Two-Color Two-Photon Ionization Spectrum of Pyrene in N-Hexane

The photoionization process of pyrene in non-polar solvent has been investigated using a two-color two-photon ionization technique. The ionization spectrum near threshold of pyrene in n-hexane was measured by a delayed irradiation of a dye laser 20 ns after an N2 laser at total excitation energies of 5.9–6.22 eV. The two-photon ionization threshold of pyrene was in the vicinity of 5.9 eV which is larger by 0.7 eV than that expected from the onset of one-photon ionization. The ionization spectrum shows maxima at 5.92 and 5.99 eV which may be assigned to an autoionization process.