Studies of molecular reorientation, translation, and vibrational relaxation of liquid 1,2,4-trichlorobenzene by depolarized Rayleigh and Raman spectroscopy

Abstract

The depolarized Rayleigh and Raman scattering spectra of 1,2,4-trichlorobenzene (TCB) in CCl4 have been measured as a function of concentration at several tempertures in high resolution. The depolarized Rayleigh spectra were obtained using a Fabry–Perot interferometer and the high resolution Raman spectra were obtained using a tandem spectrometer consisting of a Fabry–Perot interferometer and a double grating monochromator. The central dip due to shear wave coupling to reorientational motion is observed in the depolarized Rayleigh spectrum. The Rayleigh relaxation times τRay obtained for TCB depend on the TCB concentration. The concentration dependence of the Rayleigh times indicates the importance of orientational pair correlation in TCB. The single particle orientational relaxation times τs were obtained by extrapolating from τRay data to infinite dilution. The activation energy for molecular reorientation which is found to be affected by pair correlation decreases with decreasing concentration, with most rapid decrease occuring at low concentration. The spectral linewidth of the 677 cm−1 band shows a weak concentration dependence, thus suggesting that the vibrational effect of the 677 cm−1 band in neat TCB can be interpreted in terms of single particle dynamics. Further studies show that the vibrational linewidth is due to the intramolecular interaction.