Absorption Spectrum of Crystalline Anthracene. Measurements on the Absorption Edge

The absorption spectrum of single sublimation flakes of anthracene has been redetermined with a view to investigating the b polarized absorption edge. From measurements at room temperature on crystals of known thickness and also from spectra at 77° and 4°K it has been established that the major part of this absorption takes place in a region of about 50 layers below the crystal surface. The crystal energy levels are then split to a much greater extent than in the main body of the crystal, and it is suggested that this occurs because of some slight crystal structure modification. The weaker absorption lines which also occur on the absorption edge are taken to represent transitions in molecules located near or at imperfections.