Phase Interference in the Two-Photon Excitation of Phenanthrene

Abstract

Two-photon polarization measurements are shown to provide an incorrect symmetry assignment for the first excited state of phenanthrene, both in solution and in the vapor phase. Published assignments from one-photon, single-crystal measurements indicate a totally symmetric state, while the assignment from two-photon measurements indicates an antisymmetric state. Possible reasons for the failure of the two-photon symmetry assignment are low-frequency vibronic overlap, and interference among the diagonal tensor elements. Experimental evidence points to interference as the origin of the discrepancy.