Optical deformation potentials of the copper halides

The absolute Raman scattering efficiency of the copper-halides is determined in the energy range from 2 to 3.1 eV. From it the absolute values of the deformation potentials d_o are deduced. They are anomalously small (|d_o|<5 eV). This is explained theoretically with the help of a tight binding model in which the special nature of the valence band (obtained by a mixing of the 3d-Cu and p-halogen orbitals) is taken into account.