Temperature dependent Raman study of molecular motions and interactions of CH3 I in the liquid phase

Abstract

The polarized and depolarized components of the 524 cm−1 Raman band in liquid methyl iodide were measured between 196 and 300°K. A technique, utilizing the isotropic scattering intensity, allowed the separation of reorientational line broadening of the anisotropic spectrum from the broadening due to other processes. The reorientational correlation times derived from the anisotropic Raman spectrum were found to agree well with those obtained by other techniques throughout the temperature range studied. The temperature dependence of the isotropic correlation times was opposite to that predicted by current theories of vibrational relaxation and collisional broadening. The depolarization ratio was also measured as a function of temperature and is seen to vary quite markedly. The depolarized low frequency spectra of methyl iodide were also studied and the results were fit to a theoretical expression for collision induced scattering to obtain values for the linewidth parameter Δ. The temperature dependence of Δ proved to be opposite from that predicted by theory and is qualitatively similar to the temperature dependence of the isotropic linewidths, indicating that the same broadening mechanism is probably present in both spectra.