The origin of Stark shifts and splittings in molecular crystal spectra. I. The effective molecular polarizability and local electric field: Durene and naphthalene

Abstract

The origin of the linear Stark splittings observed in spectra of polar molecules dissolved in nonpolar host crystals is described. In order to obtain molecular dipole moment parameters from such splittings, the local electric field, among other things, must be known. The effective molecular polarizability and the local electric field are not determined uniquely by the crystal geometry and electric susceptibility for the general case of two or more anisotropic molecules per unit cell. The complete infinite set of solutions to the equations relating these quantities is reported for a crystal with two molecules per unit cell. Consequently, the variation or uncertainty in local field and effective molecular polarizability can be examined for specific cases. The cases of durene and naphthalene crystals are examined here, and it is found that the local field may differ by as much as a factor of two from values used previously in the analysis of Stark splittings.