THE FREQUENCY DEPENDENCE OF RAMAN SCATTERING OF BENZENE AND SOME RELATED COMPOUNDS IN THE ULTRAVIOLET

Abstract

The excitation wavelength dependence of the Raman intensities of several fundamental vibrational frequencies of benzene, toluene, fluorobenzene and m-xylene in carbon tetrachloride has been measured in a spectral region approaching the lowest lying absorption band in these molecules. Tunable UV laser radiation from 337 nm to 276 nm was used. Pre-resonance enhancement was observed for some modes and one example of anti-resonance was seen. These results are discussed within the framework of the vibronic theory of Raman scattering. Accordingly, forbidden electronic transitions (such as the $^{1}B_{2u}$ transition in benzene)are in active and Raman active electronic transitions may be identified. In general, good agreement is found between the observed pre-resonance effects and theory.