High-frequency propagating modes in vitreous silica at 295 K

Collective modes in vitreous silica (v-SiO2) are found at 295 K and at momentum transfers Q=1.5 and 2.0 nm(-1). They propagate with a sound velocity of approximate to 6000 m/s, a value equivalent to that in the Q-->0 limit, and to that recently measured at 1050 K in the 1-3.5 nm(-1) Q range. The data complete the scenario on the acousticlike dynamics in v-SiO2, showing its temperature independence and propagating rather than localized nature in the whole 295-1050 K and 0.01-2.0 nm(-1) temperature and Q ranges.