THE ORIGIN OF STARK SPLITTINGS IN MOLECULAR CRYSTAL SPECTRA

Abstract

It has been suggested that the Stark splitting of spectral lines of molecular crystals in an external electric field can be attributed to a molecular electric dipole moment $change^{1}$ interacting with the local electric field. An anisotropic Lorentz field approximation was used to obtain the local field from the macroscopic $field.^{1,2}$. Other $interactions^{3}$ in the crystal can contribute significantly to the Stark splitting, and many of these have been ignored in previous analyses of such Stark effects. By explicitly including, in a self-consistent way, the many contributions that can arise from guest and host dipole-dipole and dipole-electric field interactions, an improved analysis of the Stark splitting in the spectra of a polar impurity isolated in a nonpolar host crystal is obtained in closed $form,^{4}$ within the context of the point dipole approximation. This analysis results in a second rank tensor that couples the molecular dipole moment change to the macroscopic electric field. This tensor will be compared with that obtained from the Lorentz local field analysis.