Low frequency vibrational spectra of monosubstituted benzenes in the liquid state

Low frequency infrared and Raman spectra are investigated from 10 to 400 cm−1. The spectra are obtained in the liquid state of benzene, benzonitrile, fluorobenzene and toluene. Raman spectra are presented in the R( ν )-format. In order to avoid interference with fluorescense from trace amounts of impurities, the R( ν spectra are presented from −400 to 400 cm−1. Different scattering configurations are used in the Raman spectra in order to obtain polarization characteristics. Different sample temperatures are used for benzonitrile, fluorobenzene and toluene ranging from the melting to the boiling point. Low-frequency bands with maxima below 100 cm−1 are assigned to damped librational motions.