Transition from single-molecule to cooperative dynamics in a simple glass former: Raman line-shape analysis

Abstract

Parameters for orientational and inhomogeneous broadening are found from the line shape analysis of the Raman spectrum of the glass former alpha-picoline during cooling from low-viscous to glassy state. The orientational phase loss time tau(OPL), extracted from the analysis, coincides with the alpha relaxation time at T > T(A), where T(A) is the temperature of transition from an Arrhenius-like to a non-Arrhenius behavior for the alpha-relaxation time dependence on temperature. At lower temperatures tau(OPL) (T) continues the Arrhenius behavior, in contrast to the alpha-relaxation time. The width of inhomogeneous broadening of the Raman line decreases noticeably as temperature increases in the temperature range T(g) < T < T(A), approaching to zero at T approximately T(A). The findings evidence the transition of molecular dynamics from individual to cooperative at T = T(A).