Abstract
The laser multi-photon ionization spectra of pyrene, perylene, and naphthacene were measured in hexane. The photoionization spectra showed distinct structure and wavelengths of bands agreed roughly with those of the one-photon absorption spectra. The photocurrent signal was strong in the wavelength region where the absorption spectrum was observed as compared with that where no absorption spectrum was seen. Sequential two-photon ionization was a main process in the former region, while simultaneous two-photon ionization or three-photon ionization involving two-photon excitation in the latter region. The number of free charge carriers increased linearly with the applied electric field and was correlated with the excitation energy. The photocurrent signal was correlated with the excess excitation energy. The ionization threshold was evaluated from the photoionization spectrum in the longer wavelength region. The photoionization spectrum was simulated.
