Photoemission from Organic Crystal in Vacuum Ultraviolet Region. IV

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Abstract
The quantum yield and the energy distribution of photoelectrons were measured for organic crystals in the vacuum ultraviolet region. A model was presented for the photoemission from organic crystals with a narrow valence band, and a semiempirical power law was derived for the yield near the threshold. The ionization potentials found from the spectral distribution of the quantum yield using this model were as follows: anthracene–5.68 eV, naphthacene—5.43, pentacene—5.04, perylene—5.33, indanthrone—5.17, and tetrathionaphthacene—4.42. The effect of electrons which escape after one inelastic scattering was observed. It was shown how the contribution of once-scattered electrons can be separated in the energy distribution. The threshold for “pair production” was estimated to be nearly equal to the band gap for perylene and a little higher than the band gap for quaterrylene. The fine structures observed both in the yield spectra and in the energy distribution can be accounted for by assuming the existence of additional valence bands.