Ionization of Aniline in Nonpolar Hydrocarbon Solvents as Studied by Two-Photon Ionization Spectra

Two-photon ionization spectra (wavelength dependence of photoionization efficiency) of aniline were measured in several hydrocarbon solvents in the excitation wavelength region of 360-430 nm (two-photon energy 5.77-6.89 eV, a nonresonant process). There were two thresholds in saturated hydrocarbons; one at 6.4-6.6 eV and the other at 5.6-6.1 eV. The former was assigned to the direct ionization because the thresholds agreed with those calculated with the electron affinity of solvents and the polarization energy of aniline cation. The latter was assigned to an unidentified ion-pair formation process between aniline and saturated hydrocarbon. The spectrum in benzene, however, showed only one threshold at 6.16 eV, and this threshold was assigned to the direct ionization.