Exciton dynamics in molecular crystals from line shape analysis. The effect of crystal strain

Experimental data are presented showing effects on the polarized reflection spectrum from the (001) face of crystalline anthracene which arise upon cooling from room temperature to 80 degrees K. Different crystal mounting methods and different crystal thicknesses are considered. The band profile of only the b-polarized (0-0) region is distorted and a new resonance detected near 25290 cm(-3) at crystal temperatures below 120 degrees K with an intensity dependent on the method of crystal mounting and rate of cooling. This resonance disappears with time. The results are explained using a theory of submicroscopic voids in the crystal if the crystal hits 10(-4) of its volume in the form of extremely thin planar dislocations almost parallel to the direction of light propagation in the crystal.