ULTRAVIOLET RAMAN-SCATTERING FROM SIMPLE ALCOHOLS AND A RELATED DIOL AS A STUDY OF LOW-LYING RYDBERG-VALENCE STATE CHARACTERISTICS

Relative Raman scattering cross sections of totally symmetric vibratio nal modes of liquid methanol, ethanol, and ethylene glycol are measure d as a function of excitation wavelength in the preresonant spectral r egion 37 593-47 393 cm-1. Raman spectra are also obtained with 50043 a nd 54 198 cm-1 excitation, the latter energy being directly resonant w ith the first excited state of the alcohols. The data indicate that th e first three excited electronic states (with transition energies of a pproximately 54 600, 62 500, and 66 000 cm-1, respectively) make no si gnificant contribution to the Raman scattered intensities and are near ly entirely Rydberg in character. The low-lying electronic structure o f ethylene glycol appears to be primarily Rydberg in character as well . The dominant C-H and O-H stretching modes gain intensity largely fro m valence state(s) with transition energies near 70 000 cm-1, while th e C-O stretching and CH2,3 bending modes gain intensity from even high er energy states (approximately 85 000 cm-1).