Field Effects in Condensed Media on Polarized Absorption

Artikel i vetenskaplig tidskrift, 1977

The existence of anisotropic local field perturbation on electronic absorption is proved by non-zero linear dichroism of isotropic chromophores (Mo(CO)6) in anisotropic environment. Two sources of such effects are possible: a) perturbation of the electronic energy levels in the chromophore by the static electric solvent field (= Stark effect) or, in case of anisotropic polarizable or dipolar molecules, similar effects involving molecular orientation, and b) dielectric effects on the effective radiation field. The latter effect was considered by various models: The Lorentz field model predicts an effect with wrong sign, it also yields too large a magitude if the anisotropy of the field is considered. If no local field correction is made and the anisotropy only operates in the radiation intensity a result more in agreement with experiment is obtained. By using the Onsager-Böttcher model one may take into account specific properties of the absorbing molecule, like anisotropy in α/r3 where α is its polarizability and r its Onsager radius.