Fluctuation phenomena occurring in a system of 216 water molecules, studied by molecular dynamics at 1 g ${\mathrm{cm}}^{-3\mathrm{}}$ and 10 °C, indicate that (i) transverse currents persist in the form of propagating collective coordinates even for a wavelength of about 20 Å, with indications that the same will happen for much longer wavelengths. The velocity of propagation is 1.05 × ${10}^5$ cm ${\sec }^{-1\mathrm{}}$. In the region of 20 Å the lifetime of the fluctuation appears to increase linearly with increasing wavelength. (ii) Density fluctuations at 20 Å are found to be propagating but only marginally; the corresponding velocity of sound is 1.8 × ${10}^5$ cm ${\sec }^{-1\mathrm{}}$. (iii) The spectrum of density fluctuations exhibits a secondary maximum at a much higher frequency than the normal frequency of sound propagation and it is suggested that experiments should be directed to the region of this "high-frequency sound."

• Received 25 March 1974

DOI:https://doi.org/10.1103/PhysRevA.10.368