Two-photon Photoionization By Singlet-singlet Annihilation In Polycrystalline, Thin Perylene Films

摘要

Two-photon photoionization processes in thin, polycrystalline, α- and β-crystalline perylene films have been investigated for photon energies at the optical absorption threshold. The kinetic energy of the emitted electrons is found to be essentially independent of the photon energy, indicating that geometrically relaxed excited states are involved. The high ionization yield at such low photon energies is therefore attributed rather to the annihilation of adi-abatically relaxed singlet excitons than to the direct two-photon ionization process. This leads to hole final states different from those obtained in one-photon, vertical ionization processes.