TWO-PHOTON EXCITATION SPECTRUM OF PHENANTHRENE AT $\sim 5^{\circ}\,K$

Abstract

Two-photon excitation (TPE) spectra of neat crystals of phenanthrene, for light incident on the principal faces of the crystal are reported in the region 630-700 nm at $\sim 5^{\circ}\,K$. Important vibronic levels of the first excited $^{1}A_{1}$ state (molecular symmetry group $C_{2v}$) are studied through the angular dependence of TPE cross sections, to determine the nature of vibronic perturbations with the higher-lying $^{1} B_{2}$ and $^{1} A_{1}$ states. Polarization dependence of intensities of vibronic bands is used in the assignment of symmetry of vibrational modes. Importance of crystal field effects on intensities is assessed.