Fast Relaxational Dynamics in theo-Terphenyl Glass

The dynamic structure factor S(q,ω) of o-terphenyl, obtained by Brillouin light scattering ( q≈0.04nm^-1) in the 1 to 30 GHz range, shows signatures of relaxation phenomena at temperatures well within the glassy phase. Using a phenomenological ansatz for the density fluctuations memory function and S(q,ω) data obtained by inelastic x-ray scattering at high momentum transfer ( q0ex0ex=0ex0ex1--6nm^-1), we describe this relaxational dynamics in terms of two distinct processes: (i) one in the 10^-11s range and slightly temperature dependent, and (ii) an ``instantaneous'' one, representing the microscopic transient and giving rise to a T-independent contribution to the Brillouin linewidth.