Calculation of the Width of the Second Conduction Band in Anthracene Crystals from Photoemission Data

The spectral dependence of the photoemission of electrons from a metal into a narrow conduction band of a crystal is calculated qualitatively. It is shown that the Fowler relation jph ∼ (h v–χ)2 holds for χ ≦ h v ≦ χ + δ where χ denotes the energy difference between the Fermi level of the metal and the bottom of the conduction band and δ the band width. For h v ≧ χ + δ the current approaches a saturation value. The model is applied to the description of the photoemission of electrons from a Na and a Ca cathode into the first and the second conduction band of an anthracene crystal. The width of the second band is found to be (0.5 ± 0.1) eV. The energy gap between the top of this band and the next higher (third) conducting state is at least 0.6 eV.