Fast relaxational dynamics in the o-terphenyl glass

The dynamic structure factor S(q, omega) of o-terphenyl, obtained by Brillo uin light scattering (q approximate to 0.04 nm(-1)) in the 1 to 30 GHz rang e, 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, omega) data obtained by inelastic x-ray scatterin g at high momentum transfer (q = 1-6 nm(-1)), we describe this relaxational dynamics in terms of two distinct processes: (i) one in the 10(-11) s rang e and slightly temperature dependent, and (ii) an "instantaneous" one, repr esenting the microscopic transient and giving rise to a T-independent contr ibution to the Brillouin linewidth.