Brillouin ultraviolet light scattering on vitreous silica

New experimental data on vitreous silica, collected in a previously unexplored frequency region between 60 and 120 GHz, are reported. The Brillouin ultraviolet light scattering technique has been used to measure the dynamic structure factor for two exchanged momenta, Q = 0.078 and 0.11 nm(-1). The experiment has been performed using the IUVS beam line at the Elettra Synchrotron radiation facility in Trieste. An evidence of a transition between two different dynamical regimes is discussed.