Laser Two-Photon Ionization Spectrometry of Perylene and Naphthacene in Hexane

The two-photon Ionization spectra of perylene and naphthacene in hexane have been measured with tunable dye lasers. They have shown structure, which can be correlated with the one-photon absorption spectra. The signal-to-nolse (S/N) ratio has been evaluated as functions of the excitation wavelength and the laser pulse energy, and the detection limit depended on the excitation wavelength, the laser pulse energy, and the molar absorptivity. The lowest detection limits (S/N = 3) of peryiene and naphthacene were 50 pg/mL at 383 nm and 20 pg/mL at 407 nm, respectively; these dye laser results were superior to those obtained by nitrogen-laser excitation.