Multiphoton Ionization of Benzene in Solution*

Abstract

Two-photon absorption and excitation spectra of benzene in liquid and rigid solutions have been frequently reported.1 However, multiphoton ionization studies of benzene in liquid solution are limited and restricted to laser excitation wavelengths λexc ≲ 420 nm, which correspond to two-photon excitation energies hvexc ≳ 6 eV. Using a laser conductivity technique suitable for liquid-phase ionization investigations,2,3 we studied the multiphoton ionization spectrum of 10-3 mole dm-3 solutions of benzene in liquid n-pentane for hvexc ≲ 6 eV. We observed for the first time that the structure in the photocurrent versus hvexc (see Fig. 1) spectrum reflects the linearly polarized spectrum of the B2u-A1g transitions of benzene. Although we have not yet been able (due to the low intensity of our laser) to determine the order of the multiphoton ionization process, the spectrum in Fig. 1 is tentatively ascribed to a two-photon resonant three-photon ionization process. This spectrum is in excellent agreement with the two-photon excitation spectra reported by Friedrich et al.4