DETERMINATION OF THE INFINITE FREQUENCY SOUND-VELOCITY IN THE GLASS FORMER O-TERPHENYL

The temperature dependence of the acoustic dispersion relation, Omega( Q,T), has been determined across the liquid-glass transition in o-terp henyl using inelastic x-ray scattering in the 1-6 nm(-1) momentum tran sfer (Q) range. From this the infinite frequency sound velocity v(infi nity) (T) can be obtained. In the glass, v(infinity) (T) compares well with existing light scattering determinations, while in the liquid it s value can be used to discriminate among different phenomenological m odels previously proposed to infer v(infinity) (T) from low temperatur e data. Moreover, the Debye-Waller factors (f(Q)) in two different Q r egimes (Q approximate to 0 and Q = 2.5 nm(-1)) are determined and foun d to be mutually consistent.