Depolarized Rayleigh light scattering and NMR spectroscopy of m-cresol and p-cresol

The depolarized Rayleigh light scattering spectrum of neat m-cresol and p-cresol has been measured as a function of temperature. The depolarized Rayleigh spectra display a zero-frequency dip due to coupling of the molecular anisotropic motion to the transverse sound wave. The translation-rotation coupling constant has a value of R = 0.28 at 339 K, where the dip is most clearly resolved. The line width of the dip agrees with the theoretical width. A shear wave dip was not observed in p-cresol. The NMR correlation time has also been measured as a function of temperature. Comparison of the depolarized Rayleigh relaxation time and the NMR correlation times enabled a measurement of the orientational pair correlation factor, which for m-cresol was found to be roughly 2.3 and for p-cresol is about 3.5. The NMR and literature values of the dielectric relaxation time were also compared. The result is in good agreement with a microscopic theory with a static pair correlation factor of roughly 2.7 for m-cresol and 3.0 for p-cresol. A Stokes-Einstein-Debye plot of the single particle relaxation times is linear with a finite intercept. The slope of the plot is in good agreement with the theoretical slope predicted with slip boundary conditions. Both m-cresol and p-cresol display a relatively large intercept.