Density and temperature effects on relative Raman intensities in liquid toluene

Raman spectra of toluene at pressures up to 4.1 kbar and temperatures up to 100°C, have been studied. The frequency and intensity changes of the symmetric (ν_6a) and antisymmetric (ν_6b) ring breathing vibrations have been related principally to changes in density. Increasing density at constant temperature increases I(ν_6b/ν6a) and increases the frequency of (ν_6a) but has little effect on the frequency of ν_6b. Increasing temperature at constant density decreases I(ν_6b/ν_6a) and increases the frequency of ν_6a but has little effect on the frequency of ν_6b. An explanation of the different intensity changes with density for these two bands is suggested in terms of the contrasting volume changes associated with the two modes.