Electronic Absorption Spectroscopy-Vibronic Coupling and Band Shape Analysis

From Section III, for D 4h-CuCl4=, the parity forbiddenness of the d → d transitions in this centrosymmetric complex is overcome by vibronic or Herzberg-Teller coupling to odd parity vibrations of the nuclear framework. In addition, absorption bands in metal complexes can be greatly broadened (relative to the < 1 cm−1 expected on the basis of their lifetimes) due to coupling of the electronic transitions to distortions of the molecular framework. Both effects require two new terms in the molecular Hamiltonian which relate to nuclear motion.