Kerr effect of CN- molecules in KCl crystals

The electric field alignment of substitutional CN^- molecules in KCl crystals was studied by measurements of the field-induced optical birefringence (Kerr-effect). The electric field, temperature, wavelength and concentration dependence of the Kerr-effect and its pronounced anisotropy is found in quantitative agreement with a paraelectric alignment model for 〈111〉 oriented CN^- molecules, which have electronic absorption transitions hidden under the fundamental crystal absorption, and are characterized by an anisotropic polarizability of $\text{α}{}_6\text{? α}{}_{\mathrm{\perp }}\text{= 1.60}\text{A}\text{?}{}^3$.