TWO-PHOTON EXCITATION SPECTRUM OF PERYLENE IN $SOLUTION^{\ast}$

$^{\ast}$ Research supported in part by the U.S. National Science FoundationAuthor Institution: Department of Chemistry and the LASER Laboratory, Michigan State UniversityThe selection rules for two-photon absorption often permit one to generate excited states that cannot be accessed by one-photon transitions. In particular, for molecules with a center of symmetry the parity selection rules for two-photon transitions are g-g and u-u, instead of g-u. The two-photon excitation spectra of perylene in n-hexane at room temperature and 77 K have been obtained using both linear and circular polarized light over the excitation energy range $23,530 cm^{-1} - 35,700 cm^{-1}$. The dipole-forbidden $S_{0}. S_{2}$ transition, which is uncertain In the one-photon absorption spectrum, is observed at $- 27,000 cm^{-1}$. From measurement of the linear/circular polarization ratio, $\Omega$ as a function of excitation energy and comparison with previous experimental and calculated values, we have assigned several low-lying ``g'' symmetry excited states of perylene