Observable-dependence of the effective temperature in off-equilibrium diatomic molecular liquids

We discuss the observable-dependence of the effective temperature T-eff, defined via the fluctuation-dissipation relation, of an out-of-equilibrium system composed by homonuclear dumbbell molecules. T-eff is calculated by evaluating the fluctuation and the response for two observables associated, respectively, to translational and to rotational degrees of freedom, following a sudden temperature quench. We repeat our calculations for different dumbbell elongations zeta. At high elongations (zeta > 0.4), we find the same T-eff for the two observables. At low elongations (zeta <= 0.4), only for very deep quenches T-eff coincides. The observable-dependence of T-eff for low elongations and shallow quenches stresses the importance of a strong coupling between orientational and translational variables for a consistent definition of the effective temperature in glassy systems. (c) 2014 AIP Publishing LLC.