CHARACTERIZATION OF EXCITED ELECTRONIC STATES OF NAPHTHALENE BY RESONANCE RAMAN AND HYPER-RAMAN SCATTERING

The first resonance Raman.and hyper-Raman scattering from naphthalene are reported. Fourth harmonic of a mode-locked Nd:YAG laser is used to resonantly excite the 1B1u+ transition, producing Raman spectra that confirm the dominance of the vibronically active nu28 (b3g) mode and the Franck-Condon active a(g) modes, nu5 and nu3. A synchronously pumped stilbene dye laser and its second harmonic are employed as the excitation sources for hyper-Raman and Raman scattering from the overlapping 1B2u+ and 1A(g)- states. The Raman spectra indicate that the equilibrium geometry of naphthalene is distorted primarily along nu5, nu8, and nu7 normal coordinates upon excitation to 1B2u+. The hyper-Raman spectrum shows that nu25 (b2u) is the mode principally responsible for vibronic coupling between the 1A(g)- and 1B2u+ states. The results demonstrate the advantageous features of resonance hyper-Raman scattering for the case of overlapping one- and two-photon allowed transitions. Calculations based on simple molecular orbital configurations are shown to qualitatively agree with the experimental results.