Probing Two-Photon Molecular Properties with Surface-Enhanced Hyper-Raman Scattering: A Combined Experimental and Theoretical Study of Crystal Violet

The surface-enhanced hyper-Raman scattering spectra of crystal violet are experimentally measured and theoretically calculated for excitation energies spanning the two lowest-lying electronic states (12,700-27,400 cm^-1). The theory and experiment are in qualitative agreement over the measured energy range, indicating that first-principles calculations capture many of the complex resonance contributions in this prototypical octupolar system. The discrepancies between theory and experiment are investigated by comparing spectra obtained in different local environments as well as from higher-order surface-enhanced spectroscopies. A comparison between relative surface-enhanced hyper-Raman scattering band ratios plotted as a function of excitation wavelength and crystal violet's absorption spectra elucidates correlations between groups of vibrations and the excited-electronic states. Our results suggest that the spectral features across the range of resonance excitation energies (∼15,500-27,400 cm^-1) are dominated by strong A-term scattering.