2-COLOR 2-PHOTON IONIZATION SPECTRUM OF PYRENE IN N-HEXANE

The photoionization process of pyrene in non-polar solvent has been in vestigated using a two-color two-photon ionization technique. The ioni zation spectrum near threshold of pyrene in n-hexane was measured by a delayed irradiation of a dye laser 20 ns after an N-2 laser at total excitation energies of 5.9-6.22 eV. The two-photon ionization threshol d of pyrene was in the vicinity of 5.9 eV which is larger by 0.7 eV th an that expected from the onset of one-photon ionization. The ionizati on spectrum shows maxima at 5.92 and 5.99 eV which may be assigned to an autoionization process.