Non-Lorentzian depolarized Raman line shapes in n-pentanol

Abstract

High resolution depolarized Raman spectra of n-pentanol in the −30 to 60° C temperature range are reported. The spectra appear as a continuously decreasing line shape centered at zero frequency. A quantitative analysis of this line shape shows a high frequency exponential tail, which can safely be assigned to intermolecular collision phenomena, and a low frequency narrow contribution. The line shapes of the low frequency contribution are seen to deviate from a single Lorentzian, the effect being more pronounced as the temperature is increased. The data have been analyzed assuming the non-Lorentzian line shape as due either to a distribution of Debye relaxation times or to a single non-Debye relaxation mechanism. The analysis in terms of a distribution of relaxation times suggests a broadening of the distribution as the temperature increases, while the ‘‘average’’ relaxation time shows an Ahrenius behavior which compares well with the one observed in the ultrasonic attenuation measurements. Similar results have been obtained considering the nonexponential relaxation mechanisms. Absolute intensities are also evaluated with respect to the Brillouin doublet and discussed in terms of the possible microscopic scattering mechanisms.