Infra-Red Christiansen Filter Effect in Slurries of Organic Crystals

Abstract

The Christiansen filter effect in slurries of organic crystals is reported for the first time, in the infra‐red. The main difference between the effect in molecular and in ionic crystals is that the Christiansen (transmission) peak and the ``Reststrahlen'' (reflection) peaks are much closer together for organic crystals since they are produced by a single frequency instead of a wide band of lattice frequencies. The Christiansen effect is much more selective in organic crystals since it occurs for some bands but not for others. This is thought to be due to the nature of the coupling between the particular vibration and the atoms or groups in the molecule which make major contributions to the polarizability.