions. However, these transitions are Laporte forbidden because they involve changes in the parity of the electronic state, meaning the symmetry of the electronic wavefunction changes. This is because d orbitals are centrosymmetric, while the transition dipole moment operator has odd parity. For a transition to be allowed, the product of the initial and final state wavefunctions and the transition dipole moment operator must have even parity. Therefore, the transitions involving d orbitals in Cr(III) complexes are formally forbidden. However, the intensity of the colors suggests that these transitions are not entirely forbidden. The reason for this is that vibrational coupling can mix electronic states and relax the Laporte selection rule.
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