The laser two-photon ionization of pyrene and several aromatic compounds was investigated in three hydrocarbon solvents by exciting them at 240, 266 and 299 nm using the fourth-harmonic of a Nd:YAG laser and a Raman shifter. The photoionization process consisted of one-photon and two-photon processes at 240 and 266 nm without deaeration, but was a two-photon process even at 240 nm when oxygen was removed. The two-photon ionization efficiency of pyrene was larger upon excitation at shorter wavelengths and in solvents with a larger electron mobility. However, because of large blank signals of the solvents, the detection limits of these molecules were poorer than those previously reported.
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